Diffusively reflecting shield optically, coupled to backlit lightguide, containing LED's completely surrounded by the shield

• US 5,883,684 A
• Filed: 06/19/1997
• Issued: 03/16/1999
• Est. Priority Date: 06/19/1997
• Status: Expired due to Term

• Current Assignee: InnoLux Corporation
• Original Assignee: Three-Five Systems, Inc.
• Inventors: Petera, Michael G., Millikan, Bart D.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): HORNEY, KARI M
• Application Number:
  US08/878,899
• Time in Patent Office: 635 Days
• Field of Search: 349/65, 349/71, 362/26, 362/27, 362/31
• US Class Current: 349/65
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0073 Light emitting diode [LED]

Abstract

An LCD backlight (30) comprises generally rectangular parallelepiped light guide (36) with an exit aperture (31) that is smaller than the surface area light guide (36) and illuminates a LCD (49). The light guide is illuminated by a plurality of Light Emitting Diodes (LED) dies (32) disposed along at least one edge of the light guide. A translucent fluorescent film (40) is disposed immediately above the exit aperture to diffuse the light exiting the exit aperture and also the change in the dominant wavelengths. Further, the light guide (36), the LEDs (32), fluorescent film (40), and additional light redirecting layers (42 and 44) are completely surrounded by and optically coupled to a diffusively reflective film (50), which covers the back surface, the edges, and the front surface of the light guide except for the exit aperture. This diffusively reflective shielding is covered by a conventional reflective material layer (51) to ensure no light escapes the backlight except through the exit aperture.

Claims

1. Apparatus for backlighting a liquid crystal display, comprising:

a light guide assembly, said light guide assembly comprising;

a light guide comprising a generally rectangular parallelepiped of a transparent material having a first index of refraction, said light guide having a planar front surface having a first area, said light guide further comprising first and second edges;

a plurality of light emitting diodes disposed adjacent said first edge for providing light to said light guide;

a translucent film disposed above said front surface for diffusing light exiting therefrom; and

a first light redirecting film disposed above said translucent film, said first light redirecting film having a surface composed of a plurality of parallel repeating prisms oriented along a first axis in the plane of said first light redirecting film; and

a shield disposed at least partly around said light guide assembly and completely around said diodes to form a substantially continuous reflector, said shield defining an exit aperture having a second area, said second area having a dimension smaller than said first area, said shield and said light guide cooperating to provide a light integrating volume having a substantially Lambertian light source at said exit aperture.

2. The apparatus of claim 1, further comprising:

a second light redirecting film disposed above said first light redirecting film, said second light redirecting film having a surface composed of a plurality of parallel repeating prisms oriented along a second axis in the plane of said second light redirecting film, said second axis being orthogonal to said first axis.

3. The apparatus of claim 1, wherein:

said shield is optically coupled to said light guide with an optically coupling material.

4. The apparatus of claim 3, wherein:

said optically coupling material comprises a photopolymeric adhesive.

5. The apparatus of claim 1, wherein:

said light guide comprises a rectangular parallelepiped having a thickness of no more than 2.5 millimeters.

6. The apparatus of claim 1, wherein:

said first and second edges comprise grooves sized to receive said light emitting diodes flush with the surface of said first edge.

7. The apparatus of claim 1, wherein:

said translucent film includes a fluorescent material adapted to absorb light energy exiting said light guide and re-radiating said light energy at a predetermined distribution of wavelengths.

8. Apparatus for backlighting a liquid crystal display, comprising:

a light guide assembly having a front surface and a back surface, said light guide assembly comprising;

a light guide comprising a generally rectangular parallelepiped having a planar front surface having a first area, said light guide further comprising first and second edges;

a plurality of light emitting diodes disposed adjacent said first and second edges for providing light to said light guide, said plurality of light emitting diodes having a total power consumption of less than 400 milliwatts;

a translucent film juxtaposed said front surface for diffusing light exiting therefrom; and

a first light redirecting film juxtaposed said translucent film, said first light redirecting film having a surface composed of a plurality of parallel repeating prisms oriented along a first axis in the plane of said first light redirecting film;

a shield disposed at least partly around said light guide assembly and completely around said diodes, said shield comprising a diffusively reflective surface defining an exit aperture at said front surface of said light guide assembly, said shield and said light guide assembly cooperating to provide a substantially Lambertian light source at said exit aperture having an output of at least 300 foot-Lamberts and an illuminance uniformity of no more than 1.6 to 1.

9. A display apparatus comprising:

A liquid crystal display panel, said liquid crystal display panel being at least partially transmissive such that at least a portion of illumination is transmitted through said liquid crystal display panel;

a light guide assembly, said light guide assembly comprising;

a light guide comprising a sheet of transparent material having a first index of refraction, said light guide having a planar front surface having a first area, said light guide further comprising first and second edges;

a plurality of light emitting diodes disposed adjacent said first edge for providing light to said light guide;

a first light redirecting film disposed above said light guide, said first light redirecting film having a surface composed of a plurality of parallel repeating prisms oriented along a first axis in the plane of said first light redirecting film;

a shield disposed around said light guide assembly to form a substantially continuous reflector, said shield having an defining an exit aperture having a second area, said second area having a dimension smaller than said first area, said shield and said light guide cooperating to provide a light integrating volume having a substantially Lambertian light source at said exit aperture; and

an adhesive layer disposed between said light guide and said shield, said adhesive adapted to optically couple said shield to said light guide, said adhesive layer having an index of refraction no less than said first index of refraction.