Fiberoptic lighting system with shaped collector for efficiency

This application claims priority from U.S. Provisional Patent Application No. 60/454,816 filed Mar. 14, 2003.

The invention relates to a fiberoptic lighting system having a collector of light shaped to efficiently transfer light to multiple, discrete collecting rods. More particularly, the invention relates to such a system in which the collector of light performs an angle-to-area conversion of light it collects from a light source.

U.S. Pat. No. 6,304,693 issued Oct. 16, 2001 for Efficient Arrangement for Coupling Light from a Light Source to a Light Guide discloses a fiberoptic illumination system that efficiently couples light from a light source into a light pipe, or plurality of light pipes. The system may use a metal halide light source, a light collector comprising a coated hollow angle-to-area converter, and a single, coated quartz rod. The output of the preferred embodiment of this converter is not a circle, but two joined sections of a circle. Because of this, when a rod with a circular cross-section of equal or smaller area is placed in front of the light collector to couple light to the light pipes, not all of the light is collected. Only about 90% of the light is collected and delivered to one or more light pipes.

The single rod of the mentioned, prior art system has an output surface with a substantially even amount of illumination across its face, to allow a substantially equal amount of light to be delivered into each of several light pipes. The single rod has ultraviolet energy (UV) and infrared light (IR) filters on at least its input end to protect the light pipes, which are often made of plastic, and the rod thermally isolates the light pipe or pipes from the heat of the light source.

A disadvantage to using a single rod with a bundle of light pipes is that there are light losses due to the interstitial voids created at the interface of coupling multiple round light pipes to a single round rod. The present inventors have determined that the losses vary as the number of light pipes increase, but for four round light pipes of the same diameter, a maximum collection efficiency of typically about 72% is realized, for an overall efficiency of typically about 65% of collected light delivered into the light pipes.

It would thus be desirable to provide a fiberoptic illumination system that delivers a higher percentage of light from a light source into multiple light pipes.

A preferred form of the invention provides a fiberoptic lighting system, having a light source with a bulbous section and a plurality of plastic light pipes having substantially circular cross sections. A collector has an inlet for receiving light from the light source and an outlet. The collector performs an area-to-angle conversion on light it collects from the light source. A plurality of rods receives light from the collector and passes such light to the plastic light pipes, while thermally isolating the plastic light pipes from the light source. A perimeter of an outlet of the collector has a plurality of shaped portions, each associated with, and each substantially shaped the same as, a substantial portion of an associated perimeter of a respective one of the plurality of rods.

The foregoing system, and further forms of the invention, deliver a higher percentage of light from a light source into multiple light pipes than in the above-discussed prior art system.

In the drawing figures, like reference numerals refer to like parts.

FIG. 1 a is a view of a circle used for designing an output shape of a non-imaging collector of the prior art.

FIG. 1 b is a simplified view of the output of a prior art non-imaging collector.

FIGS. 2 a- 2 c show simplified views of the face of a thermally isolating rod overlying the output of respective light collectors, shown as cross hatched for clarity, with FIG. 2 a showing the prior art, FIG. 2 b showing the arrangement of another invention of the present assignee, Fiberstars Inc., and FIG. 2 c showing an arrangement in accordance with the present invention.

FIG. 3 a shows a simplified, side plan view of the prior art illumination system of FIG. 2 a , including light source and light pipes.

FIG. 3 b shows a simplified view of the face of four light pipes overlying the output of a single rod, with the rod shown cross hatched for clarity.

FIGS. 4 a and 4 b are like FIGS. 3 a and 3 b , respectively, but show multiple light-collecting rods rather than a single light-collecting rod.

FIGS. 5 a and 5 b are like FIGS. 3 a and 3 b , respectively, but show multiple light-collecting rods as well as a collector whose output perimeter is shaped in accordance with the present invention.

FIGS. 5 c and 5 d are perspective views of the illumination system of FIG. 5 a , in which the light-collection rods are parallel to each other, and not parallel to each other, respectively.

FIG. 5 e is similar to FIG. 5 d , but shows an illumination system in which the inlet faces of the light-collection rods extend beyond, and substantially fully cover, the perimeter of the outlet of a light collector.

FIGS. 6 a- 6 c are like FIG. 2 c , but show different numbers of light-collecting rods and differently shaped light collectors.

FIGS. 7 a and 7 b are like FIG. 2 c , but show different numbers of light-collecting rods and differently shaped light collectors.

FIGS. 8 a- 8 c are similar to FIG. 2 c , but show different arrangements of rods and collectors.

FIGS. 9 a- 9 c are simplified views of the input faces of rods for collecting light from different light-collectors shaped according to the present invention.

FIG. 10 a is a perspective view of the full length of the rods of FIG. 9 c ; and FIG. 10 b is similar to FIG. 10 a but shows one rod displaced from the other for clarity of illustration.

FIG. 10 c shows the positioning of the input faces of the rods of FIG. 9 c (or of FIG. 10 a ), with a collector shaped in accordance with the invention and a light source.

FIG. 11 is a perspective view of an illumination system in which light-collecting rods have a triangular input face and circular output face.

FIG. 12 is a perspective view of an illumination system in which light-collecting rods have a square input face and circular output face.

FIGS. 13 a and 13 b are perspective views of metal halide and halogen lamps, respectively, that may be used in the inventive illumination system.

FIG. 14 is an exploded, perspective view of a light source and a shaped light collector.

FIGS. 15 a and 15 b are perspective views of a solid collector shaped according to the present invention.

FIGS. 16 a and 16 b are simplified views of output areas of rods and associated input areas of the light-carrying portions of light pipes, shown cross hatched for clarity.

FIG. 17 is a side plan view of a light-collecting rod with optical coating(s) that may be used in the inventive light-collection system.

FIG. 18 is a bar chart comparing the outlet area of a rod used in an inventive system to the inlet area of the rod.

To put the invention in perspective, FIG. 1 a shows a circle 10 and axis 12 used for designing the output of the preferred embodiment of the non-imaging collector of prior art U.S. Pat. No. 6,304,693, mentioned above. FIG. 1 b shows circular arcs 14 a and 14 b , i.e., sections of full circles, that form an output shape of the prior art collector. The shape defined by arcs 14 a and 14 b is an oblong shape.

The remainder of this description concerns the three subjects of light-collection systems with (1) light-collection rods with circular cross section at the output of a light collector, (2) rods with a non-circular cross section at a collector output, and (3) miscellaneous aspects.

1. Rods with Circular Cross Section at Collector Output

The present invention concerns a way to increase the efficiency of light delivered into a plurality of light pipes through the use of multiple, discrete rods. FIGS. 2 a- 2 c , shown on three sequential drawing sheets, show progressive arrangements of the face of light-collecting rods 20 a , 20 b and 20 c overlying the output of light collectors 22 a , 22 b and 22 c , respectively, which are shown cross hatched for convenience. FIGS. 2 a- 2 c contrast the differences in area of collector outputs covered among various arrangements of light-collecting rods. FIG. 2 a shows single collecting rod 20 a overlying collector 22 a of above-mentioned prior art U.S. Pat. No. 6,304,693; FIG. 2 b shows four discrete rods 20 b overlying a prior art collector 22 b ; and FIG. 2 c shows, in accordance with the present invention, four discrete rods 20 c overlying a light collector 22 c shaped to match the four rods. The area of rods 20 a- 20 c in FIGS. 2 a- 2 c is directly related to the amount of light that can be collected by the rods and delivered into light pipes.

Regarding FIGS. 2 a- 2 c , the percentage of the collector's output area covered by the input of the rod or rods is as follows: FIG. 2 a , about 90%; FIG. 2 b , about 85%; and FIG. 2 c , over 95%. The maximum efficiency of the prior art system of FIG. 2 a for transferring light from collecting rod to light pipes is limited to 72%. In the prior art system of FIG. 2 a , the single rod 20 a is used to create an output face with substantially even illumination across the face, which delivers a substantially equal amount of light to each of several light pipes, while providing UV and IR protection on the input face to the rod, and thermally isolating the light pipes from the light source. However, the disadvantage to using a single rod with a bundle of multiple light pipes is that there are light losses from the interstitial voids created when trying to couple multiple round light pipes to a single round rod. This can be appreciated from considering FIGS. 3 a and 3 b.

FIGS. 3 a- 3 b show the prior art illumination system associated with FIG. 2 a , including a light source 30 , hollow light collector 22 a , a light-collecting rod 20 a of 19 mm diameter, for instance, and four light pipes 32 for receiving light from the single rod 20 a . The losses vary as the number and diameter of light pipes 32 increases, but for four 10.3-mm core diameter light pipes, as shown in FIG. 3 b , a maximum collection efficiency of 72% is realized, due to the interstices of the light pipes that result in lost light. This results in an overall delivery efficiency of 90%×72%=65% of collected light into the light pipes.

In further regard to FIG. 2 b , four 10 mm rods 20 b are able to collect about 85% of the light from collector 22 b , which is lower than the percentage (i.e., 90) in the case of FIG. 2 a showing a single rod 20 a collecting light in the prior art system. However, the system of FIG. 2 b realizes an increased efficiency over the prior art system of FIG. 2 a (or FIGS. 3 a- 3 b ), and is shown in connection with FIGS. 4 a and 4 b.

In contrast with the illumination system of FIGS. 3 a and 3 b , the illumination system of FIGS. 4 a and 4 b , associated with FIG. 2 b , uses a plurality of light-collecting rods 20 b , one for each light pipe 32 . The illumination system of FIGS. 4 a and 4 b realizes increased efficiency by eliminating light losses due to interstitial spacing between four light pipes for receiving light from a single round rod ( FIG. 3 b ). Thus, in FIG. 4 b , each of the discrete collecting rods 20 b delivers light to a single light pipe 32 . Sizing of the rods as slightly smaller than the light-carrying section of the light pipe ensures that all light collected by the rods is delivered into the light pipes. In a 4-way system based on the prior art hollow coupler, this results in an overall light-delivery efficiency of 85% because all light collected by the rods from the light collector is delivered into the light pipes. This concept relating to FIG. 2 b and FIGS. 4 a- 4 b concerns a separate invention owned by Fiberstars Corporation, the instant assignee.

The present invention as shown, for instance, in FIGS. 2 c and FIGS. 5 a and 5 b improves upon the use of multiple, discrete rods and the hollow collector—which collector per se is prior art—of FIG. 2 b and FIGS. 4 a- 4 b . Thus, FIG. 2 c shows that, by shaping collector 22 c to match the outer circumference of a grouped set of rods 20 c , more light can be delivered into the rods. More broadly, a perimeter 50 ( FIG. 2 c ) of an outlet of collector 22 c has a plurality of shaped portions 50 a , each associated with, and each substantially shaped the same as, a substantial portion 52 a of an associated perimeter of a respective one of the plurality of rods. In fact, the output perimeter of shaped collector 22 c resembles a “cloverleaf” pattern. In a 4-rod configuration as shown in FIG. 2 c , the collection of light from the collector can be greater than 95%.

In the arrangement of FIGS. 2 c and 5 a , the inlet faces of the top- and bottom-shown rods 20 c are collectively aligned substantially parallel to a main axis 31 of light source 30 . The inlet faces of the left- and right-shown rods 20 c ( FIG. 2 c ) are collectively aligned generally orthogonal, and preferably substantially orthogonal, to main axis 31 . This is a preferred arrangement of rods 20 c.

FIG. 5 b shows that, by properly sizing light pipes 32 , which are coupled to rods 20 c , so that the light-carrying element of each light pipe is equal to or greater in diameter than that of rods 20 c , 100% of the light collected by the rods is delivered into the light pipes. Coupled with the greater than 95% collection of light by the rods from the collector, the overall light delivery efficiency to the light pipes is greater than 95%. This is compared to typically 67% for the prior art 4-way light pipe bundle system of FIGS. 2 a and 3 a- 3 b , and 85% for the 4-way rod system of FIGS. 2 b and 4 a- 4 b.

FIG. 5 c shows an arrangement of the illumination system of FIG. 5 a in which light-collecting rods 20 c are parallel to each other. In contrast, FIG. 5 d shows an arrangement of the system of FIG. 5 a in which the output ends of the light-collecting rods 32 are spaced further apart from each other than their input ends. This allows easier coupling to light pipes (not shown).

FIG. 5 e shows a variation of FIG. 5 d , in which inlet faces 23 of light-collection rods 20 d exceed the perimeter of the outlet of a light collector 22 d . In this variation, rods 20 d collect substantially all the light emitted by the collector. In FIG. 5 d , in contrast, inlet faces of rods 20 c are substantially fully subsumed by an outlet face of collector 22 c.

Preferably, the light collectors described herein, such as collector 22 c in FIGS. 2 c and 5 a- 5 b , substantially conforms to non-imaging optics, and may contain contours formed from one or many compound parabolic concentrators (“CPC's). A CPC shape is described in detail in, for instance, W. T. Welford and R. Winston, High Collection Nonimaging Optics, New York: Academic Press, Inc. (1989), chapter 4 (pp. 53-76). The collectors convert light in a small area at a high angle into a larger output area at a lower angle. When changing from previous designs to the “cloverleaf”-shape collector outputs described herein, the large output area of the collectors is maintained to achieve the proper light-output angles. Because the angular distribution of light is determined by the numerical aperture of the light pipe, both types of optical couplers (i.e., of FIGS. 4 a- 4 b or FIGS. 5 a- 5 b ) must provide for the same angular distribution of light. Since both optical couplers may use the same input source and output angular distribution, the areas of both couplers are limited to a minimum determined by the conservation of Etendue.

The present inventive concept of shaping the collector to match the rods—as more precisely defined above—is not limited to just a 4-rod system. The concepts for system using 2, 3, and 5 rods are shown in FIGS. 6 a- 6 c , respectively, but the general inventive concept could be applied to systems using more than 5 rods.

Each of the rods in FIGS. 6 a- 6 c is shown tangent to, or abutting, an adjacent rod. Thus, in FIG. 6 a , rods 60 abut each other, and collector 62 is shaped accordingly. Similarly, in FIG. 6 b , adjacent ones of rods 64 abut each other, and collector 66 is shaped accordingly. Similarly, in FIG. 6 c , adjacent ones of rods 68 abut each other, and collector 70 is shaped accordingly. However, the abutting relationship of the rods in FIGS. 6 a- 6 b may not be the optimum configuration to produce substantially the same illumination in each rod.

For example, FIG. 2 c described above shows a 4-rod configuration, with the two side rods closer together than the top and bottom rods. A system using an oblong light source, where each of the four rods is tangent to (or abutting) only two other rods is likely to collect more total light, but such light is not distributed substantially evenly to all four rods. The top and bottom rods receive more light than the side rods because of imperfect light density distribution at the collector output. To compensate for this, the side rods are brought closer together and the top and bottom rods are moved further apart until each of the four rods receive the most balanced amount of light. This imbalance in the tangent (or abutting) configuration is due to the oblong shape of the light source used. A different source with a different shape would yield a different optimum configuration of the rods. This would result in a differently shaped collector to achieve a substantially even distribution of light to all rods.

In the prior art system of FIGS. 2 a and 3 a- 3 b , for instance, the shape of the light collector is formed by joining sections from two circles together, as in FIG. 1 b . The shape of the collector's output could simply match the outside circumference of the light-collection rods used or, to achieve optimum performance, would be a series of joined sections of a circle (i.e., circular arcs). The so-shaped shaped collector includes as many arcs of as many circles needed to produce the desired shape. Shaping of the collector with such circular arcs results in the light-collecting rods efficiently collecting light from the collector. The size and orientation of the arcs used would depend on the number of collection rods used and the shape of their inputs faces. Some examples of this are shown in FIGS. 7 a and 7 b.

FIGS. 7 a and 7 b show how the concept of shaping the prior art collector of FIG. 2 a (or FIG. 1 b ), which comprises two arcs from a circle joined together, can be used in a novel manner to form a shaped collector with improved coupling to multiple, discrete rods. The new shaped collector 80 , associated with rods 82 , ( FIG. 7 a ) or the new shaped collector 90 ( FIG. 7 b ), associated with rods 92 , essentially comprises several arcs of a circle joined together. This is one shape, in accordance with the invention—that is, several circular arcs joined together—, which allows for efficient collection of light by multiple, discrete light-collection rods.

FIGS. 8 a- 8 c show other designs of fiberoptic lighting systems with various spacings, or no spacing, between rods at the collector output. It is preferred to have the input faces of the rods tangent to (or abutting) each other at the output plane of the optical coupler. This idealized design is shown in FIG. 8 c , in which the rods are “spaced” from each other by a zero distance 139 , but manufacturing tolerances may make this embodiment relatively difficult to make. An alternate construction, shown in FIGS. 8 a and 8 b , for instance, is with the input faces of the rods close to, but slightly spaced from, each other, usually within about 2 mm. This helps to prevent breakage of the rods during construction or operation.

FIG. 8 a shows rods 120 spaced from each other by dimension 121 , and output of collector 124 conforming to the shape of the rods according to the shaping principles described herein. Similarly, FIG. 8 b shows rods 130 spaced from each other by dimension 131 , and output of collector 132 conforming to the shaping principles described herein. FIG. 8 b differs from FIG. 8 a in that collector 132 ( FIG. 8 b ) includes flat sections 134 , as opposed to the rounded sections 126 of collector 124 ( FIG. 8 a ). In FIG. 8 b , flattened sections 134 result in a somewhat less efficient construction that in FIGS. 8 a and 8 c , but manufacturing may be easier.

The foregoing arrangements of FIGS. 8 a and 8 b , in which the rods are spaced from each other, can be optimized by either increasing the size of the arcs that define the perimeter of the outlet region of the coupler or by increasing the number of arcs as compared to the coupler design of FIG. 8 c , in which the rods are held tangent.

In FIG. 8 a , the rounded sections 126 of collector 124 can be shaped substantially as arcs. Thus, in the design shown in FIG. 8 a , the spaced rod inputs are accommodated by increasing the number of arcs in the coupler output. Shaped collectors with rounded sections 126 of FIG. 8 a may be somewhat less efficient than the idealized design in FIG. 8 c , but are more efficient than the design in FIG. 8 b and easier to manufacture than the idealized design in FIG. 8 c.

The idealized design in FIG. 8 c shows rods 145 touching or in very close proximity (i.e., under about ½ mm from each other). The output of collector 146 conforms to the shape of the rods according to the shaping principles described herein. FIG. 8 c differs from FIGS. 8 a and 8 b because the interface 147 between arcs defining is shown as a cusp. This is the most efficient construction, but in practice somewhat difficult to produce.

2. Rods with Non-Circular Cross Section at Collector Output

The following figures relate to light-collection systems including light-collecting rods with non-circular cross sections at the output of a light collector.

FIGS. 9 a- 9 c show inlet faces of rods that can be associated with a shaped collector as described herein. FIG. 9 a shows two rods 100 , FIG. 9 b shows three rods 102 , and FIG. 9 c shows four rods 104 . The output face of each rod preferably has a generally circular cross section. This requires a change in shape of the rods, from input face to output face.

With further reference to FIGS. 10 a- 10 c , the rod input faces are non-circular but the rod output faces (not shown) are normally of another—e.g., circular—shape. For instance, FIG. 10 a shows the entire length of rods 104 of FIG. 9 c , with FIG. 10 b showing a rod 104 a displaced from the other three rods 104 so as to better portray the shaping of the rods. Rods 104 can be produced by removing two angled slices (e.g., 104 b and 104 c ) from each of the four rods. Then, the rods could be positioned together as shown in FIG. 10 a , with substantially no spacing at interstices 106 of the rods.

In FIGS. 10 a- 10 c , the non-circular rod input faces 104 could have the same areas as the areas of the circular output faces (not shown) of the rods.

FIG. 10 c shows how a collector 110 for a light source 112 could be shaped to conform to the collection of rods 104 , in accordance with the present inventive principles However, shaping of rods 104 ( FIG. 10 a ) would also improve efficiency with the prior art collector of FIG. 2 a.

As shown in FIG. 10 a , by eliminating the interstitial spaces between the rods at 106 , the perimeter or border of the rod input faces is completely defined by the projection of the rod input faces onto the collector output plane. By using a collector shaped according to the principles described herein, the light-collection rods would collect 100% of the light emitted by the collector.

It is also possible for the rods to undergo a more drastic change of shape, from an input with a generally square cross-section to an output with a generally circular cross-section, to facilitate the collection of light emitted by the collector and the delivery of light into the light pipe. The shape of the CPC would change accordingly. This would also eliminate the interstitial space with border completely defined by the projection of the rod input faces onto the collector output plane.

Thus, FIG. 11 shows a light collector 140 receiving light at an inlet 140 a from a light source 141 , and transmitting light through a square outlet 140 b to a pair of rods 142 . Inlet ends 142 a of the rods have the shape of an equilateral triangle. Outlet ends 142 b are circular in shape. Thus, the rods change shape from inlet to outlet, as shown.

FIG. 12 shows a collector 144 receiving light at an inlet 144 a , and transmitting ligth through a square outlet 144 b to four rods. Inlet ends 145 a of the rods are square in shape. Outlet ends 145 b are circular in shape. Thus, the rods change shape from inlet to outlet, as shown.

3. Miscellaneous

The following description refers to principles and variations that apply to any illumination systems according to the invention.

FIG. 13 a shows a typical metal halide arc discharge lamp 160 received in a collector 161 a shaped according the invention, and FIG. 13 b shows a quartz halogen, filamented lamp 162 received in a shaped collector 161 b according to the invention.

FIG. 14 shows a lamp 150 having input arms 150 a and 150 b for being received within notches 152 a and 152 b , respectively, of a shaped collector 152 . The concept of notches per se in a non-imaging light collector is prior art according to U.S. Pat. No. 6,304,693 mentioned above.

FIGS. 15 a and 15 b show another version of a light collector 190 according to the present invention. FIG. 15 b shows a recess 191 in the collector for receiving a bulbous section of a light source. Collector 190 is solid and can be made of quartz or borosilicate glass, for instance. A solid, or mostly solid, collector may replace any of the hollow collectors described herein.

FIG. 16 a shows a configuration of rods and light pipes wherein the output area of rods 200 and 202 exceeds, and subsumes, the input area of light-carrying sections 201 and 203 of the light pipes. As a result, only a majority of the light emitted by each rod is coupled into the light-carrying section of the light pipes.

FIG. 16 b shows a configuration of rods and light pipes wherein the output area of rods 206 and 208 is the same or less than, and is subsumed by, the input area of associated light-carrying sections 207 and 208 of the light pipes. As a result, all of the light emitted by each splitter rod is coupled into the light carrying section of the light pipes.

FIG. 17 shows a light-carrying rod 210 with optical coatings 212 and 214 . Coating 212 may comprise an infrared (IR) light filter, an ultraviolet (UV) energy filter, or both. However, coating 214 may also comprise the same options as for coating 212 , but would normally not be redundant of coating 212 . Coating 212 may also increase the amount of light transmitted into rod 210 above the amount the amount that would be transmitted into the rod if the coating were not present. Coating 214 may also increase the amount of light transmitted from rod 210 above the amount that would be transmitted into the rod if the coating were not present.

In any of the illumination systems described herein, the light collectors might not achieve the full reduction in angle of light desirable for transmitting into light pipes (not shown). In this event, the area of each respective rod output face could be increased relative to the area of the respective rod's inlet face. FIG. 18 shows this concept in the form of a bar chart 220 , measuring area on axis 220 . Chart 220 compares input area 222 of a rod with output area 224 of the rod. As indicated in the chart, output area 224 exceeds input area 222 . As a result, the respective rod would serve to further decrease the angle of light it transmits to a lower angle. Such lower angle preferably is suitable for transmitting into light pipes.

While the invention has been described with respect to specific embodiments by way of illustration, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true scope and spirit of the invention.