U.S. patent application number 13/618241 was filed with the patent office on 2013-01-10 for white light emitting apparatus and line illuminator using the same in image reading apparatus.
This patent application is currently assigned to CANON COMPONENTS, INC.. Invention is credited to Shozo Asai, Takahiro Kaihotsu.
Application Number | 20130009564 13/618241 |
Document ID | / |
Family ID | 43353692 |
Filed Date | 2013-01-10 |
United States Patent
Application |
20130009564 |
Kind Code |
A1 |
Kaihotsu; Takahiro ; et
al. |
January 10, 2013 |
WHITE LIGHT EMITTING APPARATUS AND LINE ILLUMINATOR USING THE SAME
IN IMAGE READING APPARATUS
Abstract
A white light emitting apparatus includes a light source section
in which a first white LED that emits white light whose
chromaticity deviates to a blue side from a predetermined white
region of a CIE chromaticity diagram and a second white LED that
emits white light whose chromaticity deviates to a yellow side from
the predetermined white region are adjacently disposed so as to
emit light with optical axes in substantially the same direction,
and a current regulator that independently drives the blue LED chip
in the first and second white LEDs, respectively. A color mixture
of lights emitted from the first and second white LEDs is adjusted
to a chromaticity of the predetermined white region using the
current regulator.
Inventors: |
Kaihotsu; Takahiro;
(Kanagawa, JP) ; Asai; Shozo; (Saitama,
JP) |
Assignee: |
CANON COMPONENTS, INC.
Saitama
JP
|
Family ID: |
43353692 |
Appl. No.: |
13/618241 |
Filed: |
September 14, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12853885 |
Aug 10, 2010 |
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13618241 |
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PCT/JP2008/063839 |
Aug 1, 2008 |
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12853885 |
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Current U.S.
Class: |
315/250 ;
313/498 |
Current CPC
Class: |
H01L 25/0753 20130101;
Y02B 20/30 20130101; H01L 2224/48247 20130101; H05B 45/20 20200101;
H05B 31/50 20130101; H05B 45/37 20200101; H01L 2224/48257 20130101;
H01L 2224/48091 20130101; H01L 33/50 20130101; H01L 2224/48091
20130101; H01L 2924/00 20130101; H01L 2224/48091 20130101; H01L
2924/00014 20130101 |
Class at
Publication: |
315/250 ;
313/498 |
International
Class: |
H05B 37/02 20060101
H05B037/02; H05B 33/12 20060101 H05B033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2008 |
JP |
2008-031470 |
Aug 11, 2009 |
JP |
2009-186880 |
Mar 5, 2010 |
JP |
2010-049662 |
Claims
1.-19. (canceled)
20. A white light emitting apparatus for an image reading
apparatus, that uses a white LED having a blue LED chip and a
phosphor, comprising: a light source section in which a first white
LED that emits white light at a first chromaticity point of first
chromaticity coordinates, the first chromaticity point deviating to
a blue side from a predetermined white region of a CIE chromaticity
diagram, and a second white LED that emits white light at a second
chromaticity point of second chromaticity coordinates, the second
chromaticity point deviating to a yellow side from the
predetermined white region, are adjacently disposed such that
optical axes thereof are in substantially the same direction; and a
current regulator that independently drives the blue LED chip of
the first and second white LEDs, respectively; wherein the current
regulator performs PWM control for a drive current of at least one
of the first and second white LEDs, and by setting respective pulse
widths for driving at least one of the first and second white LEDs
that are inversely proportional to a distance from a target
chromaticity point to a chromaticity point of emitted light of the
first white LED and a distance from the target chromaticity point
to a chromaticity point of emitted light of the second white LED on
a CIE chromaticity diagram, adjusts a color mixture of lights
emitted from the first and second white LEDs to a chromaticity of
the predetermined white region.
21. A white light emitting apparatus for an image reading
apparatus, that uses a white LED having a blue LED chip and a
phosphor, comprising: a light source section in which a first white
LED that emits white light at a first chromaticity point of first
chromaticity coordinates, the first chromaticity point deviating to
a blue side from a predetermined white region of a CIE chromaticity
diagram, and a second white LED that emits white light at a second
chromaticity point of second chromaticity coordinates, the second
chromaticity point deviating to a yellow side from the
predetermined white region, are adjacently disposed such that
optical axes thereof are in substantially the same direction; and a
current regulator that independently drives the blue LED chip of
the first and second white LEDs, respectively; wherein, the current
regulator: continuously supplies a constant current to one white
LED among the first and second white LEDs that emits white light
whose chromaticity is nearer to a target chromaticity point on the
CIE chromaticity diagram, and supplies a PWM-controlled current to
another white LED among the first and second white LEDs, sets a
duty ratio of the PWM control to a value of an inverse ratio
between a distance between a chromaticity of the one white LED and
the target chromaticity point and a distance between a chromaticity
of the other white LED and the target chromaticity point on the CIE
chromaticity diagram, and adjusts a color mixture of emitted lights
from the first and second white LEDs to a chromaticity of the
predetermined white region.
22. A line illuminator configured to emit light that is incident
from a light source disposed toward a light incident surface
provided at an end surface in a length direction of a bar-shaped
light guide member formed of a clear member from a light emitting
surface provided along a length direction while causing the light
to be reflected by an inner surface of the barshaped light guide
member, wherein the light source is a white light emitting
apparatus according to claim 20.
23. A line illuminator configured to emit light that is incident
from a light source disposed toward a light incident surface
provided at an end face in a length direction of a bar-shaped light
guide member formed of a clear member from a light emitting surface
provided along a length direction while causing the light to be
reflected by an inner surface of the barshaped light guide member,
wherein the light source is a white light emitting apparatus
according to claim 21.
24. The line illuminator according to claim 22, wherein an external
shape of a radiating surface that radiates a light of the white
light emitting apparatus is of dimensions that can be included in
an external shape of the light incident surface of the light guide
member.
25. The line illuminator according to claim 23, wherein an external
shape of a radiating surface that radiates a light of the white
light emitting apparatus is of dimensions that can be included in
an external shape of the light incident surface of the light guide
member.
26. A white light emitting apparatus, comprising: a first white
light emitting diode emitting yellowish white; a second white light
emitting diode emitting bluish white in the same direction of
emission by the first white light emitting diode; and a current
controller controlling drive currents of the first and second white
light emitting diodes, wherein the current controller controls duty
ratios of outputs of the drive currents.
27. The white light emitting apparatus according to claim 26,
wherein the current controller controls values of the drive
currents.
28. The white light emitting apparatus according to claim 26,
wherein each of the first and second white light emitting diodes
comprises: a blue light emitting diode chip; and a wavelength
conversion layer for wavelength conversion of a part of blue light
from the blue light emitting diode chip into yellow light.
29. A white light emitting apparatus, comprising: a first white
light emitting diode emitting yellowish white; a second white light
emitting diode emitting bluish white in the same direction of
emission by the first white light emitting diode; and a current
controller controlling drive currents of the first and second white
light emitting diodes, wherein each of the first and second white
light emitting diodes comprises: a blue light emitting diode chip;
and a wavelength conversion layer for wavelength conversion of a
part of blue light from the blue light emitting diode chip into
yellow light, and the wavelength conversion layer in the second
white light emitting diode has a thickness smaller than that of the
wavelength conversion layer in the first white light emitting
diode.
30. A white light emitting diode, comprising: first and second blue
light emitting diode chips; and a wavelength conversion layer for
wavelength conversion of a part of blue light from the first and
second blue light emitting diode chips into yellow light, wherein
the wavelength conversion layer emits yellowish white after
wavelength conversion of a part of blue light from the first blue
light emitting diode chip into yellow light, and emits bluish white
after wavelength conversion of a part of blue light from the second
blue light emitting diode chip into yellow light, wherein the
wavelength conversion layer comprises: a first fluorescent layer
covering the first and second blue light emitting diode chips; and
a second fluorescent layer covering only the second blue light
emitting diode chip of the first and second blue light emitting
diode chips.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part application of International
Application No. PCT/JP2008/063839, with an international filing
date of Aug. 1, 2008, which designating the United States of
America, the entire contents of which are incorporated herein by
reference.
[0002] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2008-031470,
filed on Feb. 13, 2008, the Japanese Patent Application No.
2009-186880, filed on Aug. 11, 2009, and the Japanese Patent
Application No. 2010-049662, filed on Mar. 5, 2010, the entire
contents of which are incorporated herein by reference.
TECHNICAL FIELD
[0003] The present invention relates to a white light emitting
apparatus and a line illuminator that uses the white light emitting
apparatus in an image reading apparatus. In particular, the present
invention relates to a white light emitting apparatus on which a
white LED is mounted and a line illuminator that uses the white
light emitting apparatus, that are used in an image reading
apparatus.
BACKGROUND ART
[0004] In a machine such as a fax machine, a copier, or a hand
scanner, an image reading apparatus such as an image sensor is used
as an apparatus for reading an original copy. Normally, a
contact-type image sensor that has a short optical path length and
that can be easily incorporated into the machine is used as this
kind of image reading apparatus.
[0005] A contact-type image sensor is equipped with a line
illuminator that linearly illuminates an original copy surface
across a main scanning area. As a line illuminator, an indirect
illumination-type line illuminator is known that uses a long light
guide member and that propagates a light incident from a light
source disposed at an end surface of the light guide member while
causing the light to be reflected by an inner surface to emit the
light from a linear emitting surface in a longitudinal
direction.
[0006] It is known that a white LED that includes a blue LED chip
and a YAG phosphor can be used as a light source in this kind of
line illuminator. A white LED light source is capable of reading
color images, and lighting control thereof is simpler in comparison
to a multi-chip LED that emits light of the three colors red, green
and blue (RGB). Further, it is said that a white LED light source
is superior in terms of brightness characteristics and with respect
to miniaturization and weight reduction, and also enhances light
emission efficiency when employed as the light source of a
contact-type image sensor.
[0007] Further, users desire that in a line illuminator in which an
LED including a plurality of light emitting elements is disposed as
a light source at an end surface of a light guide member, emitted
light colors from the plurality of chips are released after being
sufficiently mixed in the light guide member without disturbing the
color balance, and illuminate a color original copy as linear
illumination with a homogeneous hue. An invention for solving these
problems or that has a feature relating to the shape of a light
guide member is disclosed in Patent Document 1 and the other
documents.
[0008] Further, Patent Document 2 discloses that when white LEDs
are mass produced, considerable variations arise with respect to
the light emission wavelength and light emission brightness of blue
LED chips. Furthermore, white light that is mixed is also affected
by variations in the amount and dispersion of fluorescent particles
of YAG phosphor that get mixed in with a covering member and the
like, and it is considered that, as a result, large variations
arise in the hue and brightness of completed white LEDs.
[0009] The distribution of variations in the hue of emitted lights
of white LEDS that were mass produced in lots will now be described
referring to FIG. 16 using one section of the chromaticity
coordinates thereof. The distribution chart shown in FIG. 16 is
disclosed in Patent Document 2. Each black spot illustrated in FIG.
16 represent individual hue data of a white LED, and the hue is
dispersed in a band shape that slopes upward to the right as
illustrated in FIG. 16. More specifically, the hue is dispersed in
a band shape in a white region that falls approximately on a line
that passes from blue through yellow via a white point according to
the chromaticity classification of JIS Z 8110. In this case, the
dispersion in the width direction (represented by the arrowed line
A) is mainly due to hue variations caused by variations in the
light emission wavelength of blue light emitting elements, and the
dispersion in the longitudinal direction (represented by the
arrowed line B) is mainly due to hue variations caused by
variations in the amount or dispersion of fluorescent particles
that have gotten mixed into the covering member. In this
connection, since the light emission wavelength of blue light
emitting elements varies significantly between lots, the dispersion
in the width direction (represented by the arrowed line A) spreads
further in actual mass production (see Patent Document 2).
[0010] In this case, when attempting to construct a light source of
a line illuminator for an image reading apparatus using such kind
of white LED, it is preferable from the viewpoint of the central
hue and hue unevenness and the like that the light source is
constructed using only white LEDs that have been selected by
ranking the emitted light colors thereof in a desired chromaticity
range. However, when a light source is constructed using only white
LEDs that have a specific ranking, white LEDs with a different
ranking are wasted, and there is thus the problem that the total
cost for obtaining the white LEDs is comparatively high. [0011]
[Patent Document 1] Japanese Laid-Open Patent Publication No.
2006-287923 [0012] [Patent Document 2] Japanese Laid-Open Patent
Publication No. 2004-119743 [0013] [Patent Document 3] Japanese
Patent No. 3990437 [0014] [Patent Document 4] Japanese Laid-Open
Patent Publication No. 2002-134284 [0015] [Patent Document 5]
Japanese Laid-Open Patent Publication No. 2007-066969 [0016]
[Patent Document 6] Japanese Laid-Open Patent Publication No.
2006-303373
SUMMARY OF THE INVENTION
[0017] The present invention has been made in view of the above
described conventional problems, and provides a white light
emitting apparatus constructed by combining white LEDs that emit
lights with degrees of whiteness over a wide range that deviate
from a desired degree of whiteness, and that mixes the emitted
light colors to emit light with a desired chromaticity, as well as
a line illuminator that uses the white light emitting apparatus. An
object of the present invention is to improve yields of white LEDs
and lower the cost of producing a white light emitting apparatus by
increasing the usability of white LEDs that have a wide range of
chromaticities.
[0018] A white light emitting apparatus for an image reading
apparatus according to the present invention uses a white LED
having a blue LED chip and a phosphor, and includes a light source
section in which a first white LED that emits white light whose
chromaticity deviates to a blue side from a predetermined white
region of a CIE chromaticity diagram and a second white LED that
emits white light whose chromaticity deviates to a yellow side from
the predetermined white region are adjacently disposed such that
optical axes thereof are in substantially the same direction, and a
current regulator that independently drives the blue LED chips in
the first and second white LEDs, respectively; wherein the current
regulator performs PWM control for a drive current of at least one
of the first and second white LEDs, and by setting respective pulse
widths for driving the first and second white LEDs that are
inversely proportional to a distance from a target chromaticity
point to a chromaticity point of emitted light of the first white
LED and a distance from the target chromaticity point to a
chromaticity point of emitted light of the second white LED on a
CIE chromaticity diagram, adjusts a color mixture of lights emitted
from the first and second white LEDs to a chromaticity of the
predetermined white region.
[0019] A white light emitting apparatus for an image reading
apparatus according to the present invention uses a white LED
having a blue LED chip and a phosphor, and includes a light source
section in which a first white LED that emits white light whose
chromaticity deviates to a blue side from a predetermined white
region of a CIE chromaticity diagram and a second white LED that
emits white light whose chromaticity deviates to a yellow side from
the predetermined white region are adjacently disposed such that
optical axes thereof are in substantially the same direction, and a
current regulator that independently drives the blue LED chips in
the first and second white LEDs, respectively; wherein the current
regulator continuously supplies a constant current to one white LED
among the first and second white LEDs that emits white light whose
chromaticity is nearer to a target chromaticity point on the CIE
chromaticity diagram, and supplies a PWM-controlled current to
another white LED among the first and second white LEDs, sets a
duty ratio of the PWM control to a value of an inverse ratio
between a distance between a chromaticity of the one white LED and
the target chromaticity point and a distance between a chromaticity
of the other white LED and the target chromaticity point on the CIE
chromaticity diagram, and adjusts a color mixture of emitted lights
from the first and second white LEDs to a chromaticity of the
predetermined white region.
[0020] A line illuminator according to the present invention is
configured to emit light that is incident from a light source
disposed toward a light incident surface provided at an end surface
in a length direction of a bar-shaped light guide member formed of
a clear member from a light emitting surface provided along a
length direction while causing the light to be reflected by an
inner surface of the bar-shaped light guide member. The light
source is the above described white light emitting apparatus.
[0021] According to the line illuminator of the present invention,
an external shape of a radiating surface that radiates a light of
the white light emitting apparatus is of dimensions that can be
included in an external shape of the light incident surface of the
light guide member.
[0022] According to the white light emitting apparatus of the
present invention, by using a combination of white LEDs that emit
light colors whose chromaticity deviates from a predetermined white
region among ranked white regions that are being provided as
products, it is possible to utilize white LEDs that have a wide
range of chromaticities. More specifically, the white light
emitting apparatus of the present invention lowers the cost of
producing white LEDs by reducing the number of products that have
heretofore been wasted due to hue deviations that are inherent to
white LEDs that include a blue LED chip and a YAG phosphor.
[0023] Further, according to the white light emitting apparatus of
the present invention, it is possible to emit light of a
predetermined white region that is a target without employing a
complicated configuration that has been used in the conventional
technology such as newly adding a LED chip that emits light of a
different wavelength or a different kind of fluorescent substance,
or changing the phosphor composition in order to compensate for
chromaticity variations that are a drawback of white LEDs.
[0024] Further, for example, by using the white light emitting
apparatus according to the present invention as a light source of a
line illuminator, a bright line illuminator that illuminates with a
prescribed white chromaticity can be economically produced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a perspective diagram illustrating a light source
section of a white light emitting apparatus according to a First
Embodiment of the present invention;
[0026] FIG. 2 is a diagram illustrating one example of an
electrical circuit for driving the white light emitting apparatus
according to the First Embodiment of the present invention;
[0027] FIG. 3 is a diagram for describing control of the
illumination duration of two white LEDs according to the First
Embodiment of the present invention;
[0028] FIG. 4 is a view for describing a typical white region using
chromaticity coordinates according to JIS Z 8110;
[0029] FIG. 5A is a view that illustrates an example in which light
emission regions of white LEDs produced by one manufacturer are
divided into four ranks and represented on a CIE chromaticity
diagram;
[0030] FIG. 5B is a view that illustrates coordinate values of
angles of each area generated by the division of light emission
regions into ranks illustrated in FIG. 5A;
[0031] FIG. 6A is a view that illustrates an example in which light
emission regions of white LEDs produced by one manufacturer are
divided into seven ranks and represented on a CIE chromaticity
diagram;
[0032] FIG. 6B is a view that illustrates coordinate values of
angles of each area generated by the division of light emission
regions into ranks illustrated in FIG. 6A;
[0033] FIG. 7A is a view in which the chromaticity of emitted
lights of commercially available white LED products are re-ranked
into areas A, B, and C and represented on a CIE chromaticity
diagram;
[0034] FIG. 7B is a view that illustrates coordinate values of each
angle of the areas A, B, and C that have been re-ranked as
illustrated in FIG. 7A;
[0035] FIG. 8 is a chromaticity diagram that describes control that
mixes colors of lights emitted from two white LEDs of the white
light emitting apparatus according to the First Embodiment of the
present invention;
[0036] FIG. 9 is a view for describing a white light emitting
apparatus used as a first or second white LED that emits light with
a chromaticity in a band region that is outside a ranked white
region;
[0037] FIG. 10 is a view for describing the chromaticity of light
emitted by a white light emitting apparatus of a Second Embodiment
according to the present invention;
[0038] FIG. 11 is a diagram for describing control of the
illumination duration of two white LEDs of the Second Embodiment
according to the present invention;
[0039] FIG. 12 is a perspective diagram illustrating the
configuration of a line illuminator of a Third Embodiment according
to the present invention;
[0040] FIG. 13 is a view for describing a radiating surface of a
white light emitting apparatus used for a light source of the line
illuminator of the Third Embodiment according to the present
invention;
[0041] FIG. 14 is a view that illustrates a cross section of a CIS
unit that incorporates the line illuminator of the Third Embodiment
according to the present invention;
[0042] FIG. 15 is a view for describing an illuminance distribution
in a longitudinal direction when an illumination light of a line
illuminator of the Third Embodiment according to the present
invention is divided into red (R), green (G), and blue (B); and
[0043] FIG. 16 is a distribution chart that illustrates variations
in the chromaticity of white LEDs.
[0044] FIG. 17 is a perspective diagram illustrating a light source
section of a white light emitting apparatus according to a fourth
embodiment of the present invention;
[0045] FIG. 18 is a diagram illustrating one example of an
electrical circuit driving the white light emitting apparatus
according to the fourth embodiment of the present invention;
[0046] FIG. 19 is a chromaticity diagram illustrating a
relationship between chromaticities of emitted lights from the
white light emitting apparatus according to the fourth embodiment
of the present invention;
[0047] FIG. 20 is a diagram illustrating a control of illumination
duration of a white light emitting diode in the fourth embodiment
of the present invention;
[0048] FIG. 21 is a cross sectional diagram illustrating a modified
embodiment of the white light emitting apparatus according to the
fourth embodiment of the present invention;
[0049] FIG. 22 is a perspective diagram illustrating a linear
illuminator according to a fifth embodiment of the present
invention;
[0050] FIG. 23 is a cross sectional diagram illustrating a
contact-type image sensor unit in which the linear illuminator
according to the fifth embodiment of the present invention is
incorporated;
[0051] FIG. 24A is a diagram illustrating the relative illuminance
between each of R, G, and B colors before an adjustment of
illumination duration in the linear illuminator according to the
fifth embodiment of the present invention;
[0052] FIG. 24B is a diagram illustrating the relative illuminance
between each of R, G, and B colors after the adjustment of
illumination duration in the linear illuminator according to the
fifth embodiment of the present invention;
[0053] FIG. 25A is a diagram illustrating a method for
manufacturing a white light emitting diode according to a sixth
embodiment of the present invention (a configuration before a
fluorescent layer is formed);
[0054] FIG. 25B is a diagram illustrating the method subsequent to
FIG. 25A for manufacturing a white light emitting diode according
to the sixth embodiment of the present invention (a configuration
after a fluorescent layer is formed);
[0055] FIG. 26 is a diagram illustrating a state with the white
light emitting diode according to the sixth embodiment of the
present invention being mounted to a printed circuit board;
[0056] FIG. 27 is a chromaticity diagram illustrating a
relationship between chromaticity of emitted lights from the white
light emitting diode according to the sixth embodiment t of the
present invention;
[0057] FIG. 28 is a perspective diagram illustrating a linear
illuminator according to a seventh embodiment of the present
invention;
[0058] FIG. 29 is a cross sectional diagram illustrating a
contact-type image sensor unit in which the linear illuminator
according to the seventh embodiment of the present invention is
incorporated;
[0059] FIG. 30 is a chromaticity diagram illustrating a
relationship between the degrees of whiteness of a white light
emitting diode and identification areas.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0060] The present invention was completed based on the study of
properties of a white LED having a blue LED chip and a fluorescent
substance by the inventor of the present application, the study of
a white light emitting apparatus and an illuminator for emitting
white light that emit a high-power light having a uniform degree of
whiteness, and a novel finding of a configuration of these which is
easy to manufacture.
[0061] In this connection, white colors as illumination light
sources in the present embodiment are typically defined as in
reference FIG. 1 "General Chromaticity Classification of System
Color Names" of JIS Z 8110 in the Japanese Industrial Standards as
illustrated in FIG. 4. Among these, the white colors are classified
into white, (bluish) white, (purplish) white, (yellowish) white,
(greenish) white and (light) pink. These colors are referred to as
a typical "white color" according to the present invention.
[0062] A process whereby a mixture ratio of light is adjusted so
that colors of illumination light sources become a target white
color is referred to as "white balance". This adjustment is
performed using a measurement sensor device. According to the
present embodiment a spectrophotometer is used, and the luminosity,
brightness, chromaticity, and x and y coordinates on a CIE
chromaticity diagram and the like of a white LED is measured or
calculated. However, the present invention may also be implemented
satisfactorily even when the white balance is adjusted using a
measurement sensor device other than a spectrophotometer.
[0063] Each manufacturer of white LEDs ranks regions of a certain
width and length in the aforementioned typical white color region
including a white point (x=0.33, y=0.33) on the CIE chromaticity
diagram as light emission regions of white LEDs that are provided.
For example, in the product catalog (fiscal year 2008 edition) of
Nichia Corporation (hereunder abbreviated to "N. Corp."), light
emission regions are ranked and divided into four regions, namely,
a0, b1, b2, and c0, as illustrated in FIG. 5A. The coordinate
values of angles of each region are illustrated in FIG. 5B.
Further, in the product catalog (2008 edition) for white LEDs of
the type made by combining blue LEDs and phosphor of Toyoda Gosei
Co. Ltd. (hereunder, abbreviated to "T. Co."), as illustrated in
FIG. 6A, light emission regions are ranked and divided into seven
regions, namely, AA, AB, B3 to B6, and C0. The coordinate values of
angles of each region are illustrated in FIG. 6B. The total region
ranked by both companies is identical and overlapping on the CIE
chromaticity diagram, and the respective regions only differ at the
level of the segmented regions.
[0064] Here, to facilitate the description of the present
embodiment, these ranked regions are re-ranked into three regions,
namely, A, B, and C regions. More specifically, the a0 region of N.
Corp. and the (AA+AB) region of T. Co. are the same region
(hereunder, referred to as "A region"), the c0 region of N. Corp.
and the CO region of T. Co. are the same region (hereunder,
referred to as "C region"), and the (b1+b2) region of N. Corp. and
the (B3+B4+B5+B6) region of T. Co. are the same region (hereunder,
referred to as "B region"), and are overlapping regions,
respectively. The light emission regions re-ranked in this manner
are illustrated in FIG. 7A. The A region, B region, and C region
illustrated in FIG. 7A are regions for which the chromaticity of
emitted lights of commercially available white LED products are
ranked. The coordinate values of angles of each region are
illustrated in FIG. 7B. According to FIG. 7 A, the white point
(x=0.33, y=0.33) exists on the boundary between the B region and C
region. As illustrated in FIG. 7A, the B region is a region in
which the color changes towards blue from the white point.
[0065] Hereunder, the (A+B+C) region is referred to as a "ranked
white region". Further, the B region is referred to as a
"predetermined white region" (desired hue), and is the target hue
of an emitted light color of the white light emitting apparatus in
the embodiment. Thus, with respect to the ranked white region for
which manufacturers have ranked the white light emission of white
LEDs, the predetermined white region (B region) is positioned in
the centre thereof, and the A region that deviates to the blue side
and the C region that deviates to the yellow side from the
predetermined white region are regions on the CIE chromaticity
diagram that are connected to the predetermined white region (B
region). As illustrated in FIG. 7B, the predetermined white region
(B region) represents chromaticities inside a region surrounded by
four points with the coordinate values (x, y) (0.296, 0.276),
(0.283, 0.305), (0.330, 0.360) and (0.330, 0.318) on the CIE
chromaticity diagram. Further, the A region represents
chromaticities inside a region surrounded by the four points
(0.280, 0.248), (0.264, 0.267), (0.283, 0.305), and (0.296, 0.276),
and the C region represents chromaticities inside a region
surrounded by the four points (0.330, 0.318), (0.330, 0.360),
(0.361, 0.385) and (0.356, 0.351).
[0066] In an image reading apparatus in which the white light
emitting apparatus or line illuminator according to the present
invention is used, it is not intended to have the light source or
reflected light thereof directly recognized by the human eye, and a
mechanism is employed whereby a photoelectric conversion sensor
receives and recognizes the light. Accordingly, it is not necessary
that the central hue of emitted light colors must always be the
white point (x=0.33, y=0.33) on the CIE chromaticity diagram, and
the hue of the light source is selected by taking into account the
cost efficiency of the light source in an adjustable range of the
image reading apparatus.
[0067] In this connection, the coordinate values (x=0.307, y=0.315)
of a common angle of the regions B3 to B6 shown in FIG. 6A are
employed as the coordinates of the center of the B region, and are
taken as target coordinate values (target chromaticity point) which
the chromaticity should reach in the present embodiment.
Accordingly, although constructing a light source of an image
reading apparatus that is an object of the present invention using
only white LEDs of B region is preferable from the viewpoint that
hue unevenness is easily suppressed, in such case white LEDS of the
A region and C region are wasted, and this is a problem should be
considered from the cost viewpoint.
[0068] The present invention provides a white light emitting
apparatus or a line illuminator that, with respect to white LEDs
that emit light of a chromaticity of a ranked white region provided
by a manufacturer, emits light using white LEDs that emit light
colors of an A region or a C region that deviate from a
predetermined white region (B region), and adjusts the hues of the
emitted light colors. As a result, the number of wasted white LEDs
is reduced. Specific examples of the invention are described
hereunder.
First Embodiment
[0069] A white light emitting apparatus used in an image reading
apparatus according to the First Embodiment is provided with two
white LEDs. Each of the white LEDs includes a blue LED chip, and a
phosphor layer which is excited by a radiation light emitted by the
blue LED chip and emits a yellow light. Yellow is a complementary
color of blue. In the First Embodiment, a white light emitting
apparatus 20 having two white LEDs will be explained with reference
to FIGS. 1 to 4, and FIG. 9.
[0070] The white light emitting apparatus 20 of the present
embodiment includes a light source section 10 and a current
regulation section 33. FIG. 1 illustrates the light source section
10 of the white light emitting apparatus 20. The light source
section 10 includes a first white LED 11 for emitting a white light
of A region which deviates to the blue side from the predetermined
white region (B region) among the aforementioned ranked white
region (A region+B region+C region) and a second white LED for
emitting a white light of C region which deviates to the yellow
side from the predetermined white region (B region), with the first
and second LEDs 11 and 12 being adjacently mounted to a printed
circuit board 15. The first and second white LEDs 11 and 12 are
also adjacently arranged to emit light such that the principal
light-emitting directions thereof, that is, the optical axes, are
parallel to each other in approximately the same direction. The
printed circuit board 15 is provided with an anode line which is
common to the two white LEDs 11 and 12 and two cathode lines
connected to each of the white LEDs 11 and 12 as wiring 16 for
electric supply. The anode line and the two cathode lines are
connected to an external current regulation section 33 through
terminals A, K1, and K2, respectively (see FIG. 2). The current
regulation section 33 causes the first and second white LEDs 11 and
12 constituting the light source section 10 of the white light
emitting apparatus 20 to be driven independently. In this
connection, the phosphor layer covering the blue LED chip is
omitted from FIG. 1.
[0071] As the white LEDs used in this embodiment, for example,
white LEDs for which the hues of emitted lights are in the A region
and the C region may be designated and acquired. Each of these
kinds of white LED is a commercially available surface mount LED
package having a longitudinal dimension of about 2.0 mm and a
lateral dimension of about 1.2 mm (NESW007A, manufactured by Nichia
Corporation). Further, it is possible to acquire the white LEDs
with the aforementioned product number and, from among those,
identify and use white LEDs that emit light of the A region and
white LEDs that emit light of the C region in a lighting state with
a rated forward current of 10 mA by means of the aforementioned
measurement sensor device.
[0072] The white light emitting apparatus according to the present
invention is an apparatus that attempts to obtain the chromaticity
of B region by mixing the white lights of two white LEDs. That
relationship is described next referring to a CIE chromaticity
diagram illustrated in FIG. 8. The coordinate values of angles of
each region are the same as in FIG. 7B. In this case, the white
light emitting apparatus includes a first white LED that emits a
white light LA1 at a chromaticity point PA1 in A region on the CIE
chromaticity diagram illustrated in FIG. 8, and a second white LED
that emits a white light LC1 at a chromaticity point PC1 in C
region illustrated in FIG. 8.
[0073] In order to cause a color mixture produced by the emitted
light colors of the first and second white LEDs to match a point
PD0 illustrated in FIG. 8, the luminosity of the white light LA1 at
the point PA1 and the luminosity of the white light LC1 at the
point PC1 may be weighted, and the luminosity may be adjusted so
that a value that is a weighted average between the chromaticity
coordinates of the point PA1 and the chromaticity coordinates of
the point PC1 becomes a value with predetermined chromaticity
coordinates. The point PD0 is a target point which the color
mixture should reach that is taken to have the coordinate values
(x=0.307, y=0.315), and these coordinates are the center of the
aforementioned B region.
[0074] Adjustment of the luminosity (brightness) of emitted light
colors of the white LEDs of the present embodiment is performed
with PWM control that keeps a forward current that drives each LED
chip constant and changes the pulse width, which is recommended
because there are few hue changes.
[0075] Next, a method of adjusting a color mixture in the white
light emitting apparatus 20 of the present embodiment is described.
FIG. 2 is a diagram illustrating one example of an electrical
circuit for driving the white light emitting apparatus 20. The
electrical circuit includes the light source section 10 and a
current regulation section 33 that is a current regulator. The
light source section 10 corresponds to the part illustrated in FIG.
1. The current regulation section 33 includes current regulation
sections that are separately provided to control currents flowing
to each of the first and second white LEDs 11 and 12. For example,
current regulating circuits 21 and 22 are connected in parallel to
each of the first and second white LEDs 11 and 12 via two cathode
terminals K1 and K2 of the light source section 10, respectively.
Also, transistors T1 and T2 for turning each of the white LEDs 11
and 12 on and off are connected to the current regulating circuits
21 and 22, respectively. The transistors T1 and T2 are connected to
ground GND.
[0076] Each of the current regulating circuits 21 and 22 are, for
example, provided with an operation amplifier, a transistor, and a
current-limiting resistor R1 or R2. The current regulation section
33 causes a forward current that is defined for each of the white
LEDs 11 and 12 to be applied to each of the white LEDs 11 and 12,
and turns the transistors T1 and T2 on and off, respectively, by a
PWM control method so as to control the lighting of the white LEDs
11 and 12. Such current regulation section 33 functions as a
current regulator.
[0077] Next, the current control operation for causing emitted
light colors that have been mixed by the white light emitting
apparatus 20 of the present embodiment to substantially match a
target point that should be reached on a chromaticity diagram will
be described. FIG. 3 is a timing chart for performing PWM control
with respect to an illumination duration of the first and second
white LEDs 11 and 12.
[0078] First, the white light emitting apparatus 20 is operated
with a duration of pulse T being set to be 10 milliseconds, a
current for driving the first and second white LEDs 11 and 12 being
set to be a rated 10 mA using the current regulating circuits 21
and 22, and an illumination duration t1 of the first white LED 11
being set to be 5 milliseconds for each cycle. The drive currents
of the white LEDs 11 and 12 are set by the current regulating
circuits 21 and 22, respectively, and the illumination duration t1
is controlled by the transistor T1.
[0079] Next, a measurement sensor device is installed at a position
above the light emitting surface of the white light emitting
apparatus 20 that is separated from the two white LEDs 11 and 12 by
a distance such that the emitted lights are sufficiently mixed with
each other, or over a scattering plate that has been arranged, and
chromaticity measurement of emitted light colors of the white light
emitting apparatus 20 is started. In this case, chromaticity
measurement is started with a measurement time being set to be
several tens of times or more greater than the duration T.
[0080] Thereafter, an illumination duration t2 of the white LED 12
for each cycle is controlled by the transistor T2, to find an
illumination duration t2 for which a chromaticity measurement value
of light emitted by the white light emitting apparatus 20
approximately matches the point PD0 (x=0.307, y=0.315) at the
center of the B region illustrated in FIG. 8.
[0081] In this case, in order to make the chromaticity of an
emitted light color that has been mixed by the white light emitting
apparatus 20 approximately match the point PD0 that has coordinate
values at approximately the center of the B region that is taken as
the target on the CIE chromaticity diagram, the PWM control by the
current regulation section 33 may be used to cause the first white
LED 11 to light in accordance with a duty ratio D1=t1/T and cause
the second white LED 12 to light in accordance with a duty ratio
D2=t2/T.
[0082] In this connection, depending on the coordinates position
inside the A region corresponding to the emitted light color of the
first white LED or the coordinates position inside the C region
corresponding to the emitted light color of the second white LED
that have been selected, it may not be possible to match the color
mixture with the point PD0. However, since it is possible to match
the color mixture with a chromaticity inside the B region, it is
possible to satisfactorily solve the problem to be solved by the
present invention. Further, the entire ranked white region includes
the A region+B region+C region that are connected in an arch shape.
Hence, when a white LED is selected that emits light whose
chromaticity is on the inner side of a far end of the arch shape in
the A region or C region, in some extremely rare cases the
chromaticity coordinates of the color mixture may deviate outside
the B region. In such case, it is sufficient to determine whether
the chromaticity of the color mixture is allowable or not.
[0083] In contrast to the conventional white light emitting
apparatus that suppresses the occurrence of color unevenness by
selecting only white LEDs that emit light of a predetermined white
region that is comparatively narrow, the white light emitting
apparatus according to the present invention also combines and uses
white LEDs that emit light colors whose chromaticity deviates from
a predetermined white region in ranked white regions that are being
provided as products. Consequently, according to the present
invention, the product cost can be lowered by reducing the number
of white LEDs that heretofore have been screened and not used due
to hue deviations that are inherent to white LEDs that include a
blue LED chip and a YAG phosphor.
[0084] Further, according to the present invention, it is possible
to manufacture a white light emitting apparatus that can emit light
of a target predetermined white region without employing a
complicated configuration that has been used in the conventional
technology such as newly adding an LED chip that emits light of a
different wavelength or a different kind of fluorescent substance,
or changing the phosphor composition in order to compensate for
chromaticity variations that are a drawback of white LEDs.
[0085] As the current control in the white light emitting apparatus
20, instead of the control with the PWM method, the amounts of
currents for driving the white LEDs 11 and 12 may be controlled.
The amounts of currents can be controlled by the current regulating
circuits 21 and 22. Alternatively, the control with the PWM method
and the control of the current amounts may be combined.
[0086] According to the above embodiment, the chromaticity of light
emitted by white LEDs is described based on ranked white regions
provided by manufacturers. However, with respect to the
distribution of the chromaticity of light emitted from white LEDs
including a blue LED chip and a YAG phosphor, the chromaticity can
also be distributed in a white region between a light emission
region of blue of a blue LED chip and a yellow region of light
emitted by a phosphor on the CIE chromaticity diagram. This white
region is represented by a band region 66 illustrated in FIG. 9.
The typical white region 67 according to reference FIG. 1 (see FIG.
9) of the standard JIS Z 8110 that is previously defined spreads to
outside the ranked white region (A region+B region+C region) 65,
and is an ellipsoidal region with a longitudinal diameter that is
approximately a distance from a point (x=0.23, y=0.21) on a blue
side with respect to the white point in the CIE chromaticity
diagram to a point (x=0.41, y=0.41) on a yellow side thereof. The
present invention can also be used for a white LED for which a
chromaticity distributed by the emitted light color of the white
LED is in the band region 66 within the typical white region
67.
[0087] A white light emitting apparatus is manufactured that is
adapted in a similar manner to the aforementioned embodiment by
employing a white LED that emits light of a white color whose
chromaticity deviates to the blue side from the desired white
region (B region) in the band region 66 on the outside of the
ranked white region as a first white LED, and likewise employing a
white LED that emits light of a white color whose chromaticity
deviates to the yellow side from the desired chromaticity region (B
region) in the band region 66 on the outside of the ranked white
region as a second white LED. Even if the emitted light color of
the first white LED has a chromaticity in a white region that
deviates further to the blue side than the A region, or even if the
emitted light color of the second white LED has a chromaticity in a
white region that deviates further to the yellow side than the C
region, by means of PWM control of the current regulation section
33 it is possible to match the chromaticities of the emitted lights
thereof in a similar manner as the white light emitting apparatus
20 to a chromaticity inside the B region.
[0088] Thus, when the chromaticity of light emitted by the first or
second white LED is broadly selected with a wide region in the band
region 66, a target chromaticity point of a color mixture of the
lights emitted from the two white LEDs or a predetermined white
region may not necessarily be limited to inside the B region, and
the target point or predetermined white region may be a center part
between chromaticity points of lights emitted by the two white
LEDs, or the chromaticity point of the color mixture may move to a
blue side or a yellow side with respect to the B region.
[0089] By enabling selection of chromaticities of a wide area
outside of a ranked white region as emitted light colors of the
first or second white LED in this manner, the usability of white
LEDs is increased much more, and product costs can be
decreased.
Second Embodiment
[0090] The Second Embodiment relates to PWM control of drive
currents that effectively drives the two white LEDs used in the
white light emitting apparatus of the First Embodiment to further
increase the luminosity of the white light emitting apparatus that
mixes the emitted light colors of the two white LEDs. The present
embodiment also relates to a white light emitting apparatus that
enables selection and use of white LEDs in which the chromaticities
of emitted lights are distributed over a wide region by means of
PWM control. The emitted light colors of the first and second white
LEDs of the Second Embodiment are described using chromaticities
inside the A region and C region, respectively, similarly to the
First Embodiment.
[0091] First, current control that adjusts the chromaticity of a
white light emitting apparatus that includes the two white LEDs is
described in a case in which, on the CIE chromaticity diagram,
there is a difference in the distance to the target point PD0 of
the chromaticity after color mixing from the respective coordinate
points of the chromaticities of the lights emitted by the two white
LEDs 11 and 12 that are used. At this time, it is preferable to
select LEDs so that the intensity of light emitted with a rated
current by the first white LED 11 and the second white LED 12 is
approximately the same. In order to make the light intensities
uniform, the light intensity rank of the LEDs may be designated and
such LEDs may be acquired from a manufacturer, or the LEDs may be
individually driven and selected upon measuring the light
intensities thereof.
[0092] For example, as illustrated in the CIE chromaticity diagram
in FIG. 10, a chromaticity LA2 of an emitted light color from the
first white LED 11 is positioned at point PA2 in A region, and a
chromaticity of an emitted light color LC2 from the second white
LED 12 is positioned at point PC2 in C region. A case will now be
described in which the hue of the point PD0 positioned on a line
segment connecting the two points PA2 and PC2 and at approximately
the center of the B region is adjusted. For this purpose, it is
sufficient to adjust the luminosity of each of the emitted light
colors so that a weighted average for the coordinates of PA2 and
PC2 obtained by weighting the luminosity of the emitted light
colors LA2 and LC2 thereof becomes the coordinate values of PD0. In
the present embodiment, since a distance ratio between the distance
(PA2-PD0) and the distance (PC2-PD0) is 1:2 as illustrated in FIG.
10, the emitted light color of the color mixture from the white
light emitting apparatus is made approximately the chromaticity of
the point PD0 by adjusting the ratio of the luminosity between the
emitted light colors LA2 and LC2 using the ratio 2:1 that is in
inverse proportion to the distance ratio.
[0093] As illustrated in FIG. 10, the foregoing description
describes a case in which the chromaticity PA2 of the first white
LED, the target chromaticity point PD0 of the color mixture, and
the chromaticity PC2 of the second white LED are on approximately
the same straight line on the CIE chromaticity diagram. However,
even if these points are not on the same straight line, by setting
the luminosity of the emitted light colors LA2 and LC2 in inverse
proportion to the distance ratio between the distance (PA2-PD0) and
the distance (PC2-PD0), a color mixture of the emitted light colors
of both LEDs becomes approximately a chromaticity of the
predetermined white region (B region) that is a favorable
chromaticity.
[0094] This method of adjusting the color mixture can be expressed
in a different way. That is, the luminosity of a white LED that
emits light whose chromaticity is closer to the target point PD0 of
the chromaticity after mixing colors is made higher than the
luminosity of the other white LED that emits light whose
chromaticity is at a position that is farther away from the target
point PD0. According to the white light emitting apparatus of the
present embodiment for which LEDs that have approximately the same
light intensity are selected as the two white LEDs, the current
regulation section 33 is used to continuously supply a constant
current (not a pulse current) from the current regulating circuit
21 illustrated in FIG. 2 as the drive current of the white LED 11
that is closer to the target point PD0. In this state, only the
drive current of the other white LED 12 is supplied using PWM
control, and the pulse width t2 thereof is decided so that a
mixture of the colors of the two white LEDs matches a target
chromaticity by a similar method to the First Embodiment (see FIG.
11).
[0095] With respect to current control other than the current
control illustrated in FIG. 11, it was confirmed that although the
color mixture is approximately the target chromaticity when the
current regulation section 33 is used to set the duration T to 100
milliseconds, t1 (pulse width subjected to PWM control with the
drive current of the white LED 11) to 90 milliseconds, and t2 to 45
milliseconds, the luminosity is higher in the case of the current
control illustrated in FIG. 11. Naturally, it is also favorable to
set t1 to be the same as the duration and continuously drive the
white LED 11, and set t2 to be half of t1 and drive the white LED
12.
[0096] The method of setting the pulse width in the above PWM
control will now be summarized. For both the first and second white
LEDs, the chromaticity of light emitted by each LED is previously
measured with a measurement sensor device and the respective
distances to a target chromaticity point PD0 after mixing colors on
the CIE chromaticity diagram is calculated. The drive current of
the white LED for which the distance in question is shorter is
supplied using a constant current. Further, when supplying a
current using PWM control, the setting is made so that the duty
ratio of a pulse width P thereof is the maximum. On the other hand,
it is favorable to set a pulse width p for driving the white LED
for which the distance in question is longer to a value that is
inversely proportional to the distance ratio with respect to the
pulse width P. Naturally, a configuration may also be adopted as in
the First Embodiment in which the pulse width that drives the white
LED for which the distance to the target chromaticity point is
longer is adjusted while monitoring the color mixture with a
measurement sensor device.
[0097] According to the present embodiment, a ratio (t1/t2) between
the pulse width t1 of the white LED 11 that is nearer to the point
PD0 and the pulse width t2 of the white LED 12 that is farther from
the point PD0 can be set to be larger because t1 is a maximum
value. This enables the distance (PC2-PD0) to be made longer with
respect to the distance (PA2-PD0), and makes it possible to utilize
a white LED that emits light whose chromaticity is further from the
target point PD0 of the color mixture. This enhances the usability
of white LEDs that emit light whose chromaticity deviates from the
predetermined white region (B region), and can lower the total cost
when acquiring white LEDs.
Third Embodiment
[0098] The Third Embodiment relates to a line illuminator 50 that
uses the white light emitting apparatus 20 of the First Embodiment.
The line illuminator 50 is described in detail below with reference
to FIGS. 12 to 15.
[0099] The line illuminator 50 of the present embodiment is used to
illuminate an original copy surface such as a paper surface in an
image reading apparatus, for example. The line illuminator 50 is,
as illustrated in FIG. 12, provided with a bar-shaped light guide
member 51 that is formed of a clear material and has a light
incident surface 54 at one end thereof, and a light source section
10 disposed toward the light incident surface 54. The light source
section 10 is connected with the current regulation section 33 via
a terminal lead wire 62 as in the case of the First Embodiment (not
illustrated in FIG. 12). The light guide member 51 is provided with
a light guiding section 52 for guiding an incident light from the
light incident surface 54 in the longitudinal direction while
causing the light to be reflected by the inner surface of the light
guide member 51, and a light emitting section 53 having a light
emitting surface for causing light from the light guiding section
52 to be emitted linearly in the longitudinal direction.
[0100] In order that the light from the light source section 10 can
be incident from the light incident surface 54 of the light guide
member 51 without wasting the light, as illustrated in FIG. 13, the
external dimensions of a radiating surface 63 that radiates light
of the light source section 10 are designed so that the radiating
surface 63 can be included inside the external shape of the light
incident surface 54 of the light guide member 51 with a sufficient
margin. For example, on the side of a surface that radiates light
of the light source section 10, as illustrated in FIG. 13, two
white LED are arranged that each have a size of 1.2 mm.times.2 mm,
and the external dimensions of the side of the surface that
radiates light of the light source section 10 are 2.5 mm
(horizontal direction).times.2 mm (vertical direction). Further,
the external size of the light incident surface 54 of the light
guide member 51 illustrated in FIG. 12 is 3.5 mm (W
direction).times.2.5 mm (H direction). Furthermore, the design is
one in which, by disposing the radiating surface 63 of the light
source section 10 as near as possible to the light incident surface
54 of the light guide member 51, light from the white light
emitting apparatus 20 is made incident on the light guide member 51
without waste.
[0101] The light guide member 51 may be, for example, a light guide
member that is compatible with use for a three-primary color light
source that has LEDs of three wavelengths (for example, for red,
green, and blue) arranged thereon (at different positions). That
means a light guide member designed for linear illumination may be
used in which lights from a plurality of light sources that have
different wavelengths are incident from a light incident surface,
and proper reflection and scattering occur in the light guide
member for each wavelength, so that a light is emitted with the
outputs of the wavelengths being uniformly distributed in the
longitudinal direction thereof. A light guide member having such a
function is described in detail in, for example, Patent Document
1.
[0102] Therefore, even when there is a difference in the hues of
emitted light colors between the two white LEDs 11 and 12 of the
light source section 10 in the white light emitting apparatus 20
which are used as light sources, and also the central points of the
two emitted lights are not at the same position, and furthermore
even when a distance to the light incident surface 54 from the
white light emitting apparatus 20 is short and sufficient color
mixing cannot be obtained in this space, the light guide member 51
allows the colors of the incident lights from the light incident
surface 54 to be well mixed so as to emit a linear illumination
light that has a uniform color distribution of whiteness.
[0103] The inventors of the present invention checked the above
described effect of the line illuminator 50 of the present
embodiment in the following procedure. First, as illustrated in
FIG. 14, the line illuminator 50 was incorporated in a contact-type
image sensor unit (hereinafter, simply referred to as CIS unit) 60
that constitutes an image reading apparatus. Although not
illustrated in FIG. 14, the current regulation section 33 of the
white light emitting apparatus 20 was connected via a connector
61.
[0104] The CIS unit 60 was used to cause a light reflected by an
original paper copy 59 to be focused on a line sensor 56 by a lens
array 55. The line sensor 56 that was used was configured with
three linear rows of pixels that separately receive a color of red
(R), green (G), or blue (B) for photoelectric conversion
(illustration is omitted). The line sensor 56 has three color
filters that have pass bands for RGB and are disposed on each row
of pixels. Therefore, each row of pixels functions with spectral
sensitivity corresponding to each of the R, B, and G colors. Such a
sensor array is described, for example, in Patent Document 3.
[0105] Therefore, the CIS unit 60 is able to separate the white
light reflected by the original paper copy 59 into each of the R,
G, and B colors, and measure the illuminance for each pixel of the
row of pixels arranged in the longitudinal direction thereof. The
measured illuminance value for each pixel can be represented as the
illuminance distribution for the area from one end surface on the
light incident surface side to the other end surface in the
longitudinal direction of the light guide member 51.
[0106] Next, similarly to the First Embodiment, after the original
paper copy 59 was replaced with a predetermined white paper for
reference, both of the white LEDs 11 and 12 were driven with the
current regulation section 33. Further, the illumination light of
the line illuminator 50 was measured for the relative illuminance
of each of the R, G, and B colors as the illuminance distribution
in the linear direction. In the measurement, the currents applied
to both of the white LEDs 11 and 12 were set to 10 mA,
respectively. The measured result for illuminance distributions
showed generally uniform distributions in the longitudinal
direction with approximately the same values of relative
illuminance for the red and green colors as illustrated in FIG. 15.
Further, for the blue color, the result showed a substantially
uniform distribution in the longitudinal direction, with a higher
relative illuminance compared to those of the red and green
colors.
[0107] The emitted light color of the white light emitting
apparatus 20 that uses the line illuminator 50 of the Third
Embodiment is a light source that has been adjusted so as to have a
chromaticity in B region in FIG. 7A according to the First
Embodiment, and for which the relative illuminance of blue is
somewhat larger. However, differences between the sizes of the
relative illuminance of red, green, and blue can be adjusted with a
data processing section in the image reading apparatus that
controls the CIS unit. The advantage of a line illuminator that
captures emitted light from the white light emitting apparatus 20
of the First Embodiment in the light guide member 51 and linearly
illuminates a paper surface is that emitted light colors with
different hues from two white LEDs are adequately mixed in the
light guide member 51. A drawback of a white LED that includes a
blue LED chip and a YAG phosphor is that there is an inconsistency
between the color at the center of the light beam and the color at
the periphery thereof, such as a strong yellow color at the
periphery of a beam of emitted light. FIG. 15 illustrates output
obtained when the respective emitted light colors from the first
and second white LEDs are sufficiently scattered and mixed inside
the light guide member 51 and then used to illuminate an original
copy surface with a linear light beam, and the reflected light
thereof is received with the line sensor 56 via the lens array 55
and subjected to photoelectric conversion. As illustrated in FIG.
15, although there is a difference between the relative illuminance
of each of the R, G, and B colors (the relative illuminance of blue
is large), it was confirmed that reflected light from the original
copy undergoes color mixing without any inconsistency for all of
the colors in the main scanning direction (opposite surface side
from light incident surface side) of the CIS unit and the relative
illuminance is approximately constant and homogeneous. Accordingly,
the line illuminator of the present embodiment is an invention that
effectively makes use of the characteristics of the white light
emitting apparatus 20 of the First Embodiment. Further, a line
illuminator that achieves similar advantages can be obtained using
the white light emitting apparatus of the Second Embodiment.
Fourth Embodiment
[0108] A white light emitting apparatus according to a fourth
embodiment is provided with two or more white light emitting
diodes. Each of the white light emitting diodes includes a blue LED
chip, and a fluorescent layer which is excited by a radiation light
emitted by the blue LED chip and emits a yellow light. Yellow is a
complementary color of blue. In the fourth embodiment, a white
light emitting apparatus 120 having the two or more white light
emitting diodes will be explained below with reference to FIGS. 17
to 21.
[0109] FIG. 16 illustrates a light source section 110 of the white
light emitting apparatus 120 of the fourth embodiment. In the white
light emitting apparatus 120, a first white light emitting diode
111 and a second white light emitting diode 112 are adjacently
mounted to a printed circuit board 115. The first white light
emitting diode 111 emits a white light which is more yellowish and
deviated from the white point on a chromaticity diagram. The second
white light emitting diode 112 emits a white light which is more
bluish and deviated from the white point on a chromaticity diagram.
The white light emitting diodes 111 and 112 are also arranged to
emit light in parallel to each other and in the same direction
substantially. The printed circuit board 115 is provided with
wiring 116 for electric supply, including an anode line which is
common to the two white light emitting diodes 111 and 112, and two
cathode lines connected to each of the white light emitting diodes
111 and 112. The anode line and the two cathode lines are connected
to an external current control section (see FIG. 18) through
terminals A, K1, and K2 respectively. The current control section
causes the white light emitting diodes 111 and 112, which
constitute the light source section 110 of the white light emitting
apparatus 120, to be driven.
[0110] The first white light emitting diode 111 may be, for
example, a white light emitting diode that is recognized to emit a
yellowish white light in accordance with a recognition method by
lighting a constant current of 10 mA among the white light emitting
diodes of white LEDs each of which is a commercially available
surface mount LED package having a longitudinal dimension of about
2.0 mm and a lateral dimension of about 1.2 mm (NESW007A,
manufactured by Nichia Corporation). The second white light
emitting diode 112 may be, for example, a white light emitting
diode that is recognized to emit a bluish white light in accordance
with a recognition method by lighting a constant current of 10 mA
among the white light emitting diodes of white LEDs each of which
is a commercially available surface mount LED package having a
longitudinal dimension of about 2.0 mm and a lateral dimension of
about 1.2 mm (NESW007A, manufactured by Nichia Corporation).
[0111] Now, the relationship between chromaticity of the lights
emitted by each of the white light emitting diodes 111 and 112 of
the fourth embodiment will be explained below using the
chromaticity diagrams of FIG. 19 and FIG. 30. For the first white
light emitting diode 111, a white light emitting diode is selected
so that a blue light, which is emitted from a blue LED chip therein
and does not interact with fluorescent particles in a fluorescent
layer, and a yellow light, which is generated by wavelength
conversion after the interaction with the fluorescent particles,
produce a color mixture that has its color distribution on the
yellow side of the white point. For the second white light emitting
diode 112, similarly, a white light emitting diode is selected so
that a blue light and a yellow light produce a color mixture that
has its color distribution on the blue side of the white point.
[0112] The above relationship will be explained below using the
chromaticity diagram illustrated in FIG. 19. In the chromaticity
diagram, the chromaticity point of a yellow light (560 nm) after
wavelength conversion by a YAG fluorescent substance is shown by Y,
and the chromaticity point of a blue light emitted from a blue LED
chip (one representative from the range of 450 nm to 470 nm) is
shown by B. When a curved line YB is defined on the assumption that
both of the chromaticity points Y and B are positioned near a
curved line ST, which illustrates a monochromatic light in the
chromaticity diagram, the curved line YB passes near the white
color chromaticity point W (x=0.33, y=0.33). This is because the
YAG fluorescent substance is used to obtain a fluorescent white
light by compositing a light emitted from a blue LED chip and a
light emitted by the fluorescent substance.
[0113] The chromaticity point WY1 of the color mixture of the light
emitted from the first white light emitting diode 111 is
substantially positioned on the curved line WY, which is connected
between the white point W and the yellow point Y. The chromaticity
point WB1 of the color mixture of the light emitted from the second
white light emitting diode 112 is substantially positioned on the
curved line WB, which is connected between the white point W and
the blue point B.
[0114] Meanwhile, one example of chromaticity areas that can be
selected with luminescence thereof in a selection using a constant
current of 10 mA by a selector is illustrated in FIG. 30.
Therefore, as the first white light emitting diode 111, a light
emitting diode that has a chromaticity coordinate:
0.33<Cx.ltoreq.0.36; 0.33<Cy.ltoreq.0.38 when driven at a
constant current of 10 mA is preferably used, with the chromaticity
coordinate being substantially on the curved line YB. Also, as the
second white light emitting diode 112, a light emitting diode that
generally has a chromaticity coordinate: 0.27.ltoreq.Cx<0.33;
0.26.ltoreq.Cy<0.33 when driven at a constant current of 10 mA
is preferably used, with the chromaticity coordinate being
substantially on the curved line YB. As described above, in the
present invention, the yellowish white means white color the
position of which is substantially close to the white point on the
curved line WY, while the bluish white means white color the
position of which is substantially close to the white point on the
curved line WB.
[0115] FIG. 18 is a diagram illustrating one example of an
electrical circuit driving the white light emitting apparatus 120.
The electrical circuit includes the light source section 110 and a
current control section 133. The light source section 110
corresponds to the part illustrated in FIG. 17. The current control
section 133 includes current control sections that are separately
provided to set a current for each of the white light emitting
diodes 111 and 112. For example, current regulating circuits 121
and 122 are connected in parallel to each of the white light
emitting diodes 111 and 112 via two cathode terminals K1 and K2 of
the light source section 110, respectively. Also, transistors T1
and T2 turning ON/OFF each of the white light emitting diodes 111
and 112 are connected to the current regulating circuits 121 and
122, respectively. The transistors T1 and T2 are connected to
ground GND.
[0116] Each of the current regulating circuits 121 and 122 are, for
example, provided with an operation amplifier, a transistor, and
current-limiting resistor R1 or R2. The current control section 133
causes a constant current that is defined for each of the white
light emitting diodes 111 and 112 to be applied to each of the
white light emitting diodes 111 and 112, so as to control the
lighting of each of the white light emitting diodes 111 and 112 by
a pulse width modulation (hereinafter, simply referred to as PWM)
method. Such current control section 133 functions as a current
control means.
[0117] Next, the current control operation for obtaining a color
mixture of emitted lights from the white light emitting apparatus
120 of the fourth embodiment that is substantially adjusted to the
white point on a chromaticity diagram will be explained below. FIG.
20 is a timing chart illustrating a control of the illumination
durations of the white light emitting diodes 111 and 112 by a pulse
width modulation (PWM) method.
[0118] First, the white light emitting apparatus 120 is operated
with a duration of pulse T being set to be 10 milliseconds, a
current driving the white light emitting diodes 111 and 112 being
set to be 10 mA, an illumination duration t1 of the white light
emitting diode 111 being set to be 9 milliseconds for each cycle.
The drive currents of the white light emitting diodes 111 and 112
are set by the current regulating circuits 121 and 122
respectively, and the illumination duration t1 is controlled by the
transistor T1.
[0119] Next, a sensor measuring chromaticity is installed at a
position, above the light emitting surface of the white light
emitting apparatus 120, which is separated from the two white light
emitting diodes 111 and 112 by a distance so that the emitted
lights are sufficiently mixed with each other, and a measurement of
chromaticity is started, with a time for receiving time being set
to be several tens times that of the duration T.
[0120] Then, an illumination duration t2 of the white light
emitting diode 112 for each cycle is controlled by the transistor
T2, to find an illumination duration t2 for a chromaticity
measurement by a light emitted from the white light emitting
apparatus 120: Cx=0.33, and Cy=0.33, approximately.
[0121] Here, in order to allow a color mixture of emitted lights
from the white light emitting apparatus 120 to substantially reach
the white point on a chromaticity diagram, the PWM control by the
current control section 133 may be used to cause the white light
emitting diode 111 to light in accordance with a duty ratio
D1=t1/T, and the white light emitting diode 112 to light in
accordance with a duty ratio D2=t2/T.
[0122] As described above, according to the fourth embodiment, an
emission of a light having a high purity of whiteness, which was
difficult by one white light emitting diode, is achieved, and the
high power white light emitting apparatus 120 is attained. Also,
depending on the control of a drive current of each of the white
light emitting diodes 111 and 112, the chromaticity coordinate of a
light emission from the white light emitting apparatus 120 can be
changed from the chromaticity point WY1 to the chromaticity point
WB1 along the curved line YB.
[0123] As the current control in the white light emitting apparatus
120, instead of the control with the PWM method, the amounts of
currents driving the white light emitting diodes 111 and 112 may be
controlled. The amounts of currents can be controlled by the
current regulating circuits 121 and 122. Alternatively, the control
with the PWM method and the control of the current amounts may be
combined.
[0124] Next, a modified embodiment of the fourth embodiment will be
explained below with reference to FIG. 21. A white light emitting
apparatus 124 according to the modified embodiment includes two
types of white light emitting diodes 117 and 118 adjacently mounted
on the printed circuit board 115, the diodes 117 and 118 being
individually provided with a fluorescent layer 114 of a different
thickness from each other. That means the first white light
emitting diode 117 is provided with a thicker fluorescent layer
114, and the color mixture of the lights emitted from the white
light emitting diode 117 is yellowish white, similar to the white
light emitting diode 111. The second white light emitting diode 118
is provided with a thinner fluorescent layer 114, and the color
mixture of the lights emitted from the white light emitting diode
118 is bluish white, similar to the white light emitting diode 112.
The thickness of the fluorescent layer 114 is controlled during the
manufacture of the white light emitting diodes 117 and 118, for
example.
[0125] The white light emitting apparatus 124 in which the current
control section 133 is connected to the light source section 110
including the above described white light emitting diodes 117 and
118 therein can also provide high purity whiteness as in the case
of the fourth embodiment. In addition, as compared with the white
light emitting diode with one blue LED chip, a higher power
emission of white light can be obtained.
Fifth Embodiment
[0126] A linear illuminator 150 according to a fifth embodiment
uses the white light emitting apparatus 120 according to the fourth
embodiment. The linear illuminator 150 will be explained in detail
below with reference to FIGS. 22 to 24.
[0127] The linear illuminator 150 of the fifth embodiment is used
to illuminate a surface of a manuscript such as a paper in an image
reading apparatus, for example. The linear illuminator 150 is, as
illustrated in FIG. 22, provided with a bar-shaped light guide
member 151 that is formed of a transparent material and has a light
incident surface 154 at one end thereof, and the light source
section 110 disposed toward the light incident surface 154. The
light source section 110 is connected with the current control
section 133 via terminal lead 162 as in the case of the fourth
embodiment (not illustrated in FIG. 22). The light guide member 151
is provided with a light guiding section 152 guiding an incident
light from the light incident surface 154 in the longitudinal
direction of the light guide member, and a light emitting section
153 linearly emitting the light from the light guiding section 152
in the longitudinal direction.
[0128] In order to improve the light yield of the light guide
member 151 from the light incident surface 154 into the light guide
member 151, the light source section 110 is designed to have a
light emitting surface of a size that can be included in the light
incident surface 154 with margin. For example, in the case with the
light emitting surface of the light source section 110 having a
size of 2.5 mm (horizontal direction).times.2 mm (vertical
direction), the light guide member 151 is designed to have a light
emitting surface having a size of 3.5 mm (horizontal
direction).times.2.5 mm (vertical direction)
[0129] The light guide member 151 may be, for example, a member for
a light source that has light emitting diodes of three wavelengths
(for example, for red, green, and blue) arranged thereon (at
different positions). That means a light guide member designed for
linear illumination may be used, in which lights from a light
source are incident to a light incident surface, and proper
reflection and scattering occur in the light guide member for each
wavelength, so that a light is emitted with the outputs of the
wavelengths being uniformly distributed in the longitudinal
direction thereof. A light guide member having such a function is
described in detail in Japanese Laid-Open Patent Publication No.
2006-287923, for example.
[0130] Therefore, even when there is a difference in the
wavelengths of emitted lights from the two white light emitting
diodes 111 and 112 of the light source section 110 in the white
light emitting apparatus 120, which are used as light sources, and
also the central points of the two emitted lights are not at the
same position, the light guide member 151 allows the colors of the
incident lights from the light incident surface 154 to be well
mixed so as to emit a linear illumination light that has a uniform
color distribution of whiteness.
[0131] The inventors of the present invention checked the above
described effect of the linear illuminator 150 of the fifth
embodiment in the following procedure. First, as illustrated in
FIG. 23, the linear illuminator 150 was incorporated in a contact
image sensor unit (hereinafter, simply referred to as CIS unit) 160
that constitutes an image reading apparatus. Not illustrated, but
the current control section 133 of the white light emitting
apparatus 120 was connected via the connector 161.
[0132] The CIS unit 160 was used to cause a light reflected by the
paper manuscript 159 to be focused on a line sensor 156 by a lens
array 155. The line sensor 156 was the one configured with three
linear rows of pixels that separately receive a color of red (R),
green (G), or blue (B) for photoelectric conversion (illustration
is omitted). The line sensor 156 has three color filters that have
pass bands for RGB and are disposed on each row of pixels.
Therefore, each row of pixels functions with spectral sensitivity
corresponding to each of the R, B, and G colors. Such sensor array
is described in Japanese Patent No. 3990437, for example.
[0133] Therefore, the CIS unit 160 is able to separate the white
light reflected by the paper manuscript 159 into each of the R, B,
and G colors, and measure the illuminance for each pixel of the row
of pixels arranged in the longitudinal direction thereof. The
measured illuminance value for each pixel can be represented as
illuminance distribution for the area from one end surface on the
light incident surface side to the other end surface in the
longitudinal direction of the light guide member 151.
[0134] Next, as in the case of the fourth embodiment, after the
paper manuscript 159 was replaced with a predetermined white paper
for reference, both of the white light emitting diodes 111 and 112
were simultaneously driven with the current control section 133.
And the illumination light of the linear illuminator 150 was
measured for the relative illuminance of each of R, G, and B colors
as illuminance distribution in the linear direction (FIG. 24A). In
the measurement, the currents applied to both of the white light
emitting diodes 111 and 112 were controlled to be 10 mA. The
measured result for illuminance distributions showed generally
uniform distributions in the longitudinal direction with
approximately the same values of relative illuminance for red and
green colors as illustrated in FIG. 24A, but for blue color, the
result showed a substantially uniform distribution in the
longitudinal direction with a lower relative illuminance as
compared to those of red and green colors.
[0135] Then, as in the case of the fourth embodiment, after the
illumination duration for each cycle of the white light emitting
diode 112, that is the duty ratio D2, was controlled, the relative
illuminance of each of R, G, and B colors could be controlled to
have substantially the same distribution, as illustrated in FIG.
8B.
[0136] The above result of the fifth embodiment showed that the
linear illuminator 150 for illumination with the relative
illuminance of each of R, G, and B colors being well balanced can
be manufactured.
[0137] In a conventional linear illuminator that uses one white
light emitting diode as a light source, often a white light
emitting diode for pure whiteness is selected with efforts by
sacrificing cost, or a white light emitting diode having deviation
in color distribution of whiteness is selected to obtain a white
illumination light of a low quality as a result. To the contrary,
according to the linear illuminator 150 of the fifth embodiment, it
was found that when commercially available white light emitting
diodes having deviation in color distribution of whiteness are
combined and the illumination duration is controlled by controlling
a duty ratio by the PWM method, for example, a highly pure white
illumination light can be readily obtained.
[0138] The combination of the white light emitting diodes 111 and
112 may be accomplished by selecting a diode emitting a yellowish
white light and a diode emitting a bluish white light, and the
chromaticity value of each diode which is inherent property of a
white light emitting diode may not be determined at the point of
time of selection. Therefore, the white light emitting diodes 111
and 112 may be any diode that emits a light that has a position
generally on the curved line YB in the chromaticity diagram of FIG.
19, even if the position is deviated from the white point to a
large degree. As a result, white light emitting diodes that have
been determined to be defective become usable without discarding,
which leads to enhanced productivity of white light emitting
diodes.
Sixth Embodiment
[0139] In a sixth embodiment, two blue LED chips are mounted to one
package, and a YAG fluorescent layer covers each of the blue LED
chips and has a thickness different from those of others. With
reference to FIGS. 25A and 25B, a method for manufacturing a white
light emitting diode 171 of the sixth embodiment will be explained
below.
[0140] A package 172 is formed of a resin into a box shape with the
top thereof being open, and the package 172 has wiring of a lead
frame at the bottom thereof, so that an anode wiring 175 of a lead
frame at the bottom has a first blue LED chip 173 and a second blue
LED chip 174 disposed thereon. Then, the cathode terminal and the
anode terminal thereof are connected to the cathode wiring 176 and
the anode wiring 175 of the lead frame respectively by using a
wire-bonding method for example, to be mounted (FIG. 25A). The top
opening may have a dimension of about 2.5 mm or less in the
longitudinal and lateral directions thereof, for example.
[0141] Next, a resin solution for fluorescent layer is prepared by
mixing a predetermined amount of YAG fluorescent particles into a
clear thermosetting transparent resin, which is coated to both of
the blue LED chips 173 and 174 for covering. Then, the resin
solution for fluorescent layer is subjected to a heat cure
procedure, so that a first fluorescent layer 178 is formed as
illustrated in FIG. 25B. Then, a resin solution for fluorescent
layer which is the same as the above resin solution for fluorescent
layer is coated to the surface of the fluorescent layer 178 to
cover only the upper side of the blue LED chip 173. Then, the resin
solution for fluorescent layer is subjected to a heat cure
procedure, so that a second fluorescent layer 179 is formed. Then,
a seal body 180 is formed on the fluorescent layers 178 and 179
using the same thermosetting transparent resin as that included in
the resin solution for fluorescent layer. In this way, as
illustrated in FIG. 25B, the white light emitting diode 171 is
made.
[0142] The thicknesses of the fluorescent layers 178 and 179 may be
determined in advance as follows, for example. First, a plurality
of blue LED chips that are the same products as the blue LED chips
173 and 174 are provided, and fluorescent layers having different
thicknesses from each other are formed using the resin solution for
fluorescent layer that is prepared as described above. As a result,
a plurality of white light emitting diodes for evaluation can be
obtained. Next, the white light emitting diodes for evaluation are
caused to emit a light at a predetermined current, so that the
diodes that produce a color mixture of bluish white without fail
with the blue light, which does not interact with the fluorescent
particles, and the yellow light, which interacts with the
fluorescent particles in the fluorescent layer for wavelength
conversion, and a range of the thickness of the fluorescent layer
178 is determined based on the thicknesses of the fluorescent
layers. Next, a plurality of white light emitting diode that has
the fluorescent layer 178 having a thickness within the range
formed on each blue LED chip are provided, and a fluorescent layer
is formed on each diode with the resin solution for fluorescent
layer that is prepared as described above. As a result, a plurality
of white light emitting diodes for evaluation can be newly
obtained. Next, each of the white light emitting diodes for
evaluation is caused to emit a light at a predetermined current, so
that the diodes that produce a color mixture of yellowish white
without fail with the blue light, which does not interact with the
fluorescent particles, and the yellow light, which interacts with
the fluorescent particles in the fluorescent layer for wavelength
conversion, and based on the thicknesses of the fluorescent layers,
a range of the thickness of the fluorescent layer 179 is
determined.
[0143] The white light emitting diode 171 made as described above
may be used by mounting to a printed circuit board 182 as
illustrated in FIG. 26, for example. The light emitting diode 171
may be driven by the current control section 133 of the fourth
embodiment, for example, and is individually connected to a lead
wirings a of the anode wiring 175 and the lead wirings k1, k2 of
the two cathode wirings 176. In the case, the white light emitting
apparatus having the white light emitting diode 171 has an
electrical circuit configuration that is equal to that having the
blue LED chips 173 and 174 instead of the white light emitting
diodes 111 and 112 of FIG. 18.
[0144] The degree of whiteness of the light emitted from the white
light emitting diode 171 made as described above may be controlled
as follows. First, the current control section 133 is used to set
the current value which is applied to the blue LED chips 173 and
174 to be 20 mA, and the PWM method similar to that in the fourth
embodiment is used to cause both of the blue LED chips 173 and 174
to be driven. Then, the illumination duration of each of the blue
LED chips 173 and 174 for each cycle is controlled to determine a
duty ratio to drive each of the blue LED chips 173 and 174 so that
the light emitted from the white light emitting diode 171 has an
average wavelength distribution (the color mixture) generally at
the white point.
[0145] The relationship can be explained with reference to the
chromaticity diagram of FIG. 27 as follows. The color mixture of
the light emitted from the white light emitting diode 171 when only
the blue LED chip 173 is lit by applying a current of 20 mA is
detected as a chromaticity point WY3, which is substantially
positioned on the curved line WY. Similarly, the color mixture of
the light emitted from the white light emitting diode 171 when only
the blue LED chip 174 is lit by applying a current of 20 mA is
detected as a chromaticity point WB3, which is substantially
positioned on the curved line NB. This is because the thicknesses
of the fluorescent layers 178 and 179 are adequately defined. The
coordinates of the chromaticity points WY3 and WB3 on the
chromaticity diagram are (Cx=0.36 or more, Cy=0.39 or more), and
(Cx=0.26 or less, Cy=0.25 or less), for example, respectively.
Therefore, the chromaticity coordinates may be outside the
chromaticity areas a0, b1, b2, and c0 in FIG. 30 that are allowed
by selection.
[0146] Next, the duty ratios of both of the blue LED chips 173 and
174 in a PWM method driving are individually controlled, and the
illumination duration is detected which results in a chromaticity
measurement approximately equal to the whiteness point (Cx=0.33,
Cy=0.33) for the color mixture of the light emitted from the white
light emitting diode 171.
[0147] As described above, the white light emitting diode 171 of
the sixth embodiment includes two blue LED chips 173 and 174
therein, and has YAG fluorescent layers 178 and 179 that cover the
chips 173 and 174, and have adequately defined thicknesses. And the
control of the duty ratio for lighting the blue LED chip 173, which
is covered with both of the fluorescent layers 178 and 179, allows
the amount of the emitted yellowish white light to be controlled.
Also, the control of the duty ratio for lighting the blue LED chip
174, which is covered with only the fluorescent layer 178, allows
the amount of the emitted bluish white light to be controlled. The
controls make the color mixture of the light emitted from the white
light emitting diode 171 fall on the white point W.
[0148] As described above, according to the white light emitting
diode 171 of the sixth embodiment, a white light emission can be
obtained without special caring about the variation in the inherent
wavelengths of the light emitted from the blue LED chip, the
variation in the yellow wavelength due to the formation of the
fluorescent layers, and the like. Furthermore, the light emission
from the white light emitting diode 171 can be readily controlled
to be enhanced to a high-quality white light emission. In addition,
as compared with the white light emitting diode with one blue LED
chip, a higher power emission of white light can be obtained.
[0149] In the sixth embodiment, the light emission of the white
light emitting diode 171 when only the blue LED chip 173 is driven
at 20 mA is, as illustrated in FIG. 27, represented by the
chromaticity point WY3 for yellowish white without fail. Similarly,
the light emission of the white light emitting diode 171 when only
the blue LED chip 174 is driven is, as illustrated in FIG. 27,
represented by the chromaticity point WB3 for bluish white without
fail. When the thicknesses of the fluorescent layers 178 and 179
are adequately determined and reliable yellow and blue colors are
obtained, the chromaticity points WY3 and WB3 may be set at the
positions separated from the chromaticity point WY1 for "yellowish
white" and the chromaticity point WB1 for "bluish white" in the
fourth embodiment respectively (FIG. 19) based on the chromaticity
point W for white color as a reference. This is because the control
of the drive currents that are applied to each of the blue LED
chips 173 and 174 allows the chromaticity of the light emitted from
white light emitting diode 171 also to reach the white point W as
in the case of the fourth embodiment. Furthermore, according to the
white light emitting diode 171 of the sixth embodiment, the
chromaticity of emitted light can be controlled within a range from
the chromaticity point WY3 to the chromaticity point WB3 along the
curved line YB, which is wider than that of the fourth
embodiment.
[0150] In the sixth embodiment, the ratio of wavelength conversion
of the blue lights from the blue LED chips 173 and 174 to yellow
lights is controlled using the thicknesses of the fluorescent
layers 178 and 179, but the ratio may be controlled by the
concentration of YAG fluorescent particles dispersed in the
fluorescent layers 178 and 179. Also, in the sixth embodiment, the
amounts of the emitted yellowish light and the emitted bluish light
are controlled using the illumination duration per pulse, but may
be controlled using the current values applied to the blue LED
chips 173 and 174.
Seventh Embodiment
[0151] A linear illuminator 190 according to a seventh embodiment
uses the white light emitting diode 171 according to the sixth
embodiment. The linear illuminator 190 will be explained below in
detail with reference to FIGS. 28 and 29.
[0152] The linear illuminator 190 of the seventh embodiment is also
used to illuminate a surface of a manuscript such as a paper in an
image reading apparatus, for example. The linear illuminator 190 is
configured with a printed circuit board 182 to which the white
light emitting diode 171 according to the sixth embodiment is
mounted, instead of the light source section 110 in the fifth
embodiment, as illustrated in FIG. 28.
[0153] The linear illuminator 190 incorporated in a CIS unit 191
provides the image reading apparatus illustrated in FIG. 29. Not
illustrated, but similar to the fifth embodiment, the current
control section 133 is connected via the connector 161. Other
configurations are similar to those in the fifth embodiment.
[0154] Therefore, even in the case where there is a difference in
wavelengths of emitted lights between the blue LED chips 173 and
174 in the white light emitting diode 171 used as a light source
and the two central points of the emitted lights are not at the
same position, the light guide member 151 is able to emit a linear
illumination light of uniformly distributed color of whiteness
after sufficient color mixture of incident lights from the light
incident surface 154.
[0155] The inventors of the present invention checked the above
described effect of the linear illuminator 190 of the seventh
embodiment in the following procedure. As in the case of the fifth
embodiment, the linear illuminator 190 was incorporated in the CIS
unit 191 that constitutes an image reading apparatus.
[0156] Next, as in the case of the fifth embodiment, after the
paper manuscript 159 was replaced with a predetermined white paper
for reference, the blue LED chips 173 and 174 with the current
control section 133 were simultaneously driven at a current value
of 20 mA using the PWM method. Then the relative illuminance of
each of R, G, and B colors and the illuminance distribution in the
linear direction were measured.
[0157] Then, similar to the fifth embodiment, based on the measured
result, each of the duty ratios of the current pulses for driving
the blue LED chips 173 and 174 were adjusted, as the result of that
the relative illuminance of each of R, G, and B colors could be
adjusted to be generally uniformly distributed across the entire
width of the original paper copy 159.
[0158] The above result of the present seventh embodiment showed
the manufacture of the linear illuminator 190 can be achieved that
emits a light with the relative illuminance of each of R, G, and B
colors being well balanced using the white light emitting diode
171.
INDUSTRIAL APPLICABILITY
[0159] The white light emitting apparatus and line illuminator
according to the present invention are advantageously utilized in
an image reading apparatus that supports reading of color images
such as an image scanner, a facsimile machine, or a copier.
* * * * *