U.S. patent application number 09/769497 was filed with the patent office on 2001-09-06 for illuminating system.
Invention is credited to Fukui, Atsushi, Nakabayashi, Koki, Nishii, Kanji, Tatsuta, Ken, Watanabe, Hiroshi.
Application Number | 20010019479 09/769497 |
Document ID | / |
Family ID | 27292074 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019479 |
Kind Code |
A1 |
Nakabayashi, Koki ; et
al. |
September 6, 2001 |
Illuminating system
Abstract
The illuminating system comprises a linear light source, and a
light guide member with the light source placed beside a side face
thereof, in which the top face and the bottom face of the light
guide member are generally parallel to each other and in which
slits made of a different material or air are arranged at specified
intervals in the top face of the light guide member. Therefore,
most of light propagating within the light guide member is totally
reflected at the slits formed in the light guide member so as to be
outputted from the light guide member, thereby illuminating a
reflecting plate. Its reflected light is incident again on the
light guide member and the resulting totally reflected light is
transmitted to the observer's side at places other than the slits,
while the observer's field of view is not obstructed at the slit
portions.
Inventors: |
Nakabayashi, Koki;
(Neyagawa-shi, JP) ; Nishii, Kanji; (Osaka-shi,
JP) ; Fukui, Atsushi; (Osaka-shi, JP) ;
Watanabe, Hiroshi; (Yawata-shi, JP) ; Tatsuta,
Ken; (Kadoma-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27292074 |
Appl. No.: |
09/769497 |
Filed: |
January 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09769497 |
Jan 26, 2001 |
|
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|
09076123 |
May 12, 1998 |
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Current U.S.
Class: |
362/615 ; 349/64;
359/599 |
Current CPC
Class: |
G02B 6/0038 20130101;
G02B 6/0055 20130101; G02B 6/0031 20130101; G02B 6/0048 20130101;
G02B 6/005 20130101; G02B 6/0028 20130101; G02B 6/0046 20130101;
G02B 6/0036 20130101; G02B 6/0053 20130101; G02B 6/0018 20130101;
G02F 1/133616 20210101; G02B 6/0068 20130101 |
Class at
Publication: |
362/31 ; 359/599;
349/64 |
International
Class: |
G02B 013/20; G02F
001/1335; F21V 007/04; G02B 005/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 1997 |
JP |
9-122343 |
Aug 21, 1997 |
JP |
9-224992 |
Feb 26, 1998 |
JP |
10-44960 |
Claims
What is claimed is:
1. An illuminating system comprising a light source; and a
transparent plate with the light source placed beside a side face
thereof, wherein a plurality of grooves filled with a layer having
a refractive index different from a refractive index of the
transparent plate are arranged at specified intervals in a surface
or interior of the transparent plate.
2. An illuminating system according to claim 1, wherein a top face
and a bottom face of the transparent plate are generally parallel
to each other.
3. An illuminating system according to claim 1, wherein a condition
of .theta.<sin.sup.-1(n.sub.1/n)-sin.sup.-1{(1/n)sin(.beta.)} is
satisfied where n is the refractive index of the transparent plate,
n.sub.1 is the refractive index of a material as the layer that
fills the grooves which are the slits, .theta. is an angle formed
by each of the slits and the top face of the transparent plate and
.beta. is an angle of visibility of the illuminating system.
4. An illuminating system comprising: a light source; a transparent
first plate with the light source placed beside a side face
thereof; and a transparent second plate placed on a top face of the
first plate, wherein a bottom face of the first plate is a plane
surface and a plurality of stepwise slopes are arranged at
specified intervals in the top face of the first plate; in a bottom
face of the second plate, stepwise slopes are arranged so as to be
identical in configuration to the slopes of the top face of the
first plate; and the top face of the first plate and the bottom
face of the second plate are placed with a specified spacing.
5. An illuminating system according to claim 4, wherein a condition
of .theta.<sin.sup.-1(n.sub.2/n)-sin.sup.-1{(1/n)sin(.beta.)} is
satisfied where n is the refractive index of the first plate,
n.sub.2 is the refractive index of a material as the layer bonding
the first plate and the second plate to each other, .theta. is an
angle of each of the slopes of the top face of the first plate and
the bottom face of the second plate and .beta. is an angle of
visibility of the illuminating system.
6. An illuminating system according to claim 5, wherein a light
outgoing angle of a collimator placed at an outgoing exit of the
light source is within
.+-.sin.sup.-1[n.times.sin{90-.theta.-sin.sup.-1(n.sub.2/n)}].
7. An illuminating system by overhead irradiation comprising: a
light source; a transparent plate which is a light guide member in
which a plurality of grooves are arranged in a top face of the
light guide member at specified intervals in a direction parallel
to a longitudinal direction of the light source, and in which a
flat portion constituting a part of the top face is arranged
between adjacent ones of the grooves, wherein an illumination
object placed on a bottom face side of the light guide member is
observed from a top face side of the light guide member.
8. An illuminating system by overhead irradiation according to
claim 7, wherein each of the grooves of the light guide member is a
V-shaped groove having a first slope located on one side closer to
the light source and a second slope located on the other side
farther from the light source, and wherein an angle .theta..sub.1
formed by the first slope and the bottom face of the light guide
member falls within a range of
.theta..sub.1.ltoreq.90.degree.-.theta..sub.c+2.theta..sub.3, where
.theta..sub.c is a total reflection angle of the light guide member
and .theta..sub.3 is an angle formed by the flat portion and the
bottom face of the light guide member.
9. An illuminating system by overhead irradiation according to
claim 7, wherein each of the grooves of the light guide member is a
V-shaped groove having a first slope located on one side closer to
the light source and a second slope located on the other side
farther from the light source, and wherein an angle .theta..sub.1
formed by the first slope and the bottom face of the light guide
member satisfies a condition of:
.theta..sub.1.apprxeq.45+.theta..sub.3-(1/2)sin.sup.-1(1/n.times.sin.-
beta.), where n is a refractive index of the light guide member,
.theta..sub.3 is an angle formed by the flat portion and the bottom
face of the light guide member and .beta. is an angle formed by a
perpendicular of the bottom face of the light guide member and a
direction of the observer.
10. An illuminating system by overhead irradiation according to
claim 7, wherein each of the grooves of the light guide member is a
V-shaped groove having a first slope located on one side closer to
the light source and a second slope located on the other side
farther from the light source, and wherein an angle .theta..sub.2
formed by the second slope and the bottom face of the light guide
member satisfies a condition of
.theta..sub.2.ltoreq.(1/2)sin.sup.-1(1/n), where n is a refractive
index of the light guide member.
11. An illuminating system by overhead irradiation according to
claim 7, wherein in the light guide member, a pitch of the grooves
is not more than a dot pitch of the illumination object.
12. An illuminating system by overhead irradiation according to
claim 7, wherein each of the grooves of the light guide member is a
V-shaped groove having a first slope located on one side closer to
the light source and a second slope located on the other side
farther from the light source, and wherein in the light guide
member, a length of the first slope is not more than
{L.times.(0.5/60).times..sub..pi./180}, where L is a distance
between the top face of the light guide member and an observer
observing the illumination object.
13. An illuminating system by overhead irradiation according to
claim 7, wherein a transparent prism sheet is placed on the top
face of the light guide member, the prism sheet having, with
respect to a cross-sectional shape, a plurality of projected
portions having slopes of an angle .theta..sub.4 to the top face
are arranged on the bottom face so that a flat portion generally
parallel to the bottom face is interposed therebetween.
14. An illuminating system by overhead irradiation according to
claim 13, wherein the length of the slope of the prism sheet is not
more than {L.times.(0.5/60).times..sub..pi./180}, where L is the
distance between the observer who observes the illumination object
and the top face of the light guide member.
15. An illuminating system comprising: a light source; and a
transparent plate taking light from the light source through a side
face thereof and projecting illumination light through a lower face
thereof subjected to at least one of an anti-reflection treatment
and a diffuse treatment, wherein an illumination object which is
disposed at a lower face side of the transparent plate is observed
from an upper face side of the transparent plate.
16. A reflection type liquid crystal display device which
comprises: the illuminating system according to claim 1, the
transparent plate taking light from the light source through a side
face thereof and projecting illumination light through a lower face
thereof subjected to at least one of an anti-reflection treatment
and a diffuse treatment; and a reflection type liquid crystal panel
having a surface of at least one substrate thereof processed
through at least one of the anti-reflection treatment and the
diffuse treatment, wherein the surface of the substrate of the
liquid crystal panel processed through at least one of the
anti-reflection treatment and the diffuse treatment is arranged to
confront a lower face of the transparent plate, so that the
reflection type liquid crystal panel is observed from an upper face
side of the transparent plate.
17. A reflection type liquid crystal display device which
comprises: the illuminating system according to claim 1, the
transparent plate taking light from the light source through a side
face thereof and projecting illumination light through a lower face
thereof subjected to at least one of an anti-reflection treatment
and a diffuse treatment; a reflection type liquid crystal panel
having a surface of at least one substrate thereof processed
through at least either an anti-reflection treatment or a diffuse
treatment; and a touch panel having a surface processed through a
diffuse treatment, wherein the surface of the substrate of the
liquid crystal panel processed through at least either the
anti-reflection treatment or the diffuse treatment is arranged to
confront the lower face of the transparent plate and at the same
time, the touch panel is disposed to confront an upper face of the
transparent plate, so that the reflection type liquid crystal panel
is observed from an upper face side of the transparent plate.
18. A reflection type liquid crystal display device according to
claim 16, wherein a haze value of the diffuse treatment provided to
the surface of the substrate of the reflection type liquid crystal
panel, the lower face of the transparent plate or the surface of
the touch panel is set to be not larger than 20%.
19. A reflection type liquid crystal display device according to
claim 16, wherein a transparent material or a sheet of the material
which has approximately the same refractive index as that of a
material of the transparent plate and that of the substrate of the
reflection type liquid crystal panel is interposed between the
lower face of the transparent plate and the reflection type liquid
crystal panel.
20. A reflection type liquid crystal display device which
comprises: the illuminating system according to claim 1, the
transparent plate taking light from the light source through a side
face thereof and projecting illumination light from a lower face
thereof; and a reflection type liquid crystal panel having an field
angle control plate arranged on an upper face thereof, said control
plate featuring a diffuse characteristic in one direction while
being transparent in other directions, wherein the face of the
reflection type liquid crystal panel where the field angle control
plate is arranged is set to confront the lower face of the
transparent plate, and moreover an angle of the illumination light
projected from the lower face of the transparent plate is almost
agreed with a diffusion direction of the field angle control plate,
so that the reflection type liquid crystal panel is observed from
an upper face side of the transparent plate.
21. A reflection type liquid crystal display device according to
claim 20, wherein an output angle of the transparent plate and the
diffusion direction of the field angle control plate is
30-50.degree. to a normal direction of the reflection type liquid
crystal panel.
22. An illuminating system according to claim 1, wherein the light
house is a group of point light sources in which point light
sources are arranged on an almost straight line via a constant
interval to radiate in nearly the same direction, the illuminating
system further comprising: a reflector having an opening part and
disposed to cover the group of point light sources; and a diffusing
plate set at the opening part of the reflector, wherein the
diffusing plate is separated from the group of point light sources
so that quantity of light from a center of an illuminance
distribution by the point light source on the diffusing plate is
nearly equal to that between centers of illuminance distributions
of the point light sources.
23. An illuminating system according to claim 22, wherein the
reflector is L-shaped so as not to directly pass light emitted from
the point light sources to the diffusing plate.
24. An illuminating system according to claim 22, which further
comprises a light guide member which outputs light entering from a
side face thereof after emitted from the diffusing plate arranged
at the opening part of the reflector of the linear light source,
from a lower face side thereof by grooves formed in a lower face or
an upper face thereof.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an illuminating system to
be used for printed articles such as books and photographs, screen
displays of personal computers or other office automation
equipment, portable information terminals, portable video tape
recorders and the like, or reflection type liquid crystal displays
used in various monitors, and the like.
[0002] In recent years, personal computers, portable information
terminals, video tape recorders and the like have been becoming
increasingly small-sized and portable, making it an important issue
to reduce the power consumption of their image display units. On
this account, many of them have been provided with reflection type
liquid crystal displays used as their image display units.
[0003] The reflection type liquid crystal display device is given
screen brightness by reflecting outside light such as sunlight and
indoor light. However, at places of less outside light, the device
could not afford enough brightness in the screen. As a result of
this, there have been invented several reflection type liquid
crystal displays equipped with an illuminating system which enables
screen display even at places of insufficient outside light.
[0004] An example of the illuminating system to be mounted on the
reflection type liquid crystal display device is shown. FIG. 16 is
a schematic cross-sectional view of a conventional illuminating
system. As shown in FIG. 16, the conventional illuminating system
comprises a light source 1, a reflector 2, a light guide member 63
and a compensating plate 5. In order that the reflector 2
collimates the light emitted from the light source 1, the distance
from the light source 1 to a side face of the light guide member 63
is elongated. The light guide member 63 has a function of
propagating the light introduced from the reflector 2 by totally
reflecting the light, and a function of illuminating a reflecting
plate 4 by totally reflecting the light with slopes of grooves
formed in its top face to change the angle of the light. The
compensating plate 5 has a function of correcting any distortion
that occurs when the reflected light from the reflecting plate 4
passes the light guide member 63.
[0005] However, in the conventional illuminating system, when the
light that has been transmitted by the light guide member 63 to the
compensating plate 5 comes incident on the light guide member 63
again after being totally reflected by the top face of the
compensating plate 5, part of the light is reflected by the slopes
of the grooves of the top face of the light guide member 63 so that
groove lines are more visible, as an issue. Also, whereas light is
collimated by a reflector to reduce the issue of these groove
lines' visibility, the collimated light is more likely to reach one
side of the light guide member 63 opposite to the light source
without impinging on the slopes of the grooves of the light guide
member 63. This would result in a low illuminating efficiency, as
another issue.
SUMMARY OF THE INVENTION
[0006] Therefore, an object of the present invention is to provide
an illuminating system which makes groove lines less visible,
maintains an image of reflected light successful and offers a good
illuminating efficiency.
[0007] In accomplishing these and other aspects, according to a
first aspect of the present invention, there is provided an
illuminating system comprising:
[0008] a light source; and
[0009] a transparent plate with the light source placed beside a
side face thereof,
[0010] wherein a plurality of grooves filled with a layer having a
refractive index different from a refractive index of the
transparent plate are arranged at specified intervals in a surface
or interior of the transparent plate.
[0011] According to a second aspect of the present invention, there
is provided an illuminating system according to the first aspect,
wherein a top face and a bottom face of the transparent plate are
generally parallel to each other.
[0012] According to a third aspect of the present invention, there
is provided an illuminating system according to the first or second
aspect, wherein a condition of
.theta.<sin.sup.-1(n.sub.1/n)-sin.sup.-1{(1/n)sin(.beta.)}
[0013] is satisfied where n is the refractive index of the
transparent plate, n.sub.1 is the refractive index of a material as
the layer that fills the grooves which are the slits, .theta. is an
angle formed by each of the slits and the top face of the
transparent plate and .beta. is an angle of visibility of the
illuminating system.
[0014] According to a fourth aspect of the present invention, there
is provided an illuminating system comprising:
[0015] a light source;
[0016] a transparent first plate with the light source placed
beside a side face thereof; and
[0017] a transparent second plate placed on a top face of the first
plate, wherein a bottom face of the first plate is a plane surface
and a plurality of stepwise slopes are arranged at specified
intervals in the top face of the first plate;
[0018] in a bottom face of the second plate, stepwise slopes are
arranged so as to be identical in configuration to the slopes of
the top face of the first plate; and
[0019] the top face of the first plate and the bottom face of the
second plate are placed with a specified spacing.
[0020] According to a fifth aspect of the present invention, there
is provided an illuminating system according to the fourth aspect,
wherein a condition of
.theta.<sin.sup.-1(n.sub.2/n)-sin.sup.-1{(1/n)sin(.beta.)}
[0021] is satisfied where n is the refractive index of the first
plate, n.sub.2 is the refractive index of a material as the layer
bonding the first plate and the second plate to each other, .theta.
is an angle of each of the slopes of the top face of the first
plate and the bottom face of the second plate and .beta. is an
angle of visibility of the illuminating system.
[0022] According to a sixth aspect of the present invention, there
is provided an illuminating system according to the fifth aspect,
wherein a light outgoing angle of a collimator placed at an
outgoing exit of the light source is within
.+-.sin.sup.-1[n.times.sin{90-.theta.-sin.sup.-1(n-
.sub.2/n)}].
[0023] According to a seventh aspect of the present invention,
there is provided an illuminating system by overhead irradiation
comprising:
[0024] a light source;
[0025] a transparent plate which is a light guide member in which a
plurality of grooves are arranged in a top face of the light guide
member at specified intervals in a direction parallel to a
longitudinal direction of the light source, and in which a flat
portion constituting a part of the top face is arranged between
adjacent ones of the grooves, wherein an illumination object placed
on a bottom face side of the light guide member is observed from a
top face side of the light guide member.
[0026] According to an eighth aspect of the present invention,
there is provided an illuminating system by overhead irradiation
according to the seventh aspect, wherein each of the grooves of the
light guide member is a V-shaped groove having a first slope
located on one side closer to the light source and a second slope
located on the other side farther from the light source, and
wherein an angle .theta..sub.1 formed by the first slope and the
bottom face of the light guide member falls within a range of
.theta..sub.1.ltoreq.90.degree.-.theta..sub.c+2.theta..sub.3, where
.theta..sub.c is a total reflection angle of the light guide member
and .theta..sub.3 is an angle formed by the flat portion and the
bottom face of the light guide member.
[0027] According to a ninth aspect of the present invention, there
is provided an illuminating system by overhead irradiation
according to the seventh or eighth aspect, wherein each of the
grooves of the light guide member is a V-shaped groove having a
first slope located on one side closer to the light source and a
second slope located on the other side farther from the light
source, and wherein an angle .theta..sub.1 formed by the first
slope and the bottom face of the light guide member satisfies a
condition of:
[0028] .theta..sub.1.apprxeq.45+.theta..sub.3-(1/2)sin
.sup.-1(1/n.times.sin.beta.), where n is a refractive index of the
light guide member, .theta..sub.3 is an angle formed by the flat
portion and the bottom face of the light guide member and .beta. is
an angle formed by a perpendicular of the bottom face of the light
guide member and a direction of the observer.
[0029] According to a tenth aspect of the present invention, there
is provided an illuminating system by overhead irradiation
according to any one of the seventh to ninth aspects, wherein each
of the grooves of the light guide member is a V-shaped groove
having a first slope located on one side closer to the light source
and a second slope located on the other side farther from the light
source, and wherein an angle .theta..sub.2 formed by the second
slope and the bottom face of the light guide member satisfies a
condition of .theta..sub.2.ltoreq.(1/2)sin.sup.-- 1(1/n), where n
is a refractive index of the light guide member.
[0030] According to an eleventh aspect of the present invention,
there is provided an illuminating system by overhead irradiation
according to any one of the seventh to tenth aspects, wherein in
the light guide member, a pitch of the grooves is not more than a
dot pitch of the illumination object.
[0031] According to a twelfth aspect of the present invention,
there is provided an illuminating system by overhead irradiation
according to any one of the seventh to eleventh aspects, wherein
each of the grooves of the light guide member is a V-shaped groove
having a first slope located on one side closer to the light source
and a second slope located on the other side farther from the light
source, and wherein in the light guide member, a length of the
first slope is not more than
{L.times.(0.5/60).times..sub..pi.+B/180}, where L is a distance
between the top face of the light guide member and an observer
observing the illumination object.
[0032] According to a thirteenth aspect of the present invention,
there is provided an illuminating system by overhead irradiation
according to any one of the seventh to twelfth aspects, wherein a
transparent prism sheet is placed on the top face of the light
guide member, the prism sheet having, with respect to a
cross-sectional shape, a plurality of projected portions having
slopes of an angle .theta..sub.4 to the top face are arranged on
the bottom face so that a flat portion generally parallel to the
bottom face is interposed therebetween.
[0033] According to a fourteenth aspect of the present invention,
there is provided an illuminating system by overhead irradiation
according to the thirteenth aspect, wherein the length of the slope
of the prism sheet is not more than
{L.times.(0.5/60).times..sub..pi./180}, where L is the distance
between the observer who observes the illumination object and the
top face of the light guide member.
[0034] According to a fifteenth aspect of the present invention,
there is provided an illuminating system comprising:
[0035] a light source; and
[0036] a transparent plate taking light from the light source
through a side face thereof and projecting illumination light
through a lower face thereof subjected to at least one of an
anti-reflection treatment and a diffuse treatment,
[0037] wherein an illumination object which is disposed at a lower
face side of the transparent plate is observed from an upper face
side of the transparent plate.
[0038] According to a sixteenth aspect of the present invention,
there is provided a reflection type liquid crystal display device
which comprises:
[0039] the illuminating system according to the first aspect, the
transparent plate taking light from the light source through a side
face thereof and projecting illumination light through a lower face
thereof subjected to at least one of an antireflection treatment
and a diffuse treatment; and
[0040] a reflection type liquid crystal panel having a surface of
at least one substrate thereof processed through at least one of
the anti-reflection treatment and the diffuse treatment,
[0041] wherein the surface of the substrate of the liquid crystal
panel processed through at least one of the anti-reflection
treatment and the diffuse treatment is arranged to confront a lower
face of the transparent plate, so that the reflection type liquid
crystal panel is observed from an upper face side of the
transparent plate.
[0042] According to a seventeenth aspect of the present invention,
there is provided a reflection type liquid crystal display device
which comprises:
[0043] the illuminating system according to the first aspect, the
transparent plate taking light from the light source through a side
face thereof and projecting illumination light through a lower face
thereof subjected to at least one of an antireflection treatment
and a diffuse treatment;
[0044] a reflection type liquid crystal panel having a surface of
at least one substrate thereof processed through at least either an
anti-reflection treatment or a diffuse treatment; and
[0045] a touch panel having a surface processed through a diffuse
treatment,
[0046] wherein the surface of the substrate of the liquid crystal
panel processed through at least either the anti-reflection
treatment or the diffuse treatment is arranged to confront the
lower face of the transparent plate and at the same time, the touch
panel is disposed to confront an upper face of the transparent
plate, so that the reflection type liquid crystal panel is observed
from an upper face side of the transparent plate.
[0047] According to an eighteenth aspect of the present invention,
there is provided a reflection type liquid crystal display device
according to any one of the sixteenth to seventeenth aspects,
wherein a haze value of the diffuse treatment provided to the
surface of the substrate of the reflection type liquid crystal
panel, the lower face of the transparent plate or the surface of
the touch panel is set to be not larger than 20%.
[0048] According to a nineteenth aspect of the present invention,
there is provided a reflection type liquid crystal display device
according to any one of the sixteenth to eighteenth aspects,
wherein a transparent material or a sheet of the material which has
approximately the same refractive index as that of a material of
the transparent plate and that of the substrate of the reflection
type liquid crystal panel is interposed between the lower face of
the transparent plate and the reflection type liquid crystal
panel.
[0049] According to a 20th aspect of the present invention, there
is provided a reflection type liquid crystal display device which
comprises:
[0050] the illuminating system according to the first aspect, the
transparent plate taking light from the light source through a side
face thereof and projecting illumination light from a lower face
thereof; and
[0051] a reflection type liquid crystal panel having an field angle
control plate arranged on an upper face thereof, said control plate
featuring a diffuse characteristic in one direction while being
transparent in other directions,
[0052] wherein the face of the reflection type liquid crystal panel
where the field angle control plate is arranged is set to confront
the lower face of the transparent plate, and moreover an angle of
the illumination light projected from the lower face of the
transparent plate is almost agreed with a diffusion direction of
the field angle control plate, so that the reflection type liquid
crystal panel is observed from an upper face side of the
transparent plate.
[0053] According to a 21st aspect of the present invention, there
is provided a reflection type liquid crystal display device
according to the 20th aspect, wherein an output angle of the
transparent plate and the diffusion direction of the field angle
control plate is 30-50.degree. to a normal direction of the
reflection type liquid crystal panel.
[0054] According to a 22nd aspect of the present invention, there
is provided an illuminating system according to the first aspect,
wherein the light house is a group of point light sources in which
point light sources are arranged on an almost straight line via a
constant interval to radiate in nearly the same direction,
[0055] the illuminating system further comprising:
[0056] a reflector having an opening part and disposed to cover the
group of point light sources; and
[0057] a diffusing plate set at the opening part of the
reflector,
[0058] wherein the diffusing plate is separated from the group of
point light sources so that quantity of light from a center of an
illuminance distribution by the point light source on the diffusing
plate is nearly equal to that between centers of illuminance
distributions of the point light sources.
[0059] According to a 23rd aspect of the present invention, there
is provided an illuminating system according to the 22nd aspect,
wherein the reflector is L-shaped so as not to directly pass light
emitted from the point light sources to the diffusing plate.
[0060] According to a 24th aspect of the present invention, there
is provided an illuminating system according to the 22nd aspect,
which further comprises a light guide member which outputs light
entering from a side face thereof after emitted from the diffusing
plate arranged at the opening part of the reflector of the linear
light source, from a lower face side thereof by grooves formed in a
lower face or an upper face thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] These and other aspects and features of the present
invention will become clear from the following description taken in
conjunction with the preferred embodiments thereof with reference
to the accompanying drawings, in which:
[0062] FIG. 1 is a schematic view of a cross section of an
illuminating system according to a first embodiment of the present
invention;
[0063] FIG. 2 is a schematic view showing an arrangement of slits
in the first embodiment;
[0064] FIG. 3 is a view for explaining the propagation of light
within the light guide member in the first embodiment;
[0065] FIG. 4 is a view for explaining the propagation of reflected
light within the light guide member in the first embodiment;
[0066] FIG. 5 is a schematic view of a cross section of an
illuminating system according to a second embodiment of the present
invention;
[0067] FIG. 6 is a view for explaining the propagation of light
within the light guide member in the second embodiment;
[0068] FIG. 7 is a view for explaining the propagation of light
within the light guide member in the second embodiment;
[0069] FIG. 8 is a view for explaining the propagation of reflected
light within the light guide member in the second embodiment;
[0070] FIGS. 9A and 9B are a schematic sectional view and a plan
view of the collimator in the second embodiment;
[0071] FIG. 10 is a view for explaining operation of the collimator
in the second embodiment;
[0072] FIG. 11 is a schematic view of a cross section of a
modification of the illuminating system of the first embodiment of
the invention;
[0073] FIG. 12 is a schematic view of a cross section of another
modification of the illuminating system of the first embodiment of
the invention;
[0074] FIG. 13 is a schematic view of a cross section of still
another modification of the illuminating system of the first
embodiment of the invention;
[0075] FIG. 14 is a schematic view of a cross section of an example
of the illuminating system of the second embodiment of the
invention;
[0076] FIGS. 15A and 15B are a schematic sectional side view and a
plan view of the collimator of the illuminating system in the third
embodiment;
[0077] FIG. 16 is a schematic view of a cross section of an
illuminating system according to the prior art;
[0078] FIG. 17 is a schematic view of a cross section of a
modification of the illuminating system of the second embodiment of
the invention; and
[0079] FIG. 18 is a schematic view of a cross section of another
modification of the illuminating system of the second embodiment of
the invention;
[0080] FIG. 19 is a schematic view of the illuminating system by
overhead irradiation according to a third embodiment of the present
invention;
[0081] FIG. 20 is a cross-sectional schematic view of the light
guide member in the third embodiment;
[0082] FIG. 21 is a cross-sectional schematic view showing in
detail the groove in the third embodiment;
[0083] FIGS. 22A, 22B, 22C, 22D, 22E are views for explaining the
reflection of light at the top face of the light guide member in
the third embodiment;
[0084] FIGS. 23A, 23B, 23C are cross-sectional schematic views
showing another example of the illuminating system in the third
embodiment;
[0085] FIG. 24 is a cross-sectional schematic view of an
illuminating system by overhead irradiation according to a fourth
embodiment of the present invention;
[0086] FIG. 25 is a cross-sectional schematic view of the prism
sheet in the fourth embodiment;
[0087] FIG. 26 is a graph showing the radiation distribution of
light outputted from the top face of the light guide member in the
fourth embodiment;
[0088] FIG. 27 is a view for explaining the reflection of light at
prism portions in the fourth embodiment;
[0089] FIGS. 28A, 28B are cross-sectional schematic views showing
another example of prism sheet in the fourth embodiment;
[0090] FIG. 29 is a view for explaining the propagation of light
within the prism sheet in the fourth embodiment;
[0091] FIG. 30 is a view of an illuminating system by overhead
irradiation in a fifth embodiment of the present invention, as
viewed from the top;
[0092] FIG. 31 is a cross-sectional schematic view of the light
guide member in the fifth embodiment;
[0093] FIG. 32 is a more detailed cross-sectional schematic view of
the illuminating system by overhead irradiation in the third
embodiment;
[0094] FIG. 33 is a more detailed cross-sectional schematic view of
the illuminating system by overhead irradiation in the fourth
embodiment;
[0095] FIG. 34 is a more detailed cross-sectional schematic view of
the illuminating system by overhead irradiation in the fourth
embodiment;
[0096] FIG. 35 is a cross-sectional schematic view of an
illuminating system according to the prior art;
[0097] FIG. 36 is a schematically sectional view of an illuminating
system according to a seventh embodiment of the present
invention;
[0098] FIG. 37 is a schematically sectional view of a transparent
plate of the seventh embodiment of the present invention;
[0099] FIG. 38 is a schematically sectional view of a reflection
type liquid crystal display device according to the seventh
embodiment of the present invention;
[0100] FIG. 39 is a schematically sectional view of a reflection
type liquid crystal display device according to an eighth
embodiment of the present invention;
[0101] FIG. 40 is a diagram explanatory of the seventh embodiment
of a method for manufacturing the transparent plate;
[0102] FIG. 41 is a diagram showing how the transparent plate is
held in the manufacture method of FIG. 40;
[0103] FIG. 42 is a schematically sectional view of a reflection
type liquid crystal display device in a ninth embodiment of the
present invention;
[0104] FIG. 43 is a diagram explanatory of the propagation;
[0105] FIG. 44 is a schematically sectional view of an illuminating
system of a tenth embodiment of the present invention;
[0106] FIG. 45 is a plan view of the illuminating system of FIG.
44;
[0107] FIG. 46 is a perspective view of a light guide member and a
reflecting plate of the illuminating system of FIG. 44;
[0108] FIG. 47 is an enlarged view of a circular part of FIG. 46;
and
[0109] FIGS. 48 and 49 are explanatory views of distance selection
between light sources and a diffusing plate of the system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0110] Before the description of the present invention proceeds, it
is to be noted that like parts are designated by like reference
numerals throughout the accompanying drawings.
[0111] Hereinbelow, an illuminating system according to a first
embodiment of the present invention is described with reference to
the accompanying drawings.
[0112] FIG. 1 shows a schematic view of a cross section of the
illuminating system in the first embodiment of the invention
without hatching in order to clearly show the lines. In the
illuminating system of the first embodiment of the invention, an
angle at which an observer views the illuminating system from above
(hereinafter, referred to as an angle of visibility (field angle))
is assumed to be .beta..
[0113] Referring to FIG. 1, reference numeral 1 denotes a light
source, in which, for example, fluorescent lamps, such as hot
cathode-ray tubes or cold cathode-ray tubes, or light emitting
diodes are arrayed in a linear shape, or in which incandescent
lamps or organic light-emitting materials are formed into a linear
shape. The light source 1 is arranged on one side of a light guide
member 3.
[0114] In FIG. 1, reference numeral 2 denotes a reflector, which is
placed so as to cover the light source 1, and of which the inner
surface is so made as to have a high reflectance and a small
diffusivity. For example, the reflector is made up by depositing a
high-reflectance material such as silver or aluminum on a resin
sheet, and bonding this sheet to a thin metal plate or resin sheet.
When the light source 1 is fluorescent lamp(s), it is desirable to
fill the gap between the light source 1 and the reflector 2 with a
material having a refractive index close to the glass' refractive
index of 1.5. It is also desirable that the thickness of one side
face of the light guide member 3 on the light source 1 side and the
height of the reflector 2 are equal to each other. The reason of
this is that whereas the light guide member 3 is desirably thinner
than not, the lower limit value of the thickness is the height of
the reflector 2 because of the incidence efficiency.
[0115] In FIG. 1, reference numeral 3 denotes a transparent plate
(hereinafter, referred to as light guide member), which is made
from a material such as quartz, glass, transparent resin like
acrylic resin or polycarbonate, or the like. Top face and bottom
face of the light guide member 3 are generally parallel to each
other, and the light guide member 3 is generally rectangular shaped
as viewed from top. Side face and top face as well as side face and
bottom face of the light guide member 3 each form an angle of
nearly 90 degrees. Slits 31 as grooves are formed in the bottom
face of the light guide member 3.
[0116] FIG. 2 shows a detailed view of a portion of the slits 31.
The slits 31 extend generally parallel longitudinally of the light
source 1. Each slit 31 is internally filled with a material of low
refractive index, which is exemplified by air or fluorine-contained
resin. Further, the slit 31 satisfies the following condition:
.theta.<sin.sup.-1(n.sub.1/n)-sin.sup.-1{(1/n)sin(.beta.)}
[0117] where n is the refractive index of the light guide member,
n.sub.1 is the refractive index of the slit interior, .theta. is
the angle formed by the slit 31 and the top face of the light guide
member and .beta. is the angle of visibility.
[0118] In the first embodiment, the material of the light guide
member is PMMA (polymethylmethacrylate), the slit interior is air
and the angle of visibility is 40 degrees. Therefore, from n=1.5,
n.sub.1=1 and .beta.=40, an angle .theta. formed by the slit 31 and
the top face of the light guide member has been set to 16 degrees.
Besides, a length 33 of the slit 31 is 50 .mu.m, and a pitch 32 of
the slits 31 is 200 .mu.m. If the angle of visibility .beta.=30,
then .theta.=22.34.degree..
[0119] In FIG. 1, reference numeral 4 denotes a reflecting plate.
The reflecting plate 4 means a printed article such as a book or
photograph, a screen display unit of personal computers or other
office automation equipment, portable information terminals,
portable video tape recorders and the like, or a reflection type
liquid crystal display used in various monitors.
[0120] Next, propagation of light within the light guide member 3
is described with reference to FIG. 3.
[0121] Light incident on the light guide member 3 results in light
having a radiation distribution of .+-.sin.sup.-1(1/n) according to
Snell's law, given that the refractive index of the light guide
member 3 is n. Since most of the above-mentioned materials of the
light guide member 3 have a refractive index of not less than 1.42,
the radiation distribution falls within a range of .+-.44.77
degrees. In the light guide member 3, its top face and bottom face
are generally parallel to each other, and its side face and top
face as well as its side face and bottom face, the side face being
planes of incidence on the light guide member 3, form an angle of
nearly 90.degree. C., respectively. Therefore, when light incident
on a side face of the light guide member 3 comes incident on its
top face or bottom face, the minimum value of incident angle is
90-44.77=45.23 degrees. With a refractive index of not less than
1.42, because the angle of total reflection is 44.77 degrees or
lower, light incident on the side face is totally reflected by the
top face and the bottom face.
[0122] At places other than near the slits 31, light that
propagates through the light guide member 3 is totally reflected by
flat portions of the top face and the bottom face of the light
guide member 3. At the portions of the slits 31, the light is
separated into transmitted beams of light and totally reflected
beams of light depending on the angle of light. As shown in FIG. 3,
on the assumption that the angle formed by a light beam and the top
face of the light guide member 3 is .alpha., if
.alpha.>90-.theta.-sin.sup.-1(n.sub.1/n),
[0123] then the light is transmitted through the slits 31; and
if
.alpha.<90-.theta.-sin.sup.-1(n.sub.1/n),
[0124] then the light is totally reflected by the slits 31.
[0125] A beam of light transmitted through the slits 31 is totally
reflected by the flat portion of the top face of the light guide
member 3, thus propagating again. The beam of light totally
reflected by the slit 31 goes out from the bottom face of the light
guide member 3, where the angle of incidence on the bottom face is
{90 -(2.eta.+.alpha.)} and from Snell's law, if
90-(2.eta.+.alpha.)<sin.sup.-1(1/n),
[0126] then the light beam goes out from the bottom face of the
light guide member 3, thus illuminating the reflecting plate 4.
[0127] In this way, the illuminating system of the first embodiment
illuminates the reflecting plate 4. Because the light emitted from
the light source 1 does not need to be collimated, the light is
totally reflected by the slits 31 at a high rate, so that the
reflecting plate 4 can be illuminated with high efficiency. Also,
the light transmitted through the slits 31 propagates once again
through the light guide member 3, producing an effect that the
groove lines are less visible.
[0128] Next, propagation of the reflected light that has
illuminated the reflecting plate 4 is described with reference to
FIG. 4. Light outputted for illumination from the light guide
member 3 illuminates the reflecting plate 4, and turns back as
reflected light. The reflected light comes incident again on the
light guide member 3 from its bottom face, and is outputted from
the top face of the light guide member 3 as it is at portions other
than near the slits 31.
[0129] Near the slits 31, if the angle of incidence of the
reflected light on the bottom face of the light guide member 3 is
.gamma., then
.theta.+sin.sup.-1{(1/n)sin(.gamma.)}>sin.sup.-1(n.sub.1/n),
[0130] the light is totally reflected by the slits 31. On this
account, upon incidence of the reflected light 41 on the bottom
face of the light guide member 3 at an angle .gamma., if .gamma.
>.beta., then the reflected light 41 is totally reflected by the
slits 31, not reaching the observer; if .gamma..ltoreq..beta., then
the reflected light 41 is transmitted through the slits 31,
reaching the observer.
[0131] From this fact and another that the angle .theta. of the
slits 31 is
.theta.<sin.sup.-1(n.sub.1/n)-sin.sup.-1{(1/n)sin(.beta.)},
[0132] the reflected light is not totally reflected by the portions
of the slits 31 in a range of the angle of visibility .+-..beta..
Thus, the observers field of view is not obstructed, and a
successful image can be obtained.
[0133] As shown above, according to this first embodiment, the
illuminating system which makes the groove lines of the light guide
member 3 less visible, maintains an image of reflected light
successful and offers a good illuminating efficiency can be
provided. Also, since uniform illumination is enabled and the light
outputted from the light source 1 does not need to be collimated,
the reflector 2 can be reduced in size. Moreover, since the height
of the reflector 2 and the height of the side face of the light
guide member 3 are made generally equal to each other as described
above, the thickness of the side face of the light guide member 3
can be reduced according to the height of the reflector 2.
[0134] In addition, in the first embodiment, the slits 31 have been
arranged in the top face of the light guide member 3. However, it
is also possible that the slits 31 are arranged between the top
face and the bottom face of the light guide member 3 as shown in
FIG. 11, or in the bottom face of the light guide member 3 as shown
in FIG. 12, or obliquely in a direction from the top face side to
the bottom face side of the light guide member 3 as shown in FIG.
13.
[0135] Further, although top face and bottom face of the light
guide member 3 are parallel to each other in the first embodiment,
they may be non-parallel.
[0136] Furthermore, although the pitch 32 of the slits 31 has been
made to be a constant interval in the first embodiment, making the
pitch 32 decreasing with increasing distance from the light source
1 for the light guide member 3 causes the brightness difference
between near places and far places from the light source 1 to be
reduced, so that more uniform illumination can be obtained. Making
the length 33 of the slits 31 increasing with increasing distance
from the light source 1 for the light guide member 3 also allows
similar effects to be obtained. Still also, making the angle
.theta. of the slits 31 increasing with increasing distance from
the light source 1 allows similar effects to be obtained.
[0137] Now, an illuminating system according to a second embodiment
of the present invention is described below with reference to FIG.
5.
[0138] FIG. 5 is a schematic view of a cross section of the
illuminating system in the second embodiment of the invention. In
the illuminating system of the second embodiment of the invention,
the angle of visibility is assumed as .beta..
[0139] In FIG. 5, the light source 1 and the reflector 2 are
similar to those of the first embodiment.
[0140] Referring to FIG. 5, reference numeral 30 denotes a light
guide member as an example of the first transparent plate, and 6
denotes a compensating plate as an example of the second
transparent plate placed on the light guide member 30. Reference
numeral 5 denotes a collimator placed between the light source 1
and the light guide member 30, and the collimator 5 collimates
light emitted from the light source 1. Output characteristic of the
collimator 5 is within .+-.sin-.sup.1[n.times.sin{9-
0-.theta.-sin.sup.-1(n.sub.2/n)}], where .theta. is the angle of a
stepwise slope 131 of the top face of the light guide member 30, n
is the refractive index of the light guide member 30 and n.sub.2 is
the refractive index of the material between the light guide member
30 and the compensating plate 6.
[0141] For example, if .beta.=40, n=1.5 and n.sub.2=1, then
.theta.=16.degree., where the output characteristic of the
collimator 5 is .+-.52.13.degree.. Also, if .beta.=30, n=1.5 and
n.sub.2=1, then .theta.=22.34, where the output characteristic of
the collimator 5 is .+-.40.85.degree..
[0142] The structure of the collimator 5 can be implemented by, for
example, a plano-convex cylindrical lens satisfying the above
output characteristic. Further, the collimator 5 may also be a
diffraction grating. Besides, with a large angle of visibility
.beta. of the illuminating system, the output characteristic angle
of the collimator 5 is so large that the collimator 5 may be
omitted.
[0143] The light guide member 30 is made from a material such as
quartz, glass, transparent resin like acrylic resin or
polycarbonate, or the like. FIG. 6 shows a detailed view of the
light guide member 30. A bottom face of the light guide member 30
is a plane surface, and a plurality of stepwise slopes 131 are
arranged at specified intervals in the top face of the light guide
member 30. The slopes 131 are generally parallel to the
longitudinal direction of the light source 1.
[0144] Assuming that the angle of each slope 131 is 0, the
refractive index of the material of the light guide member 30 is n,
the refractive index of the material between the light guide member
30 and the compensating plate 6 is n.sub.2 and that the angle of
visibility is .beta., then angle .theta. of the slope 131 is
.theta.<sin.sup.-1(n.sub.2/n)-sin.sup.-1{(1/n)sin(.beta.)}.
[0145] A pitch 32 of the slopes 131 is preferably decreasing with
increasing distance from the light source 1 for the light guide
member 30. Also, a length 33 of the slopes 131 may be increasing
with increasing distance from the light source 1 for the light
guide member 30. Further, the angle .theta. of the slopes 131 may
be increasing with increasing distance from the light source 1. The
light guide member 30 is generally rectangular shaped as viewed
from top.
[0146] The compensating plate 6 is made from a material such as
quartz, glass, transparent resin like acrylic resin or
polycarbonate, or the like. In the compensating plate 6, stepwise
slopes 61 are arranged in its bottom face so as to be identical in
configuration to the slopes 131 of the top face of the light guide
member 30, and the top face of the compensating plate 6 is a plane
surface. The top face of the light guide member 30 and the bottom
face of the light guide member 30 are placed at a specified
spacing.
[0147] In FIG. 5, reference numeral 4 denotes a reflecting plate.
The reflecting plate 4 means a printed article such as a book or
photograph, a screen display unit of personal computers or other
office automation equipment, portable information terminals or
portable video tape recorders, a reflection type liquid crystal
display used in various monitors or the like.
[0148] Next, propagation of light within the light guide member 30
in the second embodiment is described with reference to FIG. 7.
Light incident on the light guide member 30 propagates while being
totally reflected by flat portions of the top face or bottom face
of the light guide member 30 at places other than near the slopes
131 of the light guide member 30. At the portions near the slopes
131 of the light guide member 30, the light is separated into
transmitted beams of light and totally reflected beams of light
depending on the angle of the light. On the assumption that the
refractive index of the light guide member 30 is n, the refractive
index of the material between the light guide member 30 and the
compensating plate 6 is n.sub.2, the angle formed by the bottom
face of the light guide member 30 and the light is .alpha., and
that the angle of the slopes 131 of the light guide member 30 is
.theta., if
.alpha.>90-.theta.-sin.sup.-1(n.sub.2/n)
[0149] then the light is transmitted through the slopes 131 of the
light guide member 30; and if
.alpha.<90-.theta.-sin.sup.-1(n.sub.2/n)
[0150] then the light is totally reflected by the slopes 131 of the
light guide member 30.
[0151] The light transmitted through the slopes 131 of the light
guide member 30 will not be reflected until it reaches one side of
the compensating plate 6 opposite to the light source 1 side.
Therefore, the light is highly likely to go out toward the
observer's side, causing a deterioration of the illuminating
efficiency. However, because the output characteristic of the
collimator 5 for the light source 1 is within
.+-.sin.sup.-1[n.times.sin(90-.theta.-sin.sup.-1{n.sub.2/n)}], the
light incident on the light guide member 30 is within
.+-.{90-.theta.-sin.sup.-- 1(n.sub.2/n)}, satisfying the condition
of Equation .alpha.<90-.theta.-sin.sup.-1(n.sub.2/n), so that
most of the light is totally reflected by the slopes 131 of the
light guide member 30, illuminating the reflecting plate 4.
[0152] Therefore, the light emitted from the light source 1 is
enabled to display the reflecting plate 4 with high efficiency.
Also, since the reflecting plate 4 is illuminated with high
efficiency in this way, less light is transmitted through the
slopes 131 of the light guide member 30 to the observer side,
producing an effect that the groove lines are less visible.
[0153] Next, propagation of the reflected light that has
illuminated the reflecting plate 4 is described with reference to
FIG. 8. The light beam outputted for illumination from the light
guide member 30 illuminates the reflecting plate 4, and turns back
as reflected light. The reflected light comes incident again on the
light guide member 30 from its bottom face, and is outputted from
the top face of the light guide member 30 as it is at portions
other than near the slopes 131 of the light guide member 30.
[0154] Near the slopes 131 of the light guide member 30, on the
assumption that the angle of incidence of the reflected light on
the bottom face of the light guide member 30 is .gamma., if
.theta.+sin.sup.-1{(1/n)sin(.gamma.)}>sin.sup.-1(n.sub.2/n),
[0155] then the light is totally reflected by the slopes 131 of the
light guide member 30. On this account, upon incidence of the
reflected light 41 on the bottom face of the light guide member at
an angle .gamma., if .gamma.>.beta., then the reflected light 41
is totally reflected by the slopes 131, not reaching the observer;
if .gamma..ltoreq..beta., the reflected light 41 is transmitted
through the slopes 131, reaching the observer.
[0156] From this fact and another that the angle .theta. of the
slopes 131 of the light guide member 30 is
.theta.<sin.sup.-1(n.sub.2/n)-sin.sup.-1{(1/n)sin(.beta.)},
[0157] the reflected light is not totally reflected by the portions
of the slopes 131 of the light guide member 30 in a range of the
angle of visibility .+-..beta.. Thus, the observer's field of view
is not obstructed, and a successful image can be obtained.
[0158] As shown above, according to the second embodiment, the
illuminating system which makes groove lines of the light guide
member 30 less visible, maintains an image of reflected light
successful and offers a good illuminating efficiency can be
provided.
[0159] In addition, although the groove has been formed stepwise in
the second embodiment, the groove may also be an arbitrary curve as
shown in FIG. 14. Further, although the pitch 32 of the slopes 131
has been a constant interval in the second embodiment, making the
pitch 32 decreasing with increasing distance from the light source
1 for the light guide member 30 causes the brightness difference
between near places and far places from the light source 1 to be
reduced, so that more uniform illumination can be obtained. Making
the length 33 of the slopes 131 increasing with increasing distance
from the light source 1 for the light guide member 30 also allows
similar effects to be obtained. Still also, making the angle
.theta. of the slopes 131 increasing with increase distance from
the light source 1 allows similar effects to be obtained.
[0160] Also, even if the top face of the compensating plate 6 and
the bottom face of the light guide member 30 are not parallel to
each other as shown in FIG. 17, similar effects can be
obtained.
[0161] Also, even if the top face of the compensating plate 6 is a
curved surface as shown in FIG. 18, similar effects can be
obtained.
[0162] Now, an illuminating system according to a third embodiment
of the present invention is described below.
[0163] The third embodiment of the invention is almost similar in
structure to the second embodiment, and differs therefrom only in
the structure of the collimator 5.
[0164] The structure of the collimator 5 of the third embodiment is
described with reference to FIG. 9. A light incident surface 51 of
the collimator 5 is a plane surface. An output surface 52 of the
collimator 5 is so structured as to have a plurality of conical
recessed portions with apex angle 2.delta..
[0165] On the assumption that the refractive index of the light
guide member 30 is n, the refractive index of the material bonding
the light guide member 30 and the compensating plate 6 to each
other is n.sub.2 and the refractive index of the collimator 5 is
n.sub.3, .delta. is a value that satisfies the equation:
sin.sup.-1[n.times.sin{90-.theta.-sin.sup.-1(n.sub.2/n)}]=90-.delta.-sin.s-
up.-1[n.sub.3.times.sin(90-.delta.-sin.sup.-1(1/n.sub.3)}].
[0166] Next, operation of the collimator 5 is described with
reference to FIG. 10. Light emitted from the light source 1, when
incident on the incident surface 51 of the collimator 5, results in
a radiation distribution of .+-.sin.sup.-1(1/n.sub.3). Therefore,
the angle of light incident on the slopes 52 of the collimator 5 on
its output side can be determined geometrically, where an
incident-angle minimum value i.sub.min is
i.sub.min=90-.delta.-sin.sup.-1(1/n.sub.3),
[0167] and the incident-angle maximum value i.sub.max is
+I.sub.max=90.
[0168] Also, the angle of light outputted from the collimator 5 can
be determined by Snell's law, where an outgoing angle minimum value
o.sub.min with respect to the slope 52 on the outgoing side is
o.sub.min=sin.sup.-1{n.sub.3.times.sin(i.sub.min)},
[0169] and an outgoing angle maximum value o.sub.max is
o.sub.max=90.
[0170] Because the slope 52 on the outgoing side is tilted by
.delta. with respect to the optical axis, an outgoing angle maximum
value .omega..sub.max is
.omega..sub.max=90-.delta.-o.sub.min,
[0171] and the outgoing angle minimum value .omega..sub.min is
.omega..sub.min=-.delta..
[0172] That is,
.omega..sub.max=90-.delta.-sin.sup.-1[n.sub.3.times.sin{90-.delta.-sin.sup-
.-1(1/n.sub.3)}],
.omega..sub.min=-.delta..
[0173] In this connection, if the angle of the slope 131 of the
light guide member 30 is .theta. and the refractive index of the
material between the light guide member 30 and the compensating
plate 6 is n.sub.2, then necessary output characteristic of the
collimator 5 is within
.+-.sin.sup.-1[n.times.sin{90-.theta.-sin.sup.-1(n.sub.2/n))}].
Because .delta. is a value satisfying the equation,
sin.sup.-1[n.times.sin{90-.theta.-sin.sup.-1(n.sub.2/n)}]=
90-.delta.-sin.sup.-1[n.sub.3.times.sin{90-.delta.-sin.sup.-1(1/n.sub.3)}-
], .omega..sub.max=(output characteristic of collimator 5), thus
satisfying a desired output characteristic.
[0174] For example, if angle of visibility .beta.=30, n=1.5,
n.sub.2=1 and n.sub.3=1.5, then .theta.=22.4 so that the necessary
output characteristic is 40.85.degree., where with
.delta.=46.2.degree., the resulting outgoing angle is
.omega..sub.max=+40.81.degree. and .omega..sub.min=46.2.degree., so
that a desired output characteristic of the collimator 5 is
obtained. Also, if .delta. is a value satisfying an equation,
.delta.=sin.sup.-1[n.times.sin{90-.theta.-sin.sup.-1(n.sub.2/n)-
}], then, in the above example, .delta.=40.85.degree.,
.omega..sub.max=+38.10.degree. and .omega..sub.min=40.85.degree. so
that a desired output characteristic of the collimator 5 is
obtained. In addition, under the above conditions, .delta. may be
an arbitrary value of not less than 40.85.degree. and not more than
46.2.degree..
[0175] As shown above, with the use of the third embodiment, the
collimator 5 which satisfies the output characteristic necessary
for the light guide member 30 can be implemented and the same
effects as in the second embodiment can be obtained.
[0176] In addition, the outgoing surface 52 of the collimator 5 has
been shaped into conical recessed portions with the apex angle
2.delta. in the third embodiment. However, the outgoing surface 52
may also be shaped into conical protrusions with the apex angle
2.delta.. Further, the outgoing surface 52 may be shaped into
polygonal pyramids having a cross section with the apex angle
2.delta. instead of the conical shape. Still further, the outgoing
surface 52 may be shaped into parallel grooves with the acute angle
2.delta. as shown in FIGS. 15A, 15B.
[0177] According to the present invention, light emitted from the
light source becomes incident on the transparent plate, and
propagates on and on while being iteratively totally reflected
within the transparent plate. During this process, the light is
separated into totally reflected beams of light by the slits
provided inside the transparent plate and transmitted beams of
light depending on the angle of light. The totally reflected beams
of light are changed in angle so as to be smaller than the total
reflection angle, thus being outputted to the bottom face side of
the transparent plate. Also, the transmitted beams of light are
totally reflected by the top face of the transparent plate so as to
continuously propagate within the transparent plate, thus groove
lines of the transparent plate being less visible. Further, the
light is transmitted through the grooves and the collimator that
has conventionally been needed to make the groove lines less
visible is no longer needed, so that almost all the beams of light
are outputted to the bottom side of the transparent plate, thus
offering a good illuminating efficiency.
[0178] The light outgoing from the bottom face of the transparent
plate illuminates an illumination object, and reflected light from
the illumination object is made to be incident again on the
transparent plate, where because
.theta.<sin.sup.-1(n.sub.1/n)-sin.sup.-1{(1/n)sin(.beta.)},
[0179] a successful image can be displayed without being affected
by the angle of visibility (field angle).
[0180] Thus, an illuminating system which makes groove lines less
visible and has a good illuminating efficiency can be provided.
[0181] In other words, as described above, according to the present
invention, a light source, for example a linear light source, is
placed beside a side face of a flat-shaped light guide member, and
slits as an example of grooves are arranged inside the light guide
member so as to extend generally parallel to the light source, by
which most of the light that propagates within the light guide
member can be outputted from the light guide member by total
reflection at the slits formed in the light guide member so that a
reflecting plate as an example of the illumination object can be
illuminated. Also, because beams of light transmitted without being
totally reflected by the slits propagate again within the light
guide member, the groove lines are less visible, and because the
reflected light from the reflecting plate is transmitted to the
observer side without being distorted, a successful image quality
of the reflecting plate can be maintained. Further, because the
light emitted from the light source does not need to be collimated,
the illuminating system can be downsized, and because all the beams
of light are outputted from the light guide member by the total
reflection at the slits, a good illuminating efficiency can be
obtained. Further, by arranging the slits at a specified angle, the
brightness difference between the slits and portions other than the
slits is made smaller within the observer's field of view, so that
a successful image quality of reflected light can be
maintained.
[0182] According to the present invention, light emitted from the
light source is collimated by the collimator and introduced to the
first substrate. The light incident on the first substrate is
totally reflected by the slopes of the first substrate, where the
angle of light is changed so as to be smaller than the total
reflection angle, thus being outputted to the bottom face side.
[0183] Also, the light outputted from the bottom face of the first
substrate illuminates an illumination object, and reflected light
from the illumination object is made to be incident again on the
first substrate, where the presence of the second substrate
eliminates any distortion of the image, and if
.theta.<sin.sup.-1(n.sub.1/n)-sin.sup.-1{(1/n)sin(.beta.)},
[0184] a successful image can be displayed without being affected
by the angle of visibility.
[0185] Also, if the light outgoing angle of the collimator is
within .+-.{90-.theta.- sin.sup.-1(n.sub.1/n)}, then all of the
beams of light emitted from the light source can be totally
reflected by the slopes of the first substrate to illuminate the
illumination object therewith, thus offering a good illuminating
efficiency.
[0186] Thus, an illuminating system which makes the groove lines
less visible, maintains image quality of reflected light successful
and offers a good illuminating efficiency can be provided.
[0187] In other words, according to the present invention, a light
source, for example a linear light source, is placed beside a side
face of a light guide member as an example of a first transparent
plate, and light emitted from the light source is collimated by a
collimator. Also, in the configuration of the light guide member, a
bottom face of the light guide member is a plane surface and slopes
are provided at a specified angle in the top face of the light
guide member, and to this light guide member is bonded a
compensating plate as an example of a second transparent plate
whose top face is a plane surface and whose bottom face has grooves
of the same configuration as in the light guide member formed
therein, by which most of the light that propagates within the
light guide member is totally reflected by the stepwise slopes of
the light guide member so as to be outputted from the light guide
member, thus allowing the reflecting plate as an example of the
illumination object to be illuminated. Further, because the
presence of the compensating plate allows the reflected light from
the reflecting plate to be transmitted to the observer's side
without being distorted, a successful image quality of the
reflecting plate can be maintained. Further, because the light
emitted from the light source is collimated into a specified angle
by the collimator, the light is not transmitted from the light
guide member to the compensating plate, allowing the reflecting
plate to be illuminated with high efficiency and besides making the
groove lines less visible. Further, by making the stepwise slopes
into a specified angle, the brightness difference between the
stepwise slopes and portions other than the slopes can be made
smaller within the observer's field of view, so that a successful
image quality of the reflected light can be maintained.
[0188] Further, according to still another aspect of the present
invention, the collimator which satisfies the output characteristic
necessary for the light guide member can be implemented, and the
same effects as in the foregoing aspects can also be obtained.
[0189] FIG. 35 is a schematic cross-sectional view of an
illuminating system. As shown in FIG. 35, the illuminating system
comprises a light source 101, a reflector 102, a light guide member
103 and a compensating plate 105. In order that the reflector 102
collimates the light emitted from the light source 101, the
distance from the light source 101 to a side face of the light
guide member 103 is elongated. The light guide member 103 has a
function of totally reflecting and propagating the light introduced
from the reflector 102, and a function of illuminating a reflecting
plate 104 by totally reflecting the light with slopes of grooves
formed in its top face to change the angle of the light. The
compensating plate 105 has a function of correcting any distortion
that occurs when the reflected light from the reflecting plate 104
passes the light guide member 103.
[0190] However, since the illuminating system has a double sheet
construction of the light guide member 103 and the compensating
plate 105 and since the light guide member 103 and the compensating
plate 105 are bonded together with their grooves identical in
shape, their alignment may be difficult to accomplish and the
fabrication costs high.
[0191] Therefore, following embodiments of the present invention
have an aim of solving these issues.
[0192] Hereinbelow, an illuminating system by overhead irradiation
according to a third embodiment of the present invention is
described with reference to the accompanying drawings.
[0193] FIGS. 19 and 32 are a schematic view and a more detailed
schematic view, respectively, of a cross section of the
illuminating system by overhead irradiation in the third embodiment
of the invention.
[0194] Referring to FIG. 1, reference numeral 1 denotes a light
source, in which a plurality of, for example, fluorescent lamps,
such as hot cathode-ray tubes or cold cathode-ray tubes, or light
emitting diodes are arrayed in a linear shape, or in which
incandescent lamps or organic light-emitting materials are formed
into a linear shape. The light source 1 is arranged on one side of
a light guide member 203.
[0195] In FIG. 19, reference numeral 2 denotes a reflector, which
is placed so as to cover the light source 1, and of which the inner
surface is so made as to have a high reflectance and a small
diffusivity. For example, the reflector is made up by depositing a
high-reflectance material such as silver or aluminum on a resin
sheet, and bonding this sheet to a thin metal plate or resin sheet.
When the light source 1 is a fluorescent lamp, it is desirable to
fill the gap between the light source 1 and the reflector 2 with a
material having a refractive index close to the glass' refractive
index of 1.5. It is also desirable that the thickness of one side
face of the light guide member 203 on the light source 1 side and
the height of the reflector 2 are equal to each other.
[0196] In FIG. 19, a light guide member 203 is, as an example, a
transparent plate (hereinafter, referred to as light guide member),
which is made from a material such as quartz, glass, transparent
resin like acrylic resin or polycarbonate, or the like. As shown in
FIG. 20, the light guide member 203 is set to a size equivalent to
the size of an illumination object. A bottom face 232 and an
incident surface 233 of the light guide member 203 form an angle of
about 90 degrees. The light guide member 203 is generally wedge
shaped as a whole, and a top face 231 of the light guide member 203
is tilted so as to be gradually closer to the bottom face 232 of
the light guide member 203 with increasing distance from the light
source 1. That is, if the thickness of the side face 233 of the
light guide member 203 on the light source side is d1 and the
thickness of the other side face on the side opposite to the light
source 1 is d2, then d1.gtoreq.d2. The relationship of these
thicknesses may be that d1=d2 basically, but a relationship of
d1>d2 allows the brightness to be maintained uniform, further
favorably. Also, a plurality of V-shaped grooves 204 are formed in
the top face 231 of the light guide member 203.
[0197] FIG. 21 shows a detailed view of the groove 204. The groove
204 is formed so as to extend generally parallel to the
longitudinal direction of the light source 1 (a direction vertical
to the drawing sheet), and V-shaped in its cross section. A slope
of the groove 204 on the light source side is referred to as a
first slope 241. A slope of the groove 204 on the side opposite to
the light source 1 is referred to as a second slope 242. Further, a
portion of the light guide member top face 231 where no groove 204
is present is referred to as a flat portion 243. The flat portions
243 constitute a part of the top face 231 that are one plane. An
angle .theta..sub.1 formed by the light guide member bottom face
232 and the first slope 241 of the groove 204 is within a range
that .theta..sub.1.ltoreq.90.degree.-.theta..sub.c+2.theta..sub.3
and that .theta..sub.1.apprxeq.
45.degree..theta..sub.3-(1/2)sin.sup.-1(1/n.times.- sin.beta.),
where .theta..sub.c is the total reflection angle, .theta..sub.3 is
the angle formed by the flat portion 243 and the light guide member
bottom face 232 and .beta. is the angle formed by a perpendicular
of the bottom face 232 and the observers direction. In addition, in
FIG. 21, reference numeral 332 denotes an imaginary plane parallel
to the bottom face 232.
[0198] An angle .theta..sub.2 formed by the light guide member
bottom face 232 and the second slope 242 of the groove 204 is that
.theta..sub.2.ltoreq.(1/2)sin.sup.-1(1/n), where n is the
refractive index of the light guide member 203.
[0199] It is noted that as shown in FIG. 20, both pitch p and depth
h of the groove 204 are based on the top face 231 as a reference
plane.
[0200] In FIG. 19, on the other hand, reference numeral 205 denotes
a reflecting surface. The reflecting surface 205 is a printed
article such as a book or photograph, a screen display unit of
personal computers or other office automation equipment, portable
information terminals, portable video tape recorders and the like,
or a reflection type liquid crystal display used in various
monitors.
[0201] Also in FIG. 19, reference numeral 206 denotes an observer
(more precisely, an observer's eye). The observer 206 views the
reflecting surface 205 through the light guide member 203.
[0202] Next, operation of the illuminating system according to the
third embodiment of the present invention is described.
[0203] Light that has been thrown from the light source 1 to be
incident on the light guide member 203 at its incident surface 233
results in light having a radiation distribution of
.+-.sin.sup.-1(1/n) centered on the 0.degree. direction according
to Snell's law, given that the refractive index of the light guide
member 203 is n. Since most of the material of the light guide
member 203 has a refractive index of not less than 1.42, the
radiation distribution falls within a range of .+-.44.77.degree..
Therefore, the incident light beam propagates within the light
guide member 203 at the radiation distribution of
.+-.44.77.degree.. The light beam incident on the light guide
member bottom face 232 has an incident angle of
90.degree.-44.77.degree.=45.23.d- egree. or more, which is larger
than the total reflection angle, so that the light beam is totally
reflected by the light guide member bottom face 232.
[0204] Next, operation of the light at the light guide member top
face 231 is described with reference to the accompanying drawings.
The light guide member top face 231 is so structured that a
plurality of the flat portion 243 and a plurality of the grooves
204 each composed of the first slope 241 and the second slope 242
are arranged, and the reflection at the light guide member top face
231 is classified into the following five patterns as shown in
FIGS. 22A-22E. The first pattern of FIG. 22A is light incident on
the flat portion 243. A second pattern of FIG. 22B is light
incident on the first slope 241. A third pattern of FIG. 22C is
light incident on the second slope 242. In the following
description, .alpha. is assumed to be an angle formed by the light
guide member bottom face 232 and the light reaching the light guide
member top face 231. Because the light reaching the light guide
member top face 231 is light having a distribution of the positive
direction out of the light having the radiation distribution of
.+-.sin.sup.-1(1/n) centered on 0.degree., a is not less than
0.degree. and the light has the maximum radiation distribution at
0.degree..
[0205] In the first pattern of FIG. 22A, the light is incident on
the flat portion 243 at an incident angle of
{90.degree.-.alpha.-.theta..sub.3}. Because .theta..sub.3 is a
small value, most of light is reflected. The light reflected by the
flat portion 243 results in an angle of
{-.alpha.-2.times..theta..sub.3}.
[0206] In the second pattern of FIG. 22B, the light is incident on
the first slope 241 at an incident angle of
{90.degree.-.alpha.-.theta..sub.1- }. The light that has been
incident on the first slope 241 is partly reflected by Fresnel
reflection and partly transmitted to be a loss. The light reflected
by the first slope 241 results in an angle of light of
{-.alpha.-2.times..theta..sub.1}.
[0207] In the third pattern of FIG. 22C, the light is incident on
the second slope 242 at an incident angle of
{90.degree.-.alpha.+.theta..sub.- 2}. Since the light reflected by
the second slope 242 results in an angle of light of
{-.alpha.+2.times..theta..sub.2}, the reflected light, when
.theta..sub.2 is a small value, results in more parallel light than
the light which is prior to the reflection.
[0208] Actually, the light is reflected in a composite combination
of the first to third patterns. Although not limited because of
differences depending on the size of the illuminating system, the
groove height h is set to around 5 .mu.m-25 .mu.m and the pitch p
is set to around 100 .mu.m to 250 .mu.m in this case. As a result,
not a few rays of light, after being reflected by the flat portion
243, are reflected by the first slope 241 (in a combination of the
first pattern and the second pattern). This pattern is referred to
as a fourth pattern of FIG. 22D.
[0209] In the fourth pattern of FIG. 22D, the light is incident on
the first slope 241 at an incident angle of
{90.degree.-(-.alpha.-2.times..th- eta..sub.3)-.theta..sub.1}. In
this case, since .theta..sub.1 satisfies that
.theta..sub.1.ltoreq.90.degree.-.theta..sub.c+2.theta..sub.3, the
incident angle onto the first slope 241 is
90.degree.-(-.alpha.-2.times..-
theta..sub.3)-.theta..sub.1.gtoreq..alpha.+.theta..sub.c (where
.theta..sub.c is the total reflection angle). Because .alpha. is
not less than 0.degree., all the rays of light are larger than the
total reflection angle and are totally reflected, preferably. In
addition, .theta..sub.1, when not more than 20.degree., would cause
a difficulty in the view of the observer 206, so that .theta..sub.1
is preferably set to an angle over 20.degree..
[0210] The light reflected by the first slope 241 results in an
angle of light of
{.alpha.+2.times..theta..sub.3-2.times..theta..sub.1}, and becomes
incident on the light guide member bottom face 232 at an incident
angle of
{90.degree.+.alpha.+2.times..theta..sub.3-2.times..theta..sub.1}- .
In this case, since .theta..sub.1 satisfies that
.theta..sub.1.apprxeq.4-
5.degree.+.theta..sub.3-(1/2)sin.sup.-1(1/n.times.sin.beta.), the
incident angle on the bottom face 232 is
90.degree.+.alpha.+2.times..theta..sub.3--
2.times.9.theta..sub.1.apprxeq..alpha.+sin.sup.-1(1/n.times.sin.beta.).
It is noted here that .beta. is the angle formed by the direction
perpendicular to the reflecting surface 205 and the direction of
observation by the observer 206 as shown in FIG. 19, that is,
.beta. indicates the direction of the observer 206.
[0211] Since .alpha. is at most 0.degree., the light is incident on
the bottom face at an angle distribution centered on the angle
sin.sup.-1(1/n.times.sin.beta.). Accordingly, the light goes out
from the light guide member bottom face 232 at an angle
distribution centered on the angle .beta., which is favorable for
observation in the direction of angle .beta., thus allowing an
adjust to a direction easier for the observer to view. Also, the
closer to 0.degree. the value of .alpha. is, the narrower the
radiation angle distribution centered on the direction of angle
.beta. becomes, preferably.
[0212] Also, when .theta..sub.2 is a small value, not a few rays of
light, after being reflected by the second slope 242, are reflected
by the flat portion 243 to be incident on the first slope 241 (a
combination of the first, second, and third patterns). This pattern
is referred to as a fifth pattern of FIG. 22E.
[0213] In the fifth pattern of FIG. 22E, since the light reflected
by the second slope 242 results in
{-.alpha.+2.times..theta..sub.2}, the reflected light, when
.theta..sub.2 is a small value, results in more parallel light than
before it is reflected. Therefore, the light reflected by the
second slope 242 is totally reflected by the flat portion 243 and
the first slope 241 as described in the fourth pattern of FIG. 22D,
and the distribution of radiation angle from the light guide member
bottom face 232 after the total reflection becomes narrower,
preferably.
[0214] Although not limited because of differences depending on the
size of the illuminating system, the concrete value of
.theta..sub.2 is at least such an angle that light reaches the
second slope 242 and results in parallel rays of light. Therefore,
.theta..sub.2 is such an angle that a ray of light having the
maximum angle of .alpha., sin.sup.-1(1/n) is reflected toward the
0.degree. direction, i.e., .theta..sub.2.ltoreq.(1/2-
)sin.sup.-1(1/n).
[0215] Further, on the assumption that the flat portion 243 is
absent, the necessity of the flat portion 243 is described below.
Out of the light that reaches the light guide member top face 231,
light of 0<.alpha.<.theta..sub.2 cannot reach the second
slope 242, as can be easily understood, thus reaching the first
slope 241. Therefore, the light is partly reflected by Fresnel
reflection but partly transmitted to be a loss. Also, light of
.theta..sub.2<.alpha.<2.theta..sub.2, when reflected by the
second slope 242, results in a ray of light having an angle of
-.alpha.+2.theta..sub.2 as described in the third pattern, so that
0<.alpha..theta..sub.2. Accordingly, the light is
Fresnel-reflected by the first slope 241 or transmitted to be a
loss. Further, light of
2.theta..sub.2<.alpha.<{sin.sup.-1(1/n)} is reflected by the
second slope 242 so that {-sin.sup.-1(1/n)+2.theta..sub.-
2}<.alpha.<0. The light that is reflected by the second slope
242 partly reaches the first slope 241 successfully, but partly
does not reach the first slope 241 so as to be directed toward the
light guide member bottom face 232. Therefore, the rate of light of
0<.alpha.<.theta..sub.2 increases so that the light is
transmitted by the first slope 241 to be a loss at a higher
probability. Hence it can be said that the flat portion 243 is
necessary.
[0216] As a result of the above, light reflected by the grooves 204
is outputted from the bottom face 232 of the light guide member
203. Its outgoing angle, although not limited because of
differences depending on the characteristics of the reflecting
plate 205, is desirably along the direction .beta. in which the
observer 206 usually observes.
[0217] Light outputted from the light guide member bottom face 232
reaches the reflecting plate 205, being thereby reflected. The
reflected light passes again through the light guide member 203,
reaching the observer 206. When this occur, a large distortion of
the light guide member 203 due to the grooves 204 would cause
groove lines to be conspicuous, inappropriately.
[0218] However, if the grooves 204 are provided at such a pitch p
not more than the minimum resolution (dot pitch) of the reflecting
plate 205 that moire fringes are not formed, only the light
transmittance of each dot affects the image quality and the
distortion of each dot does never affects the image quality.
[0219] Further, although not limited because of differences among
applications, a length x of the first slope 241 of the groove 204,
if not more than {L.times.(0.5/60).times..sub..pi./180}, makes the
groove lines inconspicuous on the ground that the human eye's
minimum resolution is 0.5 minute, where L is the distance at which
usually the screen is viewed (a distance between the observer 206
and the top face 231 of the light guide member 203). For example,
if L is 35 cm, then groove lines of not more than
{35.times.(0.5/60).times..pi./180}=50 .mu.m can be said to be
inconspicuous.
[0220] Thus, it is preferable that the pitch p is not more than the
dot pitch of the reflecting plate 205 or that the length
x=h/tan(.theta..sub.1) of the first slope 241 is not more than
(L.times.(0.5/60).times..pi./180}, where L is the distance at which
the observer 206 usually views the screen (the distance between the
observer 206 and the top face 231 of the light guide member 203),
in which case the groove lines are inconspicuous.
[0221] As shown above, the light emitted from the light source 1 is
outputted from the light guide member bottom face 232 by the first
slopes 241 of the grooves 204, illuminating the reflecting plate
205, in which case the light density would decrease with increasing
distance from the light source 1, resulting in non-uniform
brightness distribution. However, because the thickness d1 of the
side face of the light guide member 203 on the light source 1 side
and the thickness d2 of the side face of the light guide member 203
on the side opposite to the light source 1 have a relationship of
d1.gtoreq.d2, the light density is maintained constant so that the
brightness distribution becomes constant.
[0222] It is also preferable to make the pitch p decreasing with
increasing distance from the light source 1, in which case the
brightness distribution becomes more uniform.
[0223] It is also preferable to increase the depth h at places far
from the light source 1, in which case the brightness distribution
becomes more uniform.
[0224] Thus, according to this third embodiment, there can be
provided the illuminating system by overhead irradiation which is
simple in construction, good at illuminating efficiency,
inconspicuous in groove lines and uniform in brightness
distribution.
[0225] Concrete numerical values for the third embodiment may be
exemplified as follows. From the viewpoint of a setting under the
critical angle, a value of .theta..sub.1<49.8.degree. is set in
the condition that
.theta..sub.1.ltoreq.90.degree.-.theta..sub.c+2.theta..sub- .3, for
an improvement of brightness. Also, the outgoing angle is set by
setting a value of .theta..sub.1.apprxeq.46.2.degree. for
.beta.=30.degree. in the condition that
.theta..sub.1.apprxeq.45.degree.+-
.theta..sub.3-(1/2)sin.sup.-1(1/n.times.sin.beta.). Also, from the
viewpoint of improving the reflectance at the first slope 241 of
the groove 204 of the light guide member 203 by making the rays of
light parallel, a value of .theta..sub.2.ltoreq.20.9.degree. is set
in the condition that .theta..sub.2.ltoreq.(1/2)sin.sup.-1(1/n),
for an improvement of brightness. Further, the pitch p of the
grooves 204 is set to not more than 250 .mu.m so as to be not more
than the dot pitch of the reflecting plate 205, for a reduction in
the groove lines. Further, a value of x.ltoreq.50.9 .mu.m is set in
the condition that the length of the first slope 241 of the groove
204, x.ltoreq.{L.times.(0.5/60).times..- pi./180}, for a reduction
of the groove lines. In addition, this example is based on the
assumption that the refractive index of the light guide member 203,
n=1.5, the angle formed by the top face 231 and the bottom face 232
of the light guide member 203, .theta..sub.3=0.8.degree. and that
the distance between the top face 231 of the light guide member 203
and the observer 206, L=350 mm.
[0226] In the third embodiment, it was found as a result of
simulation experiments that the length of the flat portion is
preferably about five times as long as the length of the first
slope, in which case rays of light in the fifth pattern account for
larger portion.
[0227] It is noted here that the present invention is not limited
to the above third embodiment, and may be embodied in various
ways.
[0228] For example, it is preferable to provide a protective layer
on the surface of the light guide member 203 in the third
embodiment, in which case deteriorations of the appearance due to
flaws or the like can be prevented. Hard coating agents as an
example of the material that forms the protective layer can be
exemplified by thermosetting silicon base agents with importance
laid on the coating function, ultraviolet-curing acrylic agents or
ultraviolet-curing silicon base agents with importance laid on the
coating workability, and the like.
[0229] Further, in the third embodiment, a transparent sheet made
of acryl or polycarbonate or the like may be provided instead of
the protective layer. It is also possible to provide a protective
layer on these transparent sheets.
[0230] It is also preferable to provide an antireflection coating
on the top face 231 of the light guide member 203 in the third
embodiment, in which case the image from the reflecting plate 205
becomes sharp.
[0231] It is also possible that a collimator for collimating the
light of the horizontal direction with respect to the light source
1 is attached to a side face 233 of the light guide member 203 on
the light source side in the third embodiment. The radiation
distribution of light emitted from the light source 1 has a spread
in not only the vertical direction but also horizontal direction to
the light source 1. On this account, the light can be effectively
utilized by suppressing the horizontal rays of light by the
collimator. In other words, the front brightness is enhanced by
narrowing the radiation brightness distribution in both right and
left directions.
[0232] Furthermore, as a modification of the third embodiment, two
or more fluorescent lamps may be used for a large-screen reflecting
plate with a 13 inch or more diagonal, by which the brightness can
be maintained, favorably. Examples of this modification are shown
in FIGS. 23A, 23B, 23C. One exemplary way is, as shown in FIG. 23A,
to place two or more lamps at the site of the light source 1.
Another way is, as shown in FIG. 23B, to prepare two light guide
members 203 of the third embodiment and placed them opposite to
each other with their smaller-thickness side faces adjoining. With
this constitution, light emitted from a right-side light source 211
is internally reflected by a top face 311 of the right-side light
guide member 203 so as to be outputted from a bottom face 321,
while light emitted from a left-side light source 212 is internally
reflected by a top face 312 of the left-side light guide member 203
so as to be outputted from a bottom face 322, so that the
brightness is maintained for the large screen, favorably.
[0233] Still another way is, as shown in FIG. 23C, to prepare two
light guide members 203 of the third embodiment and position them
back to back with their larger-thickness side faces adjoining. With
this constitution, light emitted from a right-side light source 211
is internally reflected by a top face 312 of the left-side light
guide member 203 so as to be outputted from a bottom face 322,
while light emitted from a left-side light source 212 is internally
reflected by a top face 311 of the right-side light guide member
203 so as to be outputted from a bottom face 321, so that the
brightness is maintained for the large screen, favorably.
[0234] For a small-screen reflecting plate with a 4 inch or less
diagonal, employing light emitting diodes or the like as the light
source 1 is suited for miniaturization, preferably. In this case,
because the radiation distribution of light emitting diodes has
some degree of directivity, the reflector 2 may be omitted.
[0235] As described above, according to the third embodiment, light
emitted from the light source 1 becomes incident on the light guide
member 203, and propagates on and on while being iteratively
totally reflected within the light guide member 203. During this
process, the light is totally reflected by the grooves 204, . . . ,
204 provided in the top face of the light guide member 203, being
changed into an angle of light smaller than the total reflection
angle and so outputted to the bottom face side, thus illuminating
an illumination object 205. The reflection at the grooves 204 is
composite reflection at the first slopes 241, the second slopes 242
and the flat portions 243. Therefore, if the angle of the first
slope 241 is not more than {90.degree.-.theta..sub.c+2-
.theta..sub.3}, the reflectance becomes high so that the
illuminating efficiency is improved.
[0236] Further, the angle of light emitted from the light guide
member 203 by the first slope 241 varies. On this account, if the
angle of the first slope 241 is
{45.degree.+.theta..sub.3-(1/2)sin.sup.-1(1/n.times.sin.beta- .)},
then the angle of outgoing light becomes in the .beta. direction so
that angle of outgoing light can be aligned along the easy-to-view
angle for the observer 206.
[0237] Also, if the angle of the second slope 242 is not more than
{(1/2)sin.sup.-1(1/n)}, then the light reflected by the second
slope 242 becomes more parallel rays of light. On this account, the
light that reaches the first slope 241 or the flat portion 243
after being reflected by the second slope 242 is reflected at
higher reflectance. Thus, the illuminating efficiency is
improved.
[0238] Further, if the pitch of the grooves 204, . . . , 204 is not
more than the dot pitch of the illumination object 205, then the
groove lines become inconspicuous so as not to be an obstacle to
the observer 206.
[0239] Also, if the length x of the first slope 241 is not more
than {L.times.(0.5/60).times..pi./180}, where L is the distance
between the observer 206 and the top face of the light guide member
203, then the groove lines become inconspicuous so as not to be an
obstacle to the observer 206 on the ground that the human eye's
resolution is 0.5 minute.
[0240] Thus, there can be provided the illuminating system by
overhead irradiation which is simple in construction, good at
illuminating efficiency and inconspicuous in groove lines.
[0241] Next, an illuminating system by overhead irradiation
according to a fourth embodiment of the present invention is
described with reference to the accompanying drawings.
[0242] The illuminating system of the fourth embodiment of the
invention is generally similar in construction to the illuminating
system of the third embodiment, and differs therefrom only in that
a transparent plate 207 is placed on the light guide member
203.
[0243] In FIGS. 24 and 33, reference numeral 207 denotes a
transparent plate (hereinafter, referred to as prism sheet), which
is made from a material such as quartz, glass, transparent resin
like acrylic resin or polycarbonate, or the like. In particular, a
transparent resin, when used, may be a soft material formed into a
sheet shape.
[0244] One side of the prism sheet 207 is a flat surface 271, and
the other side is a prism surface 272 with the cross section formed
into a triangular, wedge shape. The shape of the prism sheet 207 is
generally equal in size to the light guide member 203, as viewed
from the top. On the prism surface 272 of the prism sheet 207, are
arrayed a plurality of combinations of at least an
isosceles-triangular (or equilateral triangular, possible)
wedge-shaped projected portion 273 (hereinafter, referred to as
prism portion) and a flat portion 274 as shown in FIG. 25, where
the wedge-shaped projected portions 273 with an
isosceles-triangular cross section each extend parallel to the
longitudinal direction of the light source 1 and are arranged at
the intervals of the pitch P in a direction perpendicular to the
longitudinal direction. If the angle formed by each slope of the
projected portions 273 with an isosceles-triangular cross section
and an imaginary plane parallel to the flat surface 271 is
.theta..sub.4, then .theta..sub.4 is preferably set within a range
of 30.degree. to 50.degree. in order that the prism sheet 207
effectively works. The prism sheet 207 is placed on the top face of
the light guide member 203 with the prism surface 272 downside.
[0245] Next, operation of the illuminating system in the fourth
embodiment is described.
[0246] Some of the light that has been incident on the light guide
member 203 from the light source 1 is transmitted through the first
slopes 241 of the grooves 204. This ray of light has a large
outgoing angle with respect to the top face 231 of the light guide
member 203. For example, the light is outputted in a direction in
the vicinity of 80.degree. in the foregoing third embodiment. FIG.
26 shows a graph of characteristics of light outputted from the
light guide member top face 231 under the conditions of
.theta..sub.1=40.degree. and .theta.2.sub.=10.degree.. In FIG. 26,
it can be understood that the leakage amount of light becomes large
at outgoing angles around 70.degree.-80.degree.. Accordingly, the
light, upon reaching the prism surface 272 of the prism sheet 207,
is reflected by the triangular projected portions 273 as
illustrated in FIG. 27 so as to be incident again on the light
guide member 203 and pass through the light guide member 203, thus
reaching the reflecting plate 205. In this process, it was derived
from experiments and simulations that slope angles .theta..sub.4
within a range of 30.degree. to 50.degree. allow a good efficiency
to be obtained. As a result of this, the light illuminating
efficiency is improved so that the brightness is enhanced.
[0247] Also, the light (image) reflected by the reflecting plate
205 would yield distortion when passing through the light guide
member 203 and the prism sheet 207. However, the cross section of
the prism sheet 207 having the flat portions 274, given a large
length ratio of the flat portion 274 to the slope of the prism
portions 273 and a small pitch P of the prism portions 273, then
less distortion results. That is, when the prism portions 273 are
provided at a pitch not more than the minimum resolution (dot
pitch) of the reflecting plate, only the light transmittance of
each dot affects the image quality and the distortion of each dot
never affects the image quality.
[0248] Further, although not limited because of differences among
applications, a length x of the slope, if not more than
{L.times.(0.5/60).times..sub..pi./180}, makes the prism-portion
lines inconspicuous on the ground that the human eye's minimum
resolution is 0.5 minute, where L is the distance at which usually
the screen is viewed. For example, if L is 35 cm, then
prism-portion lines of not more than 50 .mu.m can be said to be
inconspicuous.
[0249] Thus, it is preferable that the pitch p of the prism
portions 273 is not more than the dot pitch of the reflecting plate
or that the length of the slope of the prism portions 273 is not
more than {L.times.(0.5/60).times..sub..pi./180}, where L is the
distance at which the observer usually views the screen (the
distance between the observer and the top face of the prism sheet),
in which case the lines of the projected portions 273 are
inconspicuous.
[0250] As concrete examples of numerical values, the angle
.theta..sub.4 of the slope is set to within a range of 30.degree.
to 50.degree. for recycling of leakage light, while the pitch p is
set to not more than 250 .mu.m so as to be not more than the dot
pitch of the reflecting plate 205, for reduction in the
prism-portion lines. Further, the length of the slope of the prism
portions is set to not more than 50.9 .mu.m so as to be not more
than {L.times.(0.5/60).times..sub..pi./180}, for reduction of the
prism-portion lines.
[0251] The prism sheet 207, which is intended to recycle the light
that has leaked from the light guide member 203 by reflecting it at
the slopes, may be implemented in other shapes only if slopes and a
flat portion similar to those of the above embodiment are provided.
FIGS. 28A and 28B show examples of other shapes. For example, the
prism sheet 207 can be implemented by one arrangement in which a
plurality of grooves 276 each having a triangular cross section are
arranged as shown in FIG. 28A, or another in which a plurality of
hills 277 each having a trapezoidal cross section are arranged as
shown in FIG. 28B, or the like (see FIG. 33).
[0252] Further, the radiation distribution of light emitted from
the light source 1 has a spread in not only the vertical direction
but also horizontal direction to the light source. Therefore, by
placing the prism sheet 207 in such a direction of the prism that
the projected portions or the like extend in a direction
perpendicular to the longitudinal direction of the light source 1,
component rays of light in the direction horizontal to the light
source 1 are reflected by the slopes so as to pass again through
the light guide member 203 and illuminate the reflecting plate 205,
by which the illuminating efficiency can be improved.
[0253] Therefore, according to the fourth embodiment, light emitted
from the light source 1 becomes incident on the light guide member
203, and propagates on and on while being iteratively totally
reflected within the light guide member 203. During this process,
the light is totally reflected by the grooves 204, . . . , 204
provided in the top face 231 of the light guide member 203, being
changed into an angle of light smaller than the total reflection
angle and so outputted to the bottom face side, thus illuminating
the illumination object 205. The reflection at the grooves 204 is
composite reflection at the first slope 241, the second slope 242
and the flat portion 243. Therefore, part of the light is outputted
from the top face 231 of the light guide member 203 by the first
slopes 241. The light outputted from the light guide member top
face 231 is reflected by the slopes of the bottom face of the prism
sheet 207 so as to be incident again on the light guide member 203,
thus illuminating the illumination object 205. Thus, the
illuminating efficiency is improved.
[0254] Also, since the angle .theta..sub.4 of the slopes of the
prism sheet 207 is within the range of 30.degree. to 50.degree., a
more efficient illumination can be achieved.
[0255] Also, if the pitch P of the slopes of the prism sheet 207 is
not more than the dot pitch of the illumination object 205, the
lines of the prism sheet 207 become inconspicuous so as not to be
an obstacle to the observer 206.
[0256] Further, if the length of the slope is not more than
{L.times.(0.5/60).times..sub..pi./180}, where L is the distance
between the observer 206 and the top face 271 of the prism sheet
207, then the prism-portion lines become inconspicuous so as not to
be an obstacle to the observer 206 on the ground that the human
eye's resolution is 0.5 minute. Thus, there can be provided the
illuminating system by overhead irradiation which is simple in
construction, good at illuminating efficiency and inconspicuous in
prism-portion lines.
[0257] Next, an illuminating system by overhead irradiation
according to a fifth embodiment of the present invention is
described.
[0258] The illuminating system of the fifth embodiment of the
invention is generally similar in construction to the illuminating
system of the fourth embodiment, and differs therefrom only in the
way how the prism sheet is positioned. The prism sheet 207 in this
embodiment is positioned with the prism surface 272 upside.
[0259] The operation in this case is described with reference to
FIGS. 29 and 34. Reflected light, although varying depending on the
characteristics of the reflecting plate 205, is generally diffused
light. On this account, the light is radiated also in directions
out of the angle of visibility. This light out of the angle of
visibility is condensed by the prism surface 272 of the prism sheet
207, by which the front brightness is improved.
[0260] Assume that the reflected light is distributed around a
center of a direction generally vertical to the light guide member
203 and the prism sheet 207 (the center direction is here assumed
to be 0.degree.). The reflected light passes through the light
guide member 203 so as to be incident on a flat portion 274 of the
prism sheet 207. Assuming that the reflecting plate 205 is a
complete diffusing plate, the light after being incident on the
prism sheet 207 is distributed to .+-.sin.sup.-1(1/n.sub.- 1)
around the 0.degree. direction, where n.sub.1 is the refractive
index of the prism sheet 207.
[0261] As shown in FIG. 29, if the angle formed by the flat surface
271 and the slope of the prism portions 273 of the prism sheet 207
is .theta..sub.4, then the outgoing angle is
{.theta..sub.4+sin.sup.-1(n.tim- es.sin(.alpha.-.theta..sub.4))}.
Given a .theta..sub.4 of 50.degree. and n.sub.1=1.5, the maximum
value of .alpha..sub.1+sin.sup.-1(1/n.sub.1), is 41.8.degree., the
outgoing angle being 37.7.degree., which is smaller than
.+-.90.degree., an angle before the incidence on the prism sheet.
On this account, the radiation distribution of the reflected light
is narrowed by the slopes of the prism sheet 207. It was derived
from experiments and simulations that slope angles .theta..sub.4
within a range of 30.degree. to 50.degree. allow a good efficiency
to be obtained. That is, with the slope angle in this range, the
radiation angle distribute of reflected light can be narrowed so
that the front brightness is enhanced.
[0262] As shown above, by positioning the prism surface 272 upside,
the front brightness can be improved.
[0263] Also, the reflecting plate 205 may be other than a complete
diffusing surface or other the outgoing angle of the light guide
member 203 may be other than 0.degree., in which case also the
radiation distribution can be narrowed in a similar manner,
preferably.
[0264] Also, the light (image) reflected by the reflecting plate
204 would yield distortion when passing through the light guide
member 203 and the prism sheet 207. However, the cross section of
the prism sheet 207 having the flat portions 274, given a large
length ratio of the flat portion 274 to the slope portion of the
prism portions 273 and a small pitch of the prism portions 273,
then less distortion results. That is, when the grooves are
provided at a pitch not more than the minimum resolution (dot
pitch) of the reflecting plate, only the light transmittance of
each dot affects the image quality and the distortion of each dot
never affects the image quality.
[0265] Further, although not limited because of differences among
applications, a length x of the slope, if not more than
(L.times.(0.5/60).times..sub..pi./180}, makes the prism-portion
lines inconspicuous on the ground that the human eye's minimum
resolution is 0.5 minute, where L is the distance at which usually
the screen is viewed. For example, if L is 35 cm, then
prism-portion lines of not more than 50 .mu.m can be said to be
inconspicuous.
[0266] Thus, it is preferable that the pitch P is not more than the
dot pitch of the reflecting plate or that the length of the slope
is not more than (L.times.(0.5/60).times..sub..pi./180}, where L is
the distance at which the observer usually views the screen, in
which case the prism-portion lines are inconspicuous.
[0267] Examples of concrete numerical values are the same as in the
fourth embodiment.
[0268] In this fifth embodiment, the prism sheet 207, which is
intended to improve the front brightness by condensing the light
out of the angle of visibility by the prism surface 272 of the
prism sheet 207, may be implemented in other shapes only if slopes
and flat portions similar to those of the fifth embodiment are
provided. FIG. 34 shows an example of other shapes. For example,
out of the three kinds of prism sheets 207 in FIG. 34, a prism
sheet on the left side is the prism sheet 207 of FIG. 29, while a
prism sheet on the upper right side is one in which a plurality of
grooves 276 each having a triangular cross section are arranged in
its top face. A prism sheet on the lower right side is one in which
a plurality of hills 277 each having a trapezoidal cross section
are arranged in its top face. With these prism sheets, similar
functions can be accomplished.
[0269] Also, as can be easily understood from the above
description, the longitudinal direction of the prism of the prism
sheet 207 is not limited.
[0270] Therefore, according to the fifth embodiment, by arranging
on the light guide member 203 a prism sheet 207 comprising a
transparent plate in which, with respect to a cross-sectional
shape, a plurality of projected portions 273 having slopes of an
angle .theta..sub.4 to the bottom face are arranged on the top face
so that a flat portion (274) generally parallel to the top face is
interposed therebetween. Thus, the radiation distribution of
reflected light from the illumination object 205 can be narrowed so
that the front brightness can be improved.
[0271] Also, if the pitch p of the slope of the prism sheet 207 is
not more than the dot pitch of the illumination object 205, the
lines of the prism sheet 207 are inconspicuous so as not to be an
obstacle to the observer 206.
[0272] Also, if the length of the slope is not more than
{L.times.(0.5/60).times..sub..pi./180}, where L is the distance
between the observer 206 and the top face of the prism sheet 207,
the groove lines become inconspicuous so as not to be an obstacle
to the observer 206 on the ground that the human eye's resolution
is 0.5 minute. Thus, there can be provided the illuminating system
by overhead irradiation which is simple in construction, good at
illuminating efficiency and inconspicuous in groove lines.
[0273] Next, an illuminating system by overhead irradiation
according to a sixth embodiment of the present invention is
described with reference to the accompanying drawings. The
illuminating system of the sixth embodiment of the invention is
generally similar in construction to the illuminating system of the
third embodiment, and differs therefrom only in the shape of the
grooves of the light guide member 203.
[0274] FIG. 30 shows a view as viewed from above the illuminating
system. Lateral grooves 204 are provided along a direction parallel
to the light source 1. Besides, longitudinal grooves 208 are
provided along a direction perpendicular to the light source 1. The
lateral grooves 204 are the same as the grooves 204 of the third
embodiment. FIG. 31 shows a cross-sectional view of the
longitudinal grooves 208. The longitudinal grooves 208 are V-shaped
grooves and an apex angle .theta..sub.5 of each groove 208 is
between 80.degree. to 120.degree..
[0275] The radiation distribution of light emitted from the light
source 1 has a spread in not only the vertical direction but also
horizontal direction to the light source 1. Therefore, by placing
the longitudinal grooves 208, component rays of light in the
direction horizontal to the light source 1 are reflected by the
slopes so as to go out from the light guide member 203 and
illuminate the reflecting plate 205, by which the illuminating
efficiency can be improved. The present inventors made repeated
experiments and simulations, finding out that angles .theta..sub.5
within a range of 80.degree. to 120.degree. are effective. That is,
with the angle .theta..sub.5 in this range, the brightness can be
improved by effectively utilizing the light in the direction
parallel to the light source 1.
[0276] Examples of concrete numerical values for the pitch and the
slope length are the same as in the fourth embodiment.
[0277] Therefore, according to the sixth embodiment, light emitted
from the light source 1 becomes incident on the light guide member
203, and propagates on and on while being iteratively totally
reflected within the light guide member 203. During this process,
the light is totally reflected by the grooves 204, . . . , 204
provided in the top face 231 of the light guide member 203, being
changed into an angle of light smaller than the total reflection
angle and so outputted to the bottom face side, thus illuminating
the illumination object 205.
[0278] The radiation distribution of light emitted from the light
source 1 has a spread in not only the vertical direction but also
horizontal direction to the light source 1. Therefore, by placing
the longitudinal grooves 208, . . . , 208, component rays of light
in the direction horizontal to the light source 1 are reflected by
the slopes so as to go out from the light guide member 203 and
illuminate the reflecting surface, by which the illuminating
efficiency can be improved.
[0279] Also, since each longitudinal groove 208 is formed into a
V-shape and the apex angle .theta..sub.5 of each longitudinal
groove 208 falls within the range of 80.degree. to 120.degree., a
highly efficient illumination can be achieved.
[0280] Thus, there can be provided the illuminating system by
overhead irradiation which is simple in construction, good at
illuminating efficiency and inconspicuous in groove lines.
[0281] As described above, according to one aspect of the present
invention, the illuminating system by overhead irradiation at least
comprises a light source, a transparent plate-shaped light guide
member, at the side face of which the light source is located, in
which a plurality of grooves are arranged in a top face of the
light guide member at specified intervals in a direction parallel
to a longitudinal direction of the light source, and in which flat
portions constituting a part of the top face are arranged between
adjacent ones of the grooves, wherein an illumination object placed
on a bottom face side of the light guide member is observed from a
top face side of the light guide member. Therefore, most of light
propagating within the light guide member can be totally reflected
by the grooves so as to go out from the light guide member, thereby
illuminating the reflecting surface.
[0282] Also, by setting the angle of the first slope of the grooves
so that .theta..sub.1.ltoreq.90-.theta..sub.c+2.theta..sub.3, a
more efficient illumination can be achieved. Also, by setting the
angle .theta..sub.1 of the first slope so that
.theta..sub.1.apprxeq.45.degree.-
+.theta..sub.3-(1/2)sin.sup.-1(1/n.times.sin.beta.), the outgoing
angle can be aligned along the observer's direction .beta.,
favorably.
[0283] Also, setting the angle of the second slope of the grooves
so that .theta..sub.2.ltoreq.(1/2)sin.sup.-1(1/n), a more efficient
illumination can be achieved.
[0284] Also, setting the pitch of the grooves to not more than the
dot pitch of the illumination object, the groove lines can be made
inconspicuous.
[0285] Also, setting the length of the first slope to not more than
{L.times.(0.5/60).times..sub..pi./180}, where L is the distance
between the observer and the illuminating system, more
specifically, the top face of the light guide member, the groove
lines can be more inconspicuous.
[0286] According to the illuminating system by overhead irradiation
in another aspect of the present invention, a transparent prism
sheet is placed on the light guide member, the prism sheet having,
with respect to a cross-sectional shape, a plurality of projected
portions having slopes of an angle .theta..sub.4 to the top face
which are arranged on the bottom face so that a flat portion
generally parallel to the bottom face is interposed therebetween.
Therefore, the light that has leaked from the light guide member
can be reflected by the slopes of the angle .theta..sub.4 so as to
pass through the light guide member, thereby illuminating the
reflecting plate.
[0287] Also, by setting the slope angle .theta..sub.4 to within a
range of 30.degree. to 50.degree., the illuminating efficiency is
more improved.
[0288] Also, by setting the pitch of the slope of the prism sheet
to not more than the dot pitch of the illumination object, the
groove lines can be made inconspicuous.
[0289] Also, by setting the length of the slope of the prism sheet
to not more than {L.times.(0.5/60).times..sub..pi./180}, where L is
the distance between the observer and the illuminating system, the
groove lines can be more inconspicuous.
[0290] According to the illuminating system by overhead irradiation
in still another aspect of the present invention, a transparent
prism sheet is placed on the light guide member, the prism sheet
having, with respect to a cross-sectional shape, a plurality of
projected portions having slopes of an angle .theta..sub.4 to the
bottom face which are arranged on the top face so that a flat
portion generally parallel to the top face is interposed
therebetween. Thus, the radiation distribution of reflected light
from the reflecting surface can be narrowed, by which the front
brightness can be improved.
[0291] Also, by setting the pitch of the slopes of the prism sheet
to not more than the dot pitch of the illumination object, the
groove lines can be made inconspicuous.
[0292] Also, by setting the length of the slope to not more than
{L.times.(0.5/60).times..sub..pi./180}, where L is the distance
between the observer and the illuminating system, more
specifically, the top face of the prism sheet, the groove lines can
be made more inconspicuous.
[0293] Further, according to the illuminating system by overhead
irradiation in yet another aspect of the present invention, a
plurality of grooves are arranged in the top face of the light
guide member at specified intervals in a direction perpendicular to
a longitudinal direction of the light source. Therefore, component
rays of light in the direction horizontal to the light source can
be reflected by the slopes so as to go out from the light guide
member and illuminate the reflecting surface. Thus, the
illuminating efficiency can be improved.
[0294] Also, by setting the perpendicularly provided grooves into a
V-shape, and by setting the apex angle .theta..sub.5 of the V-shape
to within a range of 80.degree. to 120.degree., the illuminating
efficiency can be further improved.
[0295] Further, with the liquid crystal display using any one of
the illuminating systems as described above, a liquid crystal
display which can succeed the advantages of the above illuminating
systems can be achieved.
[0296] An illuminating system according to a seventh embodiment of
the present invention will be described with reference to FIGS. 36,
37.
[0297] FIG. 36 is a diagram in cross section of the illuminating
system using an example of a light guide member in the seventh
embodiment of the present invention.
[0298] In FIG. 36, reference numeral 1 denotes a light source which
is, for example, a fluorescent lamp such as a hot cathode ray tube
or cold cathode ray tube, or an array of a plurality of light
emitting diodes, or an incandescent lamp or a linearly shaped
organic light-emitting material, etc. The light source 1 is
arranged at a side face of a light guide member 303 of a
transparent plate.
[0299] Reference numeral 2 denotes a reflector in FIG. 36 which is
arranged to cover the light source 1. The reflector 2 is
constituted so that an inner face shows high reflectance and small
diffusion performance. For instance, silver, aluminum or the like
material of high reflectance is vapor-deposited to a resin sheet,
which is then bonded to a thin metallic plate or resin sheet,
thereby to constitute the reflector. If the light source 1 is a
fluorescent lamp, a gap between the light source 1 and reflector 2
is preferably filled with a material having a refractive index
close to that of glass, namely, 1.5.
[0300] Preferably, a thickness of the side face of the light guide
member 303 at the side of the light source 1 is equal to a height
of the reflector 2. When the light source 1 is composed of light
emitting diodes, the reflector 2 can be eliminated because a radial
distribution of the light source has some level of directivity. In
that case, the light guide member 303 is desirably compact in
size.
[0301] Still referring to FIG. 36, the light guide member 303 is,
e.g., a transparent plate (referred to simply as a "light guide
member" hereinbelow) formed of quartz, glass, or transparent resin
such as acrylic resin, polycarbonate, etc. The light guide member
303 is made in the same size as that of an illumination object. As
shown in FIG. 37, a lower face 332 of the light guide member 303 is
set to be approximately 90.degree. to a plane of incidence 343. The
light guide member 303 is schematically shaped like a wedge as a
whole, having an upper face 331 tilted so as to be gradually closer
to the lower face 332 with increasing distance from the light
source 1. More specifically, supposing that the thickness of the
side face 333 of the light guide member 303 at the side of the
light source is d1, and a thickness of a side face of the light
guide member at the side opposite to the light source 1 is d2,
d1.gtoreq.d2 is held. Although d1=d2 is fundamentally satisfactory,
a relation of the thicknesses of d1>d2 is more preferable to
maintain a luminance constant. A plurality of V-shaped grooves 304
are notched in the upper face 331 of the light guide member
303.
[0302] In FIG. 36, reference numeral 305 denotes a reflecting face
which is, for example, a printed article such as a book, a
photograph or the like, an image display device of a personal
computer or other Office Automation equipment, a portable
information terminal, a portable video tape recorders, etc., or a
reflecting-type liquid crystal display device used in various kinds
of monitors.
[0303] The propagation of light in the illuminating system of the
seventh embodiment will now be described.
[0304] Light projected from the light source 1 enters the light
guide member 303 directly or after being reflected at the reflector
2. The light entering the light guide member 303 is totally
reflected and propagates. The light reflected at the grooves 304
among the propagation light loses total reflection conditions and
consequently comes out from the lower face 332 of the light guide
member.
[0305] At this time, the light is reflected at the lower face 332
of the light guide member to be a reflected light 320. The light
projected from the lower face 332 of the light guide member
illuminates the reflecting face 305, when the light is reflected at
the reflecting face 305 and becomes a reflected light 500. The
reflected light 500 is an image generated by the reflecting face
305. The reflected light 320 is an unnecessary light worsening
visibility of the image.
[0306] Meanwhile, in the seventh embodiment, the lower face 332 of
the light guide member is subjected to an anti-reflection treatment
or a diffuse treatment by the known vacuum vapor deposition method,
dip method, thermal transfer method, etc. When the lower face 32 is
processed through the antireflection treatment, the total quantity
of the reflected light from the lower face 332 designated by 320 in
FIG. 36 is reduced so large as is negligible enough in comparison
with the quantity of the reflected light 500 from the reflecting
face 305. Therefore, visibility can be improved greatly.
[0307] When the lower face 32 is processed through the diffuse
treatment, the reflected light 320 from the lower face 332 of the
light guide member becomes irregularly reflected, whereby the
quantity of light sensed as bright lines by human eyes due to the
mirror reflection is reduced although the total quantity of the
reflected light is unchanged, and the visibility can be
improved.
[0308] However, the diffuse treatment to the lower face 332 causes
the reflected light 500 from the reflecting face 305 to diffuse
similarly, rather inviting blurring in outline of displayed
characters, etc. and decreasing the visibility. For avoiding this
inconvenience, a haze value of the diffuse treatment to the lower
face 332 is preferably not larger than 20%, particularly in a range
of 4-10% to reduce bright lines of the reflected light 320 in a
well-proportioned relation to the outline blurring, as is detected
from experiments with many people including women and aged people.
The "haze value" referred to here is a numerical value indicating a
degree of diffusion, i.e., a ratio expressed by % of a diffuse
transmission light and a total transmission light.
[0309] Needless to say, the visibility can be naturally improved
furthermore if both the anti-reflection treatment and the diffuse
treatment are performed to the lower face 332 of the light guide
member.
[0310] When an anti-reflection film is formed on the upper face 331
of the light guide member 303, the reflection by an external light
can be also reduced, with the visibility improved more.
[0311] A reflection type liquid crystal display device using the
light guide member according to the seventh embodiment of the
present invention will be described with reference to FIG. 3.
[0312] Those parts of FIG. 38 denoted by the same numerals as in
FIG. 36 represent the same parts. 360 is a reflection type liquid
crystal panel comprised of two substrates 361 and 362. The lower
face 332 of the light guide member 303 is subjected to the
anti-reflection treatment or diffuse treatment in the known method,
for example, vacuum vapor deposition, dipping, or thermal transfer
method or the like. A surface of the substrate 361 of the
reflection type liquid crystal panel 360 is also processed through
the anti-reflection treatment or diffuse treatment.
[0313] Because of the anti-reflection treatment to the lower face
332 of the light guide member or the surface of the substrate 361,
the total quantity of the reflected light 320 from the lower face
332 of the light guide member or the reflected light 610 from the
surface of the substrate 61 is reduced to a negligible level as
compared with the quantity of a reflected light 600 from the liquid
crystal panel 360. The visibility can consequently be enhanced.
[0314] It goes without saying that the anti-reflection treatment
may be executed to both of the lower face 332 of the light guide
member and the surface of the substrate 361.
[0315] When the diffuse treatment is carried out to either the
lower face 332 of the light guide member or the surface of the
substrate 361, the reflected light 320 from the lower face 332 or
the reflected light 610 from the surface of the substrate 361 is
irregularly reflected. As a result, the amount of light detected as
bright lines by human eyes due to the mirror reflection is reduced
although the total amount of the reflected light is not changed,
and accordingly the visibility can be improved.
[0316] In spite of the above effect, the reflected light 600 from
the reflection type liquid crystal panel 360 is diffused likewise
in consequence of the diffuse treatment, with bringing about an
issue that displayed characters are blurred in outline and
deteriorated in visibility. Therefore, the haze value of the
diffuse treatment to the lower face 332 of the light guide member
or the surface of the substrate 361 is preferably set to be 20% or
lower. Results of experiments from many people including women and
old people show that the haze value is particularly preferably
4-10% to keep an even balance between the reduction of bright lines
by the reflected light 320 or 610 and the outline blurring.
[0317] In the case where the lower face 332 of the light guide
member and the surface of the substrate 361 are both subjected to
the diffuse treatment, the haze value of the diffuse treatment to
the surface of the substrate 361 which is closer to the reflection
type liquid crystal panel 360 is set larger than that to the lower
face 332 of the light guide member separated farther from the
liquid crystal panel 360, so that the visibility is controlled not
to decrease, in other words, displayed characters are prevented
from blurring in outline, etc.
[0318] The visibility can be improved much more if both the
anti-reflection treatment and the diffuse treatment are carried out
to the lower face 332 of the light guide member or the surface of
the substrate 361.
[0319] Besides, when the anti-reflection film is formed on the
upper face 331 of the light guide member 303, the reflection
because of the external light can be lessened and the visibility
can be improved.
[0320] A reflection type liquid crystal display device according to
an eighth embodiment of the present invention will be discussed
with reference to FIG. 39.
[0321] Parts in FIG. 39 indicated by the same reference numerals as
in FIG. 38 are the same parts. 380 is a touch panel used, for
example, for inputting of information through touching via a pen or
finger, etc. A front face 381 or a rear face 382 of the touch panel
is processed through the diffuse treatment, thus diffusing the
reflected light 320 from the lower face 332 of the light guide
member and the reflected light 610 from the surface of the
substrate 361. The amount of light sensed by human eyes as bright
lines is decreased and the visibility can be improved. In this
arrangement alike, the haze value at the diffuse treatment is
preferred to be set at 20% or lower in order to prevent the outline
blurring of displayed characters. Especially when the touch panel
is provided for the purpose of inputting information via a pen and
if the haze value of the diffuse treatment to the front face 381 is
larger than 10%, a write resistance is too large for the pen to run
smoothly. On the other hand, if the haze value is smaller than 1%,
the resistance is too small. As such, the haze value for the front
face 381 is preferably 1-10%.
[0322] According to the display devices of the above-described
seventh and eighth embodiments of the present invention, a
transparent material is filled between the lower face 332 of the
light guide member 303 and the reflection type liquid crystal panel
360 in the liquid crystal display device, which has approximately
the same refractive index as that of a material of the light guide
member 303 and that of the substrate 361 of the reflection type
liquid crystal panel 360. Alternatively, a sheet of the above
transparent material is interposed. The total quantity of the
reflected light 320 and reflected light 610 is further decreased to
the reflected light 600 from the liquid crystal panel 360. The
visibility can accordingly be improved more.
[0323] A method for manufacturing the illuminating system according
to a seventh embodiment of the present invention will be depicted
with reference to FIGS. 40, 41.
[0324] The anti-reflection treatment is primarily carried out by
one of three methods, namely, vacuum vapor deposition, spin coating
and dip coating. Among the methods for the anti-reflection
treatment, the dip coating is preferred to the light guide member
303, because the spin coating is difficult if the light guide
member 303 includes grooves 304 and the vacuum vapor deposition
method costs high. CYTOP by Asahi Glass, Co., Ltd. is employed by
way of example as an anti-reflection agent in the dip coating.
[0325] The light guide member 303 is used as a front face of the
display device, and therefore a uniform coat all over the face of
the light guide member 303 is required. A drop of the agent liquid
from an end face of the light guide member 303 can be eliminated if
the light guide member 303 is inclined slantwise during the dip
coating, as shown in FIG. 40. If the end face of the light guide
member 303 is set in parallel to the liquid level without being
inclined, the antireflection agent accumulated at the end face of
the light guide member 303 drops after the dipping, resulting in an
irregular coat to the light guide member 303.
[0326] In the case where the light guide member 303 is one formed
by injection molding, the anti-reflection coating can be obtained
all over the face of the light guide member 303 by holding a gate
part 334 as illustrated in FIG. 40. In the absence of the gate part
334, the end face of the light guide member 303 is pressed from
sideways to a direction of arrows as shown in FIG. 41, whereby the
light guide member is fixed to an outer frame 341.
[0327] In the above-described manner, the anti-reflection coating
can be formed uniformly all over the face of the light guide member
303 at low cost.
[0328] Although an inclination 0 of the light guide member 303 is
preferred to be large in order to prevent the agent from dropping,
the larger the inclination .theta. is, the thicker the coating
becomes at the grooves 304 of the upper face 331 than at the other
parts. Therefore, the inclination is set as small as possible. The
present invention found from repeated experiments that the
inclination .theta. of 10.degree.-30.degree. surely presents the
dropping of the agent and makes the thickness of the coating at the
grooves 304 of the upper face 331 equal to that at the other parts.
The anti-reflection coating agent in this case has a viscosity of
approximately 10 cps and a pull-up speed of 80 mm/min.
[0329] The above range of the inclination .theta. differs depending
on the viscosity and pull-up speed of the anti-reflection coating
agent.
[0330] A reflection type liquid crystal display device in a ninth
embodiment of the present invention using the light guide member
will be described with reference to FIGS. 42, 43.
[0331] FIG. 42 is a schematically sectional view of the reflection
type liquid crystal display device according to the ninth
embodiment which is equipped with the illuminating system.
[0332] The display device of the ninth embodiment is almost the
same in structure as the eighth embodiment. A difference is an
angle of the light projected from the light guide member 303 and
the presence of an field angle control sheet 307 disposed on the
reflection type liquid crystal panel. In the ninth embodiment, the
anti-reflection treatment and the diffuse treatment are not
required to the light guide member and the reflection type liquid
crystal panel.
[0333] The field angle control sheet 307 is a sheet which has a
function to diffuse light from one direction and pass light from
the other directions, for instance, "Lumisty" by Sumitomo Chemical
Company, Limited, "Lower" by Minnesota Mining and Manufacturing
Company etc. A diffusion direction .theta. of the field angle
control sheet is not smaller than an angle of field to a normal
direction of the display device, for example, 30.degree. in the
ninth embodiment.
[0334] FIG. 43 is an explanatory diagram of the propagation of
light in the ninth embodiment.
[0335] Supposing that an output angle of the light guide member 303
is 30.degree., the unrequested reflected light 320 and also the
unrequested reflected light 610 are directed outside the angle of
visibility (field angle). Since the light projected from the light
guide member 303 is turned to diffused light when passing through
the control sheet 307, the light can illuminate the liquid crystal
panel 306. Moreover, the originally necessary light reflected at
the liquid crystal panel 306 is not diffused by the field angle
control sheet 307. Therefore, blurring of characters does not take
place and superior visibility is achieved.
[0336] Although the diffusion direction .theta. is set to be
30.degree. in the ninth embodiment, the angle .theta. may be a
different value other than 30.degree.. However, if the angle
.theta. is small, the unnecessary reflected lights 320 and 610 are
projected into the angle of visibility, narrowing an easy-to-see
angle of the display device. If the angle .theta. is large, the
luminance in the normal direction of the display device is
decreased. After conducting experiments by changing the angle
.theta. from 0.degree. to 70.degree., the inventors detected that
the easy-to-see angle is satisfied and the luminance in a direction
of the front face is appropriate particularly when the angle is
30.degree.-50.degree..
[0337] According to the light guide member of the seventh
embodiment of the present invention as described hereinabove, the
lower face of the light guide member is processed through the
anti-reflection treatment or diffuse treatment, so that the total
quantity of the reflected light from the lower face of the light
guide member is greatly reduced, specifically as much as is
negligible enough to the reflected light from the reflecting face.
The visibility can accordingly be improved large.
[0338] In the reflection type liquid crystal display device of the
seventh embodiment using the light guide member, the reflection
type liquid crystal panel is provided which has the surface of at
least one substrate processed through the anti-reflection treatment
or diffuse treatment. Moreover, the liquid crystal panel is
disposed so that the surface subjected to at least one of the
anti-reflection treatment and the diffuse treatment confronts the
lower face of the light guide member. Accordingly, the reflected
light from the lower face of the light guide member is reduced as
much as is negligible in comparison with the reflected light from
the surface of the liquid crystal panel, and the visibility can be
improved greatly.
[0339] The touch panel processed through the anti-reflection
treatment or diffuse treatment is arranged on the light guide
member, thereby easing bright lines of the reflected light from the
lower face of the light guide member and the surface of the
substrate of the liquid crystal panel and improving the visibility
eventually.
[0340] The haze value of the diffuse treatment to the surface of
the substrate of the reflection type liquid crystal panel is set
larger than that of the diffuse treatment to the lower face of the
light guide member. Decrease in visibility such as outline blurring
of displayed characters or the like can be hence restricted.
[0341] In the reflection type liquid crystal display device
according to the eighth embodiment of the present invention using
the light guide member, the transparent material of approximately
the same refractive index as that of the material of the light
guide member and that of the substrate of the reflection type
liquid crystal panel is filled into, or a sheet of the material is
interposed between the lower face of the light guide member and the
reflection type liquid crystal panel. Accordingly, the reflected
light from the lower face of the light guide member and from the
surface of the substrate of the reflection type liquid crystal
panel is reduced to such a degree negligible as compared with the
reflected light from the reflecting face of the liquid crystal
panel, so that the visibility can greatly be improved.
[0342] According to the method for manufacturing the light guide
member of the seventh embodiment, no drop of liquid is brought
about from the end face of the light guide member. The
anti-reflection treatment can be provided uniformly to the whole
face of the light guide member.
[0343] The anti-reflection treatment can be carried out simply by
holding the gate part of the light guide member.
[0344] According to the reflection type liquid crystal display
device of the ninth embodiment using the light guide member, the
field angle control plate (sheet) is arranged on the upper face of
the reflection type liquid crystal panel. Since the angle of the
illumination light projected from the lower face of the light guide
member is nearly agreed with the diffusion direction of the field
angle control plate, the light projected from the lower face of the
light guide member is diffused, whereas the reflected light from
the reflection type liquid crystal panel is not diffused, whereby
the visibility can be improved.
[0345] Further, when each of the output angle of the light guide
member and diffusion direction of the field angle control plate is
30.degree.-50.degree. to the normal direction of the liquid crystal
panel, the reflected light from the lower face of the light guide
member and from the substrate of the liquid crystal panel are sent
outside the angle of visibility, so that the visibility can be
improved.
[0346] The present invention can provide the light guide member
easy to see, the reflection type liquid crystal display device
using the light guide member and the manufacture method for the
same.
[0347] Next, a tenth embodiment of the present invention will be
described.
[0348] A back light is used by way of example as an illuminating
system for a liquid crystal panel. The back light is, as is
disclosed in Japanese Laid-Open Patent Publication No. 5-127159,
constituted of a fluorescent lamp and a light guide member of a
transparent flat plate, in which linear light from the fluorescent
lamp is inputted to a side face of the light guide member and
output as a linear light source to a liquid crystal panel with the
utilization of the diffusion of light at silk printing provided at
a rear face of the light guide member.
[0349] Lately, an illuminating system for illuminating the liquid
crystal panel used in a portable information-processing device,
consumes small power and operates at low voltage is required to
achieve a compact, battery-driven structure with a long life. When
the fluorescent lamp is used as the light source as in the
above-mentioned back light, a high voltage generation circuit is
necessitated to turn on the fluorescent lamp, and consequently, a
loss at an electric circuit and a space for the electric circuit
are to be taken into consideration. The light source using the
fluorescent lamp is not fit to carry with.
[0350] On the other hand, a light-emitting diode which will be
referred to as an "LED" hereinafter is the light source that can be
driven by a battery. Many LEDs are arranged into an array and used
as the linear light source to bring the light from the side face of
the light guide member.
[0351] In the arrangement of LEDs as above, however, an intensity
of light among the LEDs is decreased unless the LEDs are densely
installed, varying a luminance distribution at the back light.
Meanwhile, if the LEDs are arranged densely so as to eliminate the
variation in luminance distribution, a count of LEDs used is
increased, with hindering a cost reduction.
[0352] The tenth embodiment of the present invention provides a
uniform linear light source, with solving the above-discussed
inconveniences.
[0353] The linear light source according to the tenth embodiment of
the present invention will be described with reference to FIGS.
44-49.
[0354] FIGS. 44, 46 are diagrams of the linear light source in the
tenth embodiment. In FIGS. 44 and 46, 801 is a light source of a
small light-emitting part, for instance, an LED or the like. The
light sources 801 are arranged via a constant interval p. 805 is a
diffusing plate. 802 is a reflecting plate disposed to cover the
light sources 801 and diffusing plate 805. An inner face of the
reflecting plate 802 is vapor-deposited with silver or aluminum,
etc. to increase a reflectance. 803 is a light guide plate serving
as one example of the light guide member, having the reflecting
plate 802 set at a side face thereof to project light entering from
the side face to an upper face or a lower face. 804 is the groove,
849 is an anti-reflection coating layer at the lower surface of the
light guide plate 803. 851 is a liquid crystal panel, 850 is an
anti-reflection and anti-plate coating layer at the upper surface
of the panel 850. 870 is a circuit board on which the LEDs 801 are
mounted. 880 is the touch panel of the eighth embodiment.
[0355] Supposing that a radial distribution of the light sources
801 is f(.theta.) and a distance between the light source 801 and
diffusing plate 805 is L, the following expression is held;
L>p/(2 tan(.theta.))
[0356] wherein .theta. is a value satisfying
f(.theta.)cos.sup.2(.theta.)=- 0.5.
[0357] The linear light source 801 constituted as above achieves a
uniform illumination, the reason for which will be discussed with
reference to FIGS. 48 and 49. FIGS. 48 and 49 are XZ sectional
views of the linear light source 801. The light sources 801 are
arranged in an X direction via the constant interval p and
separated from the diffusing plate 805 by the distance L. One
light-emitting point of the light sources 801 is a point R, and an
intersection of a line extending in a direction vertical to the
point R, namely, in a Z direction and the diffusing plate 805 is a
point Q. An intersection between a bisector of the point R and a
light-emitting point R.sub.1 next to the point R, and the diffusing
plate 805 is a point P.sub.1. A luminance in a direction inclined
by .theta. in the Z direction at the point R is f(.theta.) where
(f(0)=1).
[0358] In order to make the light quantity from the light sources
801 uniform at the diffusing plate 805, although it is enough to
sufficiently separate the light sources 801 from the diffusing
plate 805, this makes the light source part bulky in size. For
eliminating the problem, therefore, a minimum distance between the
light sources 801 and diffusing plate 805 is calculated. Where the
light quantity is smallest at the diffusing plate 805 is in the
middle of light-emitting points R and R.sub.1 of the light sources
801, i.e., point P.sub.1. The distance L is selected so that the
light quantity at the point P.sub.1 becomes equal to that at the
point Q, whereby the uniform linear light source is obtained.
[0359] The light reaching the point Q is mostly from the point
R.sub.1 and therefore the light quantity at the point Q is
1/L.sup.2. The quantity of light reaching the point P.sub.1 is
2f(.theta.)cos.sup.2 .theta./L.sup.2. The .theta. is accordingly
set to satisfy f(.theta.)cos.sup.2 .theta.=0.5. Thus, the distance
L between the light sources 801 and diffusing plate 805 is
determined to hold;
L>p/(2 tan(.theta.))
[0360] For example, when the radial distribution f(.theta.) of the
light-emitting points of the light sources 801 is equal to
cos(.theta.), .theta. is 37.5.degree. because cos.sup.3
.theta.=0.5, and the distance L of the light source 801 and
diffusing plate 805 becomes L>0.65p.
[0361] As described hereinabove, when the light-emitting points of
the light sources 801 are arranged via the pitch p and if the light
sources 801 are separated from the diffusing plate 805 at least by
L>p(2 tan(.theta.)) wherein f(.theta.) is the radial
distribution of the light-emitting points and f(.theta.)cos.sup.2
.theta. is equal to 0.5, the uniform linear light source is
realized. Since the LED or the like light source that can be driven
at low voltage is utilizable, the illumination is achieved in a
compact and low-power structure to fit for use in a portable
information device, etc.
[0362] According to the tenth embodiment of the present invention,
the diffusing plate and the prism sheet of the light guide member
are separated from the light sources by the distance L (L>p/(2
tan(.theta.)) wherein f(.theta.) is the radial distribution of
light-emitting points and f(.theta.)cos.sup.2 .theta. is equal to
0.5. Accordingly, the linear illumination provided exerts high and
uniform luminance.
[0363] The entire disclosure of Japanese Patent Applications No.
9-122343 filed on May 13, 1997, No. 9-124992 filed on Aug. 21,
1997, and No. 10-44960 filed on Feb. 26, 1998, including
specifications, claims, drawings, and summaries are incorporated
herein by reference in their entirety.
[0364] Although the present invention has been fully described in
connection with the preferred embodiments thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications are apparent to those skilled in the art. Such
changes and modifications are to be understood as included within
the scope of the present invention as defined by the appended
claims unless they depart therefrom.
* * * * *