Definitions

• This invention relates to night vision goggle compatible (NVG) lighting and more particularly to an apparatus for backlighting a liquid crystal display (LCD).
• NVG night vision goggle compatible
• LCD liquid crystal display
• LCD liquid crystal displays
• Farrell U.S. Patent 5,143,433, September 1 , 1992
• Kalmanash U.S. Patent 5,211 ,463, May 18, 1993
• a waveguide may be placed in front of a primary light source and that secondary light sources including one or more filtered lamps can illuminate an input to the waveguide.
• the Kalamanash waveguide is transparent so that the primary illumination passes through the waveguide during the daylight mode.
• the waveguide has one or more extraction features, which direct the light from the waveguide input towards a liquid crystal display (LCD). These extraction features are configured to have minimal efficiency degradation on the day mode.
• LCD liquid crystal display
• Abileah I (U.S. Patent 5,262,880, November 16, 1993) uses a large area night vision goggle (NVG) filter over a single lamp.
• NVG night vision goggle
• Habing et al (U.S. Patent 5,661 ,578, August 20, 1997) teaches that one or more secondary filtered collimated light sources can be positioned at the bottom of the sidewall of a backlight cavity. The collimated light then gets scattered throughout the cavity providing uniform illumination for a night mode.
• the secondary light sources are configured to be as small as practical to avoid negative effects to the day mode illumination.
• Abileah II (U.S. Patent 6,111 ,622, August 29, 2000) teaches a liquid crystal display with a dual backlight, namely a large area electroluminescent (EL) lamp behind a fluorescent bulb.
• EL electroluminescent
• a typical prior art backlight that is not night vision goggle
• NVG liquid crystal display
• LCD liquid crystal display
• FIG. 1 Note that there are associated optical films and sidewalls that are not shown in FIG. 1.
• This typical array-type backlight assembly 10 is composed of an array of fluorescent 'stick lamps' 20A ... 20N mounted on a reflective mounting plate 30. There is thus a long felt need in the art for an inexpensive sunlight-readable and NVG-compatible liquid crystal display backlight.
• the present invention comprises a dual backlight for a liquid crystal display (LCD) including primary light that allows the LCD to be viewed in direct sunlight conditions and separate secondary light that allows the LCD to be viewed under night vision goggles (NVG).
• LCD liquid crystal display
• NVG night vision goggles
• the secondary light is provided by side-emitting fiber elements that are positioned between stick fluorescent lamps that provide the primary light. These side-emitting fiber elements radiate light in a manner similar to stick lamps.
• a light source energizes the side-emitting fiber elements through an optical filter connected to each of the side emitting fiber elements while a suitable power source is electrically connected to the fluorescent lamps.
• a single power source may be employed alternately to energize the optical fiber light source and the fluorescent lamp power source.
• the optical fiber elements comprise individual side-emitting optical fibers that are positioned between adjacent fluorescent lamps.
• the optical fiber a single optical fiber is sinuously wound between the fluorescent lamps.
• FIG. 1 illustrates a prior art backlight suitable for use with an active matrix liquid crystal display.
• FIG. 2 illustrates an inventive backlight suitable for use with an active matrix liquid crystal display and including multiple side-emitting optical fibers in accordance with one illustrative embodiment of our invention.
• FIG. 3 illustrates an inventive backlight suitable for use with an active matrix liquid crystal display and including a single continuous side- emitting optical fiber in accordance with a second illustrative embodiment of our invention.
• FIG. 4 depicts a light source including an optical filter and a single continuous side-emitting optical fiber suitable for use in the embodiment of our invention shown in FIG. 3.
• a dual backlight assembly 11 includes both the primary light source comprising a plurality of unfiltered fluorescent lamps 20A ... 20N and the secondary light source comprising a plurality of side emitting fiber optic cables 40A ... 40N, such as are available from Poly-Optical Products Inc. These side-emitting fiber optic cables, 40A ... 40N, are driven by an alternate light source that is filtered prior to the entrance of each cable.
• the array of small diameter, unfiltered, 'stick' fluorescent lamps 20A ... 20N are used to provide illumination. Typically these lamps are a few millimeters in diameter, and are spaced apart to achieve the desired luminous efficacy and luminous uniformity.
• a 6" x 8" (150mm x 200mm) display may employ eight stick fluorescent lamps, where each stick fluorescent lamp has a diameter of approximately 3 mm and with the stick lamps evenly spaced apart.
• Suitable stick fluorescent lamps may be available from Harison Toshiba Lighting Corporation.
• a lamp driver 22 is electrically connected by leads 23 to the fluorescent stick lamps 20.
• Suitable lamp drivers may be purchased, for example, from Endicott Research Group, Inc.
• the lamps may be driven in parallel from the lamp driver 22, be all in series with the lamp driver 22, or be paired so that some are in series and some are in parallel.
• the individual side emitting optic cables 40 are optically driven by light from a light source
• the light source 42 may be for example, an incandescent lamp or one or more light emitting diodes (LED).
• the optical cable 43 is connected to one side of each of the side emitting fiber optic cables 40. The other end of the side emitting optical cables 40 may serve to absorb the light transmitted to it, have a reflective coating to return light through the cables, or have another external optical cable connected thereto for returning the light to the light source 42.
• auxiliary light pipes such as those from Bivar, Inc., are used to couple light from individual light emitting diodes
• both the lamp driver 22 for the fluorescent lamps 20 and the light source 42 for the fiber optic cables 40 may advantageously be driven by a common power source 35 which internally has electrical switches 36 provided for alternately powering either the fluorescent stick lamps 20 or the light source 42, which in turn optically drives the fiber optic cables 40.
• power can be simultaneously applied to both light sources; the lamp driver 22 and the light source 42. In a preferred embodiment, power is applied to both light sources simultaneously, with an easy-on/ easy-off function incorporated to provide a smooth transition between day and night operational modes.
• Illumination is provided during a 'night' operational mode from side-emitting fiber optic cables 40A ... 40N, where each fiber optic cable is positioned between adjacent fluorescent stick lamps.
• the side-emitting fiber optic cables 40A ... 40N are all routed to a single lamp or light source 42, with a suitable NVG- compatible optical filter 41 situated between the lamp and the side-emitting fiber optic cables 40A ... 40N.
• the fluorescent stick lamps 20A ... 20N are extinguished, and the side emitting fibers 40A ... 40N provide the illumination for the LCD, by operation of the electrical switches 36 within the power source 35.
• the side-emitting fiber optic cables 40A ... 40N have substantially the same diameter as the fluorescent stick lamps 20A ... 20N.
• the dual backlight assembly 12 includes both the primary light source comprising a plurality of unfiltered fluorescent lamps 20A ... 20N and the secondary light source comprising a single continuous side-emitting optical fiber 50.
• This single continuous side-emitting optical fiber 50 is driven at both ends by the alternate light source 42, where the alternate light source is filtered at the entrance to each end of the cable.
• the array of stick fluorescent lamps 20A ... 20N are used to provide illumination.
• the single continuous side-emitting optical fiber 50 is used to provide illumination.
• only one end of the single continuous side- emitting optical fiber 50 may be connected to the light source 42, the other end 51 having a reflective coating for returning light back through the optical fiber 50.
• the exit aperture 61 of the light source 42 has a relatively small surface area
• the light exiting the light source can be effectively filtered using a filter 41 , such as a night vision goggle compatible filter with a small surface area.
• This small area optical filter 41 is significantly less expensive than a large area filter that has been used to cover the entire display surface, such as six (6) by eight (8) inches.
• a set of three side- emitting optical cables each providing a primary color such as red, green, or blue, can be used instead of the white light side-emitting fiber optic cables as described above.
• the optical filter 41 can also provide a color matching function so that the user perceives the desired color saturation during both day and night modes.

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• 2002
  • 2002-10-10 EP EP02795512A patent/EP1435019A2/de not_active Withdrawn

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