U.S. patent application number 11/152715 was filed with the patent office on 2006-01-05 for optical devices using reflecting polarizing materials.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Richard C. Allen, Andrew J. Ouderkirk.
Application Number | 20060001797 11/152715 |
Document ID | / |
Family ID | 23148585 |
Filed Date | 2006-01-05 |
United States Patent
Application |
20060001797 |
Kind Code |
A1 |
Allen; Richard C. ; et
al. |
January 5, 2006 |
Optical devices using reflecting polarizing materials
Abstract
Optical devices using reflective polarizers and, in particular,
diffusely reflective polarizers are provided. Many of the optical
devices utilize the diffusely reflecting and specularly
transmitting properties of diffusely reflecting polarizers to
enhance their optical characteristics. The optical devices include
a lighting system which uses a reflector formed from a diffusely
reflecting polarizer attached to a specular reflector. Another
optical device is a display apparatus which uses a diffusely
reflecting polarizer layer in combination with a turning lens which
folds shallow angle light toward a light modulating layer. Other
optical devices exploit the depolarizing characteristics of a
diffusely reflecting polarizer when reflecting light. Still other
optical devices use diffusely reflecting polarizers to recycle
light and improve display illumination.
Inventors: |
Allen; Richard C.;
(Lilydale, MN) ; Ouderkirk; Andrew J.; (Woodbury,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
23148585 |
Appl. No.: |
11/152715 |
Filed: |
June 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10878911 |
Jun 28, 2004 |
6934082 |
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11152715 |
Jun 14, 2005 |
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09871130 |
May 31, 2001 |
6829071 |
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10878911 |
Jun 28, 2004 |
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09298003 |
Apr 22, 1999 |
6515785 |
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09871130 |
May 31, 2001 |
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Current U.S.
Class: |
349/96 |
Current CPC
Class: |
G02F 1/133504 20130101;
G02F 1/133536 20130101; Y10S 385/901 20130101; G02B 5/3033
20130101; G02B 6/0046 20130101; G02B 6/0051 20130101; G02B 5/0284
20130101; G02B 27/283 20130101; G02B 6/0056 20130101; G02B 5/0236
20130101; G02B 5/3041 20130101; G02B 5/0278 20130101; G02B 6/0053
20130101 |
Class at
Publication: |
349/096 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. An optical device comprising an emissive element and a
diffusely reflecting polarizer disposed to receive light therefrom,
said diffusely reflecting polarizer attached to the emissive
element.
22. The optical device of claim 21, further comprising an absorbing
polarizer.
23. The optical device of claim 22, wherein the absorbing polarizer
is aligned with the diffusely reflecting polarizer.
24. The optical device of claim 22, wherein the absorbing polarizer
is laminated to the diffusely reflecting polarizer.
25. The optical device of claim 21, further comprising a tinted
layer.
26. The optical device of claim 21, wherein the diffusely
reflecting polarizer is built directly onto the emissive
element.
27. The optical device of claim 21, wherein the emissive element
comprises phosphor.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to optical devices
using reflective polarizers and, more particularly, to optical
devices using diffusely reflecting polarizing materials.
BACKGROUND OF THE INVENTION
[0002] Reflecting polarizers generally include materials which
transmit light of a first polarization and which reflect light of a
second, different polarization. Reflecting polarizers include, by
way of example and not of limitation, diffusely reflecting
polarizers, multilayer reflective polarizers, and cholesteric
reflective polarizers. Examples of diffusely reflecting polarizing
materials includes those disclosed U.S. Pat. Nos. 5,783,120 and
5,825,543 and in PCT Patent Application Publication Nos. WO
97/32223, WO 97/32224, WO 97/32225, WO 97/32226, WO 97/32227, and
WO 97/32230, the contents of all of which are incorporated herein
by reference. Examples of multilayer reflective polarizers are
described in U.S. Pat. No. 5,882,774, the contents of which are
incorporated herein by reference. Examples of cholesteric
reflective polarizers are described in EP 606 940 and U.S. Pat. No.
5,325,218, the contents of both of which are incorporated herein by
reference.
SUMMARY OF THE INVENTION
[0003] The present invention provides optical devices using
reflecting polarizers, such as diffusely reflecting polarizers. In
one embodiment, a display apparatus is provided. The display
apparatus includes a light modulating layer having first surface
and a light cavity for providing light to the light modulating
layer. A light guide is disposed to receive light from the light
cavity and output light at a low angle relative to the first
surface of the light modulating layer. A turning lens is disposed
to receive the low angle light output from the light guide and
redirect light towards the light modulating layer. The display
apparatus further includes a diffusely reflecting polarizer
disposed between the turning lens and the light modulating layer
for receiving the redirected light and transmitting a component of
the redirected light having a first polarization toward the light
modulating layer and diffusely reflecting a component of the
redirected light having a second polarization different than the
first polarization.
[0004] A lighting system, according to an embodiment, includes a
light source for providing light and a reflector which includes a
diffusely reflecting polarizer disposed closer to the light source
and a specular reflector attached to the diffusely reflecting
polarizer and disposed further from the light source. In use, a
component of the light having a first polarization is transmitted
by the diffusely reflecting polarizer, specularly reflected by the
specular reflector, and specularly retransmitted through the
diffusely reflecting polarizer to provide specularly reflected
light of the first polarization having a first distribution. A
second component of the light which has a second, different
polarization is diffusely reflected by the diffusely reflecting
polarizer (without reaching the specular reflector) to provide
diffusely reflected light having a second distribution different
from the first distribution. The diffused light may be used as
general ambient light while the specularly reflected light of the
first polarization may be used as task lighting, for example.
[0005] A display apparatus, in accordance with another embodiment,
includes a light modulating layer and a light cavity adapted to
provide light to a light modulating layer. The apparatus further
includes a diffusely reflecting polarizer, disposed between the
light modulating layer and the light cavity, for transmitting a
component of the light provided by the light cavity having a first
polarization for viewing and diffusely reflecting a component of
the light received from the light cavity having a second
polarization. The light cavity typically reflects incident light,
e.g., light diffusely reflected by the polarizer, with a first
degree of depolarization. The polarizer diffusely reflects the
light with a second degree of depolarization greater than the first
degree of depolarization to provide light of the first
depolarization. Due to the depolarization, at least a portion of
the diffusely reflected light of the first polarization is
reflected by the light cavity without polarization toward the
diffusely reflecting polarizer for transmission therethrough.
[0006] In another embodiment, a display apparatus is provided which
includes a light cavity for providing light and a diffusely
reflecting polarizer disposed to receive the light. The diffusely
reflecting polarizer diffusely reflects light of a second
polarization toward the light cavity and transmits light of a first
polarization. The diffusely reflective polarizer has a selected
dispersed phase concentration which provides a desired gain
distribution.
[0007] A display apparatus, in another embodiment, includes a
emissive element for providing light and a contrasting enhancing
filter disposed on the viewing side of the emissive element. The
contrast enhancing filter includes an absorbing polarizer and a
reflecting polarizer disposed closer to the emissive element than
the absorbing polarizer. The contrast enhancing filter may, for
example, further include one or more tint layers above and/or below
the diffusely reflecting polarizer. The reflecting polarizer may,
for example, be a diffusely reflecting polarizer.
[0008] The above summary of the invention is not intended to
describe each illustrated embodiment or every implementation of the
present invention. The figures and the detailed description which
follow more particularly exemplify these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0010] FIG. 1A illustrates an exemplary display apparatus in
accordance with an embodiment of the invention;
[0011] FIG. 1B illustrates an exemplary display apparatus in
accordance with another embodiment of the invention;
[0012] FIG. 1C illustrates an exemplary display apparatus in
accordance with yet another embodiment of the invention;
[0013] FIG. 2 illustrates an exemplary display apparatus in
accordance with another embodiment of the invention;
[0014] FIG. 3A illustrates an exemplary projection display system
in accordance with an embodiment of the invention;
[0015] FIG. 3B illustrates an exemplary projection display system
in accordance with another embodiment of the invention;
[0016] FIG. 3C illustrates an exemplary projection display system
in accordance with another embodiment of the invention;
[0017] FIG. 3D illustrates an exemplary microdisplay system in
accordance with another embodiment of the invention;
[0018] FIG. 3E illustrates an exemplary microdisplay system in
accordance with yet another embodiment of the invention;
[0019] FIG. 3F illustrates an exemplary microdisplay system in
accordance with yet another embodiment of the invention;
[0020] FIG. 3G illustrates an exemplary microdisplay system in
accordance with still another embodiment of the invention;
[0021] FIGS. 4A-4B illustrates an exemplary transflective display
apparatus in accordance with an embodiment of the invention;
[0022] FIG. 5A illustrates a display having a conventional contrast
enhancing filter;
[0023] FIG. 5B illustrates a display having a contrast enhancing
filter in accordance with an embodiment of the invention;
[0024] FIG. 5C is a graph illustrating relative brightness as a
function of tint for contrast enhancing displays;
[0025] FIG. 5D is a graph illustrating contrast ratio as a function
of tint for contrast enhancing displays;
[0026] FIG. 5E is a graph illustrating another contrast
characteristic graph for contrast enhancing displays;
[0027] FIG. 6 illustrates an exemplary display apparatus in
accordance with an embodiment of the invention;
[0028] FIG. 7A illustrates an exemplary lighting system in
accordance with an embodiment of the invention;
[0029] FIG. 7B illustrates an exemplary reflecting material for use
in the lighting system of FIG. 7A in accordance with an embodiment
of the invention;
[0030] FIG. 8A-8D illustrate exemplary security labels using
diffusely reflecting polarizers in accordance with embodiments of
the invention; and
[0031] FIG. 9 illustrates an exemplary display apparatus in
accordance with still another embodiment of the invention.
[0032] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0033] The present invention is believed to be applicable to a
number of different optical devices using reflecting polarizers.
Aspects of the invention are particular suited to the use of
diffusely reflecting polarizers. While the present invention is not
so limited, an appreciation of various aspects of the invention
will be gained through a discussion of the examples provided
below.
[0034] Diffusely reflecting polarizers (DRPs) typically specularly
transmit a component of incident light of a first polarization and
diffusely reflect a component of the light having a second
polarization. The terms specular and diffuse are relative terms
which can vary depending on the context of the application. As used
herein, specularly transmitted light generally refers to light
transmitted without substantial deviation from its incident path.
The term diffusely reflected light generally refers to light
reflected with considerable diffusion. By way of example and not of
limitation, specularly transmitted light may refer to light
deviated from its incident path by about 8 degrees or less, while
diffusely reflected light may refer to light deviated by about 8
degrees or more from a reflection angle equal to an incident angle
of the light.
[0035] Many of the examples illustrate display apparatus or other
optical devices which include light sources, light guides and/or
light cavities. The term light source will be used herein to refer
to a source of light, such as a light bulb. The terms optical
cavity and light cavity will be used interchangeably herein to
refer to a cavity which provides light. Such a cavity may include
one or more of the following elements: a light source, a light
guide or other transparent medium, and one or more specular or
diffuse reflectors.
[0036] FIG. 1A illustrates a display apparatus using a diffusely
reflecting polarizer according to one embodiment. The exemplary
display apparatus 100 includes a light modulating system 130 and an
optical cavity 120 for providing light to the light modulating
system 130 and illuminating the display apparatus 100. In this
embodiment, the light modulating system 130 includes a first
polarizer 105, a first transparent substrate 106, a light
modulating layer 107, a second transparent substrate 108, and a
second polarizer 109. The example display apparatus 100 may, for
example, be a liquid crystal display (LCD) having liquid crystal
light modulating layer 107. First polarizer 105 is typically a
dichroic polarizer which transmits light of a desired polarization
and absorbs light of an undesired polarization. The optical cavity
120 typically includes a light source 111 and a light guide 102 for
receiving light from the light source 111. The light source 111
may, for example, be a linear light source, such as a cold cathode
fluorescent tube, or CCFT. The light guide 102 may, for example, be
made of a transparent plastic material such as
polymethylmethacrylate (PMMA). Light guide 102 is typically wedge
shaped, as shown in FIG. 1A, but other shapes may be used.
[0037] In operation, light from light source 111 is directed, with
the aid of reflector 112, into light guide 102. Most rays of light
traveling through light guide 102 impinge upon surfaces 114 and 116
at angles greater than the critical angle, and are therefore
totally reflected by total internal reflection (TIR). In order to
extract light from light guide 102, small surface irregularities or
local angular changes may be incorporated into surface 114, to
frustrate some of the total internal reflection, a phenomenon
called frustrated total internal reflection (FTIR). Since guide 102
is typically relatively thin, light can only travel through it in a
narrow range of directions. As a result, light (e.g., rays 151 and
153) leaving guide 102 tends to leave at relatively low angles
.alpha. relative to the surface 118 of the light modulating layer
107. The angle .alpha. is typically less than 20 degrees in many
applications and, in one embodiment, ranges from 10 to 20
degrees.
[0038] To redirect the light toward the light modulating layer 107,
a turning lens 103 may be provided to fold the optical path of
illuminating rays, such as rays 151 and 153, thereby directing
light from the optical cavity 120 to the light modulating layer
107. The example turning lens 103 includes a structured surface
103a facing the optical cavity 120 and a relatively planar surface
103b on the opposite side. The structured surface 103a may, for
example, include multiple prisms. The turning lens 103 may, for
example, bend the low angle rays to a direction substantially
normal to the light modulating layer surface 118 as shown. The
optical cavity 120 may further include a reflector 101 disposed
adjacent to surface 116 to reflect light escaping from surface 116
back into guide 102, where at least some of it will eventually,
after one or more reflections, leave guide 102 through surface 114.
A diffuser 104 may, optionally, be included to, for example, widen
the range of directions of viewability of display apparatus 100,
since light rays 151 and 153 may, with some light sources, be
collimated into a relatively narrow range of directions. Optional
diffuser 104 may also, in some cases, improve the appearance of
display 100 in other ways, such as providing a more uniform
appearance to display 100.
[0039] The example display apparatus 100 further includes a
diffusely reflecting polarizer (DRP) disposed between the turning
lens 103 and the light modulating layer 107 for receiving the
redirected light and transmitting a component of the redirected
light having a first polarization toward the light modulating layer
107 and diffusely reflecting a component of the redirected light
having a second polarization different than the first polarization
toward the light guide 102.
[0040] In one embodiment, a DRP layer 110a is disposed between
turning lens 103 and diffuser 104, without being attached to other
components (as shown on the left side of FIG. 1A). Alternatively, a
DRP layer 110b may attached, e.g. laminated, to turning lens 103
(as shown on the right side of FIG. 1A). In other embodiments, a
DRP layer 110c may be attached to a diffuser 104 (as shown in the
left portion of FIG. 1B) or a DRP layer 110d may be attached to
both turning lens 103 and diffuser layer 104 (as shown on the right
side of FIG. 1B). Referring to FIG. 1C, a DRP layer 110e may be
integrated into the display apparatus 100 by attaching it to a
diffuser 104, which is in turn attached to a polarizer 105 (as
shown on the left side of FIG. 1C). A DRP layer 110f may be
attached to turning lens 103 and to a diffuser 104, which is in
turn attached to a polarizer 105 (as shown in the right side of
FIG. 1C). Where the diffuser 104 is omitted, the DRP layer may, for
example, be attached to the bottom side of the light modulating
system (e.g. to a polarizer 105).
[0041] Furthermore, in the above embodiments, the diffuser may be
omitted with the DRP layer incorporating its diffusion
functionality. For example, when a DRP layer is used in embodiments
without a diffuser, the surface roughness of the DRP layer may be
controlled to provide surface diffusion. Alternatively, a DRP may
be adjusted to provide bulk diffusion by adjusting the degree of
specular transmission of the transmitted polarization state versus
diffusion transmission of the transmitted polarization state.
[0042] The diffusely reflecting polarizer 110a-f and optical cavity
120 may advantageously be optimized for light recycling. In one
embodiment, the optical cavity 120 reflects light with little
depolarization and the diffusely reflecting polarizer 110a-f
diffusely reflects light with substantial depolarization. In other
words, the DRP layer 110a-f diffusely reflects light of the second
polarization such that the reflected light includes a relatively
large quantity of light having the first polarization. For example,
the ratio of light of the first polarization to light of the second
polarization may be 1:4 or more for many applications. In
operation, the DRP layer 110a-f transmits light of a desired first
polarization and diffusely reflects light of a second, undesired
polarization. Due to depolarization, the reflected light includes a
relatively large component of the desired first polarization. The
reflected light passes through turning lens 103 and is re-reflected
with little depolarization by optical cavity 120. Re-reflected
light of the first polarization subsequently transmits through the
DRP layer 110a-f and re-reflected light of the second polarization
is diffusely reflected and partially depolarized to continue the
recycling process. As a result, more of the light produced by the
light source 111 is utilized by the display apparatus 100. In
addition, recycling of the light reflected by DRP layer 110a-f over
a variety of different optical paths tends to even out variations
in illumination which sometimes occur in backlight
illuminators.
[0043] While this embodiment works particularly well with
reflectors providing little depolarization, the invention is not so
limited. Other, more depolarizing reflectors and optical cavities
may be employed with or without substantially depolarizing DRP
layers. In addition, in other embodiments, the angular
depolarization characteristics of the DRP and light cavity may be
set such that the optical cavity significantly depolarizes light at
incident angles containing relatively large amounts of
non-depolarized light from the DRP and vice versa.
[0044] The diffusion of a DRP is typically much higher in the plane
containing the cross-stretch and normal axis compared to the plane
containing the stretch and normal axis. Where the diffusion is
desired to obscure the extraction pattern, the extraction pattern
should be optimized for use with the DRP. For example, if the DRP
is oriented at 45.degree., the optimum orientation of, for example,
the extraction pattern is typically at 0.degree..
[0045] In some embodiments, non-polarizing components may be
included within the oriented film to achieve diffusion. For
example, the precursor film may be coextruded or coated before
stretching with a composition that does not take on significant
birefringence during stretching at conditions necessary to make the
DRP. Examples of suitable compositions include acrylic and
styrene:acrylic copolymer macrospheres in a PMMA host.
[0046] FIG. 2 illustrates a display apparatus having a DRP layer
with a selected gain distribution. The example display apparatus
200 includes a DRP layer 220 and a light cavity 230 which, in the
illustrated embodiment, utilizes a light source 232 and a reflector
233 to produce diffuse light rays 231, incident upon the DRP layer
220. The display apparatus 200 further includes a light modulating
layer 210 which, in the example embodiment, includes a liquid
crystal layer 214 disposed between two polarizers 212 and 216. The
DRP layer 220 transmits light 221 having polarization P1, thereby
separating it from light 223, which is diffusely reflected back to
cavity 230. Light 221(P1) is incident upon first polarizer 212 of
light modulating layer 210, which has its transmission axis
oriented parallel to the transmission axis of DRP layer 220, so as
to transmit light 225(P1') having polarization P1' into liquid
crystal layer 214. Polarization P1' typically differs from
polarization P1 in that it is usually more purely linearly
polarized, by virtue of having passed through polarizer 212, which
is typically an absorbing dichroic polarizer capable of producing
high levels of linear polarization.
[0047] In the example embodiment, the liquid crystal layer 214 is
made up of an array of electronically addressable liquid crystal
pixel elements which are individually addressed by the application
of electric fields through an array of electrodes to align the
liquid crystal material of each pixel in either an optically
inactive state (e.g., voltage-on, that is to say, when the electric
field is applied) or in an optically active state (e.g.,
voltage-off, or, when no electric field is applied). As used
herein, the term optically active means that the orientation of the
plane of polarization of polarized light passing through the
optically active material is altered. The second polarizer 216
functions as an analyzer to either transmit or block light
transmitted by the pixels making up liquid crystal layer 214,
depending upon the direction of polarization of the transmitted
light, as determined by whether each pixel is in an optically
active or optically inactive state. By appropriately applying
voltage to individual pixels in the liquid crystal array in an
imagewise manner, a viewable image is formed by display 210. While
a liquid crystal display with a liquid crystal layer is
illustrated, the invention is not so limited. Other types of
displays may benefit be employing selected gain distribution.
[0048] DRP layer 220 improves the light utilization of liquid
crystal display 210 by reflecting light 223 back to reflecting
cavity 230, where a portion of it is re-reflected back toward DRP
layer 220, which again transmits that portion having polarization
P1 and substantially reflects the remaining portion, thereby adding
to the illumination of display 210. This process, called light
recycling, continues until all of light 231 is either transmitted
by DRP layer 220, with polarization P1, or lost to absorption.
Light recycling has been found to significantly increase the light
utilization. Increased light utilization can increase the
brightness of a liquid crystal display, for a given level of
optical cavity illumination, or, alternatively, it can allow a
lower level of optical cavity illumination to achieve the same
brightness, thereby reducing energy consumption. The DRP layer 220
and light cavity may further be optimized to recycle light. For
example, the DRP layer 220 may, for example, substantially
depolarize diffusely reflected light to facilitate light recycling
with a light cavity having less depolarization characteristics.
Alternatively, the angular depolarization characteristics of the
two components may be set such that the light cavity significantly
depolarizes light at incident angles containing relatively large
amounts of non-depolarized light and vice versa, as noted
above.
[0049] The example DRP layer 220 includes a selected gain
distribution. Gain generally refers to the ratio of the luminance a
display with a DRP layer to the luminance of the display without
the DRP layer. The selected gain distribution can be provided by,
for example, selecting the concentration of the dispersed phase
relative to the concentration of the continuous phase. By way of
example, increasing the concentration of disperse phase relative to
the concentration of continuous phase typically increases the
on-axis gain relative to the off-axis gain. Conversely, decreasing
the concentration of disperse phase relative to the concentration
of continuous phase will typically decreases the on-axis gain
relative to the off-axis gain. For example, with a film providing
an on-axis gain of 1.35 and a 40 degree (relative to normal) gain
of 1.29, by increasing its disperse phase concentration and
decreasing its continuous phase concentration, the film's on-axis
gain may increase to 1.44 and its off-axis 40 degree gain may
decrease to 1.18. Depending on the desired gain distribution, the
concentration of the dispersed phase can be selected.
[0050] The table below illustrates on-axis gain and off-axis gain
(-60 degrees to normal) of DRPs with different dispersed phase
concentrations. TABLE-US-00001 TABLE 1 Dispersed Phase On-axis
Off-axis Concentration Gain Gain (-60.degree.) 45 1.37 1.07 40 1.36
1.27 30 1.35 1.47
[0051] The selected gain distribution can be provided to improve
the viewability of display 210 by controlling the light
distribution seen by viewers such as 201 and 202, as typified by
rays 211 and 213. A useful parameter for describing luminance
distribution is the half height angle .theta., i.e., the angle at
which the luminance is half the maximum luminance (which is assumed
to be on-axis in this case). If, for example, ray 211 represents
the luminance of a bright portion of the image displayed by display
210 when viewed at normal viewing angle, and ray 213 represents a
ray emanating from the same point on the image having half of the
luminance of ray 211, then angle .theta., called the half height
angle, is a measure of the breadth of the light distribution for
the displayed image.
[0052] It will be appreciated that for a given level of lumination
from rays 221, increasing .theta. distributes the light available
for viewing more evenly, thereby lowering the maximum luminance,
which typically occurs at normal viewing angle, as represented by
ray 211. In a display which is to be viewed from a wide range of
angles, this may be a desirable situation. In situations wherein a
single viewer is viewing the display at substantially normal
angles, however, it may be desirable to conserve energy by reducing
.theta. so as to brighten the display for that viewer. Typically,
an increase in disperse phase concentration reduces angle .theta.,
thereby narrowing the distribution of light available for viewing
and providing a brighter display for viewer 201, for example, while
trading off brightness for viewer 202. Conversely, reducing the
concentration of the disperse phase in layer 220 increases .theta.,
thereby evening out the distribution of light available for viewing
the display.
[0053] A DRP layer having a particular gain distribution may be
manufactured by selecting the relative concentrations of the
dispersed phase and continuous phase to provide a desired gain
distribution. This selection may take into account a concentration
of a compatabilizer phase. It will be appreciated that the ability
to design the light distribution in this way is a desirable feature
for display designers, since it enables them to produce displays
for a variety of different viewing applications merely by selecting
different DRP materials, based upon the concentration of disperse
phase present in layer 220.
[0054] FIG. 3A illustrates an exemplary projection display system
in accordance with another embodiment of the invention. The
exemplary projection display system 300 utilizes an illuminator 310
to illuminate a reflective imager 304, with the resulting image
being reflected by a polarizing beam splitter 303, through
projection lens 305, onto screen 320. Illuminator 310 typically
includes a light source 301, optical enclosure 308, and beam
conditioner 302. Beam conditioner 302 may comprise lenses or other
beam shaping components, optical filters to remove infrared or
ultraviolet wavelengths of light, and reflective polarizing
materials, such as a DRP layer. Optical enclosure 308 may comprise
an inner surface which is diffusely reflecting, or which contains
polarization altering means such as birefringent layers. Optical
enclosure 308 is not limited to a rectangular shape, but may be of
any suitable shape, and may further contain structures on its inner
surface which give it yet other effective internal optical
shapes.
[0055] Polarizing beam splitter 303 typically comprises a
reflective polarizing material. It is desired that beam splitter
303 reflect image rays 353 in a substantially specular manner so as
to preserve the image produced by imager 304. Therefore, it is
advantageous that the disperse phase of any multiphase reflecting
material used in beam splitter 303 be in the form of uniformly
oriented particles having a high, preferably substantially
infinite, radius of curvature, so as to reduce the diffuse
component of the reflected light. Suitable particles could include
flakes, platelets, or other particles having substantially flat,
orientable surfaces.
[0056] In use, illuminator 310 illuminates imager 304 through
polarizing beam splitter 303. It is often desired that light 350
from illuminator 310 be prepolarized to, for example, polarization
P1 by beam conditioner 302 acting in cooperation with enclosure 308
to recycle light of undesired polarization. Beam splitter 303
further polarizes light 350 and provides polarized light 351 to the
reflecting imager 304, which may, for example, include an array of
liquid crystal elements representing pixels of a digital image.
Depending upon the voltage applied to each pixel, the polarization
of light 351 striking the pixel is either rotated or left
unrotated, and reflected back toward beam splitter 303. Beam
splitter 303 reflects light 353, which has been rotated in
polarization from polarization P1 to polarization P2, through
projection lens 305, and then to screen 320, onto which the image
created by reflective imager 304 is projected. Beam splitter 303
transmits light 352 having unaltered polarization P1 back to
illuminator 310, so that the pixels representing this polarization
appear dark on screen 320. A portion of the light transmitted back
to illuminator 310 may be reflected, repolarized, and recycled.
[0057] An alternative embodiment of the above system is shown in
FIG. 3B, wherein the light reflected by beam splitter 303, rather
than the light transmitted by beam splitter 303, is used as
illumination for imager 304. The imager 304 reflects light 301 of
polarization P1 or P2 depending on its pixel states. The beam
splitter 303 then transmits P2 polarized light 353(P2) and reflects
P1 polarized light back toward the illuminator 310. In this case,
beam splitter 303 may be a diffusely reflecting polarizer, which
transmits substantially specularly. Optical layouts for projection
displays of this type can be made more compact than some
conventional projection apparatus, since it is a feature of the
diffusely reflecting polarizing materials disclosed in the
references incorporated hereinabove that they can be made quite
insensitive to angle of incidence, and therefore able to polarize
strongly diverging or converging beams, without the need for
collimating optics.
[0058] Referring to FIG. 3C, an alternative projection system is
portrayed which uses transmissive imager 306, rather than the
reflective imager used in the previous two systems. In this system,
beam conditioner 302 and, optionally, absorbing polarizer 307,
provide polarized light 350, having polarization P1, which
illuminates imager 306. Imager 306 may again include an array of
liquid crystal elements representing pixels of a digital image,
which either transmits or blocks light 350 in an imagewise manner
to form the image which is then projected, through projection lens
305, onto screen 320. The illuminator 310 may further include a
reflector for redirecting and randomizing light reflected by the
beam conditioner 302 toward the beam conditioner 302 for
transmission therethrough, thereby recycling light. In one
embodiment, the beam conditioner 302 is a DRP. In one case, the DRP
depolarizes the diffusely reflected light and/or the reflector may
depolarize light so that light not transmitted through the DRP can
be recycled and later transmitted therethrough.
[0059] Referring to FIG. 3D, an optical layout similar to that
shown in FIG. 3A can be used, with the exception that rather than
projecting a real image onto a screen, a magnified virtual image of
imager 304 is seen by viewer 1 using magnifying lens 305'. Displays
which operate in this manner will hereinafter be called
microdisplays. Referring to FIG. 3E, an optical layout similar to
that shown in FIG. 3B can be used, with the exception that rather
than projecting a real image onto a screen, a magnified virtual
image created by imager 304 is seen by viewer 1 using a magnifying
lens 305'. This layout also has the advantage that the beam
splitter 303 may be a DRP, as the beam splitter 303 does not need
to be specularly reflective, but only specularly transmissive.
[0060] In an alternative embodiment similar to FIG. 3E, polarizing
beam splitter 303 is laminated or otherwise attached to transparent
cube 306 to form a more compact layout, as shown in FIG. 3F. In yet
another embodiment, portrayed in FIG. 3G, light 350 from
illuminator 310 enters light guide 307, where it is polarized by
diffusely reflecting polarizer 303 while being reflected toward
reflecting imager 304. Imager 304, which is typically made up of an
array of liquid crystal elements representing pixels in a digital
image, reflects polarized light 351 with either unaltered
polarization P1 or rotated polarization P2, as determined by the
voltages applied to the pixel elements of imager 304. Light 353,
having polarization P2, is the portion of the light reflected from
imager 304 which has the polarization transmissible by reflective
polarizer 303, so that it passes through polarizer 303 to an
optional polarizer 308. Polarizer 308 can be, for example, an
absorbing polarizer which filters out any light having polarization
P1, thereby preventing wrongly polarized light from reaching viewer
1. Viewer 1 then views a magnified virtual image created by
reflective imager 304 through magnifying lens 309.
[0061] FIGS. 4A-4B illustrate a transflective light modulating
display apparatus using a DRP layer. In general, a transflective
display typically includes a light modulating layer made up of an
array of light valves or pixels, each of which represents a pixel
of a digital image. Transflective displays can operate in either a
reflective mode, in which the display primarily relies on ambient
light entering from the viewing side for illumination, or in a
transmissive or backlit mode, in which the display primarily relies
on light emanating from an optical cavity opposite the viewing side
for illumination. Examples of transflective light modulating
displays include those which use twisted or supertwisted nematic
liquid crystal layers. Liquid crystal displays of these types
typically operate by either rotating or leaving unrotated the plane
of polarization of a beam of linearly polarized light.
[0062] The example transflective light modulating display apparatus
400 includes an absorbing polarizer 401, a light modulating layer
402, disposed on a side of absorbing polarizer 401, a diffusely
reflecting polarizer 404, disposed on a side of the light
modulating layer 402 opposite the absorbing polarizer 401, a light
trapping layer 405, disposed on a side of the diffusely reflecting
polarizer 404 opposite the light modulating layer 402, and an
optical cavity 406 disposed on a side of the light trapping layer
405 opposite the diffusely reflecting polarizer 404. The example
display apparatus 400 further includes an optional polarization
preserving diffuser layer 403.
[0063] Operation of the example display 400 will now be described.
With reference to FIG. 4A, a pixel 402a of a light modulating
display 400 is portrayed in the voltage-off state, which produces a
bright pixel when illuminated by ambient light. In this state,
unpolarized ambient light enters the display through absorbing
polarizer 401, which passes that portion of the light having
polarization P1, represented by ray 451. Ray 451 then passes
through light modulating pixel layer 402, where its polarization is
rotated, due to the display being in the voltage-off state. This
produces light 453, which has polarization P2. Light 453 may then
passes through polarization preserving diffuser 403, which
maintains the polarization P2, and passes on to DRP layer 404,
where it is diffused backwards, as ray 455, since DRP layer 404 has
been aligned at an orientation which diffusely reflects light
having polarization P2. Depolarization of the diffusely reflected
ray 455 is typically minimized to increase the amount of
polarization P2. Ray 455 again passes through diffuser 403 and then
through light modulating pixel layer 402a, where its polarization
is again rotated to P1, thereby allowing it to pass through
absorbing polarizer and be seen as a bright pixel by viewer 1.
[0064] On the right side of FIG. 4A, a pixel 402b of the light
modulating layer 402 is portrayed in the voltage-on state, which
produces a dark pixel when illuminated by ambient light. In this
state, unpolarized ambient light enters the display through
absorbing polarizer 401, which passes that portion of the light
having polarization P1, shown as 451. Ray 451 then passes through
light modulating pixel layer 402, where its polarization remains
unchanged, due to pixel 402b being in the voltage-on state, thereby
producing ray 463, which still has polarization P1. Ray 463 may
then passes through polarization preserving diffuser 403 and passes
on to DRP layer 404, where it is transmitted, as ray 465, since DRP
layer 404 has been aligned at an orientation so as to transmit
light having polarization P1.
[0065] Ray 465 then enters light trapping layer 405, which traps
the light 465 to show a dark pixel to the viewer 1. The light
trapping layer 405 may comprise light absorbing dyes or pigments,
or polarization rotating components. In many cases, some light 465
will be reflected by the light trapping layer 405 toward the DRP
layer 404. Some light may also pass through trapping layer 405, be
reflected by cavity 406 and re-pass through trapping layer 405
toward DRP layer 404. In the latter case, the amount of light is
typically quite small due to multiple passes through the trapping
layer 405. With either component of light, the DRP layer 404 and
underlying trapping layer 405 and cavity 406 may be optimized to
rotate the polarization of the light to P2 so that it reflects off
the DRP layer 404 rather than transmits therethrough.
[0066] Referring to FIG. 4B, a pixel 402a in the voltage-on state
(left side), operated in the backlit mode, is portrayed. In the
backlit mode, the voltage-on state produces a bright pixel.
Unpolarized light is produced by optical cavity 406, after which it
passes, with some possible attenuation, through light trapping
layer 405, to DRP layer 404. DRP layer 404 diffusely reflects the
portion of ray 471 having polarization P2 back to light trapping
layer 405 and thence to optical cavity 406, where it may be
reflected, changed in polarization, and recycled back for another
try at getting through DRP layer 404. Any light which is
successfully recycled in this way contributes the improvement of
the light utilization efficiency of the display system. The portion
of ray 471 which has polarization P1 is transmitted by DRP layer
404 and passes on through optional diffuser 403 to light modulating
pixel layer 402a. Since pixel 402a is in the voltage-on state, it
passes ray 473 without altering its polarization, to absorbent
polarizer 401. Since absorbent polarizer 401 transmits light having
polarization P1, ray 473 leaves display 400 and is seen by viewer 1
as a bright pixel.
[0067] To the right side of FIG. 4B, a pixel 402b in the
voltage-off state, operated in the backlit mode, is portrayed. In
the backlit mode, a voltage-off state produces a dark pixel. The
light produced by optical cavity 406 reaches pixel 402b in the same
manner as in the voltage-on state, but in this case, since the
pixel 402b is in the voltage-off state, the polarization of ray 473
is rotated to polarization P2, after which it is absorbed by
absorbent polarizer 401, so that the pixel in this case as seen as
a dark pixel. In this manner, a transflective display is provided
in which the state, e.g. bright or dark state, of a pixel changes
between backlit mode and ambient mode for a given voltage state,
e.g., on or off. In addition, the diffusely reflecting properties
of DRP can be used in transflective displays to provide a lighted
matte surface which functions as a light background when the
display is lighted by ambient light, while providing light
recycling when the display is functioning in the backlit mode with
low ambient light.
[0068] In another embodiment, a contrast enhancing filter using a
reflective polarizer, such as a diffusely reflective polarizer, is
provided. Such a contrast enhancing filter can, for example,
provide higher display brightness with equal contrast when compared
to conventional contrast enhancing filters. Contrast enhancing
filters are often used on emissive information displays, many of
which are based on an inorganic or organic light emitting material
which is excited in an addressable matrix to form an image. The
light emitting material, e.g., phosphor, and backing typically is a
good reflector of visible light. As a result, without a contrast
enhancing filter, the reflectivity of the light emitting material
can cause the display to "wash-out" under conditions of high
ambient illumination.
[0069] A conventional CE filter shown with an emissive element is
illustrated in FIG. 5A. The conventional CE filter 500 typically
includes a transparent material, e.g., tinted polarizer 510, with a
moderately high absorptivity for visible light. Light emitted from
the emissive element 512 passes through the tinted absorber 510
once, whereas ambient light must pass through it twice. By way of
example, a sheet 510 absorbing 50% of visible light will reduce
emitted light by 50% and ambient diffuse and non-diffuse glare by
75%. In practice, the reduction is somewhat higher since the
effective reflectivity of the emissive 512 element is usually less
than 100% (e.g., due to phosphorescence and wavelength shifting).
In the above example, contrast is increased by 2 fold. The
conventional CE filter 500 may further include an absorbing
polarizer 514 with or without a tint. The principle of operation is
very similar to the simple tinted situation.
[0070] While the conventional CE filters using absorbing polarizers
improve contrast, they also substantially reduce brightness. The
reduction in brightness can significantly degrade the appearance of
the display. Therefore, a need in the display industry is a
contrast enhancing layer that has a relatively high brightness.
[0071] FIG. 5B illustrates an exemplary display which includes a
contrast enhancing (CE) filter having a reflecting polarizer in
accordance with an embodiment of the invention. The reflecting
polarizer may, for example, be a diffusely reflecting polarizer.
The example display 550 includes an emissive element 560, such as
phosphor, for example, and a CE filter 570, along with optional
tinted layer 572. The example CE filter 570 includes an absorbing
polarizer 574 and a reflecting polarizer 576 typically aligned for
highest transmission. The absorbing polarizer 574 and reflecting
polarizer 576 may be provided as a laminate, for example.
Typically, the laminate is intimately attached to the emissive
element with the reflective polarizer on the side towards the
emissive element. The emissive element 560 is typically built
directly onto the reflective polarizer 576. This can be
accomplished in evacuated displays by suitably degassing the
reflective polarizer film before sealing into the display.
[0072] One or more optional tinted layer(s) 572 may be disposed
either above or below the reflective polarizer 576, or both.
Providing a tinted layer 572 above the reflective polarizer 576, as
shown in FIG. 5B, typically increases display contrast with the
minimum effect on brightness. A tinted layer 572 disposed below the
reflective polarizer 576 will also typically increase contrast,
with a higher impact on brightness. The former position has the
advantage of reducing the distance between element 560 and DRP
576.
[0073] FIG. 5B shows two light rays interacting with the
contrast-enhanced display. One ray is display emitted light ray d.
Ray d first interacts with the reflective polarizer 576, splitting
the ray into transmitted ray d and reflected ray e. Ray d is
attenuated by the optional tint layer 572, and is transmitted by
the absorbing polarizer 574. Reflected ray e is scattered by the
emissive element 560, producing a reflected ray f. Ray f then
follows the same process as ray d. The display brightness is then
Ray d plus ray f, etc. The ambient ray a is first absorbed by the
absorbing polarizer 574, leaving about 50% of ray a transmitted.
The ray is further attenuated by the tinted absorber 572, and
transmitted by the reflective polarizer 576 to the emissive element
560. Once reflected from the emissive element 560, the attenuated
ray b follows the same process as ray d.
[0074] The reflecting polarizer 576 is typically positioned closer
to the emissive element than the absorbing polarizer 574. This can
improve the image by reducing the distance between the reflecting
polarizer and the emissive element. Since the emissive element will
typically emit light over a wide range of angles, the image could
appear diffused if the distance between the reflective polarizer
576 is significantly larger than the lateral dimensions of the
emissive element 560. In one embodiment, the distance between the
reflecting polarizer 576 and the emissive element is 3 times the
lateral distance of the emissive element or less. In another
embodiment, the distance between the reflecting polarizer 576 and
the emissive element is 2 times the lateral distance of the
emissive element or less. In a further embodiment this distance is
equal to or less than the lateral distance of the emissive
element.
[0075] The color of the tint absorber, if any, and the absorbing
polarizer, if tinted, can be optimized with displays that produce
colored light. If, for example, a display produces green light, the
tint will ideally have a relatively high absorption in the red and
blue, and a relatively low absorption in the green. This concept
may be used in full color displays by providing a matrix of the
color of the tinted sheet to match the color of the individual
emissive elements.
[0076] An emissive element may, for example, be a pixel or a
subpixel element which emits a particular color. The CE filter
using a reflective polarizer and an absorbing polarizer may be used
in a number of different systems having emissive elements. Such
systems include, by way of example, fluorescent illuminated
displays, electroluminescent displays, organic and inorganic light
emitting diode displays, vacuum fluorescent displays, field
emissive displays (FED), and plasma displays.
[0077] Additionally, while diffusely reflecting polarizers work
particularly well, the invention is not so limited. Other types of
reflective polarizers which provide linearly polarized light may be
used. These other reflective polarizers include, for example, the
multilayer reflective polarizer and the cholesteric reflective
polarizer discussed above.
[0078] Using a CE filter with a reflecting polarizer (e.g., a DRP),
a higher display brightness can be achieved for a given contrast
than with conventional CE filters without reflecting polarizers.
FIGS. 5C-5E illustrate various characteristics of the CE filter
having a reflective polarizer (hereinafter RP CE filter) of FIG. 5B
and the conventional CE filter of FIG. 5A. FIG. 5C is a graph
illustrating the relative brightness of ambient diffuse and
specular glare vs. emitted brightness as a function of tint. Curves
582 and 586 show the relative brightness of emitted and ambient
light, respectively, using the RP CE filter. Curves 584 and 588
show the relative brightness of emitted and ambient light,
respectively, using the conventional CE filter. As can be seen the
RP CE filter produces higher brightness at all tint levels.
[0079] FIG. 5D is graph illustrating the contrast ratio (i.e., the
ratio of display brightness to ambient brightness) as a function of
tint for the RP CE filter (curve 590) and the conventional filter
(curve 592). To generate the graph, ambient light and display light
were each arbitrarily set to 1 with the contrast ratio changing
with changes in the ambient light. As can be seen from the graph,
the highest contrast will be achieved at the highest level of tint.
In addition, the curves 590 and 592 substantially overlap, thus
showing that RP CE filter provides higher display brightness for
the same contrast ratio.
[0080] FIG. 5E is a graph illustrating another contrast
characteristic, ambient brightness less emission brightness, as a
function of single pass tint transmission for the two CE filters.
This contrast ratio may be used to provide an indication of the
legibility (e.g., the speed and strain involved in reading
information) of a display. Curve 594 illustrates this
characteristic for the RP CE filter and curve 596 illustrates the
characteristic of the conventional CE filter. As can be seen, the
RP CE filter provides higher contrast than the conventional CE
filter at all levels.
[0081] Diffusely reflecting polarizers of the present invention can
also be used to alter and improve the appearance and viewability of
existing backlit light valve or modulating displays, such as
backlit twisted nematic and supertwisted nematic displays. FIG. 6
illustrates a backlit display apparatus 600 which includes a light
modulating layer 606, a light cavity 610 for providing light for
illuminating the light modulating layer 606, and a DRP layer 603
disposed on a viewing side of the light modulating layer 606. The
display apparatus 600 may, for example, be an LCD with a liquid
crystal light modulating layer made up of an array of liquid
crystal elements representing pixels of a digital image. The light
cavity 610 may, for example, include a light source and usually a
light guide, for example.
[0082] Light rays 651 and 653 from the illuminator 610 are
typically unpolarized, but may have some degree of prepolarization,
and display apparatus 600 is typically provided with absorbing
polarizers 605 and 604. Light modulating layer 606 then either
transmits or blocks ray 651 in an imagewise manner, depending on
whether voltage is applied or not applied to individual pixel
elements. It has been found that interposing diffusely reflecting
polarizer layer 603 between display 620 and viewer 1 alters the
appearance of display 620 in ways which make it appear unique in
comparison to other displays. It is also possible to incorporate a
suitable amount of directionally varying transmission diffusivity
into layer 603 to adjust the angles at which the display can be
viewed, without decreasing the brightness of the display to an
unacceptable level. This can be accomplished by, for example,
controlling the amount of the dispersed phase, as described
above.
[0083] Improved viewability of information displays is not limited
to electronic displays. In a broader sense, printed matter and
graphical portrayals such as signs and billboards are also
information displays. Even more generally, it known that the
viewing of many objects, especially those requiring detailed
viewing, can be aided by use of polarized light, since light
polarized in the plane of incidence of light striking the object,
called p-polarized light, is likely to have a lower reflectivity,
and hence a lower tendency to produce glare, than the s-polarized
light, which is the light polarized perpendicular to the plane of
incidence relative to the surface of the object being viewed.
However, because of the losses of light inherent in producing
polarized light, it is sometimes difficult to produce polarized
light in an economically feasible manner in the quantities needed
for viewing large displays such as signs and billboards, or for
general room lighting. It has been found, however, that diffusely
reflecting polarizers can be used to produce light which retains
many of the benefits of polarized light while still utilizing
substantially all of the original, unpolarized, light.
[0084] FIG. 7A-B illustrate a lighting apparatus in accordance with
another embodiment. The exemplary lighting apparatus 700 may, for
example, be an overhead lighting system used in a room, such as an
office. The example lighting apparatus 700 includes a light source
707 and a reflector 708. The light source 707 typically provides
unpolarized light to the reflector 708. The light source 707 may
include a reflective backing and may be arranged to direct lighting
substantially only in directions toward the reflector 708. The
illustrated reflector 708 specularly reflects light 705 of a first
polarization (P1) to provide P1 light with a first distribution and
diffusely reflects light 706 of a second, different polarization
(P2) to provide P2 light with a second distribution different than
the first distribution. The different polarizations and
distributions may be used in different manners depending on the
application.
[0085] In the example embodiment, as best illustrated in FIG. 7B,
the reflector 708 includes a diffusely reflecting polarizer 701
disposed closer to the light source 707 and a specular reflector
702 disposed further from the light source 707. The two components
701, 702 of the reflector 708 may, for example, be fixedly attached
(e.g., by lamination). The diffusely reflecting polarizer is
arranged to diffusely reflect P2 light 706 and specularly transmit
P1 light 705.
[0086] In use, the light source 707 illuminates the DRP reflector
708 with light, e.g., incident ray 750. A component 703 of the
light having a first polarization P2 is transmitted by the
diffusely reflecting polarizer 701, specularly reflected by the
specular reflector 702, and specularly retransmitted through the
diffusely reflecting polarizer 701 to provide specularly reflected
P1 light 705. A component 704 of the light having a second,
different polarization P2 is diffusely reflected by the diffusely
reflecting polarizer 701 to provide diffusely reflected light 206
having a second distribution different than the first
distribution.
[0087] The reflector 708 may be disposed to curve about the light
source 707 such that the specularly reflected P2 light 705 has a
substantially uniform distribution and diffusely reflected P1 light
has a scattered distribution. The reflector 708 may disposed around
the light source 707 so that it focuses or directs light in to a
concentrated area. In this case, P1 light 705 can be used to
provide concentrated polarized lighting of one polarization, while
diffusely reflected P2 light 706 can be used to provide general
room lighting having an orthogonal polarization. In this manner,
both polarizations of light from source 707 are utilized, while the
benefits of polarization for lighting for a particular task
requiring higher light intensity in a smaller area are
retained.
[0088] In one particular embodiment, the diffusely reflected light
of the first polarization is p-polarized light
(vertically-polarized light) and the specularly reflected light of
the second, different polarization is s-polarized light
(horizontally-polarized light). When used as a ceiling light, the
reflector 708 may be arranged to direct the s-polarized light
toward the floor. In this manner, the s-polarized light which
contributes to glare is directed to a location which minimized
glare. On the other hand, the p-polarized light is scattered to
provide general ambient light for the room.
[0089] The lighting apparatus may further include reflective
louvers 709 arranged to specularly reflect P1 light and diffusely
reflect P2 light. Each reflective louver 709 may include, on one or
both sides, a DRP layer arranged to diffusely reflect P1 light and
specular transmit P2 and a specular reflector disposed behind the
DRP layer and arranged to specularly reflect P2 light, similar to
reflector 708. The louvers 709 typically are pivotally mounted to
the lighting apparatus frame to allow the direction of reflected
light, and in particular the specularly reflected light, to be
controlled.
[0090] Where the louvers 709 (and reflector 708 as noted above) are
configured to specularly reflect s-polarized light and diffusely
reflect p-polarized light, the louvers 709 may be pivoted so that
the s-polarized light, which causes glare, is specularly reflected
in a direction which minimizes glare, e.g., toward the floor. The
p-polarized light, which contributes little to glare, is
advantageously diffusely transmitted to provide, e.g., general room
lighting.
[0091] The louvers 709 are typically positioned to receive light
from the light source 707 via reflector 708. In the example
embodiment, the light is received via a reflector 708 having a DRP
layer for diffusely reflecting P2 light (e.g., p-polarized light)
and a specular reflector for specularly reflecting P1 light (e.g.,
s-polarized light). In alternate embodiments, a reflector 708 which
simply specularly reflects may be used with the louvers 709
functioning as the only diffusely reflecting and specularly
reflecting element.
[0092] While a DRP/specular reflector louvers 709 and reflectors
708 are illustrated and discussed above, the invention is not so
limited. Other combinations of specular and diffusely reflecting
material may be used for the reflector 708 and/or louvers 709 and
are intended to fall within the scope of the invention.
[0093] In one alternate embodiment, either or both of the
components (i.e., the reflector 708 and/or louvers 709) includes a
multilayer reflecting film disposed closer to the light source and
a diffusely reflecting surface, disposed further from the light
source. In use, the multilayer reflecting film specularly reflects
P1 light (e.g., s-polarized light) and transmits P2 light (e.g.,
p-polarized light). The diffusely reflecting surface diffusely
reflects P2 light, which is retransmitted by the multilayer
reflecting film to provide diffusely reflected P2 light. The
diffusely reflecting surface may, for example, be a textured metal
surface.
[0094] In another embodiment, either or both of the components
includes a multilayer reflective film, having one or two structured
surfaces for diffusely reflecting P2 light (e.g., p-polarized
light), and a specular reflector, disposed further from the light
source, for specular reflecting P1 light (e.g., s-polarized light).
The P1 light is then retransmitted by the multilayer film to
provide specularly reflected P1 light.
[0095] FIGS. 8A-8D illustrate security labels using one or more DRP
layers in accordance with further embodiments of the invention.
Referring now to FIG. 8A, example security label 890 comprises
label portion 800 and security portion 810. Label portion 800
comprises information portion 804, which might be, for example, a
paper or film substrate which carries printed, graphic, or other
information. Information layer 804 may be attached, by means of
adhesive layer 805, to protective layer 806 for example. Protective
layer 806 may be permanently attached to information layer 804,
e.g., where the adhesive layer 805 is a permanent adhesive.
Alternatively, adhesive layer 805 can be a pressure-sensitive
adhesive, and layer 806 can be a removable adhesive liner which
protects layer 805 until the label 890 is ready to be attached to a
package or other substrate. In the event that protective layer 806
is a permanent protective layer, additional adhesive layer 807 can
be provided to enable the label to be attached to the substrate to
be labeled.
[0096] Security portion 810 of label 890 comprises a first
diffusely reflecting polarizing layer 801a, aligned in a first
direction, and a second diffusely reflecting polarizing layer 801b,
aligned in an orthogonal direction, so as to form a pair of crossed
diffusely reflective polarizers. In addition, protective layer 803
can be provided.
[0097] In use, the authenticity of label 890 can be determined by
viewing the label from a first position 1, which produces a hazy
view of the information carried on information layer 804, and then
viewing the label at a grazing angle, as indicated by second
position 3, in which case the information becomes more clear.
Authentication may further be aided by incorporating into
information layer 804 some small or intricate printing or other
graphics which would be sensitive to the haze experienced when
viewing an authentic label from position 1.
[0098] Referring to FIG. 8B, an alternative embodiment results from
inserting clear spacer layer 809 between information layer 804 and
first diffusely reflecting polarizer layer 801a. Preferably, layer
809 is air or other fluid material which can be excluded from
between polarizing layer 801a and information layer 804 by the
application of pressure to protective layer 803. Prior to
application of pressure, viewing of information layer 804 from
either position 1 or position 3 is blocked by security portion 820,
which includes clear layer 809. With pressure applied, so that
layer 809 is eliminated, the situation depicted in FIG. 8A occurs,
wherein information layer 804 of an authentic label is hazy, though
visible, from position 1, and clearly visible from position 3.
Suitable pressure can be applied by a transparent plate, or by a
suitable ring or other device containing an aperture through which
information layer 804 can be viewed during the application of
pressure. Suitable fluid materials for layer 809 include air or
other gases, as well as clear liquids. Layers 804 and 801a can be
held apart when pressure is not applied by mechanical means, such
as by incorporating a slight waviness into these layers, or by
fluid pressure, if layer 809 is made of a fluid which can be
pressurized. It will be appreciated that providing a suitable vent
or reservoir for fluid excluded from layer 809 is also useful.
[0099] Security labels using DRPs can also be made which employ a
separate viewing device, which is used with the label by the person
authenticating it. Referring to FIG. 8C, viewing layer 802 can be
any type of polarizing layer, such as an absorbent polarizer or
other polarizing material. The distance d between viewing layer 802
and protective layer 803 is not critical, and can be any convenient
distance which allows viewer 1 to read information layer 804. Since
viewing layer 802 is reusable, it is not subject to the same cost
constraints as a disposable layer provided with the label would be.
Security layer 830 comprises diffusely reflecting polarizer layer
801 and protective layer 803. Viewer 1 views information layer 804
through viewing layer 802 and first views information layer 804 in,
for example, an orientation in which the transmission axis of
viewing layer 802 is orthogonal to the transmission axis of layer
801. Viewed in this manner, information layer 804 of an authentic
label appears hazy. Viewing layer 802 is then rotated to an
orientation in which its transmission axis is parallel to the
transmission axis of layer 801, whereupon information layer 804 of
an authentic label appears clear.
[0100] In yet another embodiment, portrayed in FIG. 8D, security
portion 840 comprises clear spacer layer 809, diffusely reflecting
polarizer layer 801, and protective layer 803. Viewer 1 then views
information layer 804 through viewing layer 802, which is oriented,
for example, with its transmission axis orthogonal to the
transmission axis of layer 801. In this case the view of
information layer 804 is completely blocked, rather than being
merely hazy, as it was when spacer layer 809 was absent, as was the
case in the previous example, portrayed in FIG. 8C. Viewing layer
802 is then rotated to an orientation in which its transmission
axis is parallel to the transmission axis of layer 801, whereupon
the information layer 804 appears clear, as it did in the previous
example.
[0101] It will be appreciated that protective layer 803 is optional
in the above embodiments, and that in some applications of the
invention, layer 801 may be sufficiently durable to be used without
additional protection. Other variations on the above embodiments
will be readily apparent to those of ordinary skill in the art.
[0102] Electroluminescent panels are a convenient and efficient
source of light for many applications, due to their compactness and
light weight. Many such applications require, in addition, that the
light panel produce polarized light. One example of this
requirement is the liquid crystal display. There is therefore a
need to efficiently produce polarized ray using such sources,
without adding excessive weight or size to the system.
[0103] Referring to FIG. 9, an electroluminescent panel 900 using a
diffusely reflecting polarizing layer 901 for providing polarized
light is provided. In operation, a light emitting layer 903 (e.g.
phosphor layer) emits light when a voltage is applied between
transparent electrodes 902 and 904 by means, for example, of power
source 910. Layer 903 emits light in all directions, so reflector
905 may be added to direct light in the general direction of DRP
layer 901. It will be appreciated that electrode 904 could be a
metallic reflective electrode, thereby obviating the need for
separate reflector 905. Light emitted by emissive layer 903 is
transmitted through transparent electrode 902 to diffusely
reflecting polarizing layer 901, which transmits light 906, having
polarization P1, and which diffusely reflects light 907 having
polarization P2. Light 907 is further diffused and reflected, with
changes in polarity, with portions of it eventually emerging from
layer 903 as light 906', which also has polarity P1. A portion 907'
is again diffusely reflected back into layer 903, where it again
undergoes changes in polarization, due to diffusion, reflection,
and other polarization-altering phenomena, until it eventually
emerges from layer 903 and is transmitted as light 906''. As a
result of this recycling of light, the amount of properly polarized
light emitted by electroluminescent panel 900 is increased. It may
be useful, in some cases, to incorporate into layer 903, in
addition to the emissive phosphor material, materials to increase
the reflection and polarization-altering effects of emissive layer
903.
[0104] The DRP layer 901 and emissive layer/reflector may further
be optimized to recycle light. For example, the DRP layer 901 may,
for example, substantially depolarize diffusely reflected light to
facilitate light recycling with an emissive layer having less
depolarization characteristics. Alternatively, the angular
depolarization characteristics of the two components may be set
such that the emissive layer significantly depolarizes light at
incident angles containing relatively large amounts of
non-depolarized light and vice versa, as discussed above.
[0105] As noted above, the present invention is applicable to a
number of different devices using diffusely reflecting polarizers.
Accordingly, the present invention should not be considered limited
to the particular examples described above, but rather should be
understood to cover all aspects of the invention as fairly set out
in the attached claims. Various modifications, equivalent
processes, as well as numerous structures to which the present
invention may be applicable will be readily apparent to those of
skill in the art upon review of the present specification. The
claims are intended to cover such modifications and devices.
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