Abstract:
An efficient system for directing light comprises a light source and a generally tubular, hollow coupling device. The coupling device has an interior light-reflective surface for receiving light from the source at an inlet and transmitting it as a generally diverging light beam through an outlet. The device is shaped in accordance with non-imaging optics and increases in cross sectional area from inlet to outlet so as to reduce the angle of light reflected from the surface as it passes through the device. The foregoing system provides a discharge-based directional light source that can be of the size of a directional halogen source (e.g., an MR16 or MR 11 lamp) while substantially preserving the discharge efficiency, light-output capacity and lifetime of discharge-based sources. This results from the coupling device that provides light with good spatial uniformity in light intensity and color. Embodiments of the invention can simply split the light to multiple (e.g., two) destinations with substantially the same efficiency.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to application Ser. No. 09/454,073, issued as U.S. Pat. No. 6,304,693, by the same inventors but owned by different assignees. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an optical lighting system for efficiently collecting and directing light, for example, downwardly from a ceiling fixture. 
     BACKGROUND OF THE INVENTION 
     Halogen directional light sources (e.g., MR16 and MR11 lamps) have been used for localized lighting applications, such as task-, accent- and down-lighting. However, since these halogen sources use filaments, they characteristically have low light-delivery efficiency. For example, an EXT lamp, a 50-watt narrow-beam halogen source, typically delivers about 500 task lumens with an energy expenditure of about 55 watts (with an electronic converter) or 60 watts (with a transformer) for a delivered efficiency of about 8-9 lumens per watt. This is for the simplest optical system. In applications where considerable beam conditioning is required through the use of multiple lenses, for example, efficiencies can drop to 5 lumens per watt or less. In addition, because the filament evaporates over time, practical lifetimes are typically limited to 4000 hours or less. Further, thermal considerations limit the practical operating power limits of these sources to about 75 watts, and, therefore, the light output to about 700 lumens or less, for the applications discussed above. Often, larger light outputs would be desirable for each light point—e.g., for down-lighting applications. 
     In recent years, owing to the desirability of replacing the foregoing directional filament-type sources with more efficient gas discharge-based alternatives, a number of new directional lamps types have been developed. Unfortunately, owing to the added optical, size and color-averaging requirements of the discharge sources used, the use of conventional imaging optics has resulted in directional light sources that, while significantly more efficient and with lifetimes significantly longer, are also significantly larger than the directional halogen sources they seek to replace. The smallest directional discharge sources are packaged as PAR 30  lamps, about 2 times the size of an MR16 lamp and 3 times the size of an MR11 lamp. It would, therefore, be desirable to provide a discharge-based directional light source that could be of the size of a directional halogen source (MR16 or MR 11) while preserving the discharge efficiency, light-output capacity and lifetime of discharge-based sources. It would also be desirable to be able to split the light output simply and with comparable efficiency where a second directional output is required. (For larger numbers of outputs, e.g. six, fiberoptic approaches may be preferable.) 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment of the invention provides an efficient system for directing light, comprising a light source and a generally tubular, hollow coupling device. The coupling device has an interior light-reflective surface for receiving light from the source at an inlet and transmitting it as a generally diverging light beam through an outlet. The device is shaped in accordance with non-imaging optics and increases in cross sectional area from inlet to outlet so as to reduce the angle of light reflected from the surface as it passes through the device. 
     The foregoing system provides a discharge-based directional light source that can be of the size of a directional halogen source (e.g., an MR16 or MR 11 lamp) while substantially preserving the discharge efficiency, light-output capacity and lifetime of discharge-based sources. This results from the coupling device that provides light with good spatial uniformity in light intensity and color. 
     Embodiments of the invention can simply split the light to multiple (e.g., two) destinations with substantially the same efficiency. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side plan view of an lighting system partially in cross section and partially in block form, in accordance with the invention. 
     FIG. 1A is a top plan view of a lamp and coupling device of FIG.  1 . 
     FIG. 2 is a side plan view of another lighting system partially in cross section and partially in block form, in accordance with the invention. 
     FIG. 3 is a side plan view of an optical lens. 
     FIG. 4 is a side plan view of yet another lighting system partially in cross section and partially in block form, in accordance with the invention. 
     FIG. 5 is a side plan view of a mirror integrally formed on a lens for conditioning and redirecting light rays. 
     FIG. 6 is a side plan view of a curved mirror for conditioning and redirecting light rays. 
     FIG. 7 is a side plan view of another lighting system partially in cross section, in accordance with the invention. 
     FIGS. 8 is a side plan view of an edge-defining member that may be used in the lighting system of FIG.  7 . 
     FIGS. 9A-9E are cross sections of an edge-defining member of FIG. 7 or FIG.  8 . 
     FIG. 10 is a side plan view of still another lighting system partially in cross section, in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 1A show a lighting system  10  according to the invention. The lighting system employs a lamp, or light source,  11  and a light coupling device  12  for illuminating a target area  14 . Lamp  11  preferably is a metal halide lamp as shown, but may also be a filament-type halogen lamp, or an electrodeless lamp, by way of example. A reflective member  15 , shown cross-hatched, directs light from the left-shown side of lamp  11  into coupling device  12 . This allows for a high amount of light to be transmitted through the coupling device. Lamp  11  has an enlarged, or bulbous, region  11   a  and upper and lower arms  11   b  and  11   c.    
     Coupling device  12  is generally tubular and has a respective, interior light-reflecting surface  12   a  for receiving light at an inlet end, nearest the lamp, and for transmitting it to an outlet end shown at the right. As best shown in FIG. 1A, most of the inlet end of the coupling device preferably extends half-way across the lamp, from right to left, with recess  13  receiving top arm  11   b  of the lamp aid another recess (not shown in FIG. 1A) receiving lower arm  11   c  of the lamp. In more detail, recess  13  extends from a first axially oriented edge  12   b  of device  12  to a second axially oriented edge  12   c  of the device and receives top arm  11   b  of the lamp, for positioning the lamp closer to the second edge  12   c . This maximizes light extraction from the lamp. 
     The coupling device increases in cross-sectional area from inlet to outlet in such manner as to reduce the angle of light reflected from its interior surface as it passes through the device, while transmitting it as a generally diverging light beam through the outlet. By “generally diverging” is meant that a substantial number of light rays diverge from main axis  16 , although some rays may be parallel to the axis. Preferably, substantially all cross-sectional segments of surface  12   a  orthogonal to a main axis  16  of light propagation substantially conform to a compound parabolic collector (CPC) shape. A CPC is a specific form of an angle-to-area converter, as 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). 
     Lighting system  10  typically illuminates target area  14  with light having high spatial uniformity in both light intensity and color distribution. This is because coupling device  12  conditions the light much more effectively than prior art reflectors (not shown) of the elliptical or parabolic type, for example. Typically, system  10  can provide substantially all of the light to target area  14  within a predetermined angle, for example, 35 degrees from main axis  16 . 
     Traditionally, reflectors (not shown) control light from light sources in a so-called “imaging” method. Elliptical reflectors, for example, image the light source, positioned at a first focus of the reflector, onto a second focus. The controlled light converges from the surface of the reflector to the second focus as the light exits the reflector. Parabolic reflectors are another example of optics using imaging. In a parabolic reflector, the controlled light is collimated so that light rays exit in a generally parallel fashion. In contrast, the coupler of the present invention uses “non-imaging” optics, and, in preferred embodiments, realizes small size and superior light-mixing properties possible with such optics. As the light leaves a non-imaging collector (e.g., coupling device  12 ), most of the light is controlled so as to be generally diverging at a directionally useful angle (for example, up to 35 degrees) as it leaves the reflector. This is an important aspect of a lighting system since the light is most highly concentrated at the exit of the non-imaging collector (e.g., coupling device  12 ). In contrast, in an elliptical system the light is most highly concentrated at the second focus. For a parabolic system, the light concentration is practically the same wherever it is collected. Although the light emitted by a parabolic system may have a high angular uniformity, its imaging quality typically precludes high spatial uniformity in light intensity (and color as well for discharge sources). 
     FIG. 2 shows a lighting system  20  that is similar to lighting system  10  (FIG. 1) but which includes conditioning optics  30  between coupling device  12  and target area  14 . Due to the typically high spatial uniformity in light intensity and color, the conditioning optics can often comprise a single lens, e.g., plano-convex lens  32  of FIG. 3 having a planar surface  32   a  through which light rays (not shown) may be received and a convex surface  32   b  through which light rays may exit. Lens  32  will typically reduce their angular distribution. Other types of lenses, such as Fresnel lenses, can be used as will be obvious to those of ordinary skill in the art based on this specification. 
     FIG. 4 shows a light distribution system  34  that is similar to lighting system  20  (FIG. 2) but which includes a moveable mirror  36  with a reflective surface  36   a  for redirecting light from conditioning optics  30 . Collection optics  30  are shown by a phantom-line box to indicate that it may be omitted if desired. 
     The function of a conditioning optics and mirror may be integrated into a single unit, such as unit  38  of FIG.  5 . Unit  38  has a planar reflective surface  38   a  and a plano-convex lens  38   b . Light rays  40  travels along paths as shown. An alternative unit  44 , shown in FIG. 6, integrates both functions as well. Unit  44  comprises a mirror with a curved, concave reflective surface  44   a , for directing light ray  46   s  in the paths shown. 
     FIG. 7 shows a lighting system  50  including lamp  11  and coupling device  12  as in FIG.  1 . It also includes an edge-defining member  52  for receiving a light beam from the coupling device and transmitting it through an outlet  52   a  with its peripheral edge more sharply defined. Member  52  can be a tubular quartz rod, by way of example, that can have one or more of IR, UV or AR coatings on either of both of its inlet (left-shown) surface and its outlet surface  52   a . System  50  can replace lamp  11  and coupling device  12  in FIGS. 1,  2 ,  4  or  7 . For instance, when replacing lamp  11  and coupling device  12  of FIG. 1, light rays are transmitted from outlet  52   a  directly to target area  14  (FIG. 1) without the use of intermediate conditioning optics, such as  30  in FIG.  2 . If redirection of the light is desired, an edge-defining member  54  with a bend, e.g., as shown in FIG. 8, can be used instead of member  52 . Thus, a light ray  56  received in the left-shown inlet of member  53  (FIG. 8) exits downwardly through outlet  54   a.    
     FIGS. 9A-9E show preferred cross sections of edge-defining member  52  (FIG. 7) or  54  (FIG. 8) along a main direction (not shown) of light propagation. FIG. 9A shows a rectangular cross section  60 ; FIG. 9B, a square cross section  62 ; FIG. 9C, an oval cross section  64 ; FIG. 9D, a trapezoidal cross section  66 ; and FIG. 9E, a hexagonal cross section  67 . Other shapes, e.g., pentagonal, can be used as will be apparent to those of ordinary skill in the art. It is known that some degree of spatial uniformity in light intensity and color results from using an edge-defining member in a conventional lighting system (not shown) using reflectors and, hence, imaging optics. However, for a square cross section, as in FIG. 9B, the length-to-width ratio of such member in a conventional system is typically about 8:1 to achieve good uniformity. The same degree of uniformity can be achieved (e.g. FIG. 1) with a much lower ratio in the present invention using non-imaging optics, e.g., about 2:1 to 3:1. 
     FIG. 10 shows a coupling system  60  using lamp  111  and coupling device  12 , as in FIG. 1, and a second coupling device  62  preferably with the same construction as device  12 . Light passing through device  12  may optionally be conditioned, redirected, or both by optional optics  64  (shown in phantom) before reaching target area  14 . With lamp  111  omitting the reflective coating  15  of lamp  11  (FIG.  1 ), light passes also through coupling device  62  with interior light-reflecting surface  62   a , and optionally may be conditioned, redirected, or both by optics  66  (shown in phantom) before reaching target area  68 . Optics  64  and  66  perform one or more optical functions as described above, for instance, with respect to lens  32  of FIG. 3, or mirror  36  of FIG.  4 . More than two coupling devices can be used if desired, but for six outputs, for instance, fiberoptic approaches may be preferable. 
     While the invention has been described with respect to specific embodiments by way of illustration, many modifications and changes will occur to those of ordinary skill in the art. For instance, with reference to FIG. 7, the function of conditioning optics  30  (FIG. 2) may be realized partially or entirely by forming edge-defining member  52  with an increasing cross section from left to right. Alternatively, with reference to FIG. 2, such function may be partially or fully realized by extending coupling device  12  to the right with increasing cross section. 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.