Polarized lighting panel

An improvement in a Radialens light control panel is comprised of the integral fabrication of a polarizing layer to the lowermost surface of the lighting panel opposing that surface of the Radialens panel in which a plurality of prismatic surfaces or lens elements is defined. The polarizing layer is laminated to the opposite surface of the Radialens panel after the Radialens panel is embossed and is still in a partially heated and plastic state. No adhesives are used to secure the bond between the polarizing layer and rear flat surface of the Radialens panel. The plurality of prisms or lenses defined in the opposing surface of the Radialens panel is embossed into the still plastic panel either immediately before or subsequent to the lamination with the polarizing sheet. As a result, polarized light is preferentially distributed to provide higher visual effectiveness and contrast, less reflective glare, increased visual comfort and less direct glare (VCP), than could be achieved with a Radialens panel along or from the polarizing sheet alone without the preferential distribution offered by the Radialens panel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to the field of lighting panels and in particular to 
panels for providing directed polarized illumination. 
2. Description of the Prior Art 
It has been appreciated by some researchers that visual effectiveness and 
visual acuity are a function both of the quality of the illumination 
employed to observe objects and detail as well as the intensity of 
illumination. In particular, it has been appreciated that the contrasts of 
observed objects are significantly more important than the intensity of 
the illumination to reflect things. For example, visual effectiveness is 
improved as much by a one percent increase in observed contrasts of 
objects as by an increase of fifteen percent of foot candle illumination 
intensity of the object. See H. Richard Blackwell, "A General Quantitative 
Method for Evaluating the Visual Significance of Reflected Glare, 
Utilizing Visual Performance Data", I.E.R.I. Project No. 70, LIGHTING, 
W.R.C. Smith Publishing Company. 
It has also been appreciated by some that the reduction in the amount of 
direct glare at wide angles from the vertical from a source of 
illumination is increased more by multilayer polarizing panels than by 
conventional prismatic acrylic panels, glass diffuser panels or various 
type of light contoured panels. See Blackwell, supra. 
It has also been determined by prior practitioners that in order to 
minimize glare reflected from on object, it is highly desirable to have 
light projected in a conical annulus defined between an inner cone at 
approximately thirty degrees from the vertical from an overhead light 
source to approximately sixty degrees from the vertical. Light impinging 
on an object, such as printed matter, above and slightly forward of a 
reader results in a considerable amount of reflection both from the black 
printed surface as well as the white surrounding paper. Thus, the normal 
contrast of printed matter is somewhat reduced and in the case of an 
extremely high illumination level, the printed matter may be totally 
unreadable. If the printed matter is illuminated from the side, direct 
reflection from the surface of the printed matter will not be directed to 
the eyes of the reader, but instead will be reflected away from the 
observer and, some of the light will be scattered and not reflected by the 
printed page. Some of the scattered light will be directed to the eye of 
the observer and light scattered from the white paper will be considerably 
different than light scattered from the black print and the contrast 
between the print and the paper will be largely undiminished. 
However, in office or school settings where a ceiling is provided with a 
plurality of illumination panels, the lighting industry has devised a 
standard for visual comfort probability (VCP) which is a measure of the 
contribution of the various light sources to the subjective feeling of 
visual comfort or discomfort in the room. VCP is based upon investigations 
performed to find the borderline between between comfort and discomfort, 
which might be interpreted as the point at which fifty percent of the 
people in the room consider it comfortable and the other fifty percent do 
not. The worst position in the room is typically used to calculate the VCP 
in a room. The Illuminating Engineering Society has set a VCP of 70 as a 
practical guide to a minimum comfort level. Thus, VCP is a percentage of 
people who, when viewing from a specified location and in a specified 
direction, will be expected to find it acceptable in terms of discomfort 
glare from the light source. 
It has been appreciated that the VCP which is required within buildings 
under arrays of illuminations panels can be better met if the illumination 
from each panel at high angles from the vertical is reduced, particularly 
if minimized at angles above sixty degrees from the vertical. JONES, 
"Lighting Panel", U.S. Pat. No. 3,829,680 (1974). A panel has been sold 
under the trademark, Radialens. This product produces maximum wide angle 
ditribution within rooms in all directions, but does not meet VCP's of 70 
or more. 
It has also been appreciated by some practitioners that when an object is 
viewed at any angle, a ray of light coming from a point in space will 
produce higher contrast when vertically polarized than when horizontally 
polarized. See Blackwell, supra. For this reason methodologies and 
materials have been developed for producing polarizing sheets as described 
in greater detail in KAHN, "Light Polarizing Structures", U.S. Pat. No. 
3,124,639 (1964) and KAHN et al., "Machine for Continuously Producing 
Large Area Light Polarizing Panels", U.S. Pat. No. 3,772,128 (1973), which 
is incorporated herein by reference. These panels meet the VCP of 70 or 
more due to their low brightness polarizing effect at wide angles. 
Therefore, the applicant has combined the prismatic structure of the JONES 
Radialens manufactured according to the methodologies and structures of 
KAHN's polarizing panel to obtain the higher visual acuity realized with 
polarized light with the wide angular light distribution of the Radialens 
panel and the desirable VCP of 70 or more into an integral structure. 
However, what is achieved is not merely the expected advantages of 
polarized and Radialens light distribution, but a marked improvement in 
visual comfort probability (VCP) due to a reduction of brightness and 
glare at wide angles. 
BRIEF SUMMARY OF THE INVENTION 
The invention is an improvement in a lighting panel including a light 
source and an embossed series of Radialens prisms on a surface comprising 
a layer or portion incorporated therein for preferentially polarizing the 
light transmitted through the panel at all angles around the panel. The 
under layer of the panel polarizes light incident on the surface of the 
panel which is then transmitted therethrough to the polarizing layers for 
preferentially distributing the light transmitted through the panel. 
The layer for polarizing the light transmitted through the panel is an 
integrally formed layer of polarizing material disposed on an lower 
surface of the panel furtherest away from the light source. The Radialens 
prisms for preferentially distributing the light at wide angeles are on 
the upper surface of the panel nearest the light source. 
The invention is also more particularly described as an improvement in an 
integral lighting panel such as that sold by assignee under the trademark, 
Radialens. The panel has at least one shaped surface comprising a 
plurality of three-dimensional elements extending from the one surface and 
a surface opposing the one shaped surface. Each element is defined by 
three generally flat triangular surfaces. Each of the triangular surfaces 
has a first and second side, and a base, and further mates the other two 
of the three triangular surfaces defining each of the elements which are 
on the first and second sides of the element. Each of the bases of the 
three triangular surfaces which define each of the elements is 
substantially coincident with the base of one of the triangular surfaces 
defining an adjacent element. All of the bases are substantially coplanar. 
Each of the three triangular surfaces is disposed at approximately 50 to 
60 degrees with respect to the plane of the bases. The improvement 
comprises at least a portion of the lighting panel being composed of a 
polarizing material so that light transmitted through the lighting panel 
and from the prismatic surface is substantially polarized. 
In one embodiment the portion of the lighting panel composed of polarizing 
material is a backing layer adhered to the lower surface of the lighting 
panel opposing the upper surface having the plurality of three-dimensional 
elements. 
More particularly the polarizing layer is always laminated to the opposing 
surface of the prismatic Radialens surface of the lighting panel. 
In the illustrated embodiment the laminated polarizing layer is laminated 
to the panel while the lighting panel is heated and plastic, and is 
laminated to one opposing surface of the lighting panel without inclusion 
of adhesives. 
In the preferred embodiment the plurality of three-dimensional elements are 
defined into the other surface of the lighting panel prior to thermal 
lamination of the polarizing layer to the opposing surface of the lighting 
panel. 
The invention can also be characterized as an improvement in a lighting 
panel having in one surface thereof a plurality of three-dimensional 
elements defined by a first set of parallel, equally spaced V-grooves 
directed downwardly into the one surface of the lighting panel. A second 
set of parallel V-grooves is directed downwardly into the panel. The 
second set of V-grooves has the same spacing as the first set and crosses 
the first set at an angle of approximately 60 degrees. A third set of 
V-grooves is also directed downwardly into the panel. The third set of 
V-grooves has the same spacing as the first set and crosses the first and 
second sets at an angle of approximately 60 degrees. The first set and 
third sets of V-grooves are disposed so that the lines defined by junction 
of the two sides of each of the V-grooves are substantially coplanar. Each 
of the two sides of each of the V-grooves is disposed at approximately 50 
to 60 degrees with respect to the plane of the lines defined by the 
junction of the two sides of each of the V-grooves. The one surface is 
opposed by a flat surface. The improvement comprises at least a portion of 
the lighting panel being composed of a polarizing material so that light 
transmitted through the lighting panel and through the surface into which 
the plurality of elements is defined, is transmitted through to the 
opposite surface and emitted as substantially polarized light distributed 
radially in all directions. 
The invention is still further characterized as an improvement in a 
lighting panel having on one surface a pattern defined therein of a 
plurality of groups of three generally triangular surfaces. Each of the 
triangular surfaces has first and second sides and a base, and mates the 
other two of the three triangular surfaces on the first and second sides 
thereof. Each of the bases of the three triangular surfaces in a group is 
substantially coincident with the base of one of the triangular surfaces 
in an adjacent group. All of the bases are substantially coplanar. Each of 
the three triangular surfaces is disposed at approximately 50 degrees to 
60 degrees with respect to the plane of the bases. The one surface has an 
unshaped opposing surface. The improvement comprises at least a portion of 
the lighting panel being composed of polarizing material so that light 
transmitted through the lighting panel from the Radialens prismatic 
surface, emerges from the other surface and is defined as substantially 
vertically plane polarized light emitted in all radial directions. 
The invention and its various embodiments may be better visualized by 
referring to the following drawings wherein like elements are referenced 
with like numerals.

The present invention may be better understood in the illustrated 
embodiment by now turning to the following detailed description. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An improvement in a Radialens light control panel results from the 
integration by fabrication of a light polarizing layer to a surface of the 
lighting panel opposing the surface of the Radialens panel in which a 
plurality of prismatic surfaces or lens elements is defined. The 
polarizing layer is laminated to the opposite surface of the Radialens 
panel after the Radialens panel has been embossed and is in a relatively 
heated and plastic state. No adhesives are used to secure the bond between 
the polarizing layer and other surface opposite the Radialens embossing. 
The plurality of prisms or lenses defined in the opposing surface of the 
Radialens panel is embossed into the plastic panel immediately before the 
lamination with the polarizing sheet. As a result, polarized light is 
preferentially distributed at wider and desirable angles to provide higher 
contrast and less reflective glare and lower direct source glare (VCP) 
than could be achieved with a Radialens panel alone or a polarizing sheet 
alone. 
FIG. 1 is a side diagrammatic view of a continuous sheet process by which 
polarized light control panels may be devised according to the invention. 
The basic manufacturing process is described in greater detail in KAHN et 
al., supra. However, a modification to the apparatus and process is 
described below in connection with the other elements of the apparatus and 
process. 
An extrusion die 10 exudes a hot plastic sheet 12 which is transported over 
a dry roller 14. Sheet 12 is typically between 200 and 280 degrees F., as 
controlled by the extrusion process and/or as modified by water cooled 
roller 14 or a cooling air jet 16. Sheet 12 is transported horizontally 
into the nip of a first set of laminating roller 18, 20 and 22. A 
polarizing material 24 in sheet form is supplied from a feed roll 26 
around tensioning rollers 28 and 30 to a lead-off roller 32. Roller 32 is 
positioned relative to plastic sheet 12 as described in greater detail in 
KAHN et al., U.S. Pat. No. 3,772,128. Polarizing material 24 may be any 
polarizing material known to the art and in particular the polarizing 
material as described in detail in KAHN, "Light Polarizing Structures", 
supra. 
The radiant heat within plastic 12 is sufficient to cause light polarizing 
sheet 24 to become adhered thereto without the necessity of introducing 
adhesives or other means of affixing polarizing sheet 24 and plastic sheet 
12 together. 
As the sheet of plastic 12 with light polarizing sheet 24 leaves the first 
set of laminating rollers 18-22, it is led to a second set of laminating 
rollers 34-38. A second plastic sheet 40 is supplied from feed roll 42 
through a plurality of tensioning rollers 44 to laminating rollers 34-38. 
At this point in the process polarized sheet 24 has been sufficiently 
heated by contact with plastic sheet 12 that a similar adhesion occurs 
between polarizing sheet 24 and second plastic sheet 40 as occurred 
between first plastic sheet 12 and polarizing sheet 24 when passed through 
laminating rollers 18-22. 
The heated and relatively soft thermoplastic first emerges from the 
embossing rollers 46 and has the negative image of a prismatic pattern 
formed in its outer cylindrical surface which is impressed into first 
plastic sheet 12 as the laminate is fed through embossing rollers 46 and 
48. 
FIG. 2 is a fragmentary perspective view which shows a corner of the 
laminate as it would appear after being embossed by roller 46. First 
plastic layer 12, which is the thickest layer, has impressed therein a 
prismatic pattern which is described in greater detail in JONES, "Lighting 
Panel", supra, which is incorporated herein by reference. Beneath the now 
shaped plastic layer 12 is an undeformed polarizing layer 24 and the thin 
second plastic sheet 40, all of which has been formed into an integral 
laminate. 
Thereafter, additional processing steps may be performed on the 
continuously moving laminated sheet 12, 24 and 40. The edges of the 
laminated sheet may be sealed by heated side bars as described in KAHN 
U.S. Pat. No. 3,772,128 and are then cooled thereby assuming a rigid and 
self-supporting form. The sheets may then be cut to size as appropriate. 
FIG. 3 is an isocandela polargraph comparatively illustrating the 
performance of the prismatic Radialens sheet without a polarizing lens, 
indicated by curve 50 and the same prismatic Radialens sheet when 
integrally fabricated with a polarizing layer indicated by curve 52. The 
light source may be considered as sited at point 54 with the radial line 
extending from point 54, the origin, to curves 50 and 52 representing the 
intensity of the illumination in lumens as a function of its angle from 
the vertical. Thus, the nadir 56 is indicated as the point directly 
beneath light source 54 as zero degrees and thereafter increasing in 
intensity in the case of a Radialens as depicted in the curve 50 out to a 
zone and between thirty and sixty degrees indicated by reference numerals 
58 and 60 in FIG. 3. 
The performance of the polarized Radialens panel is indicated at curve 52 
and shows a somewhat higher intensity at the nadir point 56, but with a 
good angular spread at wider angles between thirty and sixty degrees and 
even with lower intensities above sixty degrees than a Radialens without a 
polarizing component. 
The Radialens without a polarizing component does not meet the visual 
comfort probability (VCP) required by the Illuminating Engineering Society 
of North America or by many State codes which require a VCP of 70 or more. 
For example, in one test the Radialens panel in a light fixture without 
the polarizing sheet in a 30.times.30 room with a ten-foot ceiling 
indicated a VCP of 65. However, when the Radialens is combined with a 
polarizing component in the same fixture and same room, the VCP 
surprisingly rises to 70-79. The Radialens with the polarized component 
thus meets industry VCP criteria, thus enabling the product to satisfy 
standardized performance specifications in many additional institutional 
building lighting applications, such as in school rooms and universities 
etc. 
In addition thereto, the wide angle distribution of illumination 
characteristic of the Radialens panel without a polarizing component was 
substantially preserved when a polarizing component was included. What is 
not illustrated in FIG. 3 is the fact that the light transmitted through 
the improved Radialens acrylic panel according to the invention becomes 
polarized light after passing through the opposite layer which allows for 
substantially greater visual acuity, visual effectiveness and visual 
comfort (VCP) with lower lighting intensities, thus contributing to 
important electric conservation benefits in lighting applications. 
In addition thereto, and further not depicted in FIG. 3, lamp image 
obscuration is significantly increased with the polarized Radialens 
without any decrease in visual efficiency as compared to a conventional 
Radialens. It is aesthetically desired to have the panel, when viewed from 
underneath, appear as a more uniform sheet of illumination. However, 
conventional panels typically fail to achieve this effect in that the 
conventional panel is most intensely lit in the close proximity of the 
overhead illuminating tube within the light fixture. While a conventional 
Radialens does serve to partially reduce the precise image of the 
illuminating tubes, the illumination panel is by no means uniformly lit. A 
polarizing component when included under the Radialens panel provides a 
more highly diffuse image acting in combination with the prismatic image 
redirected by the Radialens panel. The overall performance is 
significantly better than the Radialens panel without the polarizing 
component or as viewed simply through a conventional polarizing sheet 
alone. 
Further, the combination of the Radialens panel with the polarized 
component reduces the light distribution directly beneath the light 
fixture, and hence reduces glare and increases the amount of polarized 
light which occurs at angles beyond 10 to 90 degrees as compared with a 
conventional polarizing sheet without this prismatic lens component. 
As a result, a highly aesthetic polarized panel is provided which improves 
visual contrasts of observed objects and improves color differentiation by 
increasing the amount of the light absorption and decreasing the amount of 
horizontally polarized reflected glare. Such glare, as is inherent in and 
present under conventional prismatic and diffused lighting, tends to wash 
out color distinctions, detail and contrasts. Furthermore, because of the 
wilder illumination distribution realized by a polarized Radialens as 
compared with a conventional fixture spacing of 1.7 to 1.2, the number of 
lighting fixtures per foot within an interior space may be reduced or 
alternatively the average number of illumination tubes within each fixture 
may be reduced with corresponding reduction in power consumption without 
any corresponding loss in visual acuity, visual effectiveness or increase 
in visual discomfort. 
Further, a polarized Radialens according to the present invention is 
manufactured in a continuous sheet feed process as a laminated integral 
unit and there is no requirement nor can it be duplicatd by simply 
providing an extra polarizing back panel laid upon a conventional 
Radialens panel. Such back panels are typically thicker than the 
polarizing layer which can be laminated integrally within a polarized 
Radialens sheet since such back panels must also be structurally rigid to 
allow handling. Secondly, even if cost were not a consideration, merely 
fitting a polarized back panel to a conventional Radialens panel fails to 
provide uniform clearance between the panels or requires a time consuming 
and difficult hand lamination in the field which can rarely bring 
satisfactory results in practice and would substantially increase cost. 
The salutorious performance which is described and illustrated in FIG. 3 
cannot be duplicated by merely placing a polarizing back panel on a 
Radialens sheet. 
Many modifications and alterations may be made by those having ordinary 
skill in the art without departing from the spirit and scope of the 
invention. Therefore, it must be understood that the illustrated 
embodiment has been set forth only for the purposes of example and it 
should not be taken as a limitation of the invention as defined in the 
following claims.