Abstract:
A transflective cockpit display device for aircraft has display electronics and a transflective liquid crystal display (LCD). The backlight lamp of the transflective LCD is brighter than those of common transmissive LCDs to facilitate viewing in the changing light conditions experienced by aircraft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to electronic displays and, more specifically, to displays used in aircraft. 
         [0003]    2. Description of the Related Art 
         [0004]    The liquid crystal display (LCD) screen is the most common type of display screen for computing and communication devices in use today. It is particularly suitable for mobile devices, such as laptop computers, personal digital assistants (PDAs) and telephones, because it is generally lighter in weight and more rugged, space-efficient and power-efficient than a display based upon alternative technologies. Nevertheless, LCDs are used in a wide variety of display devices, including those of aircraft and ground vehicles. LCDs are commonly backlit by a lamp built into the display housing to enhance readability in dim light. An LCD that can be backlit is referred to as “transmissive” because the light emitted by the lamp is transmitted through the screen to the viewer&#39;s eyes. 
         [0005]    Transmissive LCDs are difficult to view in bright sunlight or other bright conditions because bright light tends to produce a washed-out effect or reduced-contrast effect. Fully reflective LCDs that have no backlighting do not suffer from this problem, as they reflect all of the ambient light. Nevertheless, fully reflective LCDs are not used in display devices intended to be used in a variety of light conditions because they cannot be viewed in darkness and dim light. 
         [0006]    A compromise solution has been to provide a transmissive LCD with a very bright backlight lamp. Whereas a typical transmissive LCD may have a lamp with a brightness of 200-400 nit (candela per square meter), LCDs having lamp brightnesses on the order of 1,000 nit have been developed for devices intended for use both indoors in dim light and outdoors in bright sunlight. Such super-high-brightness transmissive LCDs are generally bulkier, less economical and less power-efficient than the standard transmissive LCDs used in the vast majority of commercially available display devices. Consequently, their use has largely been confined to military and aerospace applications, such as aircraft instrument panels, where performance is of greater concern than low cost. 
         [0007]    LCDs that mix transmitted backlight with reflected ambient light are known as “transflective” (also sometimes referred to as “transreflective”). A transflective LCD that passes or transmits a high percentage of the backlight while reflecting some of the ambient light is a good compromise between a transmissive LCD and a reflective LCD because it is highly readable in both dim and bright light. The brightness of transflective LCDs as measured off the screen in darkness, i.e., due entirely to backlighting, is typically on the order of 200-400 nit, as in a typical consumer-grade transmissive LCD. In fact, some manufacturers have retrofitted or modified commercial-off-the-shelf transmissive LCDs by installing partially reflective, partially transmissive films between the backlight lamp and the LCD. Other methods for making transflective LCDs include thin-film vacuum deposition of a material such as indium-tin oxide directly on the rear of the LCD. 
         [0008]    Accordingly, it would be desirable to provide an improved LCD display for use in aircraft. It is to such a display and method of use that the present invention is primarily directed. 
       SUMMARY OF THE INVENTION 
       [0009]    Briefly described, in a preferred form, the present invention relates to a high-brightness transflective display device for aircraft. The display device has display electronics and a transflective liquid crystal display (LCD) coupled to the display electronics. The backlight lamp of the transflective LCD preferably has a brightness selected such that it causes the display device to have a brightness (as measured in ambient darkness, i.e., brightness due entirely to the backlighting) greater than about 500 nit (candela per square meter), which is much brighter than most commercially available transmissive LCDs. Still more preferably, the LCD has a brightness greater than about 750 nit. The high-brightness transflective display device can be made economically by modifying a commercial-off-the-shelf transmissive LCD display device, adding a transmissive-reflective coating or film, and replacing the backlight lamp with a high-brightness backlight lamp. 
         [0010]    The above-described transflective display device can be included in aircraft instruments. The transflective display is easily viewable in aircraft cockpit light conditions ranging from bright sunlight to total darkness. The novel display device of the present invention provides excellent performance without the cost, power consumption and heat generation of very-high-brightness purely transmissive displays. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a high-brightness transflective display device, according to a preferred illustrative form of the present invention. 
           [0012]      FIG. 2  is a cross-sectional view of the high-brightness transflective display device of  FIG. 1 , taken on line  2 - 2  of  FIG. 1 . 
           [0013]      FIG. 3  illustrates the high-brightness transflective display device of  FIG. 1  in an aircraft instrument mounted in an aircraft instrument panel. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    As illustrated in  FIGS. 1-2 , a high-brightness transflective display device  10  has a shape similar to that of conventional display devices included in laptop computers, flat-screen computer monitors, avionics instruments, and the like. As such, display device  10  includes a relatively thin-profile rectangular housing  12  in which are mounted a transflective liquid crystal display (LCD)  14  and associated display electronics  16 . 
         [0015]    LCD  14  comprises, in layered arrangement, a cover glass  18 , a liquid crystal panel  20 , a partially transmissive, partially reflective (transflective) film  22 , a brightness-enhancing film  24 , a diffuser  26 , an edge-lit backlight or light guide  28 , and a reflective film  30 . Display electronics  16  controls liquid crystal panel  20  by applying electric charges in the conventional manner. In a manner analogous to a one-way mirror, transflective film  22  reflects a portion of the ambient light that may be incident upon cover glass  18  and transmits another portion of that ambient light. A high-brightness backlighting lamp  32 , such as a cold cathode fluorescent lamp (CCFL), is optically coupled to light guide  28 . The brightness of backlighting lamp  32  causes LCD  14  to have a measurable brightness (as measured off cover glass  18  from an observation point  33  in ambient darkness) greater than about 500 nit (candela per square meter). In an especially preferred form, LCD  14  has a brightness greater than about 750 nit. However, a lamp having a much greater brightness (e.g., greater than about 1,500 nit) may consume excessive power and generate excessive heat. With the exception of the brightness of backlighting lamp  32  and the manner in which it is controlled, the arrangement, structure and function of the individual above-referenced elements shown in  FIG. 2  are conventional, well known in the art, and therefore not described in further detail herein. 
         [0016]    In addition to controlling liquid crystal panel  20 , display electronics  16  controls the brightness of backlighting lamp  32  in response to a signal received from an ambient light sensor  31 . Preferably, the brightness of backlighting lamp  32  is maximized when ambient light is neither very bright nor very dim, as would typically occur at dusk and dawn. Still more preferably, in addition to maximizing the brightness of backlighting lamp  32  at dusk and dawn, the brightness of backlighting lamp  32  is minimized when ambient light is low and set to a medium brightness when ambient light is bright. Operating backlighting lamp  32  in this manner conserves power and works synergistically with the transflective properties of LCD  14 . In very bright ambient light, display electronics  16  may turn backlighting lamp  32  off entirely. 
         [0017]    Transflective LCD  14  can be made economically by modifying a commercial-off-the-shelf (COTS) transmissive LCD device. For example, film  22  or, alternatively, a transmissive-reflective coating (e.g., vacuum-deposited indium-tin oxide, not shown) can be added to the COTS device, and the manufacturer&#39;s original backlighting lamp (typically 200-400 nit for a consumer-grade device) can be replaced with the above-described high-brightness backlighting lamp  32 . 
         [0018]    As illustrated in  FIG. 3 , high-brightness transflective display device  10  can be included in an aircraft instrument  34  mountable in a conventional manner in a cockpit instrument panel  36 . Aircraft instrument  34  and its display device  10  and other features can be of any conventional type, shape, size, number, etc., and any such features that may be shown in  FIG. 3  are shown for purposes of illustration only. Although shown mounted in instrument panel  36  in the exemplary embodiment of the invention, in other embodiments display device  10  can be mounted in any other suitable location in an aircraft, such as in a passenger cabin. 
         [0019]    The unusually bright transflective display device  10  is easily viewable by pilots in the changing light conditions typical of aircraft cockpits. It remains viewable even if part of LCD  14  is in deep shadow and part is in bright sunlight, as often occurs as the aircraft changes attitude with respect to the sun. It also remains viewable during the problematic transition times of day of dusk and dawn. 
         [0020]    It will be apparent to those skilled in the art that various modifications and variations can be made to this invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided that they come within the scope of any claims and their equivalents. With regard to the claims, no claim is intended to invoke the sixth paragraph of 35 U.S.C. Section 112 unless it includes the term “means for” followed by a participle.