U.S. patent number 3,752,974 [Application Number 05/207,218] was granted by the patent office on 1973-08-14 for uniform illumination with edge lighting.
This patent grant is currently assigned to Coastal Dynamics Corporation. Invention is credited to Myron Lewis Baker, Lewis William Myers.
United States Patent |
3,752,974 |
Baker , et al. |
August 14, 1973 |
UNIFORM ILLUMINATION WITH EDGE LIGHTING
Abstract
Uniform illumination is provided from an edge lighted optical
medium of a given thickness by diffusing a surface portion normally
providing internal reflection of the light radiated into the edge
such that at least some of the light rays striking the diffused
area are reflected through the opposite surface of the medium and
some are refracted through the one surface. A cleared area about
the source of light free of the diffusion is provided and treated
by application of coatings on opposite surface portions of the
medium defining the cleared area. These coatings have an index of
refraction less than that of the medium such that light is
channeled by internal reflection between the surfaces of the medium
and inhibited from escaping from the medium in the vicinity of the
cleared area. This cleared area has a radius of preferably three to
four times the thickness of the optical medium. The resulting light
emmination from the surface of the medium is substantially uniform
beyond the cleared area.
Inventors: |
Baker; Myron Lewis (Seal Beach,
CA), Myers; Lewis William (Thousand Oaks, CA) |
Assignee: |
Coastal Dynamics Corporation
(Westlake Village, CA)
|
Family
ID: |
22769656 |
Appl.
No.: |
05/207,218 |
Filed: |
December 13, 1971 |
Current U.S.
Class: |
362/627 |
Current CPC
Class: |
B60Q
3/64 (20170201); B60Q 3/14 (20170201); G02B
6/0021 (20130101); G02B 6/0055 (20130101); G02B
6/0036 (20130101); B60K 2370/336 (20190501) |
Current International
Class: |
B60Q
3/00 (20060101); B60Q 3/04 (20060101); B60q
003/04 () |
Field of
Search: |
;240/1EL,2.1,8.16,16R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Braun, Fred L.
Claims
What is claimed is:
1. A method of providing substantially uniform illumination from an
edge lighted optical medium of thickness T, comprising the steps
of:
a. diffusing one surface portion normally providing internal
reflection of the light such that at least some of the light rays
striking the diffused surface are reflected through the opposite
surface and some are refracted through the one surface to escape
out of the medium;
b. providing a cleared area about the source of light free of the
diffusion; and,
c. treating the cleared area by providing an interface for the
surfaces of the optical medium defining the cleared area, said
interface having an index of refraction less than that of the
medium to assure internal reflection of light rays in the cleared
area such that light is channeled by internal reflection between
the surfaces and inhibited from escaping from the medium in the
vicinity of the cleared area, the channeled light rays expanding
towards the diffused surface portion so that the light escaping
from the medium as a consequence of the diffused surface portion is
substantially uniform with increasing distance from the lighted
edge as measured in a plane parallel to the plane of the
medium.
2. The method of claim 1 including the step of providing a highly
specular surface under the diffused portion of the optical medium
to reflect light refracted through the one surface back into the
medium so that the level of the uniform illumination from the
opposite surface is substantially increased.
3. The method of claim 2 including the additional step of providing
a highly specular surface about the edges of the optical medium
except the edge portion admitting light to block light from
escaping from the edges.
4. The method of claim 1, in which said cleared area has a circular
end boundary defined at least in part by a circle with the source
of light at the center of the circle, said circle having a radius
which lies between T and 10T.
5. The method of claim 4, in which said radius is from three to
four times the thickness T of the optical medium.
6. The method of claim 1, in which said interface is in the form of
a coating of material having an index of refraction less than that
of the medium.
7. A means for providing substantially uniform illumination over a
large surface area comprising:
a. an optical medium having opposite surfaces defining a first
surface and a second surface parallel to each other and separated
by a distance T defining the thickness of said medium; and,
b. at least one light source at an edge of said medium for
radiating light into the edge of the medium between said
surfaces;
c. said first surface having a diffused surface portion over a
large surface area for reflecting and refracting internally
reflected light radiated between said surfaces from said source out
of said medium;
d. said first surface having a cleared area about said source free
of diffusion, the periphery of said cleared area being at a
distance from said source greater than T and less than 10T;
and,
e. a coating of material having an index of refraction less than
that of said medium on the surface portions of said medium defining
said cleared area to thereby assure internal reflection of light
rays in said cleared area.
8. The subject matter of claim 7, in which said diffused surface
portion includes total reflecting means for reflecting back into
said medium any refracted light otherwise escaping out of said
medium through said first surface so that light is directed out of
said second surface.
9. The subject matter of claim 7, including total reflecting means
about the edges of said medium except for the edge portion into
which light is radiated from said source.
10. The subject matter of claim 7, in which said cleared area has a
circular end boundary defined at least in part by a circle with the
light source at the center of the circle, the radius of the circle
lying between 3T and 4T and in which said optical medium has a
refractive index of between 1.42 and 2.00.
11. The subject matter of claim 7, in which said medium comprises
an acrylic panel, said coating of material being co-extensive with
said cleared area on said first surface, said material being
transparent and covering the entire second surface of said acrylic
panel; a coating of acrylic overlying said coating of material on
said entire second surface; a coating of translucent white vinyl
overlying said coating of acrylic on said second surface; and a
coating of opaque vinyl overlying said coating of white vinyl,
portions of said opaque vinyl being removed on said second surface
to define nomenclature, the said first surface having a coating of
acrylic overlying said coating of material on said cleared area and
extending beyond said cleared area a first given distance; a
coating of opaque vinyl overlying a portion of said coating of
acrylic on said cleared area and terminating short of said cleared
area by a second given distance, said diffused surface being
provided by a coating of white vinyl on said first surface outside
said cleared area; and a coating of opaque vinyl overlying the
entire first surface whereby an edge lighted panel is provided in
which light emitted through the openings defined by said
nomenclature is substantially uniform.
12. The subject matter of claim 11, in which said cleared surface
has a circular end boundary defined at least in part by a circle
with said light source at the center of the circle, the circle
having a radius R between 3T and 4T said first given distance being
from 0.25R to 0.75R and said second given distance being from 0.1R
to 0.5R.
Description
This invention relates generally to lighting technique and more
particularly to an improved system for providing substantially
uniform illumination from edge lighted optical media.
BACKGROUND OF THE INVENTION
There are many instances in which it is desired to provide a planar
surface emitting substantially uniform illumination; for example,
x-ray viewers, light tables for facilitating tracing operations,
building business directories in which stencils or cut outs are
placed in front of the light emitting surface, edge lighted panels
having an opaque surface with etched nomenclature at various points
on the surface to indicate control functions such as used on
aircraft, and so forth. In most of these applications, it is
desirable to provide a relatively large surface area for emitting
the light with a minimum depth for the optical system and emitting
structure.
In the case of x-ray viewers, light tables, and the like, present
practice in a great many cases is simply to provide a multiplicity
of light sources beneath a diffused translucent type surface. While
such systems are effective for most purposes, there still is not
absolute uniformity simply because of the presence of individually
separated light sources in spite of the smoothing effect of the
diffuse optical covering. Further, a relatively deep depth
dimension is required to accommodate the optical sources with the
result that the final product is relatively bulky. In the case of
edge lighted panels, one or more light sources are disposed
adjacent edge portions of the panel and the light radiated into the
panel. In this instance, the panel itself constitutes an optical
medium which serves as a light pipe trapping the illumination
between its opposite parallel surfaces. Because of imperfections in
the optical medium itself, some light escapes from the flat
surfaces. However, most of the light is simply trapped within the
optical medium and is radiated from the remaining edges. As a
result, many light sources are required and still the illumination
from the surface is fairly poor compared to the light energy
provided.
The primary advantage of edge lighted panels is the minimization of
the depth dimension while sitll providing illumination from a
relatively large flat surface. As a result, edge lighting
techniques for providing flat surfaces of illumination find wide
application in those instances in which bulk must be kept to a
minimum; for example, aircraft panels. It would be desirable,
however, to be able to take advantage of the small depth dimensions
realizable by edge lighting technique for all applications in which
uniform illumination from a flat surface is desired.
In the particular field of edge lighted panels and the like,
efforts have been made to increase the illumination from the flat
surfaces of the optical medium so that etched nomenclature and the
like will be more clearly visible without increasing unduly the
number of light sources. One such technique contemplates providing
specular surfaces; that is, perfectly smooth mirrored surfaces
about the edges of the panel and the back surface of the panel to
retain light in the panel and prevent waste by escaping light rays
from the edges and rear surface. While such reflecting techniques
generally increase the intensity of light passing from the one
surface, the major portion of light is still trapped within the
optical medium simply because of the internal reflection of the
rays occuring as a result of the relatively thin nature of the
panel and the fact that the light is radiated into an edge. Further
techniques have been proposed such as diffusing a surface of the
optical medium or panel to cause irregular reflections within the
medium whereby many of the light rays strike the opposing surface
at less than the critical angle so that they are refracted out of
the medium.
While improvements have resulted from the foregoing techniques, the
resulting illumination from the surface is still not uniform; that
is, it tends to fall off with increasing distance from the light
source measured in a plane parallel to the plane of the panel or
optical medium itself.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
A primary object of the present invention is to provide a technique
for further improving the emission of substantially uniform light
from a large surface wherein the advantages of edge lighting can be
utilized and yet wasted light is kept at an absolute minimum. More
particularly, an object is to provide uniform illumination from an
edge lighted optical medium in which the light escaping from the
medium is substantially uniform with increasing distance from the
lighted edge as measured in a plane parallel to the plane of the
medium all to the end that the applications for edge lighted
techniques are greatly expanded.
Briefly, the improvement of the present invention contemplates
providing uniform illumination from an edge lighted optical medium
by diffusing one surface portion normally providing internal
reflection of the light such that at least some of the light rays
striking the diffused surface are reflected through the opposite
surface and some are refracted through the one surface to escape
out of the medium. An important feature of the invention then
contemplates providing a cleared area about the source of light
free of the diffusion but treated in a manner such that light is
channeled by internal reflection between the surfaces and inhibited
from escaping from the medium in the vicinity of the cleared area.
The treatment of the surfaces defining the cleared area comprises
the provision of a coating of material having an index of
refraction less than that of the medium thereby assuring internal
reflection and proper channeling of the light rays. The channeled
light rays expand towards the diffused surface portion so that the
light escaping from the medium as a consequence of the diffused
surface portion is substantially uniform with increasing distance
from the lighted edge as measured in a plane parallel to the plane
of the medium.
By adding mirrored surfaces to the edges and beneath the diffused
portions, the intensity of light from the surface opposite the one
surface is increased with the desired uniformity still being
retained.
The provision of a cleared area about the source is of the utmost
importance and in accord with the invention is defined by a radius
of from three to four times the thickness of the panel although for
certain applications in certain types of optical media having
abnormal indexes of refraction the radius of the cleared area may
vary as much as from one to ten times the thickness of the medium
itself.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the invention will be had by now
referring to the accompanying drawings, in which:
FIG. 1 is a perspective view, partly diagramatic in form, of an
optical medium in the form of a panel with an edge lighting source
useful in explaining certain problems encountered in the prior
art;
FIG. 2 is an enlarged fragmentary cross-section taken in the
direction of the arrows 2--2 of FIG. 1 showing the action of light
rays in the medium;
FIG. 3 is a view similar to FIG. 1 of an edge lighted optical
medium wherein improved lighting is realized by diffusion
techniques;
FIG. 4 is an enlarged fragmentary corss-section of a portion of the
panel of FIG. 3 showing the action of light rays in the panel;
FIG. 5 is another perspective view showing an edge lighted optical
medium in accord with the present invention;
FIG. 6 is a fragmentary cross-section of the panel of FIG. 5 useful
in explaining the operation of the invention;
FIG. 7 is a fragmentary perspective view of an edge lighted optical
medium wherein the light source is completely surrounded by the
medium;
FIG. 8 is a perspective view of a specific embodiment of the
invention; and
FIG. 9 is a fragmentary corss-section taken in the direction of the
arrows 9--9 of FIG. 8.
DETAILED DESCRIPTION OF THE INVENTION:
Referring first to FIG. 1 there is shown an optical medium 10 in
the form of a flat panel of light conducting material which may
constitute glass, or any number of different types of plastic
acrylics normally having a refractive index of from 1.42 to 2.00.
The optical medium is defined by first and second optically smooth
flat surfaces 11 and 12. Adjacent an edge portion of the medium 13
is a light source 14 connected to a battery 15 or equivalent
energizing means.
Light rays from the source 14 radiate into the edge of the optical
medium 10 and by internal reflection will normally all pass out the
surrounding edges such as indicated by the arrows 16 at the far
edge. Very little light passes through the flat surfaces 11 and 12
and any light that does escape is a consequence of imperfections in
the optical medium itself.
Qualitatively shown above the panel 10 in FIG. 1 is a graph
illustrating at 17 the relative illumination intensity with
increasing distance from the light source as measured in a plane
parallel to the plane of the optical medium. As is evident, a
substantial amount of light will pass perpendicularly from the
panel in the immediate vicinity of the light itself simply by
direct radiation from the source. Thereafter, there is little if
any illumination from the surface 12 of the panel.
Referring now to FIG. 2, the reason for lack of substantial
illumination from the panel surfaces will be evident. As indicated
by the ray lines 18, 19, 20, and 21, light radiated from the source
14 is completely internally reflected by the opposite first and
second surfaces 11 and 12. In instances where the edge of the panel
forms a right angle with the opposite surfaces of the panel and the
refractive index of the panel material is greater than 1.42, it is
physically impossible for any light to be refracted out of the
panel. The relationship is defined by Snell's law which states:
sin i/sin r = N2/N1
where i is the incident angle of the light ray from the source 14
into the edge of the panel, r is the angle of refraction in the
medium, n1 is the index of refraction of air which is substantially
unity, and n2 is the index of refraction of the optical medium 10
all as shown in FIG. 2. It will be immediately appreciated that
when the critical angle is 45.degree. or less no light rays can
escape from the opposite surfaces 11 and 12 when the light source
radiates into the edge of the panel.
As stated heretofore, some light as a practical matter does escape
from the opposite surfaces and thus edge lighted optical media such
as panels used for aircraft have been useful, the required
illumination levels being achieved by providing a high density of
individual light sources adjacent to the edges of the panels and/or
embedded in bores through the panel throughout its area. However,
this solution is unsatisfactory simply because of increased bulk
and expense and the high probability factor of light bulb
failure.
Referring now to FIG. 3, there is shown another optical medium in
the form of a panel 23 having flat opposite surfaces 24 and 25
which may be similar to the optical medium or panel 10 of FIG. 1.
However, in this instance, the one surface 24 is completely
diffused as by sandblasting. In addition, a highly reflective
surface or mirror 26 is positioned beneath the diffused surface 24
and also highly reflective or specular surfaces or coatings are
provided about the edges such as indicated at 27.
With the arrangement illustrated in FIG. 3, a substantial increase
in illumination from the opposite or second surface 25 is
realizable, the mirrors 26 and 27 retaining light within the panel
and the diffused surface portion 24 causing irregular internal
reflections so that light can escape through the second surface. In
FIG. 3, the escaping light is indicated by the arrows 28 and the
relative illumination with increasing distance from the source is
indicated by the graph 29 wherein the improvement over the former
graph reproduced in dotted lines at 17' in the case of FIG. 1 is
readily evident.
The reflection of light rays from the panel of FIG. 3 can be seen
by referring to FIG. 4 wherein the irregular or diffuse surface 24
results in reflection of some of the internally reflected rays such
as indicated by the lines 30, 31, 32, and 33 in a direction
perpendicular to the second surface 25 as indicated by the arrows
28. LIght rays passing directly into the medium from the edge and
thus traveling parallel to the opposite surfaces as indicated by
the ray 34 will simply be reflected back into the medium by the end
mirror 27 described in FIG. 3.
The diffuse surface 24 not only reflects portions of the light rays
upwardly to escape from the second surface of the medium but also
refract some of these light rays out of the bottom surface or one
surface of the medium. These refracted rays are simply reflected
back into the panel by the bottom mirror 26 so that substantially
all of the light radiated into the edge of the panel is eventually
passed out of the second surface 25. However, there still results a
non-uniformity in the illumination intensity as evidenced by the
falling off of the illumination with increasing distance from the
source.
Referring now to FIG. 5, there is shown a preferred embodiment of
the present invention wherein an optical medium in the form of a
panel 35 has first and second surfaces 36, and 37, a major portion
of the surface 36 being diffused as indicated. As in the case of
the panel of FIG. 3, preferably a specular reflecting surface 38 is
provided beneath the diffused one surface 36 or may simply be
incorporated as a part of the diffused surface by sandblasting the
mirror itself. An end mirror, such as indicated at 39, is provided
at the end edge and also at the other edges with the exception of
the edge portion receiving light from the source 14.
In the embodiment of FIG. 5, as opposed to that of FIG. 3, there is
provided a cleared area 40 about the light source 14; that is, a
portion of the one surface 36 in which there is no diffusion but
rather an optically smooth surface. This cleared area has a
circular end boundary defined at least in part by a circle with the
light source 14 at the center of the circle. With this arrangement,
a substantially uniform illumination is provided beyond the end
boundary of the cleared area from the upper surface 37 of the panel
as indicated by the arrows 41. This uniform illumination is
depicted in the graph above the panel by the straight line 42.
Comparison with the reproduced curve 29 of FIG. 3 shown at 29' and
the reproduced curve 17 of FIG. 1 shown at 17' graphically
illustrates the improvement provided by the cleared area. In a
sense, the cleared area holds light in the panel which would
otherwise escape in the vicinity of the source. This light is then
utilized to render uniform the remaining portion of the
illumination curve. Qualitatively speaking, the shaded portion 43
in the graph of FIG. 5 constitutes a quantity of light which
effectively is distributed over the remaining distance from the
light source to result in the uniform illumination shown by the
curve 42.
Referring to FIG. 6, the manner in which the foregoing improvement
is achieved will be understood. As shown, a given sector of light
rays from the source 14 passing into the edge of the panel will be
initially internally reflected from the upper surface 37 as
indicated by the rays 44. The interception of the edge rays
defining the ray sector with the upper surface is indicated at 45.
The internally reflected rays 44 then impinge on the cleared area
40 and are again internally reflected since this cleared area is
free of any of the diffusion. Because of the expansion of the rays
with increasing distance of travel, the interception of the
internally reflected rays 44 occupy a distance indicated at 46 on
the lower surface of the panel. These internally reflected rays
will then pass to the upper surface 37 intercepting over a distance
indicated by the line 47. The rays will then be again internally
reflected onto the initial portion of the diffused surface 36
intercepting an ever widening area as indicated at 48. The
expanding light rays continue as indicated by the even wider
interception area 49 but because of the diffused portion, irregular
reflections and refractions occur so that the light rays can now
escape out of the top of the panel as indicated by the arrows
41.
Essentially, the cleared area results in an initial channeling of
the light rays from the source to an extent that the same may
expand towards the diffused surface portion so that the light
escaping from the medium as a consequence of the diffused surface
portion is substantially uniform with increasing distance from the
lighted edge as measured in the plane parallel to the plane of the
medium. Thus, light that would have initially escaped in the
vicinity of the cleared area in the absence of such cleared area is
utilized to render uniform the remaining illumination above the
diffused area from the optical medium. The shaded portion 43 of the
graph in FIG. 5 is meant to represent the quantity of light that
might otherwise be lost in the vicinity of the light source if the
cleared area were not provided.
The extent of the cleared area from the source is important. While
some variation is possible, for a given panel thickness and a given
index of refraction, the preferred distance of the cleared area
about the source as measured by the radius R of the circle defined
in part by the end boundary of cleared area is between 3T and 4T
where T is the thickness of the panel. This dimensioning is ideal
for a panel or optical medium of index of refraction of 1.49. It
should be understood, however, that the dimension of the cleared
area as indicated by the radius R could vary in certain
circumstances from a value equal to the thickness of the panel to a
value of 10 times the thickness of the panel. Providing a cleared
area beyond these outer limits would be impractical and would
substantially decrease the area of uniform illumination relative to
the entire area of the panel.
FIG. 7 illustrates a portion of a panel 50 provided with a diffused
surface portion 51 with a cleared area 52 free of any diffusion
about a light source 53 disposed within a bore 54 formed in the
panel. The purpose of the showing in FIG. 7 is simply to illustrate
the fact that the light source may be disposed essentially within
the panel and still radiate into an edge of the panel, the interior
wall of bore 54 constituting the edge in question. In the structure
of FIG. 7 the cleared area takes the form of a complete circle with
radius R and again the relationship between R and the thickness of
the panel T would be within the limits defined for the structure of
FIGS. 5 and 6.
FIG. 8 illustrates a specific embodiment incorporating the
principles of the present invention in the form of an edge lighted
panel as might be used for aircraft instruments. The optical medium
making up the panel is designated at 55 and may constitute an
acrylic. Various lights are embedded in the acrylic as indicated at
56 and 57, there being provided cleared areas in accord with the
teachings of FIG. 7. Nomenclature such as indicated at 58, 59 and
60 may be provided on the second surface of the optical medium;
that is, the top surface. By utilizing the principles of the
present invention, the number of individual lights such as 56 and
57 required to uniformly illuminate the nomenclature may be vastly
reduced over those heretofore required.
The actual physical make-up of the panel of FIG. 8 will be
understood by now referring to FIG. 9. In FIG. 9, the thicknesses
of various coatings provided on the acrylic panel are greatly
exaggerated for purposes of clarity. Thus there is shown the basic
acrylic panel material 61 provided with a coating 62 of material
having an index of refraction less than that of the panel 61. In
the particular embodiment shown, this coating covers the entire
second or top surface of the panel. Overlying this material is a
coating of acrylic 63 which is of the same material as the acrylic
61 making up the bulk of the panel. This coating also covers the
entire second or top surface of the panel. On top of the acrylic
coating 63 there is then provided a vinyl coating 64 which is white
and translucent. Finally there is provided a black or opaque vinyl
coating 65 overlying the white vinyl 64.
Referring to the first surface of the panel 61 or bottom surface,
it will be noted that there is defined a cleared area indicated by
the radius R about the light source 56. On the bottom surface of
this cleared area there is provided a coating 62 of material having
an index of refraction less than that of the optical medium or
acrylic 61. This coating 62 is the same material as the coating 62
on the top surface and is co-extensive with the cleared area
defined by the radius R. Over the coating of material 62 there is
then provided an acrylic coating 63 of the same material as the
coating 63 on the top surface. This acrylic coating 63 extends
beyond the radius R of the cleared area by a first given distance
designated D1. Overcoating this acrylic is an opaque or black vinyl
coating 66 which terminates short of the cleared area by a second
given distance D2. The remaining first or bottom surface of the
panel is then coated with a white vinyl 64 which serves to define
the diffused surface area and over this white vinyl coating is a
black or opaque vinyl coating 65. The white vinyl coating covers
the entire bottom surface and the black or opaque vinyl coating 65
overcoats the entire bottom surface area. The white vinyl 64 and
black vinyl 65 correspond to the white and black or opaque vinyl 64
and 65 on the top surface and thus are designated by the same
numerals.
As shown in FIG. 9, the opaque or black vinyl coating 65 on the top
surface has certain portions removed to define the desired
nomenclature 59. Light can thus escape through these portions of
the top surface as indicated by the arrows 67.
In the provision of edge lighted panels, it is conventional to
provide a white translucent vinyl coating on the panel itself
followed by a black or opaque vinyl coating which is etched away to
define the nomenclature so that light can escape through the etched
or removed portions. However, it would not be possible to take
advantage of the principles of the present invention if these vinyl
coats were applied directly to the acrylic surfaces. This is
because the desired internal reflection of the light rays in the
cleared area will not take place in the absence of an air interface
or an interface at the cleared area with a material having an index
of refraction less than that of the acrylic material of the panel.
Since there is no interface because of the application of the vinyl
coatings, it is necessary to provide the coatings 62 described in
FIG. 9 which provide a material of index of refraction less than
that of the acrylic about the cleared area. Internal reflection is
thus assured in the cleared area by the provision of this
particular material. The addition of the acrylic coatings 63
overlying the material layer 62 is merely provided to enable a
vinyl such as a vinyl paint to adhere or bond. Thus, while the
material coating 62 of index of refraction less than that of the
acrylic can be bonded to the acrylic, in those instances in which
it is not possible to bond the vinyl directly to this material, the
layers or coatings 63 provide a base for the vinyl coatings. If a
material 62 were selected which was heat bondable to both acrylic
and vinyl, then the coatings 63 would not be required.
It is preferable to extend the acrylic coating overlying the
material 62 slightly beyond the cleared area radius as indicated by
the distance D1. The provision of the opaque vinyl 66 on the first
or bottom surface of the cleared area terminating short of the
radius of the cleared area provides a black spot which has been
found to eliminate halo effects from the light source 66.
As already mentioned above, the white vinyl serves as a diffusing
coating in place of sandblasting and it will be noted in FIG. 9
that this diffusion coating covers the entire bottom surface. The
final bottom black or opaque vinyl coating 65 blocks any light from
escaping from the bottom of the panel. The same coating 65 on the
top surface, of course, also blocks light from escaping from the
top surface except at those places where the vinyl has been removed
to define the nomenclature.
The various rays from the light source 56 will thus be channeled in
the clear area by internal reflection and will then provide a
desired uniform illumination throughout the remaining surface
portion of the panel all as described in conjunction with FIGS. 5
and 6.
In the actual embodiment of the panel described in FIGS. 8 and 9,
the radius R of the cleared area would preferably lie between 3T
and 4T. The first given distance D1 would preferably be between
.25R to .75R and the second given distance would be from .1R to
.5R.
From the foregoing description, it will be evident that the present
invention has provided a marked improvement in the provision of
uniform illumination from an edge lighted optical medium with the
desirable result that problems heretofore encountered are overcome.
The resulting arrangement permits the use of edge lighted optical
mediums for x-ray viewing, light tables, business directories, and
other applications wherein sufficient uniform illumination was not
heretofore available to permit such use. Further, by utilizing the
techniques of the present invention in edge lighted panels for
aircraft, the number of light sources can be substantially reduced
and the illumination of nomenclature etched on an opaque covering
on the top surface will be uniform over varied distances from the
light source.
While specific examples of uses of the invention have been set
forth, for purposes of illustration, it should be understood that
the techniques involved are applicable to a wide variety of
lighting uses. The invention, accordingly, is not to be thought of
as limited to the specific examples set forth.
* * * * *