U.S. patent number 3,829,680 [Application Number 05/309,098] was granted by the patent office on 1974-08-13 for lighting panel.
This patent grant is currently assigned to J. W. Carroll & Sons, a Division of U.S. Industries Inc.. Invention is credited to Bill F. Jones.
United States Patent |
3,829,680 |
Jones |
August 13, 1974 |
LIGHTING PANEL
Abstract
A lighting panel for use in overhead lighting fixtures and the
like which may readily be fabricated in plastic sheet by
extrusion-embossing techniques and which minimizes veiling
reflections. The panel contains a continuous pattern of triangular
projections, each having three mutually substantially perpendicular
surfaces projecting upward for disposition toward the light source.
The base lines of the mutually perpendicular surfaces are co-planar
and the pattern of projections is such that the base lines of all
projections on a panel form continuous straight lines directed in
three specific directions. This allows the fabrication of a
relatively inexpensive engraved roller for embossing the pattern on
a plastic sheet and results in a light panel which minimizes
veiling reflections from the illuminated matter. The panel in
accordance with the present invention provides a radial
distribution of light with high lighting efficiency and with the
maximum light in the area which is 30.degree. to 60.degree. from
the vertical.
Inventors: |
Jones; Bill F. (Los Angeles,
CA) |
Assignee: |
J. W. Carroll & Sons, a
Division of U.S. Industries Inc. (New York, NY)
|
Family
ID: |
23196686 |
Appl.
No.: |
05/309,098 |
Filed: |
November 24, 1972 |
Current U.S.
Class: |
362/330;
362/339 |
Current CPC
Class: |
F21V
5/02 (20130101); F21Y 2103/00 (20130101); F21V
3/049 (20130101); F21S 8/026 (20130101); F21S
2/00 (20130101); F21Y 2113/00 (20130101) |
Current International
Class: |
F21V
5/02 (20060101); F21V 5/00 (20060101); F21v
005/02 () |
Field of
Search: |
;240/16R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Peters; Joseph F.
Attorney, Agent or Firm: Spensley, Horn & Lubitz
Claims
I claim:
1. A lighting panel having on one surface thereof a pattern of
protrusions each defined by three generally flat triangular
surfaces, each of said triangular surfaces having first and second
sides and a base, and mating the other two of said three triangular
surfaces defining each of said protrusions on said first and second
sides thereof, each of said bases of said three triangular surfaces
defining each of said protrusions being substantially coincident
with the base of one of said triangular surfaces defining an
adjacent protrusion, all of said bases being substantially
coplanar, each of said three triangular surfaces being disposed at
approximately 50.degree. to 60.degree. with respect to the plane of
said bases.
2. The lighting panel of claim 1 wherein said three triangular
surfaces defining each of said protrusions being mutually
substantially perpendicular surfaces.
3. The lighting panel of claim 2 wherein there is affixed to the
surface opposite said one surface a second panel designed to
further reduce veiling reflections.
4. The lighting panel of claim 1 wherein there is affixed to said
one surface a high transmission overlay means for damping lamp
images.
5. The lighting panel of claim 1 wherein there is impressed into
the surface opposite said one surface a pattern designed to further
reduce veiling reflections.
6. A lighting panel having on one surface thereof a pattern of
protrusions defined by a first set of parallel, equidistantly
spaced V grooves directed downward into said panel; a second set of
parallel V grooves directed downward into said panel; said second
set of V grooves having the same spacing as said first set and
crossing said first set at an angle of approximately 60.degree.;
and a third set of parallel V grooves directed downward into said
panel; said third set of V grooves having the same spacing as said
first set and crossing said first and second sets at an angle of
approximately 60.degree.; said first, second and third sets of V
grooves being disposed so that the lines defined by the junction of
the two sides of each of said V grooves are substantially coplanar,
each of said two sides of each of said V grooves being disposed at
approximately 50.degree. to 60.degree. with respect to the plane of
said lines defined by the junction of the two sides of each of said
V grooves.
7. The lighting panel of claim 6 wherein each of said two sides of
each of said V grooves are disposed at approximately 57.degree.
with respect to the plane of said lines defined by the junction of
the two sides of each of said V grooves.
8. The lighting panel of claim 6 wherein there is affixed to the
side opposite said one side of the panel an acrylic sheet of high
light transmitting diffusing material for damping lamp images
visible through said panel.
9. In a lighting fixture of the type including a housing and a
light source within the housing, a lighting panel having first and
second surfaces, and having on said first surface thereof a pattern
of protrusions each defined by three generally triangular surfaces;
each of said triangular surfaces having first and second sides and
a base and mating the other two of said three triangular surfaces
defining each of said protrusions on said first and second sides
thereof; each of said bases of said three triangular surfaces
defining each of said protrusions being substantially coincident
with the base of one of said triangular surfaces defining an
adjacent protrusion, all of said bases being substantially
co-planar; said triangular surfaces being inclined with respect to
the plane of said bases by a predetermined angle so that light
coming directly toward said second surface is redirected back
toward its original direction by said pattern.
10. An improved lighting panel comprising a sheet having first and
second surfaces, and having on said first first surface thereof a
pattern of protrusions, each of said protrusions having a plurality
of surfaces extending toward an apex, each of said protrusion
surfaces being inclined at a predetermined angle with respect to a
first line perpendicular to said second panel surface, said
predetermined angle being an angle smaller than the limiting angle
at which total reflection of light impinging on a first of said
protrusion surfaces from within said panel and directed along said
first line would occur, whereby total reflection of said light
toward a second of said protrusion surfaces would occur, said
predetermined angle being an angle larger than the limiting angle
at which said light reflected by said first of said protrusion
surfaces would be totally reflected by said second of said
protrusion surfaces, whereby light impinging on said panel
substantially perpendicular to said second panel surface will be
reflected by said pattern back toward the direction said light
originated as a result of the reflection of said light from at
least a first and a second surface of said protrusions.
11. The lighting panel of claim 10 wherein each of said protrusions
is defined by a plurality of generally flat surfaces so that a
cross-section of each of said protrusions is a polygon.
12. The lighting panel of claim 11 wherein said cross-section is an
equilateral triangle.
13. A lighting panel having on one surface thereof a pattern
defined by a plurality of groups of three generally triangular
surfaces, each of said triangular surfaces having first and second
sides and a base, and mating the other two of said three triangular
surfaces on said first and second sides thereof, each of said bases
of said three triangular surfaces in a group being substantially
coincident with the base of one of said triangular surfaces in an
adjacent group, all of said bases being substantially coplanar,
each of said three triangular surfaces being disposed at
approximately 50.degree. to 60.degree. with respect to the plane of
said bases.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of lighting panels.
2. Disclosure Document Program
This application for patent is based on a disclosure filed on July
1, 1971, as Disclosure Document No. 005990, under the Disclosure
Document Program.
3. Prior Art
It is commonly recognized that an artificial lighting system should
provide not only light of the proper intensity but also light of
the proper characteristics to minimize glare and to maximize
contrast, particularly in written or printed matter. Thus, modern
lighting systems are generally comprised of a plurality of lighting
fixtures, usually fluorescent, distributed over the ceiling of a
room and having lighting panels (generally plastic panels) over the
fluorescent fixtures to redirect the light in an attempt to achieve
the desired result.
If printed matter is illuminated with light originating from a
light source above and slightly forward of the reader, a
considerable amount of the light may be directly reflected from the
surface of the printed matter into the eyes of the viewer. In such
a case, the light will tend to be reflected both by the dark
printing itself and by the background so that the printing no
longer appears black or dark, but instead approaches the lighter
color of the background. Thus, the normal contrast in the printed
matter is lost, and in the extreme the printed matter may be
totally unreadable. In any event, these veiling reflections tend to
reduce the contrast and make reading more difficult and
uncomfortable. Of course, the effect is worse on glossy surfaces
and with particularly intense lights, but control of the light
intensity and selection of the surface characteristic for the
printed matter will not totally eliminate the effect.
If printed matter is illuminated from the side, or from an area
considerably forward of the reader, the direct reflections from the
surface of the printed matter will not be directed upward for the
eyes of the reader, but instead will be reflected at a lower angle
and, therefore, will not affect the appearance of the matter being
viewed. However, some of this light which is incident upon the
surface of the printed matter will be redirected upward in a
diffuse pattern in accordance with the color of the surface.
Consequently, a white sheet of paper will clearly appear white,
whereas the black print thereon will appear in its true color.
Thus, there are no veiling reflections and a very high degree of
contract is obtained. Consequently, lighting from the side, rear
and/or considerably in front of a reader is highly desirable,
whereas lighting from a point slightly forward of the reader is
undesirable. Of course, the particular position for lighting which
is most undesirable for illumination of a task depends upon the
orientation or angular position of the task, but, in general, may
be usually characterized as above and slightly forward of the
reader. For minimal veiling reflections, it is highly desirable to
have the light projected as a conical annulus in which the light is
directed at 30.degree. to 60.degree. from the vertical in all
radial directions.
Some patterns of prismatic lenses are known to the prior art which
are intended to reduce veiling reflections. These patterns
generally are of either of two types. The first type of pattern is
a longitudinal pattern, that is, a pattern of longitudinal raised
areas generally of uniform cross-section and repetitive cross the
width of the panel. Such patterns can be produced on lighting
panels by extrusion techniques. By properly choosing the geometry
of the raised areas, redirection of the light is obtained. Since
lighting panels are generally fabricated of thermo-plastic
materials, such as, by way of example, acrylic, rolls for embossing
such a pattern in a sheet of plastic may easily be fabricated, and
inexpensive lighting panels produced therefrom. Some attempts have
been made to reduce veiling reflections in such extruded panels, as
for example, by combining the panels with a louver system or by
painting opaque areas in the extruded panel to block the path of
vertical light. However, the opaque areas reduce the amount of
light passing therethrough and the panel thereby reducing the light
efficiency of the panel and such panels deflect light only to
either side and not in the fore and aft direction.
The second type of pattern which has been utilized in the prior art
as an attempt to reduce veiling reflections is a two-dimensional
pattern, that is, a pattern of depressions which varies both across
the width of the panel and along the length of the panel. Such a
panel has a complex prismatic pattern which in the present state of
the art can be manufactured only by injection molding.
Such injection molded panels, besides their high expense, have
other disadvantages in that they are in general useful as wrap
around panels on surface mounted fixtures rather than recessed
flush fixtures.
In the prior art, the type of panels heretofore known to the art to
reduce veiling reflections transmit light primarily in two
directions only, i.e., to each side of the longitudinal axis of the
panel. That is, there are light panels known to the prior art which
project the light sideways in a twin beam pattern, rather than
downward in order to minimize veiling reflections. This is
sometimes referred to as a linear batwing light distribution. Such
panels, however, result in poor end-on distribution and control,
i.e., the light is distributed only to the sides of the panel.
Prior to the present invention, no panel, and particularly one
capable of being extruded, could accomplish what could be termed a
radial batwing distribution in which the light is transmitted in a
conical configuration while eliminating the vertical distribution,
as described more fully hereinafter.
BRIEF SUMMARY OF THE INVENTION
A lighting panel for use in overhead lighting fixtures and the like
which may readily be fabricated in plastic sheet by embossing
techniques and which minimizes veiling reflections. In the
preferred embodiment the panel contains a continuous pattern of
triangular projections, each having three mutually substantially
perpendicular surfaces projecting upward for disposition toward the
light source. The base lines of the mutually substantially
perpendicular surfaces are co-planar and the pattern of the
projections is such that the base lines of all projections on the
panel form continuous straight lines directed in three specific
directions. This allows the fabrication of a relatively inexpensive
engraved roll for embossing the pattern on a plastic sheet and
results in a panel which minimizes veiling reflections from the
illuminated matter.
The embossed pattern of the present invention can be used singly or
combined with embossed or non-embossed clear and opalescent panels
to further decrease lamp images and reduce high-angle brightness.
The lens of the present invention can be embossed on clear material
or the material can be tinted to increase the visual comfort
probability.
Additionally, the panel of the present invention transmits light
not only to the sides of the panel but also in the fore and aft
direction with respect to the longitudinal axis. The light
distribution to the sides of the vertical axis is sometimes
referred to as "batwing" distribution. By means of the present
invention, a radial batwing light distribution is accomplished in
that light distribution is in a conical shape extending from
approximately 30.degree. from the vertical to 60.degree. from the
vertical in all directions.
The use of the wholly prismatic design of the present invention
eliminates the use of opaqued areas or other light blocking means.
This results in higher efficiency of light utilization, thus
reducing the amount of electrical power needed to achieve the
visual performance conditions desired.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a section of a typical ceiling
having a plurality of fluorescent lighting fixtures therein.
FIG. 2 is a cross-section taken along lines 2-2 of FIG. 1
illustrating the construction of the fluorscent fixtures.
FIG. 3 is a top view of the lighting panel of the present invention
showing the pattern on the surface thereof.
FIG. 4 is a cross-section taken along lines 4--4 of FIG. 3.
FIG. 5 is a perspective view of a section of the lighting panel of
the present invention illustrating the pattern of projections on
the surface thereof.
FIG. 6 is a polar plot of the light intensity versus direction for
the light emitted from the lighting panel of the present invention
mounted in a fluorescent fixture, such as shown in FIG. 2.
FIG. 7 is a schematic representation of the lighting obtained from
a plurality of fluorescent fixtures using the lighting panel of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
First referring to FIG. 1, a perspective view of two fluorescent
lighting fixtures as such fixtures are characteristically mounted
in a ceiling may be seen. Such lighting fixtures are
characteristically arranged in a pattern throughout the ceiling
area so as to illuminate the entire room in as uniform manner as
possible. As viewed from within the room, the lighting fixtures
comprise a front molding or frame 20 and a lighting panel 22 to
which the present invention is directed.
Now referring to FIG. 2, a cross-section of one of the lighting
fixtures of FIG. 1 taken along lines 2--2 of that figure may be
seen. The lighting fixture is comprised of a frame 24, one or more
fluorescent tubes 26 supported by suitable mounting brackets 28, an
outer molding 20 and a lighting panel 30 supported by the molding
20 below the fluorescent tubes. The function of the lighting panel
30 in modern day lighting systems is to redistribute the
illumination from the fluorescent tubes so as to reduce the
vertical and nearly vertical components of light from the
fluorescent tubes and to redirect part of this light toward the
side, thus increasing the side illumination and decreasing the
substantially vertical illumination passing downward from the
lighting panel. The lighting panel 30 is generally a sheet of
plastic with a pattern embossed on the sheet so as to create a
pattern of prismatic lenses to redirect the light incident thereto
from the fluorescent tubes in the desired manner. It is this form
of lighting panel to which the present invention is directed and,
in particular, the present invention is a lighting panel which may
be quickly and easily fabricated from such materials as
thermoplastic materials by conventional extrusion embossing
process, utilizing rollers which may be relatively easily and
inexpensively fabricated.
Now referring to FIGS. 3, 4 and 5, the pattern on the upper surface
of the lighting panel of the present invention, that is, the
surface facing the light source, may be seen. FIG. 3 is a view
taken along lines 3--3 of FIG. 2, looking downward onto the
lighting panel 30. FIG. 4 is a cross-sectional view of the lighting
panel taken along lines 4--4 of FIG. 3. FIG. 5 is a perspective
view of the lighting panel illustrating the form of the top surface
thereof. The pattern may be most easily described by identifying
the characteristic lines, surfaces and points identifying the
pattern.
Referring first specifically to FIG. 3, and the orientation of the
pattern is depicted therein, the various surfaces of the pattern
mate so as to define a repetitive series of lines, all of which are
co-planar. The first series of lines are lines A--A having a
parallel horizontal disposition. A second set of lines identified
as the B--B lines, co-planar with and having the same spacing as
the first set of lines, cross the first set of lines at an angle of
60.degree.. A third set of lines identified as the C--C lines are
co-planar with and have the same spacing as the A--A lines and the
B--B lines. Furthermore, the C--C lines cross the A--A lines at the
same point as the B--B lines and are located 60.degree. from both
the A--A lines and the B--B lines. These various lines are defined
by the junction of triangular shaped flat surfaces projecting
upward and mating in threes to define a plurality of apexes
identified by the letter D, with each of the flat surfaces mating
to define an apex being substantially perpendicular to the two
adjacent surfaces cooperating to define the apex. Thus, the three
sides mating to define an apex D define a projecting surface having
essentially the geometrical characteristics of a corner of a
cube.
FIG. 4 is a cross-section of the panel looking along the B--B
lines, the ends of the lines being identified by the letter B in
that figure. FIG. 5 is a perspective view of a portion of the
lighting panel of the present invention having identified thereon
various of the points, lines and surfaces herein identified with
respect to FIGS. 3 and 4. It will be noted that the apexes between
any two B--B lines lie to two rows rather than a single row. Thus,
the apexes identified as D1 lie to the right of the apexes
identified as D2. The lines G joining the apexes and the lines
B--B, as shown in FIG. 4, are the side views of the triangular
surfaces having their bases on the lines B--B, whereas the lines F
in FIG. 4 are the lines extending from the lines B-B to the apexes
and defining the junction of the other two surfaces of each
protrusion.
It should be noted that though the cross-section shown in FIG. 4
was taken about a line perpendicular to the B--B lines, the
cross-section of the pattern taken along A--A lines and C--C lines
is also the same. Thus, the pattern hereinabove described may be
formed in a sheet of plastic by forming parallel, equally spaced V
grooves of the proper angle in a first direction, in a second
direction 60.degree. to one side of the first direction, and in a
third direction 60.degree. to the opposite side of the first
direction, in a pattern such that the junction of the two sides of
the second and third set of V grooves cross the junction of the two
sides of the first set of V grooves at the same points.
In order for the three surfaces projecting upward to an apex to be
substantially perpendicular to each other, that is, to have the
geometric properties of a corner of a box, each side of the V
grooves should be disposed at an angle of from 50.degree. to
60.degree. upward from the plane of the sheet of plastic thus
causing the V grooves to have an included angle of from 80.degree.
to 60.degree.. As a result of the V grooves, the lines identified
by the letter F in FIG. 4 will define the complimentary angle of
from 40.degree. to 30.degree. upward from the plane of the sheet of
plastic. In the presently preferred embodiment, each side of the V
grooves is disposed at an angle of 57.degree. upward from the plane
of the sheet, thus resulting in an included angle of 66.degree.
such that the lines F in FIG. 4 are at an angle of 33.degree.
upward from the plane of the sheet of plastic. Thus, each surface E
of the pattern is inclined at an angle of 33.degree. with respect
to the vertical.
The function of the pattern on the lighting panel of the present
invention may be described as follows: Light directed from
immediately above onto the lighting panel will strike one of the
surfaces of the protrusion at an angle of 33.degree., since all
surfaces in the pattern are inclined with respect to the vertical
by this angle. Since the light is entering a medium of higher index
of refraction, the light path will be curved toward a perpendicular
to the surface and, thus, deflected somewhat to the side in
comparison to its initial vertical path. The lower surface of the
panel being flat as shown in FIGS. 4 and 5, the light will strike
the lower surface at a substantial angle and, upon passing
therethrough into a medium (air) having a lower index of
refraction, will be further deflected away from the vertical. By
way of example, if the lighting panel is fabricated from a
polystyrene sheet having an index of refraction of approximately
1.6, most of the light incident upon the surfaces as hereinabove
described will be transmitted therethrough, rather than reflected,
and the light emerging from the lower surface of the panel will
have a total deflection from the vertical of approximately
57.degree.. The direction of any particular light ray will depend
upon which of the triangular surfaces it initially entered in the
pattern on the upper surface of the panel and, in general, light
rays which initially were purely vertical with respect to the panel
will be deflected to the side of six directions approximately
60.degree. apart.
From the lower (non-embossed) side of the panel, the elements act
to redirect any light coming into the panel from directly below
back in its original direction. By the reciprocity of light rays,
this means that no light from above the panel can penetrate into
the angles directly below the panel. (This redirection is generally
illustrated by the light ray 29 in FIG. 2. Total theoretical
reflection for redirection will generally be achieved when somewhat
different surface angles are used, depending upon the index of
refraction of material).
Referring now to FIG. 2, it will be seen that only a very limited
portion of the lighting panel 30 is located immediately below any
of the fluorescent tubes 26, and further, the portion of the panel
located immediately below any of the tubes will receive substantial
illumination from the tubes other than from the portion of the tube
directly above, that is, from portions of the tube longitudinally
displaced from that section of the panel and from the reflective
surface of the fixture. Consequently, a considerable amount of
light will strike the top surface of the panel at substantial
angles from the vertical and, therefore, the light projecting
downward from the bottom surface of the panel will be distributed
over all angles. In fact, some of the light striking the upper
surface of the panel at certain angles will be deflected on passing
through the panel, so as to be emitted from the panel in a vertical
downward direction. However, the amount of light emitted from the
panel in a vertical direction is limited and, in general, the
intensity of the light emitted to the side and fore and aft of the
panel will be substantially higher than the vertical component. By
way of example, the distribution of intensity versus angle in a
typical installation using the panel of the present invention is as
shown in FIG. 6. This figure is a plot, in a polar coordinate
system, of the intensity of illumination versus direction, with the
intensity being indicated by the distance from point 50 to a point
on the curve, and the direction being indicated by the direction of
a line point 50 to the corresponding point on the curve. It will be
noted while there is substantial vertical illumination, the
illumination to each side in any azimuthal plane is substantially
greater than the vertical illumination. Furthermore, the said
illumination is distributed over a substantial angle so that strong
veiling reflections will, in general, not be obtained regardless of
the orientation of the task. Thus, the objects of eliminating
particularly intense vertical or near vertical illumination and of
further eliminating particularly intense illumination in any
specific direction, have been achieved with the panel of the
present invention. (Orienting the panel so that the pattern is on
the surface directed away from the light source will also reduce
the vertical component of illumination since the projections will
act as retrodirective reflectors as the vertical and near vertical
components of light. However, this illumination will be lost unless
the top surface of the panel and/or the fixture enclosure are
adapted to reflect this light downward again at a different
angle.)
Now referring to FIG. 7, a schematic representation of a student in
a classroom illuminated by a plurality of overhead fixtures
utilizing the lighting panel of the present invention may be seen.
The lighting distribution of FIG. 6 is approximately indicated by
the length of the lines representing the light rays in FIG. 7. It
will be noted that the table 52 in front of the student 54 is more
strongly illuminated by light fixtures 56 and 60 to each side of
the student than by the fixture 58 immediately overhead. It should
also be noted that the lighting panels have substantial areas,
typically on the order of 2 feet by 4 feet, and thus even the light
reaching a printed page in front of the student from a particular
light panel is not light having a fixed direction, but is light
distributed over a substantial angle dependent upon the size and
orientation of the lighting panel with respect to the printed
matter. (Typically, a significant percentage of a ceiling area is
occupied by such areas.)
Other patterns for use on lighting panels which will generally
achieve the optical objects of the present invention are also
known. However, the pattern of the present invention is
particularly advantageous since lighting panels of the present
invention may be readily fabricated by an extrusion-embossing
process using simple and inexpensive rolls. By way of example, the
pattern shown in detail in FIGS. 3, 4 and 5 was characterized as
being formable in a sheet of plastic by creating parallel, equally
spaced V grooves of the proper angle in a first direction, in a
second direction 60.degree. one side of the first direction, and in
a third direction 60.degree. to the opposite side of the first
direction, in a pattern such that the junction of the two sides of
the second and third set of V grooves cross the junction of the two
sides of the first set of V grooves at the same points. The roll
for producing this pattern, of course, must have the negative of
the pattern of the surface thereof.
In some instances and in the presently preferred embodiment of the
present invention, an overlay sheet is affixed to the embossed
surface, i.e., the upper surface of the panel to reduce any visible
lamp image. In the presently preferred embodiment a high light
transmission acrylic overlay of typical thickness such as an 0.040
to 0.060 inch thick sheet of opal acrylic is used. This does not
effect the light distribution previously described but serves only
to reduce any visible image of the lamp within the fixture.
In other instances, a second panel 31 may be affixed to the
non-embossed surface, i.e., the lower surface of the panel, in
order to modify the distribution or constitute a decorative
element. Or, a decorative or modifying pattern may be impressed
into the lower (non-embossed) surface itself. One of the reasons
for an embodiment utilizing such a second panel is to redirect
light rays to reduce high-angle luminance.
The advantage of the particular pattern used on the panel of the
present invention is that the pattern is the net result of a
plurality of generated surfaces and a suitable roll (press, mold
and the like, depending upon the particular fabrication process
desired) for embossing the pattern on a sheet of thermoplastic may
similarly be easily generated. Also, while the particular pattern
described in detail above is comprised of a pattern of projections
having three mutually perpendicular surfaces, the angles generating
these surfaces may be varied somewhat from the values given herein
so that the surfaces defining each projection are not
perpendicular. By varying the angle, the distribution of
illumination may be varied. Similarly, the V grooves and thus the
plurality of triangular shaped surfaces defining the pattern may be
curved somewhat, that is, the V grooves may have curved legs,
perhaps near their junction to also vary the distribution of
illumination created by the panel. These and other variations of
the present invention panel may readily be designed and constructed
by one skilled in the art from the disclosure provided herein
without departing from the spirit and scope of the present
invention.
* * * * *