High efficiency backlighting system for rear illumination of electronic display devices

• US 5,907,222 A
• Filed: 11/11/1997
• Issued: 05/25/1999
• Est. Priority Date: 11/03/1993
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Litton Systems Incorporated
• Inventors: Spears, Loy L., Lengyel, J. Michael
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Bettendorf, Justin P.
• Application Number:
  US08/967,442
• Time in Patent Office: 560 Days
• Field of Search: 315/105, 315/309, 315/158, 315/49, 315/57, 315/94, 315/97, 315/115, 315/151, 362/84, 313/493, 313/549, 313/573, 313/576, 345/102
• US Class Current: 315/158
• CPC Class Codes: F21V 29/67 characterised by the arrangement of fans
• CPC Class Codes: G02F 1/133604 with lamps
• CPC Class Codes: G02F 1/133614 using photoluminescence, e.g. phosphors illuminated by UV or blue light
• CPC Class Codes: G02F 1/133617 Illumination with ultraviolet light; Luminescent elements or materials associated to the cell
• CPC Class Codes: H05B 41/295 with semiconductor devices and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence

Abstract

A fluorescent cavity backlight system that provides a high efficiency light source suitable for rear illumination of transmissive electronic display devices. The inventive fluorescent cavity backlight system can be adapted to a wide variety of flat panel display applications. The invention takes a complete system approach towards designing a high efficiency backlight source. The backlight system comprises three major subassemblies: a phosphor illuminator, a fluorescent cavity, and improved control/driver electronics. Each of the subassemblies has been optimized internally, and with respect to each of the other subassemblies.

Claims

1. In combination for providing backlighting of a display member to enhance viewing of an image on the display member:

(a) a plurality of tubes filled with at least one inert gas having properties of becoming energized and with an additive having properties of becoming ionized when the inert gas becomes energized and of generating ultraviolet energy upon becoming ionized, each of the said tubes possessing at least one anode and one cathode, wherein said tubes are made from material allowing substantially all UV radiation to pass through without absorption, and wherein said tubes lack any inner coating of photoluminescent material;

(b) an enclosure for the tubes comprising a front, back, sides, top and bottom, wherein the inner surfaces of said structure are comprised of a material reflective of visible light and wherein the front surface of said enclosure is comprised of a material transparent to visible light, and wherein all six said surfaces are coated with a light emissive material that is responsive to the ultraviolet energy from the tubes by converting the ultraviolet energy to visible light, said light emissive material being essentially transparent to visible light, thereby producing visible light for passage through the coated front surface to provide backlighting for the display member; and

(c) a circuit operatively coupled to a tube for simultaneously producing and controlling a plurality of independent electrical currents within said tube, including a cathode current passing through a filament type cathode and a separate arc current drawn by a voltage potential between a cathode and an anode, the arc current thereby traversing a path from a cathode to an anode within said tube, and wherein the plurality of electrical currents operate in concert to regulate and control the power discharged through the tube in the production of ultraviolet light, thereby providing a plurality of selectable levels of visible light produced within the enclosure in response to excitement of said inert gasses and ionization of said additive.

2. The combination of claim 1 wherein the circuit operatively coupled to the tube further comprises:

an analog temperature sensor mounted proximate to said cathode for monitoring the temperature of said cathode;

an analog/digital converter for converting temperature data to digital format;

a microprocessor; and

means for channeling said digital temperature to the microprocessor.

3. The combination in claim 2 wherein the voltage potential between the anode and cathode is controlled by said microprocessor using an algorithm that takes into account data from a group consisting of the arc current, cathode currents, cathode temperatures or any combination of these elements.

4. The combination of claim 2 wherein said circuit transmits the arc current at a variable frequency as determined by said microprocessor.

5. The combination in claim 4 wherein the variable frequency arc comprises a sinusoidal waveform.

6. The combination in claim 4 wherein the variable frequency arc comprises a square wave.

7. The combination in claim 2 wherein the voltage potential between the anode and cathode is controlled by said microprocessor and wherein said voltage is regulated in a continuous sequence of pulses or duty cycles of approximately four-millisecond duration each duty cycle being comprised of an "on" period of voltage and an "off" period of no voltage, and wherein the length of time said voltage is in the "on" state can be increased incrementally in increments of approximately 1/2 microsecond duration, ranging from zero microseconds to the entire 4 millisecond period of said duty cycle, thereby providing approximately 8,000 incremental levels of luminescence.

8. The combination in claim 7 wherein the voltage potential between the anode and cathode is selectable in at least two levels in addition to an off state.

9. The combination in claim 2 wherein the cathode temperature can be raised or lowered by running a controlled current through the filament-type cathode, said current being adjustable to at least two different current levels in addition to an off state, and wherein said current is controlled by said microprocessor.

10. The combination in claim 2 wherein said microprocessor controls an on/off state of a fan which is positioned to provide cooling for said cathode.

11. The combination of claim 1 wherein the front surface of said enclosure is selected from a group comprising `white water` glass, ceramics or plastics which are resistant to UV radiation while being transparent to visible light, and wherein said light emissive material covering the inner surfaces of said enclosure is a phosphor that efficiently converts the ultraviolet energy to visible light.

12. The combination of claim 1, wherein the additive in each of the tubes is mercury and there is more than one inert gas in each of the tubes the inert gases including argon and neon.

13. The combination in claim 12, wherein the inert gases are approximately 95% argon and approximately 5% neon.

14. The combination in claim 1 wherein the enclosure is substantially sealed to prohibit escape of ozone from said enclosure.

15. The combination of claim 1 wherein the tubes within the enclosure are configured in a serpentine or other non-linear shape, and wherein the non linear configuration is achieved by mitering.

16. The combination of claim 1 wherein said plurality of tubes are fit into a single backlighting enclosure through interdigiting or interlacing of the tubes.

17. The combination of claim 1 wherein the inside diameter of said tubes are on the order of 7 mm to 13 mm.