Illumination – Illuminated scale or dial – Internal light source
Reexamination Certificate
1999-08-27
2002-08-27
O'Shea, Sandra (Department: 2875)
Illumination
Illuminated scale or dial
Internal light source
C362S812000, C362S800000, C362S230000, C362S561000, C349S061000
Reexamination Certificate
active
06439731
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to liquid crystal display devices, and more particularly to backlighting of such liquid crystal display devices.
BACKGROUND OF THE INVENTION
The liquid crystal display, more commonly known as LCD, is well known to those of ordinary skill in the art. As briefly described in U.S. Pat. No. 5,046,829, Liquid Crystal Display Backlighting Apparatus Having Combined Optical Diffuser And Shock Dampening Properties, issued to Worp on Sep. 10, 1991, the complete disclosure of which is incorporated herein by reference, the LCD is made up of cells containing a thin layer of liquid crystal material between a plurality of segmentary electrodes. An electric field applied between the electrodes of any one of the segmentary electrodes causes the liquid crystal material therebetween to align with the electric field, and the light that passes through the polarizer on one side of the liquid crystal material is absorbed by the polarizer on the opposing side of the material, such that the absorbing polarizer appears “on.”
Some LCD devices absorb or reflect ambient light impinging on the display face from outside the device. Therefore, ambient sun light or room light is required to view the display. These passive LCD devices have advantages of low power consumption combined with low weight and cost. Generally, however, passive LCD devices are inefficient in low ambient light conditions or at night. Therefore, LCD devices intended for low light conditions use internally supplied supplemental illumination. In a simple supplemental illumination system, one or more light sources, usually incandescent lamps, are placed behind the display, i.e., backlighting the display. One disadvantage of these simple supplemental illumination systems is lack of uniformity in the illumination. Incandescent lamps create localized “hot spots” which reduce the display's readability. While an optical diffusion panel placed between the illumination source and the display more evenly distributes the light from the internal sources and helps correct “hot spots,” unevenness in brightness is unavoidable absent some natural diffusion. Natural diffusion requires sufficient space between the illumination source and the display. However, thinness is a requirement of automobile dashboard or aircraft control panel displays which does not permit sufficient space for natural diffusion. One solution presented in U.S. Pat. No. 4,649,381, Liquid Crystal Panel Display Device, issued to Masuda et al. on Mar. 10, 1987, the complete disclosure of which is incorporated herein by reference, divides the display panel into “display blocks,” each displaying information in different small sectors of the panel, each sector including its own dedicated illumination source behind the respective panel sector and an optical diffuser shared by all of the panel sectors. While dividing the panel into discrete sectors may result in sufficiently uniform illumination within each sector, such discrete sectors do not address the problem presented by a full screen graphical or textual display. Another disadvantage of the divided display is the complete loss of information in any discrete sector if the illumination source fails in that sector of the display.
Another disadvantage of incandescent lamps is the high energy costs of powering the lamps. Today, many LCD devices use florescent lamps to control energy costs. However, florescent lamps are subject to the same unevenness in illumination from which incandescent lamps suffer. Also, florescent lamps present additional drawbacks. For example, more sophisticated LCD devices include the ability to adapt the display's light level to the ambient conditions. An automobile dashboard or aircraft control panel display usually includes a dimmer switch for adjusting the display brightness to a comfortable viewing level. Florescent lamps, however, require complex and expensive circuitry to adjust, or dim, the brightness of the supplemental internal illumination.
Another supplemental illumination configuration is side, or peripheral, lighting, which provides illumination at the sides of the display and uses a light guide to illuminate the interior portions of the display. Clearly, side lighting results in an unacceptably dark or under-lighted area in the central portion of a large area display due, at least in part, to attenuation at the illumination panel. In particular, in a large area LCD display, the central portion of the display remote from the illumination source is inevitably darker than the peripheral areas adjacent to the illumination source. To date, light guides in various configurations have attempted to adequately distribute the illumination rays across the display surface, as disclosed, for example, by U.S. Pat. No. 4,714,983, Uniform Emission Backlight, issued to Lang on Dec. 22, 1987; U.S. Pat. No. 4,929,062, Light Guide For LCD, issued to Guzik et al. on May 29, 1990; U.S. Pat. No. 4,729,185, Display Panel Illumination Device, issued to Baba on Mar. 8, 1988, the complete disclosures of which are incorporated herein by reference; and above incorporated U.S. Pat. No. 5,046,829. Such light guides are generally unsuccessful in providing uniform illumination of the display.
More recently, supplemental illumination has been provided using light emitting diodes, or LEDs. While the useful life or mean-time-between-failures (MTBF), is estimated at ten times (10×) or more of florescent lamps, the current high cost of LEDs has restricted their use to configurations using side lighting in combination with light guides, as disclosed for example by above incorporated U.S. Pat. No. 5,046,829. These attempts suffer the same limitation as light guides used with incandescent and florescent lamps: side lighting results in an unacceptably dark area in the central portion of a large area display remote from the illumination source.
Furthermore, side lighting of LCD displays with white light was previously possible using a mixture differently colored LEDs, i.e., using a mixture of LEDs radiating the three primary colors, the combination of which appears as white light to the viewer. However, LEDs radiating at some wavelengths are more expensive than those radiating at others due to differences in the chemical ingredients and manufacturing processes required to develop florescence at the proper wavelength. Therefore, the cost savings normally available from mounting a large number of same colored LEDs in a circuit has been unavailable in a white lighted LCD display.
Thus, until now, the long-felt need for a practical low cost, thin or low profile, backlighted large display LCD device having long lamp life, a high degree of illumination uniformity and simple brightness adjustment circuitry has been unattainable due to the nonuniformity of illumination using either florescent or incandescent lamps to illuminate large displays, even when combined with optical diffusers or light guides; the complex circuitry required to adjust brightness using florescent lamps; and the relatively high cost of colored LEDs. Furthermore, the long-felt need for such a practical low cost, thin or low profile, backlighted large display LCD device having white colored supplemental illumination sources has been unattainable due to the need to mix various differently colored LEDs to provide white side or back lighting.
SUMMARY OF THE INVENTION
The present invention overcomes display nonuniformity, display brightness control circuitry complexity, high cost, and short lamp life limitations of the prior art by providing a liquid crystal display device having essentially uniform backlighting in a flat panel display provided by multiple light emitting diodes mounted in backlighting relationship with a conventional liquid crystal display panel. The light emitting diodes providing a mean-time-between-failures, or MTBF, estimated at ten times (10×) that of prior florescent lamps. Furthermore, the illumination level or brightness of the light emitting diodes provided by the present invention is control
Barakchi Saied
Deutch Keith
Henke Darrell
Hoffman Scott
Johnson Rick
Honeywell International , Inc.
O'Shea Sandra
Sawhney Hargobind S.
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