111111
`
`1111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20050073495Al
`
`(19) United States
`(12) Patent Application Publication
`Harbers et al.
`
`(10) Pub. No.: US 2005/0073495 Al
`Apr. 7, 2005
`(43) Pub. Date:
`
`(54) LCD BACKLIGHT USING
`TWO-DIMENSIONAL ARRAY LEDS
`
`(76)
`
`Inventors: Gerard Harbers, Sunnyvale, CA (US);
`William D. Collins III, San Jose, CA
`(US)
`
`Correspondence Address:
`PATENT LAW GROUP LLP
`2635 NORTH FIRST STREET
`SUITE 223
`SAN JOSE, CA 95134 (US)
`
`(21)
`
`Appl. No.:
`
`10/678,541
`
`(22) Filed:
`
`Oct. 3, 2003
`
`Publication Classification
`
`(51)
`Int. CI? ....................................................... G09G 3/36
`(52) U.S. Cl. .............................................................. 345/102
`
`ABSTRACT
`(57)
`One embodiment of the invention provides a backlight for
`an LCD display. The backlight uses a two-dimensional array
`of single color or white LEDs and a diffusing or phosphor
`coated cover plate. Various electrical connections of the
`LEDs and various phosphor color-conversion techniques are
`described.
`
`14
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`SONY 1008
`Page 1
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 1 of 15
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`US 2005/0073495 A1
`
`FIG 1A PRIOR ART
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`Page 2
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 2 of 15
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`US 2005/0073495 Al
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`FIG. 2
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`Page 3
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 3 of 15
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`US 2005/0073495 Al
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`Page 4
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 4 of 15
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`US 2005/0073495 Al
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`FIG. 4
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`Page 5
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 5 of 15
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`US 2005/0073495 Al
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`FIG. 5
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`Patent Application Publication Apr. 7, 2005 Sheet 6 of 15
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`US 2005/0073495 Al
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`Page 7
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 7 of 15
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`US 2005/0073495 Al
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`FIG7A
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`Page 8
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 8 of 15
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`US 2005/0073495 Al
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`FIG. SA
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`Page 9
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 9 of 15
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`US 2005/0073495 Al
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`FIG. 9
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`Page 10
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`Patent Application Publication Apr. 7, 2005 Sheet 10 of 15
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`US 2005/0073495 A1
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`FIG. 10
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`Page 11
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 11 of 15
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`US 2005/0073495 Al
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`FIG. 11A
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`Page 12
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 12 of 15
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`US 2005/0073495 A1
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`Page 13
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 13 of 15
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`US 2005/0073495 A1
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`FIG.12A
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`Page 14
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`

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`Patent Application Publication Apr. 7, 2005 Sheet 14 of 15
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`US 2005/0073495 A1
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`42
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`Page 15
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`Patent Application Publication Apr. 7, 2005 Sheet 15 of 15
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`US 2005/0073495 A1
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`FIG 13A
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`Page 16
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`

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`US 2005/0073495 Al
`
`Apr. 7, 2005
`
`1
`
`LCD BACKLIGHT USING TWO-DIMENSIONAL
`ARRAYLEDS
`
`FIELD OF THE INVENTION
`
`[0001] This invention is related to backlighting a liquid
`crystal display (LCD) panel and, in particular, to backlight(cid:173)
`ing an LCD panel with light emitting diodes (LEDs).
`
`BACKGROUND
`
`[0002] LCD TVs and monitors use backlights consisting
`of arrays of cold cathode fluorescent lamps (CCFLs) to
`create a visible image on the LCD. For large displays a direct
`backlight type is used, where the lamps are directly placed
`behind the LCD, as shown in FIG. 1A. FIG. 1A shows the
`CCFLs 10, a diffuser plate 12, and an LCD panel 14.
`Disadvantages of using CCFLs are that they require mer(cid:173)
`cury, have a low color gamut, and have a limited brightness.
`
`[0003] Alternative solutions have been proposed that use
`LEDs, which use either a waveguide and edge illumination,
`or a direct backlight with side emitting LEDs (i.e., U.S.
`application Ser. No. 10/442,346, assigned to Lumileds
`Lighting U.S. LLC). In both approaches, a long mixing
`length is created to deal with the flux and color variations
`that are inherent to LEDs. In the direct backlight approach,
`each LED illuminates a large area of the LCD, or, in other
`words, each pixel of the LCD is illuminated by a large
`number of LEDs such that variations in output of each LED
`do not show up in the LCD image. In the edge lit as well as
`the side-emitting direct backlight approach, the flux and
`color mixing properties come at an efficiency penalty.
`
`In U.S. Pat. No. 6,582,103 B1 (to John Popovich et
`[0004]
`al, assigned to Teledyne Lighting and Display Products),
`low profile LED illumination fixtures are proposed, consist(cid:173)
`ing of a cavity, including reflective walls, an output aperture,
`and at least one point source, such as an LED. In this patent,
`a diffuser covers the output aperture, and each LED includes
`a side-emitting lens. The solution presented in the present
`application does not require such side-emitting lens. Other
`distinguishing feature exist.
`
`[0005] A complete other illumination approach was intro(cid:173)
`duced by Whitehead et al. of the University of British
`Columbia in Canada (WO 02/069030 A2; SID 03 Digest,
`Helge Seetzen, Lome A. Whitehead, A High Dynamic
`Range Display Using Low and High Resolution Modulators,
`p. 1450-1454), who proposed and demonstrated, as shown in
`FIG. 1B, an array of LEDs 16 directly behind the LCD 18.
`Only a few pixels 20 are illuminated by a single LED. The
`benefit of this approach is that the intensity of the LEDs can
`be modulated to represent the low spatial frequencies in the
`image, while the LCD modulates the high frequencies. The
`big advantage of this is that the dynamic range and contrast
`of the display are greatly enhanced (16 bit versus 8 bit
`displays). This is of great advantage in professional (e.g.,
`medical) applications, but would create much better picture
`quality for an LCD display as well. One of the big challenges
`in this approach is the variation in color and flux of the
`LEDs. This is especially true if red, green, and blue LEDs
`are used to create white, but for white LEDs as well. Without
`a sufficient density of the LEDs, it will be very difficult to get
`adequate brightness uniformity with the configuration as
`suggested by Whitehead. Another disadvantage of this
`approach is the cost of the system. In the SID03 paper, it is
`
`suggested to place the LEDs at a pitch of 5 mm. For a 37"
`diagonal LCD-TV, 16,000 LEDs would be required. Besides
`the cost, one has to cope with driver and connection reli(cid:173)
`ability issues as well.
`
`[0006] Another illumination approach where a high effi(cid:173)
`ciency LCD display is obtained is disclosed by Mueller(cid:173)
`Mach et al.
`in U.S. application publication US2002/
`0145685A1, assigned to Lumileds Lighting U.S., LLC. In
`this illumination scheme, a blue backlight is used in com(cid:173)
`bination with a phosphor dot pattern consisting of red and
`green phosphor dots, which are aligned with LCD pixels
`representing the red, and green image pixels, respectively,
`while the blue pixels are left blank or applied with a
`non-phosphor scattering material. A related approach was
`suggested by Gallen et al. (WO 02/075440) where an UV or
`near UV emitting LED array was used, and red, green, and
`blue phosphors where applied (screen printed) onto the
`LCD. A collimating means is used to limit the cross-talk
`between the LCD pixels and the phosphor dots. Both appli(cid:173)
`cations have the advantage that the color uniformity is
`determined by the phosphor and the phosphor printing
`process, and that the system efficiency can be very high, as
`the absorbing color filters are no longer needed. However,
`efforts in this area have not yet resulted in introduction of
`this technology to the market.
`
`SUMMARY
`[0007] One embodiment of the invention provides a back(cid:173)
`light for an LCD display, having a high efficiency, good
`color uniformity, and spatially and temporal adjustable lumi(cid:173)
`nance profile, for obtaining better contrast and lower power
`consumption at a low cost. The backlight uses an array of
`single color or white LEDs and a diffusing or phosphor
`coated cover plate. To obtain a high efficiency, no additional
`optics is used in between the LEDs and the cover plate. In
`this invention, a good compromise has been found between
`color and flux mixing properties of the LEDs and control
`over the luminance profile.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`[0008] FIG. 1A illustrates a prior art LCD backlight
`approach using CCFLs.
`
`[0009] FIG. 1B is a cross-section and a partial front view
`of a prior art LCD backlight using a densely packed array of
`LEDs.
`
`[0010] FIG. 2 is a side view of an LCD using a backlight
`in accordance with one embodiment of the invention.
`
`[0011] FIGS. 3A and 3B are graphs of light intensity vs.
`angular displacement for two types of LEDs that may be
`used in the backlight of FIG. 2A.
`
`[0012] FIG. 4 illustrates the preferred ratio of the height
`(thickness) of the backlight and the pitch of the LEDs.
`
`[0013] FIGS. 5 and 6 illustrate two possible arrangements
`of the LEDs in the backlight.
`
`[0014] FIG. 7A illustrates the use of a light sensor in the
`backlight for adjusting the brightness of the LEDs or LCD
`output to compensate for degradation of the LEDs' light
`output.
`
`[0015] FIG. 7B is a block diagram of one technique for
`receiving the sensor signals and adjusting the brightness of
`the LEDs or the LCD output.
`
`Page 17
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`

`

`US 2005/0073495 Al
`
`Apr. 7, 2005
`
`2
`
`[0016] FIGS. SA, SB, 9, 10, llA, and llB illustrated
`different wiring configurations for the LEDs in the backlight.
`
`[0017] FIGS. 12A, 12B, 12C, 13A, and 13B illustrate
`various techniques for phosphor-converting the LED light
`output.
`
`DETAILED DESCRIPTION
`
`[001S] FIG. 2A is a side view of an LCD display 22. An
`array of LEDs 24 is placed on the rear panel of the backlight
`26. The backlight 26 is covered with a diffusing cover plate
`(diffuser 2S). The diffuser 2S is for example made of acrylic
`or glass, with a roughened surface for diffusing light. Alter(cid:173)
`natively, the diffuser 2S may have light scattering particles
`with the acrylic or glass sheet. Many types of diffusers are
`known and may be used with the backlight 26. A transparent
`plate may be used instead of the diffuser 2S if the light output
`of the backlight 26 is sufficiently diffused without a diffuser.
`Additional films (not shown) for increasing the brightness or
`efficiency might be used on top of the diffuser, just before the
`LCD, as for example Brightness Enhancement Film and
`Dual Brightness Enhancement Film, as for example pro(cid:173)
`duced by 3M.
`
`[0019] The back plane 30 and the sidewalls 32 of the
`backlight 26 are covered with high reflective materials.
`Good results have been obtained with a white diffuse reflec(cid:173)
`tive film on the back (e.g., E60L, produced by Toray, Japan),
`and a specular reflecting material on the sidewalls (e.g.,
`Mira material, as produced by Alanod, Germany), but other
`configurations work as well. The materials used should have
`a high coefficient of reflection, preferably >90%. By using
`these high reflective materials, a high recycling efficiency is
`achieved. This is in particular important when Brightness
`Enhancement Films are used, as mentioned above, as these
`films reflect the light which can not be used in the first pass,
`and which needs to be recycled in order to contribute to the
`output of the LCD during a second or third pass.
`
`[0020] The LCD panel14 is placed in front of the back(cid:173)
`light 26. The LCD panel14 may be a conventional LCD,
`having a first polarizing filter, a thin film transistor array for
`developing an electric field across selected areas of the
`liquid crystal layer, a liquid crystal layer, an RGB color filter
`array, and a second polarizing filter. The color filter array has
`red, green and blue subpixels. Between the LCD panel 14
`and the backlight 26, additional films can be used, such as
`a brightness enhancement film (BEF) or polarization recov(cid:173)
`ery film (DBEF).
`
`[0021] The preferred intensity profiles of each LED 24 for
`obtaining a good balance between light mixing and lumi(cid:173)
`nance control are shown in FIGS. 3A and 3B. FIG. 3A
`shows an example of a Batwing type intensity pattern, and
`FIG. 3B shows a so-called Lambertian radiation profile.
`These types of LEDs are produced by Lumileds (LXHL(cid:173)
`BW01 & LXHL-BR02 for the batwing white and blue, and
`LXHL-PW01 & LXHL-PR03 for the Lambertian type
`white and blue).
`
`[0022] FIG. 4 shows the preferred relationship between
`the total thickness (H) of the backlight 26 and diffuser 2S
`and the pitch (P) of the LEDs 24. We found that, if the
`thickness is between 0.3 times and 1.2 times the pitch of the
`LEDs, the best results are obtained with respect to unifor(cid:173)
`mity, and luminance profile control. For example, good
`
`results were achieved with a 16" (diagonal) backlight, with
`a thickness of 40 mm and an LED pitch of 50 mm. In this
`case 31 Lumileds Luxeon™ Lambertian emitters where
`used.
`
`[0023] The power of these emitters is between 1 and 3W.
`For a 32"display, using the same pitch and thickness, about
`124 LEDs would be needed. When lower power LEDs are
`used, like for example Nichia surface mount devices, with
`an average power of 0.15W, about 6x-20x as many LEDs are
`required to achieve the same performance, but the pitch of
`the LEDs would of course be smaller, and therefore the
`thickness as well. In another example, the pitch of the LEDs
`used in the present backlight is 20 mm or greater.
`
`[0024] FIG. 5 shows one example of the layout of the
`LEDs 24 in the backlight 26. In this case, the LEDs 24 are
`placed in a square pattern using 36 LEDs. The actual number
`of LEDs needed depends on the size of the display, the
`luminous flux of each LED, and the required brightness. As
`LEDs do vary in light output and efficiency with production
`tolerances, and for a cost effective solution all LEDs have to
`be used (high yield), and in general the center of the display
`will have a higher brightness (luminance) than the edge of
`the display, it is preferred to put the most efficient, highest
`output LEDs in the center of the backlight and the less
`efficient dimmer parts near the edge of the backlight.
`
`[0025] An alternative configuration of an LED layout is
`shown in FIG. 6, where a layout using 31 LEDs is shown,
`and where the LEDs are places in a hexagonal structure. This
`layout has the advantage that each LED has six equidistant
`neighbors, and that the brightness of individual LEDs are
`averaged over its neighbors.
`
`[0026] LEDs do degrade over time, and it can happen that
`nonuniformities will occur if the LEDs degrade differently.
`By including sensors in the backlight this degradation can be
`measured and can be compensated for by either adjusting the
`drive currents of the LEDs or by adjusting the transmission
`of the LCD, by changing the grey values of the pixels. FIG.
`7 A illustrates an arrangement where in between the LEDs 24
`a light sensor 34 is placed to measure the luminance (bright(cid:173)
`ness) uniformity over the backlight 26. Of course, placing
`the sensors 34 at larger spacing than the LEDs can lower the
`number of sensors. A preferred configuration is where the
`spacing of the sensors is between 1x and 3x the spacing of
`the LEDs.
`
`[0027] FIG. 7B illustrates one type of circuit that detects
`the sensor 34 signals and controls the LEDs or LCD panel
`to compensate for degradation of the LED brightness. The
`detector 36 samples each sensor 34 output using any suitable
`technique, such as by multiplexing. A sensor 34 that mea(cid:173)
`sures a reduced light output is associated with one or more
`specific LEDs 24 in the array or a group of pixels in the LCD
`panel14. A control unit 3S, such as a current supply for the
`LEDs or an LCD controller, then adjusts the current to the
`affected LEDs or controls the gray scale level of the affected
`LCD pixels to compensate for the brightness degradation.
`Other suitable techniques may be used.
`
`[002S] FIG. SA shows an electronic driving scheme for
`the backlight 26. In this example, 31 LEDs 24 are connected
`in series. Such a configuration is especially suited to reduce
`the costs of an electronic driver or inverter, as the forward
`voltage per LED is approximately 3.5V, and the total voltage
`
`Page 18
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`

`US 2005/0073495 Al
`
`Apr. 7, 2005
`
`3
`
`of 31 LEDs in series approximates 110V, which is the
`standard supply voltage in the U.S. and Japan. In such a
`case, the driver can consist of a simple rectifier and smooth(cid:173)
`ing capacitor to drive this string of LEDs. More or less LEDs
`would be connected in series depending on the voltage drop
`across each LED or the power supply voltage.
`[0029] FIG. 8B shows a similar configuration, but for a
`bigger backlight and using four strings of approximately 31
`LEDs. In this case, the four strings of LEDs could even be
`used as diodes in the power supply full-wave rectifier,
`reducing the costs of the driver even further.
`
`[0030] A preferred embodiment of the invention is where
`the LEDs are driven in groups, where the LEDs are con(cid:173)
`nected in series, and where the forward voltage of each
`group matches the supply voltage of the power grid. For the
`U.S. and Japan, where this voltage is about 110 V, every
`group would contain between 28 and 37 LEDs in series. For
`Europe and other countries, this supply voltage is between
`220 and 240V, resulting in about 60 to 80 LEDs per group.
`
`If lowest cost is not the primary concern, but lower
`[0031]
`power consumption and high contrast are key requirements
`for the application, which is the case for high-end LCD-TV,
`other driving schemes are more preferred. An extreme
`example for this category is shown in FIG. 9, where every
`LED can be driven independently. In this configuration, the
`LEDs are connected in a matrix, and the LEDs can be driven
`row at a time, or column at a time, where every LED in a row
`or column can be driven at a different power. Especially the
`row-at-a-time option is attractive, since it resembles the way
`images are produced on a cathode ray tube (CRT), and the
`motion artifacts are greatly reduced.
`
`[0032] A different driving scheme, where the LEDs 24 are
`driven in groups between three and seven LEDs, is shown in
`FIG. 10. In this example, the hexagonal structure is used for
`14 groups, where each group can be driven independently.
`[0033] FIG. llA shows a simple geometry where the
`LEDs 24 are connected in series per row, and each row can
`be operated independently. This example shows six LEDs
`per row, but of course the actual number of LEDs depends
`on the size, thickness and brightness of the display. In this
`configuration, the brighter LEDs would be placed in the
`center of the display, while the dimmer parts would be
`placed towards the side of the backlight.
`
`[0034] An example of such geometry for a bigger display,
`where the left half of the display can be driven indepen(cid:173)
`dently of the right half of the display, is shown in FIG. lB.
`Of course, this configuration can be extended to operate the
`backlight in three segments as well, which is preferable for
`the large wide format screens.
`
`[0035] FIG. 12A shows a backlight configuration when
`only blue, UV, or near-UV LEDs are used, and where the
`color-converting phosphor layer 39 is on the cover plate 40.
`The cover plate 40 may or may not be a diffuser, depending
`on the amount of diffusing performed by the phosphor. The
`phosphor layer 39 is a uniform layer, consisting of one or
`more different type of phosphors. Preferably, a green and a
`red phosphor are used, but a yellow (YAG) phosphor could
`be used as well. This layer 39 can, for example, be applied
`by spray painting, screen-printing, or electrophoretic depo(cid:173)
`sition, or might be a film with uniform density of particles
`or a luminescent dye distributed throughout the film. This
`
`configuration is attractive because the phosphor is not on top
`of the LED die, and light emitted from the phosphor to the
`rear of the backlight 26 has a larger recycling efficiency than
`into the LED chips, due to the high reflectivity of the films
`used in the backlight 26. And in addition to the recycling
`efficiency, the phosphor can be operated at a lower tempera(cid:173)
`ture and does not have chemical compatibility issues with
`the LED die, improving the efficiency and lifetime consid(cid:173)
`erably. From a logistics point of view, this solution is
`attractive as well, as the blue backlight can be used for a
`large range of different displays, with different types of color
`filters, and only the phosphor layer thickness and phosphor
`concentration has to be optimized to fit a particular LCD.
`
`If blue LEDs 24 are used that match the desired
`[0036]
`blue pixel color of the LCD, then some blue-light transmis(cid:173)
`sivity of the green-red phosphor layer is desirable so that
`red, green, and blue light components are transmitted to the
`LCD.
`
`In another embodiment, one type of phosphor is
`[0037]
`applied to the cover plate 40, preferably the green or amber
`phosphor, while another phosphor, preferably the red phos(cid:173)
`phor, is applied to the rear panel 48 of the backlight
`configuration. The rear panel acts as a diffuser. This phos(cid:173)
`phor is not applied as a uniform coating, but is applied as a
`dot pattern. The combination of blue light from the LEDs
`and the red and green light from the phosphor layers
`produces a substantially white backlight for the LCD panel.
`By separating the phosphor in such a configuration, higher
`conversion efficiency is achieved, while by optimizing the
`size and spacing of the phosphor dots the required color
`balance and gamut can be achieved.
`
`[0038] FIG. 12B shows an alternative configuration,
`where the phosphor is integrated into the cover plate 42.
`Cover plate 42 may or may not provide additional diffusion,
`depending on the diffusion performed by the phosphor.
`
`[0039] FIG. 12C shows another embodiment, in which a
`uniform phosphor coating 39 is applied directly onto the
`LCD 14, more specifically, on the TFT array glass. Applying
`phosphors to glass is a well-developed and inexpensive
`process. Furthermore, by integrating the phosphor onto the
`LCD, the number of parts is reduced.
`
`[0040] FIGS. 13A and 13B show a configuration where a
`phosphor bulb 44 or 46 is formed around the blue LED 24,
`effectively creating a white lamp. In this approach, the
`mixing is done in two stages, first in the bulb, and second,
`between the bulb and the diffuser 28. For large spacing of the
`LEDs, this configuration has the benefit that the amount of
`phosphor used is smaller than it would be had the phosphor
`coated the cover plate. In another embodiment, phosphor is
`deposited directly on the LED chip.
`
`[0041] Although red, green, and blue LEDs in the array
`may be used if the pitch is small enough, it is preferable to
`use either all LEDs of a single color or white light LEDs
`(e.g., using a phosphor bulb) to obtain better color unifor(cid:173)
`mity at the output of the backlight. Having described the
`invention in detail, those skilled in the art will appreciate
`that, given the present disclosure, modifications may be
`made to the invention without departing from the spirit of
`the inventive concept described herein. Therefore, it is not
`intended that the scope of the invention be limited to the
`specific embodiments illustrated and described.
`
`Page 19
`
`

`

`US 2005/0073495 Al
`
`Apr. 7, 2005
`
`4
`
`What is claimed is:
`1. A display device comprising:
`
`a housing comprising reflective surfaces and a top open(cid:173)
`ing through which light is emitted for backlighting a
`liquid crystal display (LCD) panel;
`
`an array of substantially identical light emitting diodes
`(LEDs) supported on a reflective bottom surface in the
`housing, each LED emitting light through top and side
`portions of the LED, the LEDs being separated from
`one another by a distance greater that the width of a
`single LED; and
`
`a diffuser above the LEDs for providing diffused light to
`an LCD panel.
`2. The device of claim 1 further comprising an LCD panel
`over the diffuser.
`3. The device of claim 1 wherein the housing has a height,
`and wherein a ratio of the height to the pitch of the LEDs is
`between approximately 0.3 to 1.2.
`4. The device of claim 1 wherein a pitch of the LEDs is
`greater than 20 mm.
`5. The device of claim 1 wherein each of the LEDs output
`light having red, green, and blue components.
`6. The device of claim 1 wherein the LEDs comprise only
`blue LEDs.
`7. The device of claim 1 wherein the LEDs comprise only
`UV or near-UV LEDs.
`8. The device of claim 1 further comprising phosphor over
`the LEDs to convert light output by the LEDs into at least
`red and green light.
`9. The device of claim 1 further comprising phosphor over
`the LEDs to convert light output by the LEDs into red,
`green, and blue light.
`10. The device of claim 1 further comprising a phosphor
`layer beneath the diffuser.
`11. The device of claim 1 further comprising a phosphor
`layer deposited on the diffuser.
`12. The device of claim 1 further comprising phosphor
`surrounding top and side portions of each LED for color(cid:173)
`converting light emitted by the LEDs.
`13. The device of claim 1 wherein the diffuser comprises
`a phosphor, and the phosphor performs a diffusing function.
`14. The device of claim 1 wherein a number of LEDs are
`connected in series, a total voltage drop across the serially
`connected LEDs approximately equaling a publicly supplied
`standard voltage.
`15. The device of claim 1 wherein a number of LEDs are
`connected in series, a total voltage drop across the serially
`connected LEDs approximately equaling a publicly supplied
`standard AC supply voltage that has been rectified and
`filtered to be DC.
`16. The device of claim 1 wherein a number of LEDs are
`connected in series, a total voltage drop across the serially
`connected LEDs approximately equaling a publicly supplied
`standard AC supply voltage that has been rectified and
`filtered to be DC, wherein LEDs in the array are connected
`to perform a rectification of the AC supply voltage.
`17. The device of claim 1 wherein the LEDs are arranged
`in a rectangular grid.
`18. The device of claim 1 wherein the LEDs are arranged
`in a hexagonal grid.
`
`19. The device of claim 1 wherein the LEDs are connected
`in groups of series-connected LEDs.
`20. The device of claim 1 wherein the LEDs are connected
`such that a light output of individual LEDs or a portion of
`the LED array can be independently controlled to adjust the
`light output to improve uniformity of the light applied to the
`LCD panel.
`21. The device of claim 1 further comprising a plurality of
`light sensors in the housing for detecting an intensity of
`light, the sensors being coupled to a controller for control(cid:173)
`ling a brightness of LEDs associated with a sensor.
`22. The device of claim 1 further comprising a plurality of
`light sensors in the housing for detecting an intensity of
`light, the sensors being coupled to a controller for control(cid:173)
`ling a gray scale level of pixels in the LCD panel.
`23. The device of claim 1 further comprising:
`
`a first type of phosphor above the LEDs for converting
`light emitted by the LEDs to a first color; and
`
`a second type of phosphor on the bottom surface in the
`housing for converting light emitted by the LEDs to a
`second color.
`24. The device of claim 23 wherein a combination of the
`light emitted by the LEDs, the first type of phosphor, and the
`second type of phosphor produces a substantially white light
`for backlighting the LCD panel.
`25. The device of claim 23 wherein the first type of
`phosphor is in the form of dots.
`26. The device of claim 25 wherein the dots are deposited
`on the diffuser.
`27. The device of claim 23 wherein the first type of
`phosphor converts blue light to one of red light or green
`light, and the second type of phosphor converts blue light to
`the other of red light and green light.
`28. The device of claim 1 further comprising a phosphor
`layer for converting light from the LEDs to one or more
`other colors, the phosphor layer being formed on the LCD
`panel.
`29. The device of claim 28 wherein the phosphor layer is
`formed on a thin film transistor transparent layer in the LCD
`panel
`30. The device of claim 1 wherein the reflective bottom
`surface in the housing comprises a bottom surface forming
`the housing.
`31. A method for constructing a display comprising:
`
`providing a housing comprising reflective surfaces and a
`top opening through which light is emitted for back(cid:173)
`lighting a liquid crystal display (LCD) panel;
`
`providing an array of substantially identical light emitting
`diodes (LEDs) supported on a reflective bottom surface
`in the housing, each LED emitting light through top and
`side portions of the LED, the LEDs being separated
`from one another by a distance greater that the width of
`a single LED; and
`
`providing a diffuser above the LEDs for providing dif(cid:173)
`fused light to an LCD panel.
`32. The method of claim 31 further comprising an LCD
`panel over the diffuser.
`
`* * * * *
`
`Page 20
`
`