HIGH-UNIFORMITY LIMITED-SPREAD POINT SPREAD FUNCTION LIGHT EMITTER

• US 20150167904A1
• Filed: 06/04/2013
• Published: 06/18/2015
• Est. Priority Date: 06/04/2012
• Status: Active Grant

• Current Assignee: A.L. Whitehead Ltd.
• Original Assignee: A.L. Whitehead Ltd.
• Inventors: Whitehead, Lorne A.
• Granted Patent: US 9,534,746 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: F21K 9/62 using mixing chambers, e.g. housings with reflective walls
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133605 including specially adapted reflectors
• CPC Class Codes: G02F 1/133611 including means for improving the brightness uniformity
• CPC Class Codes: G09F 13/04 Signs, boards or panels, illuminated from behind the insignia
• CPC Class Codes: G09F 2013/222 with LEDs

Abstract

Simple yet powerful mathematical solutions are provided for producing a minimally-spreading de-pixelization light spread function with four-fold bilateral symmetry to create a High Dynamic Range LED-LCD display where the point spread functions of each LED regardless of intensity can be designed such that adjacent rows and columns of LEDs within an array blend smoothly and uniformly to create a non-pixelated continuous image in two dimensions on the diffuser screen and with minimal luminance overlap to minimize the computational demands required at video rate of an HDR display. The resulting image has substantially visually perfect uniform luminance, linear luminance and quadratic luminance gradient. Additionally a new display architecture is unveiled and described that emulates the mathematically developed light spread functions mentioned. This new architecture comprises several sub-aspects to tune the display device to the desired design requirements.

Claims

1. A light distribution system for producing a smoothly varying Lambertian luminance output on an output surface that emits light in a frontward direction towards the viewer, which is structurally periodic in the two perpendicular directions that are perpendicular to the frontward direction, thus comprising a two dimensional array of unit cells, each unit cell comprising:

a. A rear optical cavity having the following characteristics;

i. containing one or more electric light sources

ii. a rear surface with transmission less than about 5% and reflectance greater than about 70%

iii. side surfaces with transmission less than about 5% and reflectance greater than about 70%

iv. a front Lambertian transmission surface having absorption less than about 20% and which, by means of diffusion within the surface,

achieves a Lambertian angular distribution for the transmitted light and wherein the transmission percentage varies with position according to a predetermined transmission function T(x,y) having four-fold bilateral symmetry in a square unit cell array or six-fold bilateral symmetry in a hexagonal unit cell array matching the symmetry of the unit cell array and where x and y are measured from the center of the surface in their respective perpendicular directions

b. Adjacent to and in front of the rear optical cavity, a baffled diffusion cavity, comprising;

i. air or an optically clear material in the interior, with a thickness of about 30% of the width of the cavity

ii. a baffle with transmission less than about 5% located on each of the four sides of the cavity, with the baffle having a thickness less than about 10% of the width of the cavity

c. Adjacent to and in front of the baffled diffusion cavity, a non-baffled diffusion cavity, comprising;

i. Air or an optically clear material in the interior, with a thickness of about 30% of the width of the cavity

ii. A front Lambertian light output surface having absorption less than about 20% and which by means of diffusion within the surface achieves a Lambertian angular distribution for the transmitted light and wherein the transmission percentage exceeds at least about 30%

wherein the transmission function T(x,y) is predetermined by deterministic ray trace or experimental optimization to minimize the visual perception of dis-uniformity arising from the combination of dis-uniform light output, dis-uniform linear gradient light output variation, and dis-uniform quadratic gradient light output variation.

2. A light distribution system according to claim 1 wherein the electric light sources of said rear optical cavity are multi-colored to enable a greater gamut when illuminating color liquid crystal displays.

3. A light distribution system according to claim 2 wherein the multi-colored electric light sources of said rear optical cavity are comprised of red, green and blue light emitting diodes.

4. A light distribution system according to claim 1 wherein the rear and side surfaces of said rear optical cavity are sufficiently inter-reflective such that all electric light sources contained within the rear optical cavity produce substantially the same spatial variation of output light.

5. A light distribution system according to claim 1 wherein the Lambertian transmission surface of said rear optical cavity is comprised of titania or other high index particles dispersed within a continuous lower index polymer matrix such as acrylic or polycarbonate.

6. A light distribution system according to claim 1 wherein the unit cells are arranged in a square-like or hexagonal-like evenly spaced array.

7. A light distribution system according to claim 1 wherein the said baffled diffusion cavity is comprised of baffles with a reflective or retro-reflective surface.

8. A light distribution system according to claim 1 wherein the said baffled diffusion cavity is comprised of baffles with a first inner diffuse reflector layer and a second outer retro-reflective layer.

9. A light distribution system according to claim 1 wherein the optical structures interact to produce a point spread function that is a minimally-spreading de-pixelization light spread function for a two dimensional light emitting array.

10. A light distribution system according to claim 9 that achieves a point spread function that is a minimally-spreading de-pixelization light spread function for a two dimensional light emitting array further comprises light emitting diodes as the electric light sources contained within the rear cavity.

11. A light distribution system according to claim 1 that further comprises a light modulating LCD panel adjacent to the front Lambertian light output surface such that the light modulating LCD panel is disposed between the viewer and the front Lambertian light output surface.

12. A light distribution system according to claim 11 that further comprises light emitting diodes as the electric light sources in the rear cavity.

13. A light distribution system according to claim 12 in which the light emitting diodes and LCD panel are controlled in a manner that produces a high dynamic range.

14. A light distribution system according to claim 1 wherein the optical structures interact in such a way that for each individual cell, its point spread function emits more than about 30% of the source'"'"'s light out of that cell, more than about 60% of the source'"'"'s light from a combination of that cell and its immediate neighbors, and more than about 90% of the source'"'"'s light from a combination of that cell plus its immediate neighbors plus their immediate neighbors.

15. A light distribution system according to claim 8 wherein the optical structures interact to produce a point spread function that is a minimally-spreading de-pixelization light spread function for a two dimensional light emitting array.

16. A light distribution system according to claim 15 wherein the electric light sources of said rear optical cavity are comprised of light emitting diodes.

17. A light distribution system according to claim 16 further comprises a light modulating LCD panel adjacent to the front Lambertian light output surface such that the light modulating LCD panel is disposed between the viewer and the front Lambertian light output surface.

18. A light distribution system according to claim 3 wherein the said baffled diffusion cavity is comprised of baffles with a first inner diffuse reflector layer and a second outer retro-reflective layer.

19. A light distribution system according to claim 18 that further comprises a light modulating LCD panel adjacent to the front Lambertian light output surface such that the light modulating LCD panel is disposed between the viewer and the front Lambertian light output surface.

20. A light distribution system according to claim 19 that further comprises light emitting diodes as the electric light sources in the rear cavity.

21. A light distribution system according to claim 20 in which the light emitting diodes and LCD panel are controlled in a manner that produces a high dynamic range.

22. A light distribution system according to claim 21 wherein the optical structures interact in such a way that for each individual cell, its point spread function emits more than about 30% of the source'"'"'s light out of that cell, more than about 60% of the source'"'"'s light from a combination of that cell and its immediate neighbors, and more than about 90% of the source'"'"'s light from a combination of that cell plus its immediate neighbors plus their immediate neighbors.