Abstract:
A color display device ( 210, 310, 410 ) includes a backlight ( 214, 414 ) that cyclically emits first, second, and third component color backlighting in turn over a cycle period. The cycle period repeats at a cycling frequency (f) that exceeds a maximum human visual response frequency. A liquid crystal display (LCD) ( 112, 312, 412 ) generates a first display during the first component color backlighting, a second display during the second component color backlighting, and a third display during the third component color backlighting.

Description:
[0001]     This application is a continuation of prior application Ser. No. 10/248,037, filed Dec. 12, 2002, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     The following relates to the lighting and display arts. It is especially relates to active matrix liquid crystal display (LCD) devices, and will be described with particular reference thereto. However, it will also find application in other types of LCD displays, and in other types of backlit display devices.  
         [0003]     With reference to  FIG. 1 , a conventional flat screen display  10  includes an active matrix liquid crystal display (LCD)  12  and a backlight  14 . The LCD  12  includes a matrix of thin film transistors (TFTs)  16  fabricated on a substrate  18  of glass or another transparent material. A liquid crystal film  20  is disposed over the substrate  18  and the TFTs  16 . Addressing of the TFTs  16  by gate lines (not shown) deposited on the substrate  18  during TFT fabrication cause selected TFTs  16  to conduct electrical current and charge the liquid crystal film  20  in the vicinity of the selected TFTs  16 . Charging of the liquid crystal film  20  alters the opacity of the film, and effects a local change in light transmission of the liquid crystal film  20 . Hence, the TFTs  16  define display cells or pixels  22  in the liquid crystal film  20 . Typically, the opacity of each pixel  22  is charged to one of several discrete opacity levels to implement an intensity gray scale, and so the pixel  22  is a gray scale pixel. However, pixel opacity also can be controlled in a continuous analog fashion or a digital (on/off) fashion.  
         [0004]     A color-selective filter  26 ,  28 ,  30  is disposed over each pixel  22 . Specifically, first color filters  26  of a first color component, second color filters  28  of a second color component, and third color filters  30  of a third color component are distributed on pixels  22  across the display area of the LCD  12  to produce a color display. Typically, the first, second, and third colors include red, green, and blue primary colors to produce a red-green-blue (RGB). Preferably, a top matrix  32  of opaque lines separating pixels  22  is arranged between the color filters  26 ,  28 ,  30  to improve visual contrast. Specifically,  FIG. 1  shows a single color or RGB pixel that includes a first component color (e.g., red output by the pixel  22  covered by the filter  26 ), a second component color (e.g., green output by the pixel  22  covered by the filter  28 ), and a third component color (e.g., blue output by the pixel  22  covered by the filter  30 ) that are selectively combined or blended to generate a selected color.  
         [0005]     In operation, the backlight  14 , which includes a white compact fluorescent lamp (CFL), an array of white light emitting diodes (LEDs), or other white light source  34 , produces a substantially uniform white planar illumination directed toward the LCD  12 . A polarizer  36  of the LCD  12  disposed on a backside of the substrate  18  optimizes the light polarization with respect to polarization properties of the liquid crystal film  20 . The opacity of the pixels  22  is modulated using the TFTs  16  as discussed previously to create a transmitted light intensity modulation across the area of the display  10 . The color filters  26 ,  28 ,  30  colorize the intensity-modulated light emitted by the pixels to produce a color output. By selective opacity modulation of neighboring pixels  22  of the three color components, selected intensities of the three component colors (e.g., RGB) are blended together to selectively control color light output. The pixels  22  of a particular color or RGB pixel such as that shown in  FIG. 1  are blended. As is known in the art, selective blending of three primary colors such as red, green, and blue can generally produce a full range of colors suitable for color display purposes. Spatial dithering is optionally used to provide further color blending across neighboring color pixels.  
         [0006]     Conventional flat screen displays such as the exemplary display  10  suffer certain disadvantages. The light output efficiency is poor due to light absorption within the LCD  12 . Typically, the polarizer  36  reduces the light intensity by about 50%. The TFTs  16  produce further shadow losses of a magnitude dependent upon the TFT device area. Typical losses due to TFT shadowing in present active matrix liquid crystal displays are about 15%. The color filters  26 ,  28 ,  30  each substantially absorb two of the three color components to produce a pure third color component output, and hence have transmissivities no higher than about 30%. Combining these losses, the light output efficiency for the LCD  12  is about 5%.  
         [0007]     Another disadvantage of conventional LCD-based flat screen displays is manufacturing complexity. In particular, for each gray scale pixel  22  one of the color filters  26 ,  28 ,  30  is precisely aligned and bonded. Precision in the filter alignment is critical since misalignment can create gaps through which white light can pass. This alignment process is time-consuming and error-prone.  
         [0008]     Yet another disadvantage of conventional LCD-based flat screen displays is a relatively large color (RGB) pixel size since each color pixel is comprised of at least three component gray scale pixels  22 . In some arrangements, a second green pixel is included to compensate for visual color sensitivity differences, leading to a still larger color pixel size. Increased color pixel size corresponds to reduced display resolution.  
         [0009]     The following contemplates an improved apparatus and method that overcomes the above-mentioned limitations and others.  
       BRIEF SUMMARY  
       [0010]     According to one aspect, a color display device is disclosed. A backlight cyclically emits at least first, second, and third component color backlighting in turn over a cycle period. The cycle period repeats at a cycling frequency that exceeds a maximum human visual response frequency. A liquid crystal display (LCD) generates a first display during the first component color backlighting, a second display during the second component color backlighting, and a third display during the third component color backlighting.  
         [0011]     According to another aspect, a color display is disclosed. A backlight includes an array of backlight elements that produce backlight illumination. Each backlight element includes a plurality of lamps each of which emit illumination of a selected component color when energized. The backlight further includes backlight circuitry communicating with the backlight elements for energizing the plurality of lamps. A liquid crystal film is arranged to receive the backlight illumination. An array of liquid crystal control elements operatively define liquid crystal cells. Each liquid crystal control element is selectively operated to control transmission of the illumination through the liquid crystal cell. The liquid crystal control elements cooperatively produce a color display that selectively blends the selected component colors.  
         [0012]     According to another aspect, a display method is provided. A liquid crystal display is configured with a first light transmission pattern. A first illumination of a first color is generated. The first illumination is transmitted through the liquid crystal display configured with the first light transmission pattern. The configuring, generating, and transmitting are repeated for at least two other colors. The above operations are repeated to produce an updateable display.  
         [0013]     According to another aspect, a color display device is disclosed, including a light-transmissive liquid crystal display (LCD). A backlight is arranged to illuminate the light-transmissive LCD. The backlight includes at least first color component light emitting diodes (first color component LEDs), second color component light emitting diodes (second color component LEDs), and third color component light emitting diodes (third color component LEDs). LED circuitry cyclically alternates between powering the first color component LEDs to produce first color component backlighting, powering the second color component LEDs to produce second color component backlighting, and powering the third color component LEDs to produce third color component backlighting. LCD circuitry updates a display shown on the LCD. The updates of the LCD are synchronized with color changes of the backlight.  
         [0014]     According to yet another aspect, a color display device is disclosed. A backlight emits illumination with a selected temporal sequence of color components. A light-transmissive backlit display includes light-transmissive pixels distributed over a display area. The light-transmissive pixels are backlit by the backlight. The pixels have controlled opacity that is updated synchronously with the selected sequence of color components to effect full-color pixels.  
         [0015]     According to still yet another aspect, a color display device is disclosed. A planar light transmissive display includes an array of light-transmissive pixels each having selectable opacity. A backlight includes backlight elements. Each backlight element includes a plurality of light sources. Each light source emits light of a selected color component that is coupled to a selected one pixel. The plurality of light sources and the coupled pixels define a color picture element.  
         [0016]     Numerous advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.  
         [0018]      FIG. 1  shows a cross-sectional schematic view of a conventional color flat screen display including a liquid crystal display (LCD) with color filters and a backlight.  
         [0019]      FIG. 2  shows a cross-sectional schematic view of a flat screen display including an LCD coupled with a backlight of light emitting diodes of three component colors, in which each LCD gray scale pixel modulates light output from a light emitting diode of a selected color.  
         [0020]      FIG. 3  shows a cross-sectional schematic view of a flat screen display including an LCD coupled with a backlight of light emitting diodes of three component colors, in which each LCD pixel receives light from each of the three component color light emitting diodes in turn.  
         [0021]      FIG. 4  shows suitable control circuitry for driving the flat screen display of  FIGS. 3, 5 , and  6 .  
         [0022]      FIG. 5  shows a cross-sectional schematic view of a flat screen display including an LCD coupled with a backlight of light emitting diodes of three component colors, in which each LCD pixel receives light from light emitting diodes of each of the three component colors in turn. The display of  FIG. 5  has a lower resolution but higher light output efficiency than the display of  FIG. 3 .  
         [0023]      FIG. 6  shows a cross-sectional schematic view of a flat screen display including an LCD coupled with a backlight that produces generally planar illumination directed toward the LCD. The generally planar illumination cycles through three color components in succession. 
     
    
     DETAILED DESCRIPTION  
       [0024]     With reference to  FIG. 2 , a flat screen display  110  includes an active matrix liquid crystal display (LCD)  112  and a backlight  114 . The LCD  112  includes a matrix of thin-film transistors (TFTs)  116  fabricated on a substrate  118  of glass or another transparent material. In a suitable embodiment, the TFTs  116  are polysilicon or amorphous silicon transistors. A liquid crystal film  120  is disposed over the substrate  118  and the TFTs  116 . Addressing of the TFTs  116  by gate lines (not shown) deposited on the substrate  118  during TFT fabrication cause selected TFTs  116  to conduct electrical current and charge the liquid crystal film  120  in the vicinity of the selected TFTs  116 . Charging of the liquid crystal film  120  alters the opacity of the film, and effects a local change in light transmission of the liquid crystal film  120 . Hence, the TFTs  116  define display cells or pixels  126 ,  128 ,  130  in the liquid crystal film  120 . Typically, the opacity of each pixel is charged to one of several discrete opacity levels to implement an intensity gray scale, and so each pixel  126 ,  128 ,  130  is a gray scale pixel. Alternatively, pixel opacity can be controlled in an analog fashion to produce a continuous range of intensities, or in a digital (on/off) fashion in which each pixel  126 ,  128 ,  130  either transmits light with limited attenuation or substantially completely blocks light transmission.  
         [0025]     Unlike the conventional display  10  of  FIG. 1 , the flat screen display  110  does not include color filters. Rather it uses the backlight  114  to colorize the display. Specifically, an array of backlight elements  140  each include a first component color light emitting diode (LED)  142 , a second component color light emitting diode (LED)  144 , and a third component color light emitting diode (LED)  146 . For example, in one specific embodiment the first LED  142  emits red light, the second LED  144  emits green light, and the third LED  146  emits blue light, so that each backlight element  140  can emit red, green, or blue light. In this arrangement, the backlight element  140  corresponds to a color pixel. As is known in the art, selective blending of three primary colors such as red, green, and blue can generally produce a full range of colors suitable for color display purposes.  
         [0026]     Moreover, each of the three LEDs  142 ,  144 ,  146  is optically coupled to a corresponding pixel of the LCD. Specifically, the red LED  142  couples to the pixel  126 , the green LED  144  couples to the pixel  128 , and the blue LED  146  couples to the pixel  130 . Hence, the pixel  126  emits gray scale intensity-modulated red light, the pixel  128  emits gray scale intensity-modulated green light, and the pixel  130  emits gray scale intensity-modulated blue light. Hence, the color filters of the flat screen display  110  are preferably omitted. Optionally, the backlight  114  includes a wave guiding material  148  that improves optical coupling of the LEDs  142 ,  144 ,  146  with the respective pixels  126 ,  128 ,  130 .  
         [0027]     In operation, the red, green, and blue LEDs  142 ,  144 ,  146  emit light toward the LCD  112 . A polarizer  136  of the LCD  112  disposed on a backside of the substrate  118  optimizes the light polarization with respect to polarization properties of the liquid crystal film  120 . The opacity of each of the pixels  126 ,  128 ,  130  is modulated using the TFTs  116  to create a transmitted light intensity modulation across the area of the display  110 . In particular, pixels  126  coupled to the red LEDs  142  modulate the red light component, pixels  128  coupled to the green LEDs  144  modulate the green light component, and pixels  130  coupled to the blue LEDs  146  modulate the blue light component. By selective operation of the pixels  126 ,  128 ,  130  for each backlight element  140 , a selected color blending is achieved. The combination of gray scale pixels  126 ,  128 ,  130  define a full-color or RGB pixel.  
         [0028]     Advantageously, the LCD  112  omits light-absorbing color filters of the type  26 ,  28 ,  30  used in displays that combine an LCD with a white backlight. That is, the LCD  112  does not include the color filters  26 ,  28 ,  30  of the conventional display shown in  FIG. 1 . This simplifies manufacturing because there are no color filters to precisely align and affix to the LCD. Instead, a large-area cover sheet  150 , optionally including a top matrix  132  defined therein, is preferably included with the LCD  112 .  
         [0029]     Moreover, because color filters are preferably eliminated, the flat screen display  110  exhibits greatly improved light output efficiency compared with the conventional flat screen display  10 . Assuming a 50% loss at the polarizer  136 , TFT shadow losses of about 15%, and additional small reflection and absorption losses in the liquid crystal film  120  and the cover sheet  150 , a light output efficiency of about 22% is typically expected for the display  110 . The flat screen display  110  may also beneficially retain the LCD driving electronics of the conventional display  110  in a generally unmodified form, and each LED of the backlight  114  is driven continuously during display operation, further simplifying construction.  
         [0030]     However, the display  110  can retain a large color (RGB) pixel area, and manufacture of the display  110  includes alignment of the TFTs  116  with the red, green, and blue LEDs  142 ,  144 ,  146 . Moreover, depending upon the relative dimensions of the various components, there may be an issue with cross-coupling of LED light between the designated pixels  126 ,  128 ,  130 . Such cross coupling can cause, for example, blue light to leak into in an image region which is principally red. Optionally, color filters can be included to block cross-coupling and/or to improve spectral quality of the LED light outputs or otherwise alter the LED light output characteristics. In such an arrangement, since component colors pass through filters which are closely spectrally matched to the LED light outputs, light output losses in the filters is minimal.  
         [0031]     With reference to  FIG. 3 , in another display  210  the LCD  112  is coupled with a different backlight  214  to colorize the display. In the backlight  214 , an array of backlight elements  240  each include a first component color light emitting diode (LED)  242 , a second component color light emitting diode (LED)  244 , and a third component color light emitting diode (LED)  246 . For example, in one specific embodiment the first LED  242  emits red light, the second LED  244  emits green light, and the third LED  246  emits blue light, so that each backlight element  240  can emit red, green, or blue light.  
         [0032]     However, the flat screen display  210  differs from the display  110  in that each LED  242 ,  244 ,  246  is not coupled to a single gray scale cell or pixel of the LCD  212 . Rather, the LEDs  242 ,  244 ,  246  of the backlight element  240  are arranged close together as compared with the LEDs  142 ,  144 ,  146  of the backlight element  140  of the display  110 , and each of the LEDs  242 ,  244 ,  246  couples to all three of the three gray scale pixels  126 ,  128 ,  130 . Optionally, the backlight  214  includes a wave guiding material  248  that improves optical coupling of the each backlight element  240  with the three pixels  126 ,  128 ,  130 .  
         [0033]     When used in conjunction with the backlight  214  in the display  210 , the three gray scale pixels  126 ,  128 ,  130  do not cooperate to form a single color or RGB pixel. Rather, each of the gray scale pixels  126 ,  128 ,  130  is an independent color or RGB pixel which is capable of transmitting the first, second, or third component colors or any selected combination or blending of these three component colors. Hence, the LCD  112  provides substantially improved resolution when operated with the backlight  214  to define the display  210 , as compared with when the LCD  112  is operated with the backlight  114  of the display  110 .  
         [0034]     Because each gray scale pixel  126 ,  128 ,  130  is also a full-color or RGB pixel, it will be recognized that there is no distinction between gray scale pixels  126 ,  128 ,  130  and color or RGB pixels in the display  210 .  
         [0035]     With continuing reference to  FIG. 3  and with further reference to  FIG. 4 , to achieve color control for each of the pixels  126 ,  128 ,  130 , the backlight  214  is cycled through the three component colors by control circuitry  260  at a frequency f. In the illustrated embodiment, an oscillator or other frequency generator  262  produces a timing signal at the frequency f which is input to an LED pulse driver circuit  264 . The pulse driver circuit  264  successively pulses or energizes each of the LED groups R, G, B of first, second, and third primary colors, respectively, at the frequency f.  
         [0036]     At the same time and in a synchronous manner, an LCD update driver circuit  270  receives a synchronous timing signal at a frequency 3f generated by a frequency multiplier  272 , and modulates an LCD at the frequency 3f such that the LCD has a selected and generally different light transmission pattern during each of the pulsing of the R LED group, the pulsing of the G LED group, and the pulsing of the B LED group. That is, the LCD acts as a selectable gray scale mask through which each of the R, G, and B LED group illuminations successively pass, and the gray scale mask pattern is changed between each of the R, G, and B LED group illuminations.  
         [0037]     The frequency f is selected to be substantially higher than a human visual response frequency or visual “refresh” rate. That is, the frequency f is fast enough that the first, second, and third component colors produced during each cycle period 1/f blend together visually to produce a composite color. Hence, by spatially modulating transmission of the first, second, and third component colors through LCD pixel modulation during the cycle period 1/f, the display produces a selected composite color pattern that is visually perceived as a color image by a human viewer. The human eye “refreshes” at less than 50 Hz, and a critical flicker frequency for bright ambient light is typically around 30-35 Hz. Hence, the frequency f is preferably about 60 Hz or higher.  
         [0038]     In one specific embodiment, for each cycle period 1/f: (i) first primary color LEDs R (e.g., the LEDs  242  of the backlight  214 ) are energized for a time period ⅓f; (ii) second primary color LEDs G (e.g., the LEDs  244  of the backlight  214 ) are energized for a time period ⅓f, offset however by a temporal offset ⅓f to avoid overlap with the first primary color illumination (this frequency is designated f to indicate the ⅓f temporal offset); and (iii) third primary color LEDs B (e.g., the LEDs  246  of the backlight  214 ) are energized for a time period ⅓f, offset however by a time period ⅔f to avoid overlap with the second primary color illumination (this frequency is designated f″ to indicate the ⅔f temporal offset). Energizing of the first primary color LEDs R produces a first illumination of the first primary color; energizing of the second primary color LEDs G produces a second illumination of the second primary color; energizing of the third primary color LEDs B produces a third illumination of the third primary color.  
         [0039]     During generation of a first illumination produced by the energizing of the LEDs R, the LCD produces a first display through which the first primary color transmits. The first illumination is then extinguished, the LCD is updated, and the second illumination is produced by energizing the second LEDs G, which transmits through the updated LCD display. The second illumination is then extinguished, the LCD is again updated, and the third illumination is produced by energizing the third LEDs G, which transmits through the updated LCD display. The first, second, and third illuminations are repetitively cycled at the frequency f whose period is less than a response time of a human eye, to produce selected individual color blending for each pixel as selected by the LCD update driver circuit  270  based on image data  274  to display a selected image.  
         [0040]     Those skilled in the art can readily modify the above-described synchronous timing sequence for specific situations. For example, generally any ordering of the first, second, and third illuminations can be employed. Moreover, the first, second, and third illumination times need not be equal. For instance, in an RGB display the green illumination time can be extended relative to the red and blue times to account for lower human visual sensitivity to the green component. Furthermore, brightness differences between the first, second, and third LED groups R, G, B can be corrected by adjusting the corresponding illumination times.  
         [0041]     In yet another variation, additional colors can be added to the display to provide improved color rendering. For instance, white LED component can be added to red, green, and blue components of the backlight element  240  to provide improved white coloration. In this case, the frequency multiplier  272  should produce an output at 4f to provide independent LCD modulation for the R, G, B, and white components. Indeed, instead of the red, green, and blue primary colors, any combination of color components which is combinable to provide the desired color rendering range can be used. For example, four, five, six, or more LED types that produce four, five, six, or more color components can be used to provide highly accurate blended color rendering. It will particularly be appreciated that such improved color rendering using a four or more color components, using extended green illumination time, or the like are achieved without increasing the color pixel size.  
         [0042]     With continuing reference to  FIGS. 3 and 4 , in operation the red, green, and blue LEDs  242 ,  244 ,  246  produce red, green, and blue illumination cycled at a frequency f using the control circuitry  260 . The illumination is directed toward the LCD  112 . The polarizer  136  of the LCD  112  disposed on a backside of the substrate  118  optimizes the light polarization with respect to polarization properties of the liquid crystal film  120 . The opacity of the pixels  126 ,  128 ,  130  are independently modulated for each of the red, green, and blue illuminations using the TFTs  116  to selectively blend the red, green, and blue component colors to produce a selected color blending at each of the pixels  126 ,  128 ,  130 . Since for each cycle period 1/f there are three different illuminations (red, green, and blue), the LCD  112  is modulated at a frequency 3f by the LCD update driver circuit  270 .  
         [0043]     The LCD  112  used in the display  210  retains the high light output efficiency of about 22% it exhibits in the display  110 . Alignment of the backlight  214  with the LCD  112  to form the display  210  is substantially relaxed compared with alignment of the backlight  114  with the LCD  112  to form the display  110 . Each backlight element  240  is generally aligned with the three pixels  126 ,  128 ,  130 . Cross-coupling of light between the pixels  126 ,  128 ,  130  is substantially less problematic in the display  210  because only a single color component is being generated at any given time. Cross-coupling in the display  210  can produce blurring at color change boundaries, but does not inject a color component into an extended region which should be substantially devoid of that color component.  
         [0044]     In the described operating mode, the display  210  has improved spatial resolution compared with the display  110  because each color or RGB pixel consists of a single one of the gray scale pixels  126 ,  128 ,  130 . Or, stated conversely, each of the gray scale pixels  126 ,  128 ,  130  corresponds to a single full-color pixel.  
         [0045]     However, the display  210  can also be operated in a different mode, in which the gray scale pixels  126 ,  128 ,  130  are operated together to define a single larger full-color pixel. In this operating mode, the resolution is the same as that of the display  110  but the light output is greatly increased compared with the display  110 . For example, with the display  110  a pure red light output transmits only the pixel  126 , whereas with the display  210  a pure red light output transmits through all three gray scale pixels  126 ,  128 ,  130 . However, it will be recognized that in this latter operating mode there is electronic redundancy since the three TFTs  116  perform identical tasks. Moreover, cooperative employment of three TFTs  116  unnecessarily increases the shadowing losses.  
         [0046]     With reference to  FIG. 5 , a flat screen display  310  employs the same backlight  214  of the display  210  with the same control circuitry  260  of  FIG. 4 . However, in the display  310  the backlight  214  is coupled to a slightly modified liquid crystal display (LCD)  312  compared with the LCD  212 . The LCD  312  is structurally similar to the LCD  212 , and includes analogous components: a transparent substrate  318 , thin film transistors (TFTs)  316 , a liquid crystal film  320  that cooperates with the TFTs  316  to define pixels  322 , a polarizer  336  disposed on a backside of the substrate  318 , and a cover sheet  350 .  
         [0047]     However, the LCD  312  of the display  310  includes only a single full-color pixel  322  coupled with each backlight element  240 . This arrangement reduces the TFT shadowing losses to improve the light output efficiency. The three pixels  126 ,  128 ,  130  in a linear direction of the LCD  212  are reduced to a single pixel  322  in the LCD  312 , and so the number of TFTs in a given area is substantially reduced. However, each TFT  316  operates to charge an area substantially larger than the area charged by each TFT  216 , and so the TFT  316  is typically a larger device. Accounting for both TFT size and density, the display  310  is expected to have an improved light output efficiency of about 27% due to the reduced TFT shadowing losses.  
         [0048]     In both flat screen displays  210 ,  310  there is a selected coupling between defined backlight elements  240  and selected corresponding pixels. In the display  210 , each backlight element  240  has three pixels  126 ,  128 ,  130  optically coupled therewith. In the display  310 , each backlight element  240  has a single pixel  322  coupled therewith. However, as discussed next, it will be appreciated that particularized coupling of first, second, and third (or more) primary or component color LEDs with each pixel is optional.  
         [0049]     With reference to  FIG. 6 , a flat screen display  410  includes a liquid crystal display (LCD)  412  which is substantially similar to the LCD  212  of the display  210 . In particular, the LCD  412  includes analogous components: a transparent substrate  418 , thin film transistors (TFTs)  416 , a liquid crystal film  420  that cooperates with the TFTs  416  to define pixels  422 , a polarizer  436  disposed on a backside of the substrate  418 , and a cover sheet  450 .  
         [0050]     A backlight  414  of the flat screen display  410  is similar to the backlight  214  in that the backlight  414  includes analogous first color component LEDs  442 , second color component LEDs  444 , and third color component LEDs  446 . However, unlike the backlight  214  of the displays  210 ,  310 , the backlight  414  does not have the LEDs  442 ,  444 ,  446  grouped into backlight elements. Rather, the first component color LEDs  442  are distributed substantially uniformly over the display area. The second component color LEDs  444  are interspersed among the first component color LEDs  442  and are also distributed substantially uniformly over the display area. The third component color LEDs  446  are interspersed among the first component color LEDs  442  and among the second component color LEDs  444 , and are also distributed substantially uniformly over the display area.  
         [0051]     There is no particular correspondence or coupling between particular LEDs  442 ,  444 ,  446  and the pixels  422 . Rather, the spatially distributed first color LEDs  442  produce a generally planar illumination of the first color generally directed toward the LCD  412 . Similarly, the spatially distributed second color LEDs  444  produce a generally planar illumination of the second color generally directed toward the LCD  412 , and the spatially distributed third color LEDs  446  produce a generally planar illumination of the third color generally directed toward the LCD  412 . Optionally, the backlight  414  includes a wave guiding material  448  that improves optical coupling of the first component color LEDs  442 , the second component color LEDs  444 , and the third component color LEDs  446  with the LCD  412 . The LCD  414  and the backlight  412  are suitably operated by the control circuitry  260  at the frequency f as described previously with reference to the display  210 .  
         [0052]     In operation, the flat screen display  410  should generate each of the first component color illumination, the second component color illumination, and the third component color illumination in a substantially uniform spatial distribution across the display area to define a substantially uniform planar illumination that impinges upon the liquid crystal film  420 . To improve planar illumination uniformity, a high density of closely packed, relatively small LEDs can be employed. Moreover, thick wave guiding material  448  advantageously provides for substantial spreading of the LED light outputs for improved planar illumination uniformity. Optionally, the wave guiding material  448  includes light scattering centers such as reflective suspended particulates to scatter and distribute the LED light.  
         [0053]     The backlight  412  produces planar illumination of selected component colors, such as the primary colors red, green, and blue, under control of the pulse driver circuit  264 . It will be appreciated that the distributed discrete LEDs  442 ,  444 ,  446  can be replaced by other types of lamps or planar light sources. For example, red, green, and blue compact fluorescent lamps (CFLs) can be employed. Preferably the red, green, and blue CFLs are intertwined to provide overlapping illumination, and are preferably coupled to a wave guide to improve planar illumination uniformity across the display area. Additionally, the CFLs should use phosphorescent materials that have very rapid light decay times, so that each CFL can be cycled on and off at the frequency f. Similarly, incandescent color backlights can be employed with a wave guide that effects substantial light mixing. In an incandescent backlight embodiment, the incandescent filaments should each have a low thermal mass to promote rapid light cycling at the frequency f.  
         [0054]     Moreover, the LEDs of the backlights  112 ,  212 ,  312 ,  412  can be semiconductor devices, organic light emitting diodes, semiconductor lasers, or other types of lamps or light emitting devices. For the cycled backlights  212 ,  412  the various color component LEDs need not be identical or even similar, since variations in the light output intensity between the component colors can be corrected by varying the duration of each component color illumination in the sequence of the backlight cycling. For example, if high-power phosphide-based red LEDs are combined with lower power nitride-based blue LEDs, the blue illumination duration is suitably increased relative to the red illumination duration to correct for the intensity difference. Moreover, substantial differences in component color illumination intensity can also be corrected by increasing the number of LEDs of the lower illumination type in each backlight element. For example, each backlight element can include one red LED, one blue LED, and two green LEDs to adjust for reduced visual sensitivity to green. In the backlight  412 , an analogous modification is to increase the density of LEDs of the lower illumination type relative to the density of LEDs of the higher illumination type.  
         [0055]     Preferably, in each of the described embodiments, the LCD should transmit light with substantially no change in color properties of the light. That is, the LCD opacity for a given stored electrical charge is preferably substantially similar for the first, second, and third (or more) component colors. However, it will be recognized that relative differences in LCD opacity for the component colors is functionally equivalent to variations in the relative illumination intensity of the backlight color components. Hence, such absorption non-uniformities can be corrected, for example, by adjusting the relative color duty cycles for illumination cycling, or by increasing a number or relative density of LEDs corresponding to colors that are preferentially absorbed.  
         [0056]     Moreover, although active matrix LCD components have been described herein, those skilled in the art will appreciate that passive matrix LCDs or other light-transmissive backlit displays can also be used in place of the active matrix LCDs  112 ,  312 ,  412 . In general, any display which effects a selectable gray scale mask can be employed.  
         [0057]     When using either of the cycled backlights  214 ,  414 , each gray scale pixel of the corresponding LCD selectively transmits the first, second, and third component colors to generate substantially any selected component or blended composite color. That is, each pixel of the LCD operates as a full-color pixel. However, those skilled in the art will recognize that this in no way prohibits or limits optional cooperative color blending between neighboring full-color pixels to achieve various types of spatial dithering effects which are well-known in the color display arts. Such dithering is known to provide smooth color transitions, better color rendering, and other beneficial effects. Dithering is suitably incorporated into the image input data  274  received by the control circuitry  260  using known methods.  
         [0058]     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.