Backlighting apparatus for uniformly illuminating a display panel

• US 5,892,325 A
• Filed: 10/27/1997
• Issued: 04/06/1999
• Est. Priority Date: 10/05/1993
• Status: Expired due to Term

• Current Assignee: InnoLux Corporation
• Original Assignee: Teledyne Lighting & Display Products, Inc. (Teledyne Technologies Incorporated)
• Inventors: Gleckman, Philip L.
• Primary Examiner(s): O'Shea, Sandra
• Assistant Examiner(s): HAYNES, MACK NELSON
• Application Number:
  US08/958,222
• Time in Patent Office: 526 Days
• Field of Search: 313/110, 313/112, 313/113, 313/578, 313/580, 313/116-117, 313/491-93, 313/631, 313/634-35, 313/495, 359/48-50, 359/40, 359/42, 362/19, 362/26, 362/257
• US Class Current: 313/578
• CPC Class Codes: F21S 8/00 Lighting devices intended for fixed installation F21S9/00, F21S10/00 take precedence; using a string or strip of light sources F21S4/00
• CPC Class Codes: F21V 7/00 Reflectors for light sources characterised by cooling arrangements F21V29/505
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02F 1/133507 Films for enhancing the luminance
• CPC Class Codes: G02F 1/133605 including specially adapted reflectors
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/1337 Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers

Abstract

A light source for backlighting a display panel comprises a light-emitting device such as an incandescent light bulb or LED array disposed within a cavity having diffusely reflecting walls and an aperture. A diffuser and brightness enhancing film are situated proximate the opening of the aperture which illuminates the display to be backlit. Preferably, light emerging from the aperture is substantially uniform in intensity and color, and in one embodiment, a color filter is employed to whiten the light emerging from the aperture. One embodiment has an aperture in which the ratio of the area of the aperture to the sum of such area and the surface area of the cavity is at least 0.05. In this embodiment, the ratio of the depth of the cavity to an edge to edge dimension of the cavity is at least 0.1.

Claims

1. An apparatus for illuminating a display panel having a rear surface and a front surface, said display panel being at least partially transmissive such that at least a portion of illumination on said rear surface is transmitted to said front surface, said apparatus comprising:

a light source for backlighting said display panel, said light source comprising;

a device that emits light;

a housing having diffusive reflective interior surfaces forming a cavity, said cavity having a depth, said light emitting device mounted to illuminate said cavity, said housing having an aperture which opens into said cavity, said aperture permitting light to emerge from said cavity, whereby said aperture, when juxtaposed with said rear surface of said display panel, illuminates said rear surface of said display panel, said cavity having a diffusive reflective surface area and said aperture having an area, the ratio of said area of said aperture to the sum of (i) said area of said aperture and (ii) said surface area of said cavity being at least 0.05, said aperture having an edge to edge dimension, the ratio of said depth to said edge-to-edge dimension being at least 0.1;

a diffuser;

a brightness enhancing material which concentrates illumination so as to enhance the brightness of light illuminating the display panel;

wherein said light emitting device emits light from a single location within said cavity, said single location being small compared to the size of said cavity; and

wherein said diffuser and said brightness enhancing film are positioned on said housing in generally parallel relationship such that illumination emitted by said light emitting device passes through both said diffuser and said brightness enhancing film prior to emerging from the apparatus to illuminate said display panel.

2. The apparatus of claim 1, wherein said light emitting device comprises an incandescent light bulb.

3. The apparatus of claim 2, wherein said dimension is a bisector dimension.

4. The apparatus of claim 2, wherein said apparatus additionally comprises a color filter having characteristics selected to increase the whiteness of light from said incandescent bulb, whereby said color temperature is above 4,000°

K.

5. The apparatus of claim 2, wherein said incandescent bulb has a filament enclosed by an envelope, and wherein the ratio of the depth of said housing to the diameter of said envelope enclosed by said filament is less than 1.8.

6. The apparatus of claim 2, wherein said incandescent bulb has a filament enclosed by an envelope, and wherein the depth of said housing is not substantially greater than the diameter of said envelope enclosed by said filament.

7. The apparatus of claim 1, wherein the interior surfaces of said cavity are coated with white paint having a reflectance higher than 88 percent.

8. The apparatus of claim 1, wherein the reflective interior surfaces of said housing further comprise high-reflectance plastic.

9. The apparatus of claim 4, wherein the color filter is disposed between said cavity and said display panel.

10. The apparatus of claim 1, wherein said brightness enhancing material comprises a film of linear pyramidal structures.

11. The apparatus of claim 10, wherein said viewing angle is no more than about 35 degrees.

12. The apparatus of claim 10, wherein said brightness enhancing material further comprises a second film of linear pyramidal structures disposed in a direction orthogonal to said film of linear pyramidal structures.

13. The apparatus of claim 2, wherein said incandescent bulb is disposed within said cavity outside of a viewing aperture portion of said cavity.

14. The apparatus of claim 1, wherein the ratio of said depth to said dimension is at least 0.2.

15. The apparatus of claim 2, wherein said incandescent bulb is disposed within a viewing aperture portion of said cavity and wherein said housing further comprises a baffle positioned between the bulb and said aperture.

16. The apparatus of claim 1, wherein said aperture is rectangular, and wherein none of the sides of said aperture exceeds 2 inches in length.