U.S. patent application number 13/307111 was filed with the patent office on 2012-03-22 for energy efficient transflective display.
This patent application is currently assigned to I2iC CORPORATION. Invention is credited to Balaji Ganapathy, Udayan Kanade.
Application Number | 20120069271 13/307111 |
Document ID | / |
Family ID | 38834215 |
Filed Date | 2012-03-22 |
United States Patent
Application |
20120069271 |
Kind Code |
A1 |
Kanade; Udayan ; et
al. |
March 22, 2012 |
ENERGY EFFICIENT TRANSFLECTIVE DISPLAY
Abstract
An energy efficient transflective display system is disclosed.
In one embodiment, the system comprises a reflector sheet and a
multicolored illuminator sheet placed in front of the reflector
sheet. A display panel is placed in front of the multicolored
illuminator sheet where the display panel has a light valve.
Inventors: |
Kanade; Udayan; (Pune,
IN) ; Ganapathy; Balaji; (Atlanta, GA) |
Assignee: |
I2iC CORPORATION
Foster City
CA
|
Family ID: |
38834215 |
Appl. No.: |
13/307111 |
Filed: |
November 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11754223 |
May 25, 2007 |
8089580 |
|
|
13307111 |
|
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Current U.S.
Class: |
349/62 |
Current CPC
Class: |
G02F 1/133514 20130101;
G02F 1/133555 20130101; G02F 1/133605 20130101 |
Class at
Publication: |
349/62 |
International
Class: |
G02F 1/13357 20060101
G02F001/13357 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2006 |
IN |
797/MUM/2006 |
Claims
1. An apparatus, comprising a reflector sheet, a multicolored
illuminator sheet placed in front of the reflector sheet, a display
panel placed in front of the multicolored illuminator sheet, the
display panel having a light valve.
2. The apparatus of claim 1, further comprising color filters.
3. The apparatus of claim 1, wherein the light valve comprises a
liquid crystal sheet situated between polarizer sheets.
4. The apparatus of claim 1, wherein the reflector sheet includes
one or more of: a metallic surface, a distributed Bragg reflector,
a hybrid reflector, a total internal reflector, an omni-direction
reflector, and a scattering reflector.
5. The apparatus of claim 1, further comprising a partial mirror
sheet placed between the display panel and the transparent
backlight sheet.
6. The apparatus of claim 1, further comprising a manual control
that adjusts backlight power.
Description
[0001] The present application is a division of patent application
Ser. No. 11/754,223 entitled "ENERGY EFFICIENT TRANSFLECTIVE
DISPLAY" filed on May 25, 2007 at the USPTO, which in turn claimed
the benefit of and priority to Indian Provisional Patent
Application No. 797/MUM/2006 entitled "ENERGY EFFICIENT
TRANSFLECTIVE DISPLAY" and filed on May 25, 2006.
FIELD
[0002] The present invention relates to displays. More
particularly, the invention relates to an energy efficient
transflective display system.
BACKGROUND
[0003] A transflective display is a type of display which can be
used in both transmissive and reflective modes. In transmissive
mode, a backlight is provided which is used to illuminate the
display. In the reflective mode, the ambient light is used to
illuminate the display. A combination of these two provides the
advantage that in areas of low illumination, the transmissive mode
can be used, while when there is sufficient light, the reflective
mode can be used, which helps in reducing the energy
consumption.
[0004] FIG. 1 illustrates the cross section of a prior art
transflective display system 199. Polarizers 103, 106 are placed in
such a way that their transmission axes are aligned at 90 degrees
with respect to each other. Polarizers 103, 106, also referred to
as crossed polarizers henceforth, and liquid crystal 105 form a
light valve. A light valve is a light modulator with controllable
transmittance. The display uses a partial mirror 102 which is
placed between the bottom polarizer 103 and the backlight 101.
Color filter 104 is placed between polarizer 103 and liquid crystal
105. Mirror 109 is placed behind the backlight 101. The display
works in transmissive and reflective modes.
[0005] The partial mirror 102 may be a mirror with holes.
Alternately, partial mirror 102 may be a transflector. A
transflector is an optical sheet designed to reflect as much light
as possible incident from one face and to transmit as much light as
possible incident from the other face. The transflector may be
scattering in nature, to help even illumination.
[0006] Prior art systems are inefficient in transmissive and
reflective modes. In system 199, in the transmissive mode,
backlight 101 emits light 108. Part of light 108 passes through the
partial mirror 102 and illuminates the display. The remaining part
gets reflected back from the partial mirror. Light reflected back
from the partial mirror is not recycled efficiently. Thus the
display is inefficient in the transmissive mode. In the reflective
mode, ambient light 107 gets reflected from the partial mirror 102
and illuminates the display. However, part of ambient light 107
passes through the partial mirror. Light which passes through the
partial mirror is not recycled efficiently. Thus the display is
inefficient in the reflective mode.
SUMMARY
[0007] An energy efficient transflective display system is
disclosed. In one embodiment, the system comprises a reflector
sheet and a multicolored illuminator sheet placed in front of the
reflector sheet. A display panel is placed in front of the
multicolored illuminator sheet where the display panel has a light
valve.
[0008] The above and other preferred features, including various
details of implementation and combination of elements are more
particularly described with reference to the accompanying drawings
and pointed out in the claims. It will be understood that the
particular methods and systems described herein are shown by way of
illustration only and not as limitations. As will be understood by
those skilled in the art, the principles and features described
herein may be employed in various and numerous embodiments without
departing from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The accompanying drawings, which are included as part of the
present specification, illustrate the presently preferred
embodiment and together with the general description given above
and the detailed description of the preferred embodiment given
below serve to explain and teach the principles of the present
invention.
[0010] FIG. 1 illustrates a prior art transflective display system
which uses a partial mirror;
[0011] FIG. 2A illustrates an exemplary transflective display
system with a transparent backlight according to one
embodiment;
[0012] FIG. 2B illustrates an exemplary transflective display
system with a transparent backlight when the pixel is bright,
according to one embodiment;
[0013] FIG. 2C illustrates an exemplary transflective display
system with a transparent backlight when the pixel is dark,
according to one embodiment;
[0014] FIG. 3A illustrates an exemplary transflective display
system with a transparent backlight and partial mirror according to
one embodiment;
[0015] FIG. 3B illustrates an exemplary transflective display
system with a transparent backlight and partial mirror when the
pixel is bright, according to one embodiment;
[0016] FIG. 3C illustrates an exemplary transflective display
system with a transparent backlight and partial mirror when the
pixel is dark, according to one embodiment;
[0017] FIG. 4A illustrates an exemplary transflective display
system with a multi-colored illuminator according to one
embodiment;
[0018] FIG. 4B illustrates an exemplary transflective display
system with a multi-colored illuminator when the pixel is bright
according to one embodiment;
[0019] FIG. 4C illustrates an exemplary transflective display
system with a multi-colored illuminator when the pixel is dark
according to one embodiment;
[0020] FIG. 5A illustrates a block diagram of an exemplary
transparent light source according to one embodiment;
[0021] FIG. 5B illustrates a block diagram of an exemplary
transparent light source as viewed from the side, according to one
embodiment.
[0022] FIG. 6 illustrates a block diagram of an exemplary element
of core of an exemplary light source in the form of a surface,
according to one embodiment;
[0023] FIG. 7 illustrates a diagram of an exemplary light source in
the form of a surface having a varied concentration of diffuser
particles, according to one embodiment.
[0024] FIG. 8 illustrates an exemplary light source in the form of
a surface having two light sources, according to one
embodiment;
[0025] FIG. 9 illustrates a diagram of an exemplary light source in
the form of a surface having a mirrored core, according to one
embodiment;
[0026] FIG. 10 illustrates a multi-colored backlit system,
according to one embodiment;
[0027] FIG. 11A illustrates a block diagram of an exemplary column
of an exemplary multicolor backlit display system as viewed from
the top, according to one embodiment;
[0028] FIG. 11B illustrates a block diagram of an exemplary column
of an exemplary multi-colored backlit display system as viewed from
the front, according to one embodiment;
[0029] FIG. 11C illustrates a block diagram of an exemplary column
of an exemplary backlit display system as viewed from the side,
according to one embodiment.
[0030] FIG. 12 illustrates a block diagram of an exemplary element
of an illuminator column, according to one embodiment;
[0031] FIG. 13 illustrates a diagram of an illuminator column
having a varied concentration of diffuser particles, according to
one embodiment;
[0032] FIG. 14 illustrates an exemplary illuminator column having
two light sources, according to one embodiment;
[0033] FIG. 15 illustrates a diagram of an exemplary mirrored
illuminator column, according to one embodiment.
DETAILED DESCRIPTION
[0034] An efficient transflective display system is disclosed. In
one embodiment, the system comprises a reflector sheet and a
multicolored illuminator sheet placed in front of the reflector
sheet. A display panel is placed in front of the multicolored
illuminator sheet where the display panel has a light valve.
[0035] FIG. 2A illustrates a cross section of an exemplary
transflective display system 299, according to one embodiment. A
transparent backlight 202 is a transparent light source taking the
form of a surface. A mirror 201 is placed behind the transparent
backlight. Mirror 201 may be any light reflector, including
metallic surfaces, distributed Bragg reflectors, hybrid reflectors,
total internal reflectors, omni-directional reflectors or
scattering reflectors. Polarizers 203, 205 are oriented such that
their transmission axes are aligned at 90 degrees with respect to
each other. Polarizers 203, 205, also called crossed polarizers
henceforth, and liquid crystal 204 form a light valve 206. Light
valve 206 may be configured to be in bright state or dark state. In
the bright state of the light valve, both light from the
transparent backlight and ambient light illuminate the pixel. In
the dark state of the light valve, both the ambient light and light
from the transparent backlight is blocked. This is explained
below.
[0036] FIG. 2B illustrates the cross section of an exemplary
transflective display system 299 when the pixel is bright,
according to one embodiment. Light 209, emanated from the backlight
202 gets polarized when it passes through polarizer 203. The liquid
crystal 204 twists the polarization direction of light 209 by 90
degrees. Since polarizers 205 and 203 are crossed, light 209 passes
through the polarizer 205. Thus, light from backlight 202
illuminates the pixel. Ambient light 210 gets polarized when it
passes through the polarizer 205. The liquid crystal 204 twists the
polarization direction of light 210 by 90 degrees. Since the
polarizers 205 and 203 are crossed, light enters the transparent
backlight through polarizer 203. Since the backlight 202 is
transparent, light passes through it and gets reflected from
reflector 201. Reflected light 211 passes through polarizer 203
since it is of correct polarization for transmission. The liquid
crystal 204 twists the polarization direction of light 211 by 90
degrees. Since polarizers 203 and 205 are crossed, light 211 passes
through polarizer 205 and emerges out of the pixel. Thus both
backlight 202 and ambient light illuminate the pixel in the bright
state of the pixel.
[0037] The transflective display system 299 may be used with the
backlight 202 turned off, such that it is not emanating any light.
The ambient light present still illuminates the pixel. The
transflective display system 299 may be used without any ambient
light. The backlight 202 will illuminate the pixel in this
case.
[0038] FIG. 2C illustrates the cross section of an exemplary
transflective display system 299 when the pixel is dark, according
to one embodiment. Light 207 emanated from the transparent
backlight gets polarized due to polarizer 203. The liquid crystal
204 does not affect the polarization state of light 207. Since the
polarizers are crossed, light 207 gets blocked by the polarizer
205. Ambient light 208 gets polarized as it passes through
polarizer 205. The liquid crystal 204 does not affect the
polarization state of light 208. Since the polarizers 205 and 203
are crossed, light 208 gets blocked by polarizer 203. Thus both
ambient light and light from the backlight get blocked in the dark
state of the pixel.
[0039] In another embodiment, in outdoor environments or in places
where sufficient ambient light exists, the display is used in a
primarily reflective mode. Since both ambient light and light from
the backlight 202 illuminate the display simultaneously, light from
backlight 202 can be reduced when ample ambient light is present.
This helps in saving power consumed by the backlight 202.
[0040] In one embodiment, a manual backlight intensity control is
provided so that the user can adjust display brightness according
to the level of ambient light present to suit his requirement. The
manual control may be an electronic hardware control. In another
embodiment, the manual control is implemented in software or
firmware running on a programmable device connected to the display.
In yet another embodiment, the backlight intensity is controlled
automatically by software or firmware running on a programmable
device connected to the display.
[0041] In another embodiment, the ambient light intensity is sensed
by sensors and the backlight power is automatically adjusted as a
function of this ambient light intensity. The backlight power may
be adjusted so as to provide a required illumination intensity.
[0042] Ambient light 210 passes through the pixel twice before
illuminating the pixel. The light from the backlight 202, however,
passes through the pixel only once before illuminating the pixel.
For a liquid crystal light valve, the fraction of ambient light 210
reflected back by the system 299 is approximately half the square
of the transmittance of the light valve 206. The fraction of light
207 from the backlight 202 which emanates out from the system 299
is approximately half the transmittance of the light valve 206.
This is represented mathematically by the equation L=0.5Af
2+0.5Bf,
where [0043] stands for exponentiation [0044] L is the illumination
intensity of the considered pixel. [0045] A is intensity of ambient
light [0046] B is intensity of light from the backlight 202, and
[0047] f is the transmittance of the light valve 206.
[0048] In an embodiment, a given illumination intensity L is
achieved by setting the transmittance of the light valve 206 to
approximately the value (-B+sqrt(B 2+8AL))/2A, where `sqrt` is the
square root function. The transmittance of the light valve 206 is
set by adjusting the excitation voltage of the liquid crystal
cell.
[0049] In one embodiment, the backlight illumination B is adjusted
to be at least (2Lmax-A), where Lmax is the largest required
illumination intensity over all pixels. Alternately, the backlight
illumination B is adjusted to be at least (2Lwhite-A), where Lwhite
is the expected illumination intensity of a completely white
pixel.
[0050] In one embodiment, color filters are placed between the
transparent backlight and light valve. A particular setting of the
light valve produces a color picture in transmissive mode as well
as in reflective mode.
[0051] FIG. 3A illustrates the cross section of an exemplary
transflective display system 399, according to one embodiment. A
transparent backlight 302 is a primarily transparent light source
in the form of a surface. A mirror 301 is placed behind the
transparent backlight. Mirror 301 may be any reflector including
those described above in conjunction with FIG. 2A. Crossed
polarizers 304, 306 and liquid crystal 305 form a light valve 307.
A partial mirror 303 is placed in between polarizer 304 and
transparent backlight 302. The display 399 works in both
transmissive and reflective modes as explained below. Light valve
307 may be configured to create a bright state or a dark state. In
the bright state of the light valve 307, both light from the
backlight 302 and ambient light illuminate the pixel. In the dark
state of the light valve 307, both the ambient light and light from
the backlight 302 is blocked.
[0052] FIG. 3B illustrates the cross section of an exemplary
transflective display system 399, when the pixel is in bright state
according to one embodiment. Unpolarized light 308 from the
backlight 302 gets partially transmitted and partially reflected by
partial mirror 303. The transmitted part, light 315, passes through
the polarizer 304 and gets polarized. Liquid crystal 305 twists the
polarization direction of light 315 by 90 degrees. Since the
polarizers are crossed, light 315 emerges out from the light valve
307 through polarizer 306. The partially reflected light 317 is
efficiently recycled by the transparent backlight 302 as follows.
Since the backlight 302 is transparent, reflected light 317 passes
through the transparent backlight 302 and gets reflected from
mirror 301. Reflected light 317 behaves like light 308. Some part
of light 317 gets transmitted by the partial mirror 303 and some
part gets reflected. The transmitted part emerges out from the
light valve like light 315. The reflected part behaves like light
317. After multiple reflections, almost all light emerges out from
the light valve 307. Ambient light 312 enters the light valve 307
through polarizer 306 and gets polarized. Liquid crystal 305 twists
the polarization direction of light 312 by 90 degrees. Since the
polarizers 304, 306 are crossed, light 312 passes through polarizer
304. Some part of light 312 gets reflected from the partial mirror
303. This reflected light 313 passes through polarizer 304 since it
has the same polarization direction as the transmission axis
direction of polarizer 304. Liquid crystal 305 twists the
polarization direction of light 313 by 90 degrees. As the
polarizers are crossed, light 313 emerges out from polarizer 306.
The remaining part of light 312 gets transmitted through the
partial mirror 303. Since the backlight 302 is transparent, this
transmitted light gets reflected from the mirror 301 and emerges
out from the light valve 307 like light 308. Thus both backlight
302 and ambient light illuminate the pixel in the bright state of
the pixel.
[0053] FIG. 3C illustrates the cross section of an exemplary
transflective display system 399, when the pixel is in dark state,
according to one embodiment. Ambient light 309 enters the light
valve 307 through polarizer 306 and gets polarized. Liquid crystal
305 does not change the polarization direction of light 309. Since
the polarizers are crossed, light 309 gets blocked by polarizer
304. Light 308 from the backlight 302 gets partially reflected from
partial mirror 303. Some part of light 308 passes through the
polarizer 304 and gets polarized. Liquid crystal 305 does not
change the polarization direction of light 311. Since the
polarizers are crossed, light 311 gets blocked by polarizer 306.
Thus, in the dark state of the pixel, both ambient light and light
from the backlight 302 get blocked.
[0054] FIG. 4A illustrates the cross section of an exemplary
transflective display system 499 which uses a multi-colored
illuminator, according to one embodiment. A multi-colored
illuminator consists of transparent columnar light sources which
emit light of more than one distinct spectra. An exemplary column
402 is depicted. Column 402 of a particular color has a color
filter 403 of that particular color on top of it. A mirror 401 is
placed behind the columnar source. Mirror 401 may be any reflector
including those described above in conjunction with FIG. 2A.
Crossed polarizers 404, 406 and liquid crystal 405 form a light
valve 407. Light valve 407 may be configured to create a bright
state or dark state. In the bright state of the light valve 407,
both light from the multicolored backlight 402 and ambient light
illuminate the pixel. In the dark state of the light valve 407,
both the ambient light and light from the multicolored backlight
402 is blocked.
[0055] FIG. 4B illustrates the cross section of an exemplary
transflective display system 499 when the pixel is bright,
according to one embodiment. Light 409, emanated from the
multicolored backlight column passes through color filter 403 and
gets polarized when it passes through polarizer 404. Since the
color filter 403 is of the same color as that of the column source,
no energy is wasted in the color filter 403. Liquid crystal 405
twists the polarization direction of light 409 by 90 degrees. Since
polarizers 406 and 404 are crossed, light 409 passes through the
polarizer 406. Thus light from the backlight column illuminates the
pixel. Ambient light 408 gets polarized when it passes through the
polarizer 406. Liquid crystal 405 twists polarization direction of
light 408 by 90 degrees. Since the polarizers 406 and 404 are
crossed, light enters the transparent columnar source 402 through
the color filter 403. Since the columnar source is transparent,
light passes through it and gets reflected from mirror 401. Light
410 passes through polarizer 404 since it is of correct
polarization for transmission. Liquid crystal 405 twists
polarization direction of light 410 by 90 degrees. Since polarizers
404 and 406 are crossed, light 410 passes through polarizer 406 and
the pixel gets illuminated. Since reflected light 410 has passed
through the color filter 403, it illuminates the pixel with the
correct color. Thus both backlight 402 and ambient light illuminate
the pixel in the bright state of the pixel.
[0056] FIG. 4C illustrates the cross section of an exemplary
transflective display system 499 when the pixel is dark, according
to one embodiment. Light 409 emanated from the columnar source 402
passes through the color filter 403 and gets polarized due to
polarizer 404. Liquid crystal 405 does not affect the polarization
state of light 409. Since the polarizers are crossed, light 409
gets blocked by the polarizer 406. Ambient light 408 gets polarized
as it passes through polarizer 406. Liquid crystal 405 does not
affect the polarization state of light 408. Since the polarizers
406 and 404 are crossed, light 208 gets blocked by polarizer 404.
Thus both ambient light and light from the backlight 402 get
blocked in the dark state of the pixel.
[0057] In an alternate embodiment, color filter 403 is placed
between liquid crystal 405 and polarizer 404. In another
embodiment, color filter 403 is placed between liquid crystal 405
and polarizer 406. In yet another embodiment, color filter 403 is
placed after polarizer 406.
[0058] In another embodiment the color filter 403 is not exactly
matched to the color of the columnar source. A broad spectrum color
filter, which primarily passes the color of the columnar source is
used. Since the color filter is broad spectrum, loss in the color
filter in the reflective mode is reduced. Thus the efficiency of
the display in the reflective mode improves.
[0059] In another embodiment, the color filter 403 is not provided.
A particular setting of the light valve 407 produces a color
picture in transmissive mode and a gray-scale picture in reflective
mode. Ambient light is not wasted in the color filter 403.
Transparent Backlight
[0060] FIG. 5A illustrates a block diagram of an exemplary
transparent light source 599, according to one embodiment. Light
source 599 is primarily transparent and may include a light guide
506 with a core 504 surrounded by low index cladding sheets 503 and
505. The core 504 includes a diffuser, which is a sparse
distribution of light dispersing particles. The diffuser in the
core 504 is made up of metallic, organic, or other powder, or
pigment, which reflects light incident on it. Alternatively, the
diffuser in the core 504 may be constituted of small transparent
particles or bubbles, which disperse light by refraction,
reflection at the boundary, by diffusion inside the particle, or by
total internal reflection. Linear light source 502 illuminates the
light guide 506 from its edge. Reflector 501 concentrates light
from the linear light source 502 into the light guide 506. The
light from a primary light source 502 is dispersed over the entire
surface of the light guide 506 and exits from its large faces. The
light guide 506 is thus primarily transparent and clear when viewed
from one of its faces.
[0061] FIG. 5B illustrates a block diagram of an exemplary
transparent light source 599 as viewed from the side, according to
one embodiment. The core 504 is surrounded by low index cladding
sheets 503 and 505. Linear light source 502 illuminates the light
guide 506 from its edge. Reflector 501 concentrates light from the
linear light source 502 into the light guide 506.
[0062] FIG. 6 illustrates a block diagram of an exemplary core
element 699 of core 504 of a light source in the form of a surface
599, according to one embodiment. Core element 699 has the
thickness and breadth of the core 504 but has a very small height.
Light 600 enters element 699. Some of the light gets dispersed and
leaves the light guide as illumination light 602, and the remaining
light 604 travels on to the next core element. The power of the
light 600 going in is matched by the sum of the powers of the
dispersed light 602 and the light continuing to the next core
element 604. The fraction of light dispersed 602 with respect to
the light 600 entering the core element 699 is the photic
dispersivity of core element 699. The photic dispersivity of core
element 699 is in direct proportion to the height of element 699.
The ratio of the photic dispersivity of core element 699 to the
height of element 699 is a photic dispersion density of core
element 699. As the height of core element 699 decreases, the
photic dispersion density approaches a constant. This photic
dispersion density of core element 699 bears a certain relationship
to the diffuser concentration at the core element 699. The
relationship is approximated to a certain degree as a direct
proportion. The relationship is determined by knowing the diffuser
concentration of an element, that permits evaluation of the photic
dispersion density of core element 699, and vice versa.
[0063] As the height of core element 699 is reduced, power in the
emanating light 602 reduces proportionately. The ratio of power of
the emanating light 602 to the height of core element 699, which
approaches a constant as the height of the element is reduced, is
the emanated power density at element 699. The emanated power
density at core element 699 is the photic dispersion density times
the power of the incoming light (i.e. power of light traveling
through the element). The gradient of the power of light traveling
through the core element 699 is the negative of the emanated power
density. These two relations give a differential equation. This
equation can be represented in the form "dP/dh=-qP=-K" where: h is
the height of a core element from the primary light source edge 507
[0064] P is the power of the light being guided through that
element; [0065] q is the photic dispersion density of the element;
and [0066] K is the emanated power density at that element.
[0067] This equation is used to find the emanated power density
given the photic dispersion density at each element. This equation
is also used to find the photic dispersion density of each element,
given the emanated power density. To design a particular light
source in the form of a surface with a particular emanated power
density, the above differential equation is solved to determine the
photic dispersion density at each element of the light source, such
as the light source 599. From this, the diffuser concentration at
each core element of the core is determined. Such a core is used in
a light guide, to give a light source of required emanated energy
density over the surface of the light source.
[0068] If a uniform concentration of diffuser is used in the core,
the emanated power density drops exponentially with height. Uniform
emanated power density may be approximated by choosing a diffuser
concentration such that the power drop from the edge near the light
source (such as edge 507) to the opposite edge 508, is minimized.
To reduce the power loss and also improve the uniformity of the
emanated power, opposite edge reflects light back into the core. In
an alternate embodiment, another light source sources light into
the opposite edge.
[0069] To achieve uniform illumination, the photic dispersion
density and hence the diffuser concentration has to be varied over
the length of the core. This can be done using the above
methodology. The required photic dispersion density is q=K/(A-hK),
where A is the power going into the linear light source 604 and K
is the emanated power density at each element, a constant number
for uniform illumination. If the total height of the linear light
source is H, then H times K should be less than A, i.e. total power
emanated should be less than total power going into the light
guide, in which case the above solution is feasible. If the
complete power going into the light guide is utilized for
illumination, then H times K equals A. In an exemplary light
source, H times K is kept only slightly less than A, so that only a
little power is wasted, as well as photic dispersion density is
always finite.
[0070] FIG. 7 illustrates a diagram of an exemplary light source in
the form of a surface 799 with a core having a varied concentration
of diffuser particles, according to one embodiment. The
concentration of the diffuser 702 is varied from sparse to dense
from the light source end of linear light source column 704 to the
opposite edge of core 704.
[0071] FIG. 8 illustrates an exemplary light source in the form of
a surface 899 having two light sources, according to one
embodiment. By using two light sources 808, 809, high variations in
concentration of diffuser particles 802 in the core is not
necessary. The differential equation provided above is used
independently for deriving the emanated power density due to each
of the light sources 808, 809. The addition of these two power
densities provides the total light power density emanated at a
particular core element.
[0072] Uniform illumination for light source 899 is achieved by
photic dispersion density q=1/sqrt((h-H/2) 2+C/KA2) where sqrt is
the square root function, stands for exponentiation, K is the
average emanated power density per light source (numerically equal
to half the total emanated power density at each element) and C=A
(A-HK).
[0073] FIG. 9 illustrates a diagram of an exemplary light source in
the form of a surface 999 having a mirrored core 904, according to
one embodiment. By using a mirrored core 904, high variations in
concentration of diffuser 902 in the core 904 is not necessary. Top
edge of the core 910 is mirrored, such that it will reflect light
back into the core 04. The photic dispersion density to achieve
uniform illumination in light source 999 is:
q=1/sqrt((h-H) 2+D/K 2) [0074] where D=4A (A-HK).
[0075] For any system described above (such as the light sources in
the form of surfaces 799, 899 and 999), the same pattern of
emanation is sustained even if the light source power changes. For
example, if the primary light source of light source 799 provides
half the rated power, each element of the core will emanate half
its rated power. Specifically, a light guide core designed to act
as a uniform light source as a uniform light source at all power
ratings by changing the power of its light source or sources. If
there are two light sources, their powers are changed in tandem to
achieve this effect.
Multi-Colored Illuminator
[0076] FIG. 10 illustrates a multi-colored backlit system 1099,
according to one embodiment. A multi-colored illuminator system
comprises a backlight such that each pixel column of the backlit
display is illuminated by light of a particular color. The light
illuminating different pixel columns may be of different colors.
The columnar light sources 1002 provide illumination for the
display. Mirror 1003 is placed behind the columnar sources 1002.
Liquid crystal matrix 1001 is placed in front of the columnar
sources 1002.
[0077] FIG. 11A illustrates a block diagram of an exemplary column
1199 of an exemplary multicolor backlit display system as viewed
from the top, according to one embodiment. Polarizer 1106, liquid
crystal 1105 and polarizer 1104 together form a light valve that
modulates the intensity of light passing through it. Illuminator
column 1102 and cladding sheet 1103 together form a waveguide,
illuminator 1102 having higher refractive index than cladding sheet
1103. Color filter 1108 is placed in front of the cladding sheet
1103. Illuminator 1102 has a small concentration of light
dispersing particles. Light inside the waveguide undergoes
continuous total internal reflection. Back-mirror 1101 reflects
light from the back surface. Side-mirrors 1107 reflect light from
the side surfaces. Side-mirrors 1107 prevent light from leaking
into the adjacent columns. The mirrors 1101 and 1107 may be any
light reflector, including metallic surfaces, distributed Bragg
reflectors, hybrid reflectors, total internal reflectors,
omni-direction reflectors or scattering reflectors.
[0078] FIG. 11B illustrates a block diagram of an exemplary column
1199 of an exemplary multi-colored backlit display system as viewed
from the front, according to one embodiment. Polarizer 1106, liquid
crystal 1105 and polarizer 1104 together form a light valve that
modulates the intensity of light passing through it. Illuminator
column 1102 and cladding sheet 1103 together form a waveguide where
the illuminator 1102 has a higher refractive index than cladding
sheet 1103. Color filter 1108 is placed in front of the cladding
sheet 1103. Illuminator 1102 has a small concentration of light
dispersing particles. Light inside the waveguide undergoes
continuous total internal reflection. Back-mirror 1101 reflects
light from the back surface. Side-mirrors 1107 reflect light from
the side surfaces. Side-mirrors 1107 prevent light from leaking
into the adjacent columns.
[0079] FIG. 11C illustrates a block diagram of an exemplary column
1199 of an exemplary backlit display system as viewed from the
side, according to one embodiment. Side-mirrors 1107 prevent light
from leaking into the adjacent columns.
[0080] FIG. 12 illustrates a block diagram of an exemplary core
element 1299 of the illuminator column 1102. Core element 1299 has
a very small height. Light 1200 enters core element 1299. Some of
the light gets dispersed and leaves the light guide as illumination
light 1202, and the remaining light 1204 travels on to the next
illuminator column element. As has been discussed in conjuction
with the core element 699 in FIG. 6, the differential equation
pertaining to the columnar source relating the power (P) of light
being guided through the core element, the height (h) of the
element and the photic dispersion density (q) of the core element
1299 is represented as "dP/dh=-qP=-K" where K is the emanated power
density at that core element 1299.
[0081] If a uniform concentration of diffuser is used in the
illuminator, the emanated power density drops exponentially with
height. Uniform emanated power density may be approximated by
choosing a diffuser concentration such that the power drop from the
end near the light source to the opposite end, is minimized. To
reduce the power loss and also improve the uniformity of the
emanated power, opposite end reflects light back into the
illuminator column. In an alternate embodiment, another light
source sources light into the opposite end.
[0082] To achieve uniform illumination, the photic dispersion
density and hence the diffuser concentration has to be varied over
the illuminator surface. This can be done using the above
methodology. The required photic dispersion density is q=K/(A-hK),
where A is the power going into the illuminator column 1102 and K
is the emanated power density at each element, a constant number
for uniform illumination. If the total height of the illuminator is
H, then H times K should be less than A, i.e. total power emanated
should be less than total power going into the light guide, in
which case the above solution is feasible. If the complete power
going into the light guide is utilized for illumination, then H
times K equals A. In one exemplary column, H times K is kept only
slightly less than A, so that only a little power is wasted, as
well as photic dispersion density is always finite.
[0083] FIG. 13 illustrates a diagram of an illuminator column 1399
having a varied concentration of diffuser particles, according to
one embodiment. The concentration of the diffuser 1302 is varied
from sparse to dense from the light source end of illuminator
column 1304 to the opposite end. Light source 1308 provides light
to illuminator column 1304.
[0084] FIG. 14 illustrates an exemplary illuminator column 1499
having two light sources. By using two light sources 1408, 1409,
high variations in concentration of diffuser 1402 in the
illuminator column is not necessary. The differential equation
provided above is used independently for deriving the emanated
power density due to each of the light sources 1408, 1409. The
addition of these two power densities provides the total light
power density emanated at a particular core element.
[0085] Uniform illumination for light source 1499 is achieved by
photic dispersion density q=1/sqrt ((h-H/2) 2+C/KA2) where sqrt is
the square root function, stands for exponentiation, K is the
average emanated power density per light source (numerically equal
to half the total emanated power density at each element) and C=A
(A-HK).
[0086] FIG. 15 illustrates a diagram of an exemplary mirrored
illuminator column 1599. By using a mirrored illuminator 1504, high
variations in concentration of diffuser 1502 in the core 1504 are
not necessary. Top end 1510 of the central illuminator column 1504
is mirrored, such that it reflects light back into central
illuminator column 1504. The photic dispersion density to achieve
uniform illumination in light source 1599 is:
q=1/sqrt((h-H) 2+D/K 2) [0087] where D=4A (A-HK).
[0088] For any system (such as the light sources in the form of
surfaces 1399, 1499 and 1599), the same pattern of emanation is
sustained even if the light source power changes. For example, if
the light source of illuminator column 1199 provides half the rated
power, each element of the core will emanate half its rated power.
Specifically, a light guide core designed to act as a uniform
illuminator acts as a uniform illuminator at all power ratings by
changing the power of its light source or sources. If there are two
light sources, their powers are changed in tandem to achieve this
effect.
[0089] In another embodiment, a light valve comprises a liquid
crystal sheet situated between polarizer sheets such that the
transmission axes of the polarizers are aligned parallel to each
other. The present display technology may be used in conjunction
with light valves other than liquid crystal light valves, like
electrowetting light modulators.
[0090] An energy efficient transflective display system is
disclosed. It is understood that the embodiments described herein
are for the purpose of elucidation and should not be considered
limiting the subject matter of the present patent. Various
modifications, uses, substitutions, recombinations, improvements,
methods of productions without departing from the scope or spirit
of the present invention would be evident to a person skilled in
the art.
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