Light distribution for illuminated keyboard switches and displays

• US 5,397,867 A
• Filed: 03/23/1993
• Issued: 03/14/1995
• Est. Priority Date: 09/04/1992
• Status: Expired due to Term

• Current Assignee: Lucas Industries Inc (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: Lucas Industries Inc (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Demeo, Gregory B.
• Primary Examiner(s): Friedhofer, Michael A.
• Assistant Examiner(s): Hoff, Marc S.
• Application Number:
  US08/035,967
• Time in Patent Office: 721 Days
• Field of Search: 200/5 R, 200/5 A, 200/511, 200/512, 200/310, 200/311, 200/312, 200/313, 200/314
• US Class Current: 200/5.00A
• CPC Class Codes: G02B 6/0043 provided on the surface of the light guide
• CPC Class Codes: H01H 13/702 with contacts carried by or formed from layers in a multilayer structure, e.g. membrane switches
• CPC Class Codes: H01H 2219/056 Diffuser; Uneven surface
• CPC Class Codes: H01H 2219/064 Optical isolation of switch sites

Abstract

Disclosed is the backlit display and/or backlit keyboard display which have a controlled level of illumination at the surface thereof. Where such switch and/or display are illuminated by a light emitting diode, the present invention interposes an optical filter between the light emitting diode and the surface of the cover. The optical filter contains a pattern thereon having a variable density distribution of opaque material which in a preferred embodiment is densest in the area closest to the light emitting diode and decreases in density in areas away from the light emitting diode. In a preferred embodiment the optical filter is a "negative" of the illumination without a filter present. The result in both the switch and display embodiments is a substantially constant level of illumination across the surface of the cover. Further disclosed is at least one slot in translucent layers which may be incorporated in a switch or display which reduces "crosstalk" between switches and/or displays. Additionally the use of a reflective material as the optical filter, in combination with and separated from a reflective layer near the LED by a separator layer, provides increased illumination of the display or switch.

Claims

1. A multi-layer backlit membrane switch, said switch comprising:

an at least partially light transmissive external membrane switch cover;

at least one electrical switch;

at least one light source means for illuminating at least a portion of said cover, said at least one light source means having a light intensity distribution along said at least a portion of said cover; and

at least one means for modifying said light intensity distribution along said at least a portion of said cover, said modifying means located at least partially between said light source and said switch cover and comprising a variable transmittance layer, said variable transmittance layer comprising a photoemulsion negative of light distribution from said light source means at said modifying means.

2. A multi-layer backlit membrane switch according to claim 1, wherein said at least one light source means comprises at least one light emitting diode.

3. A multi-layer backlit membrane switch according to claim 1, wherein said at least partially light transmissive outer cover comprises a means for diffusing light passing therethrough.

4. A backlit display, said display comprising:

an at least partially light transmissive outer cover;

at least one light source means for illuminating at least a portion of said cover, said at least one light source means having a variable light intensity distribution along said at least a portion of said cover; and

at least one means for modifying said light intensity distribution along said at least a portion of said cover, said modifying means located at least partially between said light source and said cover and comprising a variable transmittance layer, said variable transmittance layer comprising a photoemulsion negative of light distribution from said light source means membrane at said modifying means.

5. A backlit display according to claim 4, wherein said at least one light source means comprises at least one light emitting diode.

6. A backlit display according to claim 4, wherein said at least partially light transmissive outer cover comprises a means for diffusing light passing therethrough.

7. A multi-layer backlit membrane switch, said switch comprising:

an at least partially light transmissive external membrane switch cover including a key;

at least one electrical switch;

at least one light source means for illuminating at least a portion of said cover, said at least one light source means having a light intensity distribution along said at least a portion of said cover; and

an at least partially light transmissive layer located at least partially between said switch cover and said light source means, said layer including at last one means for reducing light transmittance in a direction parallel to said membrane switch, said reducing means comprising at least one slot, said at least one slot not completely surrounding said key.

8. A multi-layer backlit membrane switch according to claim 7, wherein said reducing means includes a plurality of slots, each of said slots partially surrounding said key, each of said slots separated from an adjacent slot by a portion of said light transmissive layer.

9. A multi-layer backlit membrane switch according to claim 7, wherein said at least one light source means comprises at least one light emitting diode.

10. A multi-layer backlit membrane switch according to claim 7, wherein said at least partially light transmissive outer cover comprises a means for diffusing light passing therethrough.

11. A backlit display, said display comprising:

an at least partially light transmissive outer cover;

at least one light source means for illuminating at least a portion of said cover; and

an at least partially light transmissive layer located at least partially between said outer cover and said light source means, said layer including at least one means for reducing light transmittance in a direction parallel to said backlit display, said reducing means comprising at least one slot, said at least one slot not completely surrounding at least one limited area of said cover.

12. A backlit display according to claim 11, wherein said reducing means includes a plurality of slots, each of said slots partially surrounding said limited area, each of said slots separated from an adjacent slot by a portion of said light transmissive layer.

13. A backlit display according to claim 11, wherein said at least one light source means comprises at least one light emitting diode.

14. A backlit display according to claim 11, wherein said at least partially light transmissive outer cover comprises a means for diffusing light passing therethrough.

15. A multi-layer backlit membrane switch, said switch comprising:

an at least partially light transmissive external membrane switch cover;

at least one electrical switch;

at least one light source means for illuminating at least a portion of said cover, said at least one light source means having a light intensity distribution along said at least a portion of said cover;

at least one means for modifying said light intensity distribution along said at least a portion of said cover, said modifying means located at least partially between said light source and said switch cover and comprising a variable transmittance layer, wherein said layer is comprised of an at least partially light transmissive material, at least portions of which are covered by a material at least partially reflective of visible light from said light source means, said covered portions comprising a percentage of the area of said layer, said percentage varying along said layer;

a further visible light reflective layer means, located with said light source means at least partially between said light reflective layer means and said switch cover, for reflecting visible light from said at least partially reflective material back towards said switch cover; and

an at least partially light transmissive spacer layer at least partially between said further visible light reflective layer means and said at least partially reflective material.

16. A multi-layer backlit membrane switch according to claim 15, wherein said covered portions of said variable transmittance layer is comprised of a plurality of dots of reflective material.

17. A multi-layer backlit membrane switch according to claim 16, wherein said reflective material has an area, and the area of reflective material per unit area of said variable transmittance layer increases and decreases in relation to increases and decreases in light intensity at said layer.

18. A multi-layer backlit membrane switch according to claim 17, wherein there is an even distribution of number of dots but the area of each dot increases and decreases in relation to increases and decreases in light intensity at said layer.

19. A multi-layer backlit membrane switch according to claim 17, wherein said dots are of equal area but the distribution density of dots increases and decreases in relation to increases and decreases in light intensity at said layer.

20. A multi-layer backlit membrane switch according to claim 15, wherein said covered portions of said variable transmittance layer is comprised of a dot of reflective material surrounded by a plurality of concentric circles of reflective material.

21. A multi-layer backlit membrane switch according to claim 20, wherein the reflective material has an area, and the area of reflective material per unit area of variable transmittance layer increases and decreases in relation to increases and decreases in light intensity at said layer.

22. A multi-layer backlit membrane switch according to claim 21, wherein there is an even distribution of number of rings but the area of each ring increases and decreases in relation to increases and decreases in light intensity at said layer.

23. A multi-layer backlit membrane switch according to claim 15, wherein said light source means is located on said reflective layer means.

24. A multi-layer backlit membrane switch according to claim 15, wherein said light source means extends at least partially through said reflective layer means.

25. A backlit display, said display comprising:

an at least partially light transmissive outer cover;

at least one light source means for illuminating at least a portion of said cover, said at least one light source means having a light intensity distribution along said at least a portion of said cover;

at least one means for modifying said light intensity distribution along said at least a portion of said cover, said modifying means located at least partially between said light source and said cover and comprising a variable transmittance layer, wherein said layer is comprised of an at least partially light transmissive material, at least portions of which are covered by a material at least partially reflective of visible light from said light source means, said covered portions comprising a percentage of the area of said layer, said percentage varying along said layer;

a further visible light reflective layer means, located with said light source means at least partially between said light reflective layer means and said cover, for reflecting visible light from said at least partially reflective material back towards said cover; and

an at least partially light transmissive spacer layer at least partially between said further visible light reflective layer means and said at least partially reflective material.

26. A backlit display according to claim 25, wherein said covered portions of said variable transmittance layer is comprised of a plurality of dots of reflective material.

27. A backlit display according to claim 26, wherein said reflective material has an area, and the area of reflective material per unit area of said variable transmittance layer increases and decreases in relation to increases and decreases in light intensity at said layer.

28. A backlit display according to claim 27, wherein there is an even distribution of number of dots but the area of each dot increases and decreases in relation to increases and decreases in light intensity at said layer.

29. A backlit display according to claim 27, wherein said dots are of equal area but the distribution density of dots increases and decreases in relation to increases and decreases in light intensity at said layer.

30. A backlit display according to claim 25, wherein said covered portions of said variable transmittance layer is comprised of a dot of reflective material surrounded by a plurality of concentric circles of reflective material.

31. A backlit display according to claim 30, wherein the reflective material has an area, and the area of reflective material per unit area of variable transmittance layer increases and decreases in relation to increases and decreases in light intensity at said layer.

32. A backlit display according to claim 31, wherein there is an even distribution of number of rings but the area of each ring increases and decreases in relation to increases and decreases in light intensity at said layer.

33. A backlit display according to claim 25, wherein said light source means is located on said reflective layer means.

34. A backlit display according to claim 25, wherein said light source means extends at least partially through said reflective layer means.

35. A method of providing an even distribution of light at a specific plane from a light source means, said method comprising the steps of:

providing a light transmissive substrate covered with a reflective layer, said layer coated with a positive photoresist, positive photoresist is defined as photoresist which is not polymerized by exposure to light and is polymerized by the lack of exposure to light, after completing photoresist processing;

making a negative, by a photographic process, of the light distribution from said light source means at said plane;

locating said negative over said photoresist covered reflective layer;

exposing said photoresist layer to light travelling through said negative;

processing said substrate to polymerize any non-exposed photoresist;

etching all unpolymerized photoresist and associated portions of said reflective layer from said substrate; and

locating said substrate at said plane with said reflective layer towards said light source means, whereas said substrate blocks a greater portion of light from said light source means where the illumination level is higher and said substrate blocks a lesser portion of light from said light source means where the illumination level is lower, resulting in the appearance to an observer of a generally even level of illumination at said plane.

37. A method of providing an even distribution of light in accordance with claim 35, further including the step of providing a further reflective layer for reflecting light from said light source means and said substrate towards said substrate.

36. A method of providing an even distribution of light at a specific plane from a light source means, said method comprising the steps of:

providing a light transmissive substrate covered with a reflective layer, said layer coated with a negative photoresist, negative photoresist is defined as photoresist which is polymerized by exposure to light and is not polymerized by the lack of exposure to light, after completing photoresist processing;

temporarily locating said substrate and said photoresist covered reflective layer at said plane over said light source means;

exposing said photoresist layer to light from said light source means;

processing said substrate to polymerize any non-exposed photoresist;

etching all unpolymerized photoresist and associated portions of said reflective layer from said substrate; and

locating said substrate at said plane with said reflective layer towards said light source means, whereas said substrate blocks a greater portion of light from said light source means where the illumination level is higher and said substrate blocks a lesser portion of light from said light source means where the illumination level is lower, resulting in the appearance to an observer of a generally even level of illumination at said plane.

38. A method of providing an even distribution of light in accordance with claim 36, further including the step of providing a further reflective layer for reflecting light from said light source means and said substrate towards said substrate.