WO2001057435A1

WO2001057435A1 - High reliability illumination device employing light fibers

Info

Publication number: WO2001057435A1
Application number: PCT/US2000/035208
Authority: WO
Inventors: David J. Lundin
Original assignee: 3M Innovative Properties Company
Priority date: 2000-02-03
Filing date: 2000-12-26
Publication date: 2001-08-09
Also published as: AU2001225968A1

Abstract

An illumination device includes a bundled light transport device having a plurality of light guides (12(1), 12(N)) with input ends (16(1), 16(N)) and output ends (18(1), 18(N)) . The output ends (18(1), 18(N)) are arranged in a contiguous light emission surface. A plurality of light sources (420(1), 420(2)) are each positioned to provide light into one of the input ends (416(1), 416(2)) of the light guides (412(1), 412(2)). An adjustable controller (430) is electrically coupled to the plurality of light sources (420(1), 420(2)) for selectively activating and deactivating the light sources independently of one another. The plurality of light sources (420(1), 420(2)) each generate light of the same color, thus providing redundancy in case one light source should fail. Alternatively, the plurality of light sources (420(1), 420(2)) may generate light of different colors, thus increasing the flexibility of the device.

Description

HIGH RELIABILITY ILLUMINATION DEVICE EMPLOYING

LIGHT FIBERS

FIELD OF THE INVENTION The present invention relates to an illumination device, and more particularly, to an illumination device employing a plurality of light fibers and a plurality of light sources.

BACKGROUND OF THE INVENTION

Optically transmissive materials, such as glass or polymers may be used as a light guide to propagate light. A light guide typically includes at least one surface adapted to receive light from a light source and an optically smooth surface for reflecting light propagating through the light guide. Common examples of light guides include optical fibers traditionally used in the data communication industry and more recently, light fibers of the type disclosed in U.S. Patent No. 4,422,719 (Orcutt) which are used for illumination purposes. In these devices, at least one end surface of the light fiber is adapted to receive light from a light source, and the light so received propagates between the two major surfaces of the light guide. Such illumination devices may be used, for instance, in any of a number of situations that require task lighting. Among the many desirable features that task lighting devices should provide, one primary feature involves their reliability.

In particular, an important factor that must be considered when using devices that provide task lighting is the degree of safety that is required. Such devices are often used in critical situations where failure would be hazardous. For example, illumination devices employed in vehicles or surgical theatres should provide illumination with high reliability. The component of the illumination device typically most prone to failure is the light source.

-l- Accordingly, reliability can be readily increased by providing a redundancy of light sources so that if one should fail another light source would be available to immediately take its place.

In addition to reliability, another desirable feature of an illumination device is its degree of operational flexibility. For example, the operational flexibility of an illumination device can be enhanced by allowing various characteristics of the illumination emitted by the device to be altered. Specifically, if the color or intensity of the light could be changed by the user, then the illumination could be tailored so that the most suitable lighting is provided for any particular task.

There is thus a need in the art for an illumination device that is highly reliable and which allows the user to select and change the color or intensity of light that it emits.

SUMMARY OF THE INVENTION In accordance with one aspect of the invention, an illumination device includes a bundled light transport device. The bundled light transport device includes a plurality of light guides having input ends and output ends. The output ends are arranged in a contiguous light emission surface. A plurality of light sources are each positioned to provide light into one of the input ends of the light guides. An adjustable controller is electrically coupled to the plurality of light sources for selectively activating and deactivating the light sources independently of one another. In accordance with another aspect of the invention, the plurality of light sources each generate light of the same color, thus providing redundancy in case one light source should fail. Alternatively, the plurality of light sources may generate light of different colors, thus enhancing the operational flexibility of the device. Further, in another alternative, at least two of the light sources generate light of a first color and at least another of the plurality of light sources generates light of a second color.

In accordance with another aspect of the invention, a mechanism is provided for selectively varying at least one characteristic of the illumination provided by the illumination device. The characteristic of the light that is varied may be its color and/or intensity, for example.

In accordance with yet another aspect of the invention, the light emission surface is essentially free of voids and the interior of the light emission surface is essentially free of cladding materials. In some embodiments of the invention, the output ends of the plurality of light guides are assembled into a void-free light emission surface essentially without deformation.

In accordance with another aspect of the invention, the output end of at least one of the plurality of light guides has an essentially non-circular cross-section while the input end of the light guide has an essentially circular cross-section, or alternatively, a non-circular cross- section.

In accordance with yet another aspect of the invention, the noncircular output ends of the bundled light transport device may each describe a sector, which may or may not subtend angles that are equal to another. Alternatively, the noncircular output ends may each describe a polygon such as a hexagon or rectangle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 depicts a perspective view of a bundled light transport device that may be employed in the present invention; FIG. 2 depicts a perspective view of another example of a bundled light transport device that may be employed in the present invention;

FIG. 3 depicts a front view of the light emission surface seen in FIG. 2; FIG. 4 depicts a simplified diagram of an illumination device constructed in accordance with the present invention; and FIG. 5 depicts a simplified diagram of an alternative embodiment of the illumination device constructed in accordance with the present invention. DETAILED DESCRIPTION In accordance with the present invention, an illumination device is provided that provides a redundancy of light sources in case one or more should fail. Such a device is particularly useful in those situations where high reliability is important. The present invention also provides the beneficial ability to change the nature of the illumination provided by the device. That is, the intensity and/or color of the emitted light can be adjusted by the user. It should be noted that the light provided by the illumination device is not limited to visible wavelengths but may encompass other portions of the electromagnetic spectrum such as ultraviolet wavelengths, for example. In some embodiments of the invention the wavelengths of interest extend from about 200 nm to 1200 nm. Moreover, the term color as used herein should not only be construed as corresponding to a single wavelength. Rather, the term color is also used to describe the appearance of an object as perceived by a viewer, which typically corresponds to a band of wavelengths over which there is some nonuniform intensity distribution. That is, color can refer to a single wavelength or a range of wavelengths. The present invention incorporates a bundled light transport device that transports light from a plurality of sources to a single location, an example of which is depicted in FIG. 1. As shown, a plurality of light guides such as light fibers 12„ 12₂, ... 12_N are brought into contact with one another at their respective output ends 18„ 18₂, ... 18_N. Output ends 18,, 18₂, ... 18_N form a light emission surface 14 from which light from one or more light sources is emitted. Fibers 12,, 12₂, ... 12_N have input ends 16,, 16₂, ... 16_N that receive light generated by light sources. As is well known, light injected into the individual input ends of each fiber is transported along the fiber core in accordance with the principles of total internal reflection. Since the light fibers are flexible and need to remain in contact with one another only at their output ends, the input ends of the light fibers may be arranged in any desired configuration so that light can be received from different sources located at different positions. For example, as seen in FIG. 1, fibers 12,, 12₂, and 12₄ are each oriented to receive light from a different location. In a typical bundled light transport device the emission surface contains voids, such as void 19, because of the circular cross-sectional shape of the individual light fibers. When light is directed into the input ends of fibers 12,, 12₂, and 12₄, the portions of light emission surface 14 containing voids will appear dark in comparison to the portions of light emission surface 14 at which the fiber output ends 18,, 18₂, ... 18_N are located.

Examples of bundled light transport devices that are particularly suitable for use in the present invention are disclosed in U.S. Patent No. 5,058,985 (Davenport et al.) and U.S. Appl. Serial No. 09/203,951 filed December 2, 1998. These references disclose devices in which the ends of a bundle of light fibers are brought together to form a light emission surface that is free of voids, thus avoiding nonuniform light emission over the light emission surface that would otherwise occur in the presence of voids. FIGS. 2 and 3 shows an example of the light emission surface of the bundled light transport device disclosed in U.S. Appl. Serial No. 09/203,951. Output ends 18„ 18₂, ... 18_N of light fibers 12,, 12₂, ... 12_N have cross-sectional shapes that differ from the circular shape of a conventional light fiber. Specifically, the output ends of the light fibers are sectors which contact one another without creating any empty space or voids therebetween. That is, the outer edge surfaces of the output ends of adjacent fibers are brought together so that they are completely contiguous with one another without requiring deformation of the light fibers. Since the bundled light transport device depicted in FIG. 2 employs five light fibers, each output end is a sector that subtends an angle of 72 degrees. Of course, if a fewer or greater number of fibers are employed, the arc length and associated angle of each sector can be adjusted accordingly to form a light emission surface that is circular or some other desired shape. The sectors need not be of equal area. For example, three sections could each subtend an angle of 60 degrees, while the remaining two sectors could subtend angles of 90 degrees each. Likewise, the output ends (as well as the input ends) may have any shape and are not limited to circular sectors. For example, the output ends may have a shape describing a polygon such as a hexagon or rectangle. Further, the light fibers may undergo a gradual transition in their cross-sectional shape between their respective input and output ends. The transition may occur over the entire length of the fiber, or only over a portion thereof. The output ends of the light fibers forming the light emission surface may be held in place by heat shrink tubing or by other appropriate mechanical or chemical bonding means. Additional details concerning this exemplary bundled light transport device, including methods of manufacturing, may be found in the previously mentioned patent application.

FIG. 4 shows an illumination device constructed in accordance with the present invention. The illumination device includes a bundled light transport device 400 formed from a plurality of light guides 412, and 412₂, a plurality of light sources 420, and 420₂, and a controller 430 for selectively activating the light sources. Bundled light transport device 400 may be of any type known to those of ordinary skill in the art, such as those disclosed in the previously mentioned references and depicted in FIGS. 1 and 2, for example. However, as previously mentioned, bundled light transport devices having emission surfaces that are free of voids are particularly advantageous because they will provide more uniform illumination over the emission surface. It should be noted FIG. 3 shows only two light guides and two light sources for illustrative purposes only and that in general the present invention encompasses bundled light transport devices having any number of light guides. Light sources 420, and 420₂ may be LEDs, incandescent bulbs or any other appropriate generator of illumination. Controller 430 includes electronic circuitry that allows selective activation and deactivation of the light sources independently of one another. That is, light source 420, can be activated, for example, while allowing light source 420₂ to remain inactive. Devices that perform the function of controller 430 are well-known and thus will not be discussed in greater detail.

Each input end 416, and 416₂ of light fibers 412, and 412₂ is arranged to receive light from one of the light sources 420, and 420₂. When activated, light from a given light source propagates through its respective light guide and is emitted at its output end located in light emission surface 414. In one embodiment of the invention the plurality of light sources all generate light of the same color, e.g., white. In this case any given light source may be activated at a time. Should that light source fail, another light source can be activated. Accordingly, the device provides as many levels of redundancy as there are light guides and light sources. In addition to providing redundancy, the intensity of the light can be controlled. The intensity is determined by the number of light sources that are active at any given time. Thus, for example, two or more of the light sources may be activated simultaneously in order to increase the total intensity of the emitted light. In an alternative embodiment of the invention the plurality of light sources generate light of different colors, e.g., red, green, and blue. As shown in FIG. 5, this embodiment of the invention requires as least three light guides 512,, 512₂, and 512₃ and three light sources 520,, 520₂, and 520₃. In this case the color of light emitted by the device can be controlled by activating the appropriate light source via controller 530. By activating and deactivating the light sources, the color of the emitted light can be changed. In some cases it may be advantageous to activate more than one light source at a time. For example, if red, green, and blue light sources are employed, all three light sources may be activated simultaneously so that the illumination device emits white light. Of course, redundancy also may be achieved in an illumination device employing multiple color light sources simply by providing two or more light sources for each color that is used.

One particular advantage of the present invention arises when the illumination device employs a bundled light transport device of the type shown in FIG. 2. More particularly, this advantage arises when the light guides forming the bundled light transport device are free not only of voids, but also of any materials or features (e.g., cladding) that interfere with the transmission of light into the fibers. In other words, the light fibers may consist simply of a core that is free of any surrounding cladding material. In these embodiments of the invention, adjacent fiber cores are in direct contact with one another. In the absence of cladding material, light propagating through fiber cores in direct contact with one another will be free to undergo coupling among the various fiber cores. As a result of the coupling process, the light in different fibers will be mixed, reducing any inhomogeneities in color or intensity that may have initially been present among them. Accordingly, in those cases where two or more light sources are activated simultaneously, the present invention advantageously mixes the light propagating in the different fibers so that the degree of uniformity in color and intensity obtained at the output of the device is substantially greater than would otherwise be the case.

Claims

What is claimed is:

1. An illumination device, comprising: a bundled light transport device that includes a plurality of light guides having input ends and output ends, said output ends being arranged in a contiguous light emission surface; a plurality of light sources each positioned to provide light into one of the input ends of the light guides; and an adjustable controller electrically coupled to the plurality of light sources for selectively activating and deactivating the light sources independently of one another.

2. The illumination device of claim 1 wherein the plurality of light sources generate light of the same color.

3. The illumination device of claim 1 wherein the plurality of light sources generate light of different colors.

4. The illumination device of claim 1 wherein first and second light sources generate light of a first color and at least another of the plurality of light sources generates light of a second color.

5. The illumination device of claim 1 wherein the light emission surface is essentially free of voids, the interior of said light emission surface being essentially free of cladding materials.

6. The illumination device of claim 5 wherein the output ends of the plurality of light guides are assembled into said light emission surface essentially without deformation.

7. The illumination device of claim 6 wherein said light emission surface is substantially planar.

8. The illumination device of claim 6 wherein each of said output ends is rigid.

9. The illumination device of claim 6 wherein said output end of at least one of the plurality of light guides has an essentially non-circular cross-section, and wherein said input end of said one of the plurality of light guides has an essentially circular cross-section.

10. The illumination device of claim 6 wherein said input end of each of the plurality of light guides has an essentially circular cross-section.

11. The illumination device of claim 6 wherein each of the plurality of output ends has a unique cross-sectional shape.

12. The illumination device of claim 6 wherein said output ends of the plurality of light guides have essentially identical cross-sectional shapes.

13. The illumination device of claim 6 wherein said input and output ends of the plurality of light guides have essentially identical cross-sectional shapes.

14. The illumination device of claim 6 wherein each of said plurality of light guides has a longitudinal axis, and wherein the cross-sectional shape of each of said plurality of light guides undergoes a transition along said longitudinal axis from a first cross-sectional shape to a second cross-sectional shape.

15. The illumination device of claim 14 wherein said transition occurs over substantially the entire length of the light guide.

16. The illumination device of claim 6 wherein at least one of said output ends has non-circular cross-sectional shape.

17. The illumination device of claim 6 wherein said non-circular cross-sectional shape is essentially a sector.

18. The illumination device of claim 6 wherein said bundled light transport device comprises N light guides, where N is an integer greater than 1, and wherein each of said N light guides has a cross-sectional shape essentially defining a sector.

19. The illumination device of claim 18 wherein each of said N sectors subtends an angle of 360/N degrees.

20. The illumination device of claim 18 wherein a first of said N sectors subtends an angle φ„ wherein a second of said N circular sectors subtends an angle φ₂, and wherein φ, ≠ φ₂.

21. The illumination device of claim 6 wherein each of said output ends has a cross-section that essentially describes a polygon.

22. The illumination device of claim 21 wherein said polygon is a hexagon.

23. The illumination device of claim 21 wherein said polygon is a rectangle.

24. The illumination device of claim 1 further comprising binding means for releasibly binding said light guides together.

25. The illumination device of claim 24 wherein said binding means comprises a band disposed about the exterior surfaces of said light guides in the vicinity of said output ends.

26. A method of providing illumination comprising the steps of: selectively activating at least one light source from among a plurality of light sources to generate light; and transmitting the light from the activated light source into an input end of a first light guide that is incorporated in a bundled light transport device, said bundled light transport device including a plurality of light guides that includes the first light guide, said plurality of light guides having output ends assembled into a contiguous light emission surface.

27. The method of claim 26 wherein the step of selectively activating at least one light source includes the step of selectively activating a light source generating a given color of light from among a plurality of light sources generating light of different colors.

28. The method of claim 26 further comprising the steps of: selectively activating a second light source upon failure of said at least one light source; and transmitting light from the second light source into an input end of a second light guide that is incorporated in said bundled light transport device.

29. The method of claim 26 wherein the light emission surface is essentially free of voids, the interior of said light emission surface being essentially free of cladding materials so that light propagating in adjacent light guides undergoes mixing by being coupled from one light guide to another.

30. The method of claim 29 wherein the output ends of the plurality of light guides are assembled into said light emission surface essentially without deformation.

31. The method of claim 30 wherein said output end of at least one of the plurality of light guides has an essentially non-circular cross-section, and wherein said input end of said one of the plurality of light guides has an essentially circular cross-section.

32. The method of claim 30 wherein said output ends of the plurality of light guides have essentially identical cross-sectional shapes.

33. The method of claim 30 wherein at least one of said output ends has non- circular cross-sectional shape.

34. The method of claim 30 wherein said non-circular cross-sectional shape is essentially a sector.

35. The method of claim 30 wherein each of said output ends has a cross-section that essentially describes a polygon.

36. The method of claim 21 wherein said polygon is a hexagon.

37. An apparatus for providing illumination, comprising: a bundled light transport device that includes a plurality of light guides having input ends and output ends, said output ends being arranged into a contiguous light emission surface; a plurality of light sources each positioned to provide light into one of the input ends of the light guides such that illumination is emitted from the light emission surface; and means for selectively varying at least one characteristic of the illumination.

38. The apparatus of claim 37 wherein the at least one characteristic of the illumination is intensity.

39. The apparatus of claim 37 wherein the at least one characteristic of the illumination is color.

40. The apparatus of claim 37 wherein said selectively varying means includes means for selectively activating and deactivating the light sources independently of one another.

41. The illumination device of claim 37 wherein the light emission surface is essentially free of voids, the interior of said light emission surface being essentially free of cladding materials.

42. The illumination device of claim 41 wherein the output ends of the plurality of light guides are assembled into said light emission surface essentially without deformation.

43. The illumination device of claim 42 wherein said output end of at least one of the plurality of light guides has an essentially non-circular cross-section, and wherein said input end of said one of the plurality of light guides has an essentially circular cross-section.

44. The illumination device of claim 42 wherein said output ends of the plurality of light guides have essentially identical cross-sectional shapes.

45. The illumination device of claim 42 wherein at least one of said output ends has non-circular cross-sectional shape.

46. The illumination device of claim 42 wherein said non-circular cross-sectional shape is essentially a sector.

47. The illumination device of claim 42 wherein each of said output ends has a cross-section that essentially describes a polygon.

48. The illumination device of claim 47 wherein said polygon is a hexagon.