U.S. patent application number 13/746450 was filed with the patent office on 2013-05-30 for reflective display system with enhanced color gamut.
This patent application is currently assigned to 3M INNOVATIVE PROPERTIES COMPANY. The applicant listed for this patent is 3M Innovative Properties Company. Invention is credited to Gregory G. Jager, Manoj Nirmal, Michael F. Weber.
Application Number | 20130135556 13/746450 |
Document ID | / |
Family ID | 44258289 |
Filed Date | 2013-05-30 |
United States Patent
Application |
20130135556 |
Kind Code |
A1 |
Nirmal; Manoj ; et
al. |
May 30, 2013 |
REFLECTIVE DISPLAY SYSTEM WITH ENHANCED COLOR GAMUT
Abstract
A display system includes a reflective display panel and a light
source tailored to enhance the color gamut of the system. The
panel, which may be a Cholesteric liquid crystal display panel,
includes an array of reflective pixels, each pixel comprising a
first, second, and third subpixel of different first, second, and
third colors. The light source illuminates a front of the display
panel with source light to enable observers to view images formed
by the panel. The light source includes a lamp and an enhancing
element. The lamp, which may be a metal halide lamp, emits lamp
light that includes the first, second, and third colors. The
enhancing element may be an optical filter, a supplemental LED
light source or other light source, or both. The enhancing element
enhances the system color gamut, for example, by increasing the
color gamut area relative to illumination with the lamp alone.
Inventors: |
Nirmal; Manoj; (Saint Paul,
MN) ; Jager; Gregory G.; (Oakdale, MN) ;
Weber; Michael F.; (Shoreview, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M Innovative Properties Company; |
St. Paul |
MN |
US |
|
|
Assignee: |
3M INNOVATIVE PROPERTIES
COMPANY
ST. PAUL
MN
|
Family ID: |
44258289 |
Appl. No.: |
13/746450 |
Filed: |
January 22, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12685330 |
Jan 11, 2010 |
8384851 |
|
|
13746450 |
|
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Current U.S.
Class: |
349/61 |
Current CPC
Class: |
G02F 1/133603 20130101;
H04N 9/3108 20130101; G02F 2203/34 20130101; G02F 1/133621
20130101; G02F 2001/13478 20130101; G02F 2001/133616 20130101; G02F
1/1336 20130101; H01J 61/38 20130101; H04N 9/3158 20130101; G02B
5/28 20130101; G02F 1/13476 20130101; G02F 2001/133624 20130101;
G02F 1/13718 20130101 |
Class at
Publication: |
349/61 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Claims
1. A display system, comprising: a display panel having a front
surface and a back surface, the display panel further including
electronically addressable reflective pixels, each pixel comprising
a first, second, and third subpixel of different first, second, and
third colors, respectively,. the subpixels being separately
electronically addressable; and a light source configured to
illuminate the front surface of the display panel with broadband
source light, such that the broadband source light is selectively
reflected by the pixels to provide a color image to an observer
disposed in front of the display panel; wherein the light source
comprises a first lamp that emits a first broadband lamp light, the
first broadband lamp light including light components of the first,
second, and third colors; wherein a combination of the first
broadband lamp light and the display panel provide a first color
gamut associated with reflection of the first broadband lamp light
selectively from the first subpixel, and with reflection of the
first broadband lamp light selectively from the second subpixel,
and with reflection of the first broadband lamp light selectively
from the third subpixel; wherein a combination of the broadband
source light and the display panel provide a second color gamut
associated with reflection of the first broadband source light
selectively from the first subpixel, and with reflection of the
first broadband source light selectively from the second subpixel,
and with reflection of the first broadband source light selectively
from the third subpixel; and wherein the light source includes a
first enhancing element such that the second color gamut has an
area greater than that of the first color gamut.
2. The system of claim 1, wherein the first lamp comprises a metal
halide lamp.
3. The system of claim 1, wherein for each of the pixels, the
first, second, and third subpixels have the same size as the
pixel.
4. The system of claim 1, wherein the display panel comprises a
Cholesteric liquid crystal display (ChLCD) panel.
5. The system of claim 1, wherein the area of the second color
gamut is at least 10% greater than that of the first color
gamut.
6. The system of claim 1, wherein the area of the second color
gamut is at least 20% greater than that of the first color
gamut.
7. The system of claim 1, wherein the area of the second color
gamut is at least 30% greater than that of the first color
gamut.
8. The system of claim 1, wherein the first enhancing element
comprises a first filter disposed to filter the first broadband
lamp light.
9. The system of claim 8, wherein the first filter comprises a
multilayer optical interference filter.
10. The system of claim 8, wherein the first filter comprises an
absorptive filter.
11. The system of claim 8, wherein the first filter selectively
blocks light from 570 to 590 nm.
12. The system of claim 8, wherein the light source further
includes a second enhancing element, the second enhancing element
comprising one or more light-emitting diode (LED).
13. The system of claim 12, wherein the one or more LED emits
visible light whose peak wavelength is greater than 600 nm.
14. The system of claim 13, wherein the first filter transmits
green and blue portions of the first broadband lamp light and
blocks a red portion of the first broadband lamp light.
15. The system of claim 14, wherein more of a red portion of the
broadband source light is provided by the one or more LEDs than by
the first lamp.
16. The system of claim 15, wherein substantially all of the red
portion of the broadband source light is provided by the one or
more LEDs.
17. The system of claim 1, wherein the first enhancing element
comprises one or more light-emitting diode (LED).
18. The system of claim 17, wherein the one or more LED emits
visible light with a peak wavelength greater than 600 nm.
19. The system of claim 17, wherein more of the broadband source
light is provided by the first lamp than is provided by the one or
more LED.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to display systems, with
particular application to reflective display systems in which the
display is illuminated from the front. The invention also relates
to associated articles, systems, and methods.
BACKGROUND
[0002] Display systems of various types are known. Many such
systems utilize a display panel that must be backlit with a large
area backlight in order for the user to perceive the image
generated by the display panel. Such systems are popular in display
screens for laptop computers, mobile communication devices, and
similar electronic devices. The backlight, which may include one or
more diffusing film, reflecting film, prismatic film, light guide,
and light source, for example, emits white light over an output
area that is substantially the same size as the display panel. The
display panel, e.g., a liquid crystal (LC) display panel, has a
matrix of individually addressable elements (referred to as picture
elements or "pixels") that can be controlled via an electronic
control unit to transmit red, green, and/or blue light from each
pixel. In many cases, the area of a given pixel in plan view is
subdivided into three smaller independently addressable areas--one
to regulate red light, one to regulate green light, and one to
regulate blue light--and these are referred to as subpixels. In
some display technologies, however, the subpixels are coextensive
with the associated pixel, i.e., they do not have a smaller area
than the associated pixel.
[0003] Display systems that operate based on reflected light,
rather than transmitted light, are less common than
transmissive-type displays. This may be due in part to
complications relating to the choice of the external light source,
its placement relative to the display panel and the viewer, and
challenges in providing adequate brightness. In some cases, ambient
daylight may be relied upon as the source of external light. In
other cases, an electrically powered light source may be used, and
mounted in a specific location designed to provide optimum
viewing.
[0004] Metal halide lamps have become increasingly popular in
commercial, residential, and industrial lighting applications. For
example, metal halide lamps are used to illuminate sports stadiums
and other athletic facilities. One reason for the popularity of
these lamps is their relatively efficient operation relative to
incandescent, fluorescent, and mercury vapor lamps, and their
ability to provide white light of suitable color temperature and
color rendering index (CRI) for many applications.
BRIEF SUMMARY
[0005] We have found that the performance of reflective display
systems can be disappointing in some respects depending on the
combination of components selected for the various system
functions. For example, depending on the type of external light
source selected and the type of reflective display panel selected,
a given reflective display system may exhibit a range of possible
output colors (referred to generally as the "color gamut" of the
system, discussed further below) which is limited relative to other
types of display systems. We have found this to be the case, for
example, even when using a white light emitting metal halide lamp
as the external light source.
[0006] We have developed several techniques for improving the color
gamut of such reflective display systems. In some cases, we
selectively filter the nominally white light source. In some cases,
we add a supplemental light source to the original light source to
boost the output at selected wavelengths. In some cases, we do
both, i.e., we add a supplemental light source and selectively
filter the light source.
[0007] The present application therefore discloses, inter alia, a
display system that includes a reflective display panel and a light
source tailored to enhance the color gamut of the system. The
panel, which may be a Cholesteric liquid crystal display panel, may
include an array of reflective pixels, each pixel comprising, for
example, a first, second, and third subpixel of different first,
second, and third colors. The light source illuminates a front of
the display panel with source light to enable observers to view
images formed by the panel. The light source includes a lamp and an
enhancing element. The lamp, which may be a metal halide lamp or
other suitable gas discharge or vapor lamp, emits lamp light that
includes the first, second, and third colors. The enhancing element
may be an optical filter, a supplemental LED light source or other
light source, or both. The enhancing element enhances the system
color gamut, for example, by increasing the color gamut area and/or
the brightness relative to illumination with the lamp alone.
[0008] We also disclose display systems that include a display
panel and a light source configured to illuminate the display panel
with source light. The display panel may have a front and back
surface, and may also include electronically addressable reflective
pixels, each pixel comprising a plurality of different colored
subpixels, e.g., a first, second, and third subpixel of different
first, second, and third colors, respectively. The light source is
configured to illuminate the front surface of the display panel
with the source light, such that the source light is selectively
reflected by the pixels to provide a color image to an observer
disposed in front of the display panel. The light source may
include a first lamp that emits a first lamp light, the first lamp
light including light components of the first, second, and third
colors. For example, if the first second, and third colors comprise
red, green, and blue, respectively, the lamp light may include
substantial emission in the red, green, and blue regions of the
spectrum, such that the lamp light is nominally white. A
combination of the first lamp light and the display panel may
provide a first color gamut, and a combination of the source light
and the display panel may provide a second color gamut.
Significantly, the light source includes a first enhancing element
such that the second color gamut has an area greater than that of
the first color gamut.
[0009] In some cases, the first lamp may be or include a metal
halide lamp. In some cases, the display panel may be or include a
reflective liquid crystal (LC) display panel, e.g., in particular a
Cholesteric liquid crystal display (ChLCD) panel, or an
electrophoretic type display.
[0010] The second color gamut may have an area on the 1931 CIE
chromaticity diagram that is at least 10%, or 20%, or 30% greater
than that of the first color gamut.
[0011] The first enhancing element may be or include a first filter
disposed to filter the first lamp light. The light source may
include a filter assembly that at least partially surrounds the
first lamp, and the first filter may be disposed on the filter
assembly. The first filter may be or include a multilayer optical
interference filter and/or an absorptive filter. The first filter
may selectively block light from 560 to 600 nm, for example.
[0012] The light source may also include a second enhancing
element, e.g., one or more light-emitting diode (LED). In some
cases the one or more LED may emit visible light whose peak
wavelength is greater than 600 nm. Alternatively, such supplemental
LED may be used as the first enhancing element in embodiments that
omit the first filter.
[0013] Related methods, systems, and articles are also
discussed.
[0014] These and other aspects of the present application will be
apparent from the detailed description below. In no event, however,
should the above summaries be construed as limitations on the
claimed subject matter, which subject matter is defined solely by
the attached claims, as may be amended during prosecution.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a perspective view of a reflective display
system;
[0016] FIG. 2 is a schematic close-up plan view of a portion of a
pixelated display panel;
[0017] FIG. 3 is a schematic side or sectional view of a light
source that may be used in a reflective display system;
[0018] FIG. 4 is a schematic perspective view of one pixel of a
reflective display panel;
[0019] FIG. 5 is a combination graph showing the spectral
reflectivity of certain reflective subpixels, and the spectral
transmissivity of certain filters used in the construction of a
reflective pixel;
[0020] FIG. 6 is a combination graph showing the spectral
reflectivities of the subpixels of FIG. 5, and the spectral
intensity of a typical metal halide lamp;
[0021] FIG. 7 is a combination graph of the spectral intensity of a
typical metal halide lamp, and the reflected intensity or radiance
of such lamp when reflected from a red, green, and blue subpixel of
a Cholesteric liquid crystal display (ChLCD) panel;
[0022] FIG. 8 is a CIE chromaticity diagram showing the color gamut
of a reflective display system that incorporates the metal halide
lamp and the Cholesteric liquid crystal display (ChLCD) subpixels
of FIG. 7;
[0023] FIG. 9 is a combination graph of the spectral intensity of a
typical metal halide lamp, and the spectral transmissivity of an
exemplary multilayer optical interference filter useable as a
filter for the light source;
[0024] FIGS. 10a-c are graphs of the spectral intensity or radiance
of a metal halide lamp as reflected from the red, green, and blue
subpixels of a Cholesteric liquid crystal display (ChLCD) panel,
and as filtered by the filter of FIG. 9;
[0025] FIG. 11 is a CIE chromaticity diagram showing the
improvement to color gamut that can be achieved with the filter of
FIG. 9;
[0026] FIG. 12a is a schematic side or sectional view of a portion
of a light source that includes a lamp and a filter assembly;
[0027] FIG. 12b is a schematic side or sectional view of an
alternative light source to that of FIG. 12a;
[0028] FIG. 13 is a combination graph of the spectral intensity of
a typical metal halide lamp, and the spectral transmissivity of
exemplary absorptive filters that may be used in the light
source;
[0029] FIGS. 14a-c are graphs of the spectral intensity or radiance
of a metal halide lamp as reflected from the red, green, and blue
subpixels of a Cholesteric liquid crystal display (ChLCD) panel,
and as filtered by one of the filters of FIG. 13;
[0030] FIG. 15 is a CIE chromaticity diagram showing the
improvement to color gamut that can be achieved with the same
filter used in FIGS. 14a-c;
[0031] FIG. 16 is a graph of the spectral intensity or radiance of
a metal halide lamp as reflected from a red subpixel of a
Cholesteric liquid crystal display (ChLCD) panel, and where the
metal halide lamp is supplemented with light from a red LED;
[0032] FIG. 17 is a combination graph of the spectral intensity of
a typical metal halide lamp, and the spectral transmissivity of a
filter that may be suitable for use in a system that incorporates
red LED supplemental light sources; and
[0033] FIGS. 18a-c are graphs of the spectral intensity or radiance
of a metal halide lamp that has been filtered with the filter of
FIG. 17 and supplemented with red LED light, as reflected from the
red, green, and blue subpixels of a Cholesteric liquid crystal
display (ChLCD) panel.
[0034] In the figures, like reference numerals designate like
elements.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0035] In the following detailed description we describe, among
other things, display illumination systems that improve the optical
performance of a reflective display. The appearance--e.g. the
brightness, contrast, and color gamut--of a reflective display may
be determined by the product of the illumination spectrum of the
light source, and the reflectance spectrum of the display medium.
Desirably, the illuminant spectrum is matched to the display
reflection spectrum for optimal performance. Some of the light
emitted by metal halide lamps, and potentially by other types of
lamps and light sources, undesirably occurs at wavelengths that
fall between, or overlap, the response curves of different colored
subpixels of the display system. This can produce an inferior color
gamut for the system. We propose one or more filters that
selectively remove such undesirable spectral components, in order
to significantly improve the color gamut. In addition, the light
source desirably has a sufficient intensity at the primary colors
(e.g., red, green, and blue) of the display medium to maximize the
accessible color gamut of the display. This may be achievable with
a single illuminant, but is more feasible with a hybrid
illumination system that combines the strengths of two or more
illumination technologies. This may improve the optical performance
and maximize the cost efficiency (cost/lumen) of the overall
system.
[0036] In FIG. 1, a reflective display system 110 is shown in
perspective view. The system is depicted as a relatively large area
display made for an outdoor environment. The system may thus use
materials and components that are suitable for use in outdoor
display applications. Alternatively, the display system may be
designed for indoor use, or it may be made in a smaller format
suitable for mobile applications in which it may be carried from
place to place by a user.
[0037] The system 110 includes a reflective display panel 112 and
some external light sources 114a, 114b, collectively referred to as
a light source 114. The display panel may include or may be coupled
to an electronic controller (not shown) that controls the images
displayed on the panel 112. This control is accomplished by
controlling the reflective state of a multitude of pixels arranged
in an orderly array over an extended active area or output surface
112a of the panel 112. Any given pixel can be controlled to reflect
light of a particular primary color, such as red, green, or blue,
or to reflect none, some, or all of these colors so as to cover a
range from substantially black (non-reflective) to substantially
white (reflecting over substantially the entire visible spectrum),
and many colors in between, including each of the primary colors
themselves. When illuminated by a white light source, the
appropriate portion(s) of the visible spectrum are reflected by
each pixel so that all of the pixels in the array collectively form
the desired image in full color. The reflected light which forms
the image is perceived by an observer 116 positioned generally in
front of the display panel 112.
[0038] The output surface 112a of panel 112 may correspond to a
front surface of the panel, beneath or behind which lies a back or
rear surface of the panel. In contrast to many display systems that
rely exclusively on a backlight (disposed behind the back surface
of the display panel) to make the image visible to observers, the
system 110 need not include such a backlight to make the image
visible. Instead, the system may, if desired, rely only on one or
more external light sources such as light source 114, which
illuminate the front surface, rather than the back surface, of the
panel.
[0039] FIG. 2 is a schematic close-up plan view of a portion of a
pixelated display panel 212, which may be the same or similar to
the reflective panel 112 of FIG. 1. The view of FIG. 2 may be a
front view of the panel 212. The panel 212 comprises an ordered
array of individually addressable pixels 215, each of which can be
controlled to reflect light of a particular primary color, or to
reflect none, some, or all such colors as described above so as to
cover a range from black to white, and many colors in between. In
the embodiment of FIG. 2, the subpixels of each pixel are not
separately shown because they are assumed to be substantially
co-extensive with their respective pixel. Thus, for example, for
each pixel 215, there may be a separate red, green, and blue
subpixel, each having the same size as the pixel 215, and arranged
in a sandwich construction discussed further below in connection
with FIG. 4.
[0040] The selectively controllable reflectivity of the display
panel pixels relies on a source of broadband (e.g. "white") light
which can thus be selectively reflected. FIG. 3 is a schematic side
or sectional view of an exemplary light source 310 that may be used
for this purpose in a reflective display system. The source 310
includes a lamp 312, lamp housing 314, reflector 316, filter plate
318, and lenslet cover 320, all situated on a suitable light source
fixture 322. Note that not all of these elements are required, and
other suitable light source designs may omit at least some of the
elements shown in the embodiment of FIG. 3, and may include other
elements not shown in FIG. 3. A discussion of filters, which may be
disposed in or on the filter plate, or on the lamp 312, lamp
housing 314, reflector 316, and/or lenslet cover 320, or elsewhere
in the light source, is provided below.
[0041] The lamp 312 is typically electrically powered, and converts
the electricity into emitted light referred to herein as lamp
output light, or simply lamp light (shown schematically in the
figure by arrows 324). The lamp light 324 is preferably broadband,
e.g., emitting at wavelengths extending at least over substantially
the entire visible spectrum, particularly including the primary
colors that are reflected by the subpixel elements. However, the
broadband lamp light 324 need not be, and typically is not,
uniformly distributed over the visible spectrum. On the contrary,
exemplary lamps 312, including but not limited to metal halide
lamps, emit light in narrow lines or bands that are scattered
irregularly over the visible spectrum as a function of the
composition of the lamp. In exemplary display systems discussed
herein, characteristics of the irregular lamp light 324 are such
that, if the lamp 312 is used by itself to illuminate the
reflective display with the lamp light 324, the range of perceived
colors that can be obtained is characterized by a first color
gamut. However, if an enhancing element is included in the light
source, as discussed elsewhere herein, the light source provides a
source output light, or simply source light (shown schematically in
the figure by arrows 326), whose spectral composition differs
substantially from that of lamp light 324. When the reflective
display is illuminated with this source light 326, the range of
perceived colors that can be obtained is characterized by a second
color gamut that is enhanced relative to the first color gamut. For
example, the second color gamut may have an area, as plotted on a
CIE chromaticity diagram, that is at least 10%, or 20%, or 30%
greater than that of the first color gamut. The spectral
composition of the source light 326 may differ from that of the
lamp light 324 in a subtractive way, by filtering the lamp light at
selected wavelengths, or in an additive way, by supplementing the
lamp light with light emitted by an LED source or other suitable
source, or in both a subtractive way and an additive way.
[0042] One reflective display technology of particular interest,
but not the only reflective display technology contemplated herein,
is referred to as a Cholesteric Liquid Crystal (ChLC) display. ChLC
displays generally comprise a nematic liquid crystal and a chiral
additive blended together to spontaneously form a helical structure
with a well defined pitch. This pitch determines the wavelength of
light reflected by and hence the color of the material. The color
can be adjusted by varying the ratio of the nematic liquid crystal
and chiral components. A pixel in a ChLC display can be switched
between its planar reflective (colored) state and its
semi-transparent focal conic state, by application of an
appropriate drive signal.
[0043] Unlike a conventional nematic liquid crystal (NLC) based
display, a ChLC display does not require polarizers or color
filters, resulting in a simpler device construction at a
potentially lower cost. In a full color NLC display, the RGB
subpixels are arranged side-by-side. As result, only about a third
of the viewing area is occupied by a given set of subpixels of a
given primary color. In contrast, each subpixel in a ChLC display
reflects a single primary color while transmitting the other
primary colors. A full color ChLC display can be constructed by
stacking a set of RGB panels, with the individual RGB subpixels
overlapped on top of each other and reflecting different regions of
the spectrum.
[0044] One embodiment of a full color ChLC pixel 410 is shown in
schematic perspective view in FIG. 4. The pixel 410 has a front
surface 410a and a back surface 410b. Source light from the
external light source impinges upon the front surface 410a. In the
figure, the reference numerals have the following meanings
[0045] 412, 424: clear substrates;
[0046] 414: blue-reflecting ChLC layer;
[0047] 416: yellow-transmitting filter layer;
[0048] 418: green-reflecting ChLC layer;
[0049] 420: red-transmitting filter layer;
[0050] 422: red-reflecting ChLC layer;
[0051] 426: black absorbing layer; and
[0052] 430a-f: electrode layers used to control the reflectivities
of the respective ChLC layers.
[0053] Each subpixel may consist essentially of the appropriate
ChLC mixture sandwiched between two transparent electrodes, which
may comprise indium tin oxide (ITO), for example. Thus, layers 414,
430a, 430b may comprise a blue-reflecting subpixel, layers 418,
430c, 430d may comprise a green-reflecting subpixel, and layers
422, 430e, 430f may comprise a red-reflecting subpixel. The
depicted construction may comprise four substrates (layers 412,
416, 420, 424), where the two interior substrates (layers 416, 420)
are coated with ITO on both sides, and the two exterior substrates
(layers 412, 424) are coated with ITO on just one side. Incident
light enters through the front surface 410a, and the individual
subpixels reflect the red, green, and blue (R, G, and B) primary
colors or spectral regions. Any remaining light is absorbed by the
black absorber at the back of the stack. Individual subpixels can
be switched continuously between a reflective planar and
semi-transparent focal-conic state using the appropriate drive
signal, thus enabling a full color display.
[0054] One drawback of ChLC-type reflective displays is the
relatively broad nature of the reflectance spectra of the
individual subpixels, which can result in overlapping spectral
response and poor color saturation. The color saturation can be
improved to some extent by introducing red and yellow color filters
in the construction, as provided in the construction of FIG. 1 by
layers 420 and 416, respectively. These filters serve to trim or
block the short wavelength edges of the red- and green-reflecting
ChLC reflection spectra. In this regard, FIG. 5 provides a
combination graph that shows the spectral reflectivity of exemplary
red-, green-, and blue-reflecting ChLC subpixels as curves 510,
512, 514 respectively. These curves, which are centered at about
660, 540, and 480 nm, are drawn to scale according to the
normalized reflectance scale on the left-hand side of the figure.
Superimposed on these curves are curves 516 and 518, which
represent the measured (single-pass) transmission of exemplary
yellow-transmitting and red-transmitting filter layers,
respectively, such as layers 416, 418. The curves 516, 518 are
drawn to scale according to the percent transmission scale on the
right-hand side of the figure. By narrowing the observed reflection
spectra, color filters such as 416, 418 can increase the color
gamut of a ChLC-based reflective display system significantly.
[0055] As an alternative to ChLC technology, other suitable
reflective displays may comprise electrophoretic type displays.
[0056] As mentioned already above, the appearance of a reflective
display can also strongly depend on characteristics of the
illumination source. One class of illumination sources of
particular interest is the class of so-called "metal halide" lamps.
Such lamps produce light by passing an electric current through a
gas/vapor mixture. In typical metal halide lamps currently
available, a sealed transparent tube made of fused silica or other
suitable material includes a noble gas such as argon under high
pressure. The tube also includes mercury, and a variety of metal
halides (typically iodides or bromides) of metals such as scandium,
sodium, thallium, indium, sodium, dysprosium, tin, holmium,
thulium, gallium, and/or lead. When the lamp is initially turned
on, an electric arc is set up through the noble gas, across two
electrodes that extend into the tube. Heat generated by the arc
then slowly vaporizes the mercury and the metal halides, which emit
light as the pressure and temperature in the tube increase further
to steady-state operating levels. The mixture of metals used in the
tube control or determine the output spectrum of the lamp light.
Typically, the output spectrum comprises a number of sharp lines
unevenly distributed over the visible spectrum. The foregoing
description is not meant to be limiting, and any developments in
metal halide lamps that may occur after the filing of this
application are intended to be encompassed by the term "metal
halide" lamp or source.
[0057] FIG. 6 is a combination graph showing the spectral
reflectivities of the subpixels of FIG. 5, and the spectral
intensity of a typical metal halide lamp. Since the reflectivities
of the subpixels are the same as in FIG. 5, the same reference
numerals 510, 512, 514 are used for the red-, green-, and
blue-reflecting ChLC subpixels. These curves are drawn to scale
according to the normalized reflectance scale on the left-hand side
of the figure. Superimposed on these curves is a curve 610 which
represents the lamp output of an exemplary metal halide lamp. The
curve 610 is drawn to scale according to the intensity scale (in
arbitrary units) on the right-hand side of the figure. Significant
spectral lines are identified by a decimal number representing the
peak wavelength in nanometers, which decimal numbers are enclosed
in parenthesis to distinguish them from ordinary reference
numerals.
[0058] An ideal source would have narrow spectral features of
sufficient intensity, centered at the R, G, & B primary colors
of the subpixels of the display, to provide acceptable system
brightness and color gamut. In the case of the metal halide source
depicted in FIG. 6, spectral features at about 474 nm and those
from about 535 to 550 nm satisfy this criterion. On the other hand,
the blue-green line at about 510 nm lies between the display blue
and green primary colors (curves 514, 512). This imparts a greenish
hue to light reflected by the blue subpixel and a bluish hue to
light reflected by the green subpixel, hence degrading color
saturation and gamut. An appropriate yellow color filter (see FIGS.
4 and 5) may be used to partially block this spectral line. For
example, suitable dyed films may be obtained from CPFilms, a
subsidiary of Solutia Inc., for use as yellow-transmitting and
red-transmitting color filters. The lamp emission features from
about 570 to 592 nm lie between the display green and red primary
colors (curves 512, 510). Of particular concern is the feature at
about 592 nm. This line is present in most metal halide sources.
Due to its spectral location and high intensity, it imparts a
yellowish hue to light reflected by the green subpixel and
desaturates light reflected by the red subpixel. Metal halide lamps
contain a mixture of substances that determine the spectral
features present in the lamp emission spectrum. One potential
solution would be to eliminate the substances that generate the
unwanted spectral features. This, however, would require the design
of a custom lamp.
[0059] The product of (i.e., the result of multiplying) the lamp
output curve 610 with each of the subpixel reflectivity curves 510,
512, 514 yields spectral information that represents the intensity
or radiance of light that is reflected by each ChLC subpixel when
using a metal halide lamp as the source of illumination.
Alternatively, a reflective display system can be set up, and light
at various points in the system can be analyzed with a
spectrophotometer or other suitable device. This was done using a
metal halide lamp as the light source, and a particular ChLC panel,
referred to hereinafter as "the RGB ChLC panel", as the reflective
display panel. The RBG ChLC panel had a construction similar to
that of FIG. 4, with red, green, and blue subpixels, and with a
red-transmitting filter (layer 420), but no yellow-transmitting
filter (layer 416) was included in the construction. This panel was
controlled with suitable electrical signals applied to the various
electrodes so as to activate only the red subpixels, or only the
green subpixels, or only the blue subpixels as needed during
testing. Light that was reflected from the panel could then be
analyzed under each of these conditions. This was done, and the
resulting curves, labeled 710, 712, 714 for light reflected by the
red-, green-, and blue-reflecting state of the RBG ChLC panel,
respectively, are shown in FIG. 7. The curves 710, 712, 714 are
drawn to scale according to the radiance scale on the left-hand
side of the figure. Superimposed on these curves is the measured
spectral output 716 of the metal halide lamp used in the setup. The
output 716 is drawn to scale according to the intensity scale (in
arbitrary units) on the right-hand side of the figure.
[0060] The sharp features seen in FIG. 7 in the curves 710, 712,
714 are similar to those present in the metal halide lamp light,
which is included for reference (curve 716). While each of the
primary color subpixels, when activated, highlights those spectral
features of the lamp centered around its respective reflection
peak, features from all across the illumination spectrum are
present in each subpixel curve to some extent. This is due to the
broad reflection spectra of the ChLC subpixels, and the long tails
that extend far out on both sides of the reflection peaks as shown
in FIGS. 5 and 6. Broadband front surface and interfacial
reflections in the stack (Fresnel reflections) also contribute to
this.
[0061] The net effect is to desaturate the primary colors reflected
by the subpixels, and to limit the color gamut of the display
system. The color gamut of the described display system, which
again uses a metal halide lamp having a lamp output as shown in
FIG. 7 as the illumination source, and the RGB ChLC panel as the
reflective display panel, is shown in FIG. 8. This figure makes use
of the well-known 1931 CIE chromaticity diagram, promulgated by the
Commission International de l'Eclairage (International Commission
on Lighting) or "CIE". Those skilled in the art will be familiar
with the CIE chromaticity diagram, and will recognize it as a
convenient tool or standard used to characterize and quantify
perceived colors. The color (or "chromaticity" or "chromaticity
coordinates") of a light source or article can be precisely
measured or specified by a point or region expressed in terms of
one or more chromaticity coordinates (x,y) on the CIE chromaticity
diagram, using the CIE 1931 standard colorimetric system. Such a
chromaticity diagram is shown in FIG. 8. For a color display, the
set of all possible colors the display can generate is represented
by a region, zone, or area on the chromaticity diagram referred to
as the "color gamut" of the display. For a tri-color based display
(i.e., a display that uses exactly three distinct subpixel colors,
e.g., red, green, and blue), the color gamut is triangle-shaped,
with each corner of the triangle corresponding to the perceived
display color when only one of the subpixel colors is "on". The
color gamuts of different displays can be compared by comparing
their respective areas on the chromaticity diagram.
[0062] Thus, in FIG. 8, the triangle 810 represents the color gamut
of the above-described reflective display system. The triangle 810
has endpoints 810a, 810b, 810c, representing the color of the
system with only the red-reflecting subpixels, with only the
green-reflecting subpixels, and with only the blue-reflecting
subpixels (respectively) turned "on" or activated.
[0063] Another shortcoming with current metal halide sources is the
lack of sufficient intensity in the red region of the spectrum, as
seen in FIG. 7, for example. In spite of these issues, metal halide
sources offer significant advantages over alternative sources such
as LEDs and tungsten halogen sources. The metal halide sources
typically provide superior power efficiency (display brightness per
watt consumed by the light source), lower weight (light source
weight/display brightness), and cost (lumens per dollar, for
example). As a result, metal halide sources have become popular in
many regions for large area illumination applications such as
outdoor vinyl billboards.
[0064] As mentioned above, we propose two independent, but
combinable, techniques for overcoming the deficiencies of metal
halide sources when used as light sources in reflective display
systems. In a subtractive technique, we propose filtering the lamp
light provided by the metal halide source in one or more selective
spectral region. In an additive technique, we propose supplementing
the lamp light with one or more additional light sources, such as
LED sources of a particular color.
[0065] We first address the filtering technique.
[0066] Unwanted spectral line(s) of the lamp light may be removed
using a filter that selectively blocks such line(s), and placing
the filter at an appropriate point in the light path from the lamp
to the reflective display so as to intercept the unwanted light.
Such a filter may be or include an interference filter of
appropriate design. For example, the interference filter may
comprise a substrate on which is coated a stack of alternating
layers of high- and low-refractive index inorganic materials, such
as TiO.sub.2 and MgF.sub.2 or other suitable materials. The total
number of layers, and the thickness profile of the layers or the
optical repeat units (typically, a pair of adjacent layers), can be
tailored to reflect a given wavelength band. Alternatively, the
filter may be polymeric in construction, with tens, hundreds, or
thousands of optically thin polymer layers that combine to
selectively reflect light as desired. Again, the total number of
layers and the layer thickness profile can be tailored to
selectively reflect light as desired. See, for example, any of the
multilayer optical films made by coextrusion, casting, and
orientation (stretching) processes described in: U.S. Pat. No.
5,882,774 (Jonza et al.) "Optical Film"; U.S. Pat. No. 6,531,230
(Weber et al.) "Color Shifting Film"; and U.S. Pat. No. 6,783,349
(Neavin et al.) "Apparatus for Making Multilayer Optical Films".
Polymeric multilayer optical films that have at least one set of
birefringent layers, as well as such films that have only isotropic
layers (although less desirable), may be used.
[0067] The transmission spectrum of such a multilayer optical
interference filter of inorganic construction (Omega Optical, type
589RB35) suitable for use as a filter is shown (curve 910) in the
combination graph of FIG. 9 along with the spectral intensity of a
typical metal halide lamp (type Ushio MHR-100 D, shown by curve
912). Strictly speaking, the curve 910 represents the transmission
of the filter for normally incident light. In the figure,
significant spectral lines of the lamp are again identified by a
decimal number representing the peak wavelength in nanometers,
which decimal numbers are again enclosed in parenthesis.
[0068] The filter of curve 910 blocks the unwanted spectral lines
from about 570 to 590 nm, and has a relatively high transmission in
other regions of the spectrum. Source light that results from using
this filter to filter the lamp light of curve 912, when reflected
from the RGB ChLC panel described above (alternately controlled to
reflect red, green, and blue light by separately activating the
red, green, and blue ChLC subpixels), yields a radiance or
intensity of reflected light for the red, green, and blue
reflective states of the panel shown in FIGS. 10a, 10b, and 10c
respectively. Thus, in FIG. 10a, curve 1010 shows the reflected
intensity or radiance from the red-activated RGB ChLC panel without
the curve 910 interference filter, and curve 1012 shows the
reflected intensity with the interference filter. In FIG. 10b,
curve 1020 shows the reflected intensity or radiance from the
green-activated RGB ChLC panel without the curve 910 interference
filter, and curve 1022 shows the reflected intensity with the
interference filter. In FIG. 10c, curve 1030 shows the reflected
intensity or radiance from the blue-activated RGB ChLC panel
without the curve 910 interference filter, and curve 1032 shows the
reflected intensity with the interference filter.
[0069] The filter of curve 910 can thus be seen to substantially
eliminate the unwanted emission lines at about 570 and 590 nm. The
elimination of these lines also has a beneficial effect on the
color gamut of the system. FIG. 11 is a CIE chromaticity diagram
showing the color gamut 1110 of a (baseline) display system that
uses a metal halide lamp and the RGB ChLC panel as a reflective
display, which color gamut is similar to color gamut 810 of FIG. 8.
When a filter having the transmission of curve 910 is added to the
baseline system, the result is color gamut 1112, which is
substantially larger and thus enhanced relative to gamut 1110. In
fact, the area of color gamut 1112 is about 30% larger than the
area of color gamut 1110. In comparing the gamuts 1110, 1112, one
can see that the green subpixel (represented by the uppermost
corner of each triangle) exhibits the largest improvement in color
saturation with the addition of the blocking filter.
[0070] The spectral characteristics of interference filters are
known to change as a function of incidence angle. For example,
reflection bands (and transmission bands) tend to shift to shorter
wavelengths as the incidence angle changes from normal incidence to
more oblique angles. Thus, for example, the filter represented by
the normal incidence transmission curve 910 of FIG. 9 will
effectively block the 570 and 590 nm metal halide emission lines
for incidence angles of less than 15 degrees, but for larger
incidence angles blocking of these lines (particularly the 590 nm
line) will be weaker and may eventually become unacceptable. In
order to promote strong blocking of the undesirable emission lines
by the interference filter, the light source may include a filter
assembly that at least partially surrounds the metal halide lamp in
such a way as to limit the amount of light striking the
interference filter at unacceptably oblique angles. The filter
assembly may be composed of a transparent, rigid (or at least
self-supporting) material to which the interference filter can be
bonded, applied, or otherwise attached or coupled. Alternatively,
the interference filter itself, if it is self-supporting, may form
the filter assembly. The geometry of the filter assembly may be
such that light from the lamp that passes through the filter
assembly impinges upon the filter assembly at normal or near-normal
incidence angles, e.g., angles less than about 15 degrees. A filter
that is applied to such a filter assembly may thus be more
effective at blocking undesirable emission lines from the lamp.
Light sources that include suitable filter assemblies such as this
are shown in schematic side or sectional view in FIGS. 12a and 12b.
In each of those figures, a lamp 1210 is shown centrally located or
mounted. Around this lamp, which may be a metal halide lamp or
other suitable broadband lamp, a suitably shaped filter assembly
can be provided. In FIG. 12a, a spherically-shaped filter assembly
1212 is used; in FIG. 12b, a near-spherical faceted filter assembly
1214 is used. In each figure, arrows are used to show
representative light rays emanating from the lamp 1210. In FIG.
12b, the angle 1216 subtended by one of the facets may characterize
an acceptance angle of the interference filter.
[0071] For the spherical geometry (globe) of FIG. 12a, the light
rays originating from the lamp are all at substantially normal
incidence to the filter assembly, and the interference filter
(which may be attached to an inner or outer surface of the filter
assembly) can effectively block the unwanted emission lines. In the
faceted geometry of FIG. 12b, the light rays are substantially all
within a predetermined acceptance angle of the interference filter.
In the faceted construction, smaller flat sections of filters may
be mounted on a frame (e.g. a soccer ball-like construction) around
the light source to form the filter assembly. FIGS. 12a and 12b
show the filter assemblies completely surrounding the lamp 1210,
but in alternative embodiments the filter assemblies may only
partially surround the lamp, e.g., as in the case of a hemisphere
or other partial sphere.
[0072] Instead of, or in addition to, an interference filter, one
or more absorptive filters may also be used to selectively block
unwanted emission lines. The filtering properties of absorptive
filters are much less sensitive to changes in incidence angle of
the light, compared to interference filters. FIG. 13 is a
combination graph of the spectral transmissivity of exemplary
absorptive filters that may be used in the light source, on which
is superimposed the spectral intensity of a typical metal halide
lamp. Curves 1310, 1312, 1314 represent the spectral transmissivity
(percent transmission as a function of wavelength) of various
absorptive filters, and are drawn to scale according to the percent
transmission scale on the left-hand side of the figure. Curve 1316
represents the spectral output of a conventional metal halide lamp,
which is drawn to scale according to the intensity scale (in
arbitrary units) on the right-hand side of the figure.
[0073] The absorptive filters depicted in FIG. 13 are each in the
form of a plate or layer of glass that has been doped with rare
earth materials, namely, neodymium and praseodymium. These filters
selectively absorb light from about 570 to 590 nm. The degree of
absorption can be tailored by controlling the thickness of the
filter, the doping level of the rare earth material, or both. For
example, the filter of curve 1310 (Hoya Corporation, type V-30) had
a 2.5 mm thickness, the filter of curve 1312 (Hoya Corporation,
type V-10) had a 1.0 mm thickness, and the filter of curve 1314
(Hoya Corporation, type V-10) had a 2.5 mm thickness. By proper
adjustment of the absorptive filter thickness and doping level, the
absorption can be made to provide sufficient blocking of the
unwanted emission lines while maintaining acceptable transmission
in other regions of the spectrum.
[0074] The effect of adding the absorptive filter of curve 1312 to
a light source that also includes a metal halide lamp, in a display
system utilizing the above-described RGB ChLC panel, is shown in
FIGS. 14a-c. In FIG. 14a, curve 1410 shows the reflected intensity
or radiance from the red-activated RGB ChLC panel without the
absorptive filter, and curve 1412 shows the reflected intensity
with the absorptive filter. In FIG. 14b, curve 1420 shows the
reflected intensity or radiance from the green-activated RGB ChLC
panel without the absorptive filter, and curve 1422 shows the
reflected intensity with the absorptive filter. In FIG. 14c, curve
1430 shows the reflected intensity or radiance from the
blue-activated ChLC panel without the absorptive filter, and curve
1432 shows the reflected intensity with the absorptive filter. As
seen from the figures, the absorptive filter largely eliminates the
unwanted 570 and 590 nm emission lines while maintaining high
transmission in the desired regions of the spectrum. This results
in a significant improvement in the color gamut as seen in FIG.
15.
[0075] FIG. 15 is a CIE chromaticity diagram showing the
improvement to color gamut that can be achieved using a light
source that combines a metal halide lamp with the absorptive filter
used in FIGS. 14a-c. Curve 1510 represents the color gamut of a
(baseline) display system that uses a metal halide lamp and the RGB
ChLC panel, which color gamut is similar to color gamut 1110 of
FIG. 11 and color gamut 810 of FIG. 8. When an absorptive filter
having the transmission of curve 1312 is added to the baseline
system, the result is color gamut 1512, which is substantially
larger and thus enhanced relative to gamut 1510. In fact, the area
of color gamut 1512 is more than 30% larger than the area of color
gamut 1510.
[0076] While the degree of blocking provided by absorptive filters
may in some cases not be as high as that provided by interference
filters, absorptive filters can offer significant advantages. Due
to reliance on absorption, absorptive filters exhibit little to no
angular dependence, in comparison to interference filters.
Absorptive filters are also relatively inexpensive compared to
multilayer interference based filters.
[0077] Whether one or more interference filter, one or more
absorptive filter, or both, are used in the light source, the
filter(s) may be disposed at any one or more of a variety of
locations in the light source fixture. Interference filters, due to
their angular dependence, may preferably be applied to a lamp
housing such as lamp housing 314 of FIG. 3. The filter assemblies
discussed in connection with FIGS. 12a and 12b, or modified
versions therof, may also be used as a type of lamp housing 314
(see FIG. 3), and/or as a type of filter plate 318 (see FIG. 3),
and/or as a type of lenslet cover 320 (see FIG. 3). Absorptive
filters may be incorporated in the lamp housing and/or as a filter
plate and/or mounted on a reflector such as reflector 316 (see FIG.
3). In some cases a front lenslet structure, used to focus the lamp
onto the display, may be formed from the absorptive filter
material. Absorptive and/or interference filters may also be
incorporated in the light source in a reflector such as reflector
316 (see FIG. 3).
[0078] Having discussed the subtractive or filtering technique for
overcoming the deficiencies of metal halide sources, we now turn to
the additive or supplemental light source technique.
[0079] One shortcoming of metal halide sources, and potentially
other broadband emitting lamps, is the lack of sufficient intensity
in the red region of the spectrum (see e.g. FIG. 6). We have found
that this shortcoming can be overcome by supplementing the lamp
with at least one secondary or supplemental source that has higher
brightness in the red.
[0080] One promising class of sources that can be used for this
purpose is visible LED sources. A visible "light emitting diode" or
"LED" in this regard may refer to a diode that emits visible light.
It includes incoherent encased or encapsulated semiconductor
devices marketed as "LEDs", whether of the conventional or super
radiant variety, and whether of the forward-emitting or
side-emitting variety. The LED may initially emit non-visible light
such as ultraviolet light, but it may be packaged to include an
organic or inorganic phosphor (or it may illuminate a remotely
disposed phosphor) to convert short wavelength light to longer
wavelength visible light. An "LED die" is an LED in its most basic
form, i.e., in the form of an individual component or chip made by
semiconductor processing procedures. For example, the LED die is
typically formed from a combination of one or more Group III
elements and one or more Group V elements (III-V semiconductor).
The LED die may be configured for surface mount, chip-on-board, or
other known mounting configurations.
[0081] Thus, in at least some embodiments, we propose modifying the
light source so that it includes both a broadband emitting lamp
such as a metal halide lamp, as well as one or more red light
emitting LEDs that are suitably mounted in the light source fixture
so that both lamp light and red LED light illuminate the front of
the reflective display panel. The reflected intensity or radiance
of the red-activated RGB ChLC panel under illumination by a metal
halide lamp only, and by a metal halide lamp in combination with a
supplemental red LED (Philips/Color Kinetics, ColorReach), is shown
in curves 1610 and 1612, respectively, of FIG. 16. The supplemental
red LED results in an almost 5-times increase in the peak
brightness of the red reflection peak. Furthermore, due to the
relatively narrow emission peak of the red LED, the color
saturation of the ChLC red subpixel is also improved compared to
metal-halide-only illumination. In such a hybrid system (i.e., a
system including both the broadband lamp and the supplemental light
source), the bulk of the illumination (lumens) may still be
provided by the broadband lamp. Consequently, the brightness,
weight, and cost advantages of such lamps may still be
substantially maintained.
[0082] The hybrid system or so-called additive technique can be
combined with subtractive technique discussed above in connection
with the filters. The filters may thus be used to block unwanted
emission lines in the broadband lamp light, and the supplemental
light source (such as one or more red LEDs) may be used to
supplement the lamp in the selected region(s) of the spectrum. In
some embodiments, a filter that transmits only the blue and green
lamp emission lines may be used with one or more red LEDs that
would then provide substantially all of the illumination in the
red. Such a filter may be easier to fabricate than one designed to
selectively block only certain spectral lines, and to substantially
transmit light on both sides (longer wavelengths and shorter
wavelengths) of such lines. The simpler interference filter design
could have a wider acceptance angle than one with a narrow blocking
region. For a wider acceptance angle, the filter assembly shown in
FIG. 12b may be more easily constructed with a fewer number of
facets. The transmission spectrum of one such interference filter
is shown in FIG. 17.
[0083] Thus, FIG. 17 is a combination graph of the spectral
intensity 1710 of a typical metal halide lamp, and the spectral
transmissivity 1712 of an interference filter that may be suitable
for use in a system that incorporates red LED supplemental light
sources. The spectral intensity 1710 is drawn to scale according to
the intensity scale (in arbitrary units) on the left-hand side of
the figure; the spectral transmissivity 1712 is drawn to scale
according to the percent transmission scale on the right-hand side
of the figure. The interference filter has high transmission from
about 425 to 575 nm, and effectively blocks all other
wavelengths.
[0084] When this interference filter is used in a light source that
also includes a metal halide lamp and supplemental red LEDs, the
radiance or intensity of the light reflected by the RGB ChLC panel
(when separately controlled to reflect red, green, and blue light
by the red, green, and blue ChLC subpixels) is shown by curves
1812, 1822, and 1832 in FIGS. 18a, 18b, 18c respectively. Note that
these curves were obtained with the interference filter positioned
to filter the metal halide lamp, but not the red LEDs. In these
same figures, curves 1810, 1820, and 1830 depict the reflected
radiance of the same reflective display system except where the
interference filter and the supplemental LEDs were removed from the
light source (i.e., the light source consisted essentially of the
metal halide lamp).
[0085] The reflected red, green, and blue light from the system of
FIGS. 18a-c is able to achieve a system color gamut whose area is
more than 40% greater than the area of a comparable baseline
system.
[0086] We have shown that subtractive techniques and/or additive
techniques can be used to enhance the performance of reflective
display systems. In cases where a ChLC display panel is used as the
reflective display, we believe that even better performance than
that reported above may be obtained by including both a
yellow-transmitting filter (see layer 416, FIG. 4) and a
red-transmitting filter (see layer 420, FIG. 4) in the ChLC display
panel.
[0087] The reader will keep in mind that numerous variations can be
made with respect to the measurement devices, systems, and methods
disclosed herein, and all such variations are considered to be
encompassed by this disclosure. For example, the techniques
disclosed herein may be practiced on reflective displays that have
any desired combination of subpixel colors, and are not limited to
displays having the primary subpixel colors of red, green, and
blue. Other numbers of subpixels, and other subpixel colors, may
instead be used.
[0088] Unless otherwise indicated, all numbers expressing
quantities, measurement of properties, and so forth used in the
specification and claims are to be understood as being modified by
the term "about". Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the specification and claims
are approximations that can vary depending on the desired
properties sought to be obtained by those skilled in the art
utilizing the teachings of the present application. Not as an
attempt to limit the application of the doctrine of equivalents to
the scope of the claims, each numerical parameter should at least
be construed in light of the number of reported significant digits
and by applying ordinary rounding techniques. Notwithstanding that
the numerical ranges and parameters setting forth the broad scope
of the invention are approximations, to the extent any numerical
values are set forth in specific examples described herein, they
are reported as precisely as reasonably possible. Any numerical
value, however, may well contain errors associated with testing or
measurement limitations.
[0089] Various modifications and alterations of this invention will
be apparent to those skilled in the art without departing from the
spirit and scope of this invention, and it should be understood
that this invention is not limited to the illustrative embodiments
set forth herein. For example, the reader should assume that
features of one disclosed embodiment can also be applied to all
other disclosed embodiments unless otherwise indicated. It should
also be understood that all U.S. patents, patent application
publications, and other patent and non-patent documents referred to
herein are incorporated by reference, to the extent they do not
contradict the foregoing disclosure.
* * * * *