Abstract:
The present invention is directed to an optical lens for capturing, homogenizing and transmitting substantially all of the light emitted by a light source, such as a light emitting diode. The optical lens includes a light transmitting structure having a TIR collector portion, a projector portion and a transition portion disposed between the TIR and projector. The structure is characterized by the length of the transition portion being longer than the focal length of the TIR portion. The light source is disposed within a recess in one end of the TIR portion. The light output from the light source is captured by the TIR portion and homogenized to form a uniform, circular near field image within the transition portion. The projector portion then projects the circular near field image into a uniform, circular far field image. The present invention transmits 85% of the light emitted by the light source and produces a uniformly illuminated circular image in the far field of the device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to solid catadioptric lens arrangement. More particularly the present invention relates to a solid catadioptric lens arrangement that incorporates a total internally reflective (TIR) collector portion that encompasses a light source to capture and collimate the light output and a projector lens portion that re-images the collimated light from the collector into the far field of the lens. 
     It is well known in the art that various combinations of lenses and reflectors can be used in conjunction to change the radiation distribution of the light emitted from a light source. For example, many flashlights available on the market today include a reflector cup around a light source to capture the radiation that is directed from the sides of the light source and redirect it in forward direction, and a convex lens that captures and focuses both the direct output from the light source and the redirected light from the reflector cup. While this is the common approach used in the manufacture of compact lighting devices such as flashlights, this method includes several inherent drawbacks. First, while this arrangement can capture much of the output radiation from the light source, the captured output is only slightly collimated. Light that exits from the light source directly without contacting the reflector surface still has a fairly a wide output angle that allows this direct light output to remain divergent in the far field of the lighting device. Therefore, to collimate this light in an acceptable manner and provide a focused beam, a strong refractive lens must be used. The drawback is that when a lens of this type is used, the image of the light source is directly transferred into the far field of the beam. Second, the light output is not well homogenized using an arrangement of this type. While providing facets on the interior of the reflector surface assists in smearing edges of the image, generally a perfect image of the actual light-generating source is transferred directly into the far field of the beam. In the case of an incandescent, halogen or xenon light source this is an image of a spirally wound filament and in the case of light emitting diodes (LEDs) it is a square image of the emitter die itself. Often this direct transfer of the light source image creates a rough appearance to the beam that is unattractive and distracting for the user of the light. Third, most of these configurations are inefficient and transfer only a small portion of the radiational output into the on axis output beam of the lighting device. Finally, these devices require several separate components to be assembled into mated relation. In this manner, these devices create additional manufacturing and assembly steps that increase the overall cost of the device and increase the chance of defects. 
     Several prior art catadioptric lenses combine the collector function with a refractive lens in a single device that captures and redirects the radiational output from a light source. U.S. Pat. No. 2,215,900, issued to Bitner, discloses a lens with a recess in the rear thereof into which the light source is placed. The angled sides of the lens act as reflective surfaces to capture light from the side of the light source and direct it in a forward mariner using TIR principals. The central portion of the lens is simply a convex element to capture the on axis illumination of the light source and re-image it into the far field. Further, U.S. Pat. No. 2,254,961, issued to Harris, discloses a similar arrangement as Bitner but discloses reflective metallic walls around the sides of the light source to capture lateral radiation. In both of these devices, the on-axis image of the light source is simply an image of the light generating element itself and the lateral radiation is transferred as a circle around the central image. In other words, there is little homogenizing of the light as it passes through the optical assembly. Further, since these devices anticipate the use of a point source type light element, such as is found in filament type lamps, a curvature is provided in the front of the cavity to capture the divergent on axis output emanating from a single point to create a collimated and parallel output. Therefore, a relatively shallow optical curvature is indicated in this application. 
     Another prior art catadioptric lens is shown in U.S. Pat. No. 5,757,557. This type collimator is referred to as the “flat top tulip” collimator. In its preferred embodiment, it is a solid plastic piece with an indentation at the entrance aperture. The wall of the indentation is a section of a circular cone and the indentation terminates in a shallow convex lens shape. A light source (in an appropriate package) injects its light into the entrance aperture indentation, and that light follows one of two general paths. On one path, it impinges on the inner (conic) wall of the solid collimator where it is refracted to the outer wall and subsequently reflected (typically by TIR) to the exit aperture. On the other path, it impinges on the refractive lens structure, and is then refracted towards the exit aperture. This is illustrated schematically in FIG.  1 A. As stated above, the collimator  10  is designed to produce perfectly collimated light  16  from an ideal point source  12  placed at the focal point of the lens  10 . A clear limitation is that when it is used with a real extended source  14  of appreciable surface area (such as an LED chip) as seen in FIG. 1B, the collimation is incomplete and the output is directed into a diverging conic beam that includes a clear image of the chip as a central high intensity region  18  and a secondary halo region  19 . 
     There is therefore a need for a catadioptric lens assembly that collimates the light output from a light source while also homogenizing the output to produce a smoothly illuminated and uniform beam image in the far field of the device. 
     BRIEF SUMMARY OF THE INVENTION 
     In this regard, the present invention provides an optical attachment for a light source. In particular, the present invention provides an optical element that is well suited for use with LED light sources, which do not approximate a point source for luminous flux output. The optical attachment includes a recessed area into which the light source is placed. The front of the recess further includes an inner lens area for gathering and focusing the portion of the beam output that is emitted by the light source along the optical axis of the optical attachment. Further, the optical attachment includes an outer reflector area for the portion of the source output that is directed laterally or at large angles relative to the optical axis of the device. The reflector portion and the inner lens direct the light output through a transition region where the light is focused and homogenized. The convex optics at the front of the transition region images this focused and homogenized light into the far field of the device. The present invention also relates to lens assembly as described above for use with other light sources such as incandescent, halogen or xenon, since these types of light sources are also well known in the art and are manufactured to be interchangeable with one another. The invention also relates to a flashlight device that includes a high intensity light source in conjunction with the optical lens described herein. 
     Accordingly, one of the objects of the present invention is the provision of compact one piece optical assembly that can be used with a high intensity light source to capture both the on axis and lateral luminous output and collimate the output to create a homogenous beam image in the far field of the device. Another object of the present invention is the provision of a one piece optical assembly for use with a high intensity light source that includes a TIR reflector assembly in conjunction with an on axis beam collimator at the input end thereof and a light tube that creates a focused and homogenous beam image for transfer into the far field of the device. A further object of the present invention is the provision of an optical assembly that creates a homogenous and focused beam image on the interior thereof that is further imaged into the far field of the output beam of the device to create a low angle beam divergence. Yet a further object of the present invention is the provision of a flashlight that includes a high intensity light source in combination with a one-piece optical assembly that creates a uniformly illuminated beam image in the far field of the device. 
     Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
     FIG. 1 a  is a cross-sectional view of a prior art catadioptric lens showing ray traces from a theoretical point source; 
     FIG. 1 b  is a cross-sectional view of a prior art catadioptric lens showing ray traces from a high intensity LED source; 
     FIG. 2 is a cross-sectional view of the optical lens of the present invention; 
     FIG. 3 is a cross-sectional view thereof in conjunction with a light source and ray tracing; 
     FIG. 4 a  is a plan view showing the light beam pattern of a prior art lighting assembly; 
     FIG. 4 b  is a plan view showing the light beam pattern of the present invention; 
     FIG. 5 a  is a side view of the optical lens of the present invention; 
     FIG. 5 b  is a side view of a first alternate embodiment thereof; 
     FIG. 5 c  is a side view of a second alternate embodiment thereof; 
     FIG. 6 is a side view thereof shown with an aperture stop; 
     FIG. 7 a  is a front perspective view of the front surface of the present invention with honeycomb facets shown thereon; 
     FIG. 7 b  is a front perspective view of the front surface of the present invention with circular facets shown thereon; and 
     FIG. 8 is a flashlight with the optical lens of the present invention installed therein. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, the unique lens configuration of the present invention is illustrated and generally indicated at  20 . The lens  20  can be seen to generally include a total internal reflection (TIR) collector portion  22 , a projector lens portion  24  and a transition portion  26  disposed between the collector  22  and the projector  24 . As will hereinafter be more fully described, the lens  20  is configured to capture a large amount of the available light from a light source  28 , collimate the output and redirect it in a forward fashion to provide a uniformly illuminated circular beam image in the far field of the device. In general the lens  20  of the present invention can be used with any compact light source  28  to provide a highly efficient lens assembly that is convenient and economical for assembly and provides a high quality light output that has not been previously available in the prior art. 
     Turning to FIGS. 1 a  and  1   b , as stated above, the catadioptric lenses  10  of the prior are designed to operate with theoretical point sources  12 . By following the ray traces shown in FIG. 1 a , it can be seen that a highly focused beam output  16  is generated when the output source is a theoretical point source  12 . However, while many high intensity light sources  12  theoretically approximate a point source, in practice, when the output energy  16  is captured and magnified, the light source  12  actually operates as an extended light source  14 . As can be best seen in FIG. 1 b , a high intensity light emitting diode (LED)  14  is shown in combination with the prior art catadioptric lens  10 . The resulting ray traces clearly illustrate that the output includes a central hot spot  18  that is essentially a projected image of the emitter chip  14 , resulting from the finite size of the chip  14  and a halo region  19  that results from the emissions from the sides of the chip  14 . 
     The lens  20  of the present invention is shown in cross-sectional view in FIGS. 2 and 3. The preferred embodiment of the present invention generally includes a TIR collector portion  22 , a projector lens portion  24  and a transition section  26  disposed therebetween. The collector portion  22  is configured generally in accordance with the well-known principals of TIR optics. This avoids having to add a reflective coating on the outer surface  30 . The collector portion  22  has an outer curved or tapered surface  30  that roughly approximates a truncated conical section. The outer surface  30  may be a straight linear taper, a spherical section, a hyperbolic curve or an ellipsoidal curve. As illustrated in FIG. 2, an ellipsoidal shape has been demonstrated as the most highly efficient shape for use with the preferred high intensity LED light source as will be further described below. The collector  22  includes a recess  32  in the rear thereof that is configured to receive the optical portion  34  of the light source  28 . The recess  32  has inner sidewalls  36  and a front wall  38 . The inner sidewalls  36  may be straight and parallel or tapered to form a truncated conic section, although some taper is typically required to ensure that the device is moldable. The inner sidewalls  36  act to bend rays toward the collector portion  22  and enhance the collection efficiency of the device. The outer surface  30  and the inner sidewalls  36  are shaped to focus the light from the source within the transition region  26  and near the focal point of the projector lens  24 . This generally means that the outer surface  30  will be an asphere, although a true conic shape can be used with only moderate reduction in performance. 
     The front wall  38  of the recess  32  may be flat or rearwardly convex. In the preferred embodiment, the front wall  38  is formed using an ellipsoidal curve in a rearwardly convex manner. The preferred light source  28  is a high intensity LED device having a mounting base  40 , an optical front element  34  and an emitter chip. Generally, LED packages  28  such as described are available in outputs ranging between one and five watts. The drawback is that the output is generally released in a full 180° hemispherical pattern. The light source  28  in accordance with the present invention is placed into the cavity  32  at the rear of the collector  22  and the collector portion  22  operates in two manners. The first operation is a generally refractive function. Light that exits the light source  28  at a narrow exit angle that is relatively parallel to both the optical axis  42  of the lens and the central axis of the light source  28  is directed into the convex lens  38  at the front wall of the cavity  32 . As this on axis  42  light contacts the convex surface  38  of the front wall, it is refracted and bent slightly inwardly towards the optical axis  42  of the lens  20 , ultimately being relatively collimated and homogenized as it reaches the focal point  44  of the collector portion  22 . 
     The second operation is primarily reflective. Light that exits the light source  28  at relatively high output angle relative to the optical axis  42  of the lens  20  travels through the lens  20  until it contacts the outer walls  30  of the collector section  22 . The outer wall  30  is disposed at an angle relative to the light exiting from the light source  28  as described above to be above the optically critical angle for the optical material from which the lens  20  is constructed. The angle is measured relative to the normal of the surface so that a ray that skims the surface is at 90 degrees. As is well known in the art, light that contacts an optical surface above its critical angle is reflected and light that contacts an optical surface below its critical angle has a transmitted component. The light is redirected in this manner towards the optical axis  42  of the lens  10  assembly and the focal point  44  of the collector portion  22 . The curve of the outer wall  30  and the curve of the front surface  38  of the cavity  32  are coordinated to generally direct the collected light toward a single focal point  44 . In this manner nearly 85% of the light output from the light source  28  is captured and redirected to a homogenized, focused light bundle that substantially converges at the focal point  44  of the collector portion  22  to produce a highly illuminated, substantially circular, light source distribution. 
     It is important as is best shown in FIG. 3, that a parallel fan of rays traced from the output face of the lens  10  back towards the source  28  will be distributed across nearly the entire face of the source  28 . This manner of using a parallel fan of rays and applying them in a reverse manner through the lens  10  and back to the source  28  is important because the distribution of the rays will indicate whether the optical design of the lens will maximize the on axis intensity of the output beam. The prior art was focused on high collection efficiency and no attempt was made to minimize the fraction of the reverse distributed rays that miss the source  28 . The disclosed lens  10  device using a combination of a TIR collector  22  and a projector portion  24  provides this important maximum on-axis intensity advantage, especially when one considers that the angle of inner surface  36  is particularly tailored such that these rearward traced rays that ordinarily just skim the surface of the source  28  are now better focused to cover the entire face of the source  28 . Further, this aspect of the lens  10  of the present invention is a novel disclosure that is equally useful with respect to a unitary lens  10  or a lens  10  that is formed in two spaced pieces using a collector portion  22  and a projector portion  24  without a transition section  26 . 
     While a specific high intensity LED light source  28  is described, it is clear that the present invention can be used interchangeably with any available light source including but not limited to, incandescent, xenon and halogen. To accommodate the use of these other light sources the curvature of the outer sidewalls  30  and the front wall  38  of the cavity  32  simply must be changed to operate with the geometry of the light-emitting component within the desired light source. While the ellipsoidal geometry shown in the preferred embodiment of the present invention is particularly suited for use with the large horizontal emitter chips in LED light sources  28 , other geometry may be selected for use with light sources having different output configurations. 
     In the lens  20  configuration of the present invention, the placement of the projector portion  24  of the device relative to the collector portion  22  of the device is critical to the proper operation of the lens  20 . The projector portion  24  must be placed at a distance from the collector portion  22  that is greater than the focal length  44  of the collector  22 . In this manner, the collector  22  can function as described above to focus and homogenize a substantial portion of the light output from the light source  28  into a high intensity, circular, uniformly illuminated near field image. This near field image is produced at a location on the interior of the transition section  26 . The near field image is in turn captured by the projector lens  24  and re-imaged or projected into the far field of the device as a uniform circular beam of light as illustrated in FIG. 4 b . The transitional portion  26  simply serves as a solid spacer to maintain the ideal relationship between the collector portion  22  and the projector portion  24 . This configuration eliminates the prior art approach where two separate devices were employed that had to be spaced apart during the assembly process. 
     The novelty of the present invention is that the entire lens  20  structure is formed in a single unitary lens  20  from either a glass material or an optical grade polymer material such as a polycarbonate. In this manner, a compact device is created that has a high efficiency with respect to the amount of light output that is captured and redirected to the far field of the device and with respect to the assembly of the device. This simple arrangement eliminates the prior art need for combination reflectors, lenses, retention rings and gaskets that were required to accomplish the same function. Further, as can best be seen in FIG. 2, the lens  20  may include an annular ring  46  that lies outside the optically active region of the lens  20 . The annular ring  46  forms a mounting surface for installing and retaining the lens  20  in an assembly without affecting the overall operation of the device. 
     Turning to FIGS. 4 a  and  4   b , images from a prior art conventional LED flashlight using a standard piano convex lens (FIG. 4 a ) and from a light source in conjunction with the lens of the present invention (FIG. 4 b ) are shown adjacent to one another for comparison purposes. The image in FIG. 4 a  can be seen to have poor definition between the illuminated  48  and non-illuminated  50  field areas and an uneven intensity of light can be seen over the entire plane of the illuminated field  48 . Areas of high intensity  52  can be witnessed around the perimeter of the illuminated field  48  and in an annular ring  54  near the center of the field  48 . In addition, a particularly high intensity area of illumination can be seen in a square box  56  at the center of the field  48  and corresponds to the location of the emitter chip within the LED package. In contrast, FIG.  4   b  shows an image from the present invention. Note that the illuminated field  58  has a uniform pattern of illumination across the entire plane and the edge  60  between the illuminated  58  and non-illuminated  62  fields is clear and well defined providing high levels of contrast. The relationship between the LED and optical lens components are critical to the operation of the present invention and in providing the results shown in the illumination field in FIG. 4 b.    
     Since the transition portion  26  of the lens  20  is optically inactive, the shape can vary to suit the particular application for the lens  20 . FIGS. 5 a ,  5   b  and  5   c  show several different shapes that the transition section  26  can be formed into without affecting the overall performance of the lens  20 . FIG. 5 a  shows that the transition section  26  is simply a straight-sided cylinder. FIG. 5 b  shows the walls having a slight taper. FIG. 5 c  shows the center of the transition section  26  pinched at approximately the focal point  44  of the collector section  22 . In this manner, the edges of the light image may be further controlled and the material required to form the lens  20  can be reduced. FIG. 6 illustrates the use of an aperture stop  64  to further control the shape of the beam image. The stop  64  may form a perfect circle to clip the edges of the beam and make a sharp near field image that is captured and transferred to the far field by the projector portion  24 . As can be appreciated this aperture stop  64  could also be formed into many other shapes to create novel beam outputs such as stars, hearts, etc. 
     To further homogenize the beam output and create a more uniform far field image, the front face  66  of the projector section  24  may include facets. FIGS. 7 a  and  7   b  illustrate two possible facet configurations. FIG. 7 a  shows a honeycomb facet pattern and FIG. 7 b  shows a concentric circular facet pattern. As is well known in the art the facets serve to smear the light image thereby having a homogenizing effect on the overall output image that levels out beam hot spots. 
     FIG. 8 illustrates the lens  20  of the present invention incorporated into a flashlight  68  assembly. As can be seen the lens  20  of the present invention is installed into the front of a flashlight housing  70 . The annular mounting ring  46  serves to retain the lens  20  in its operative position within the housing  70 . The light source  28  is installed into the recess  32  of the lens and operates as is described above to provide a uniform, collimated and highly efficient light output beam. The housing  70  further contains a power source  72  such as a battery and a means  74  for selectively completing an electrical circuit between the battery and the light source to energize the device. 
     It can therefore be seen that the present invention provides a compact lens  20  configuration that includes integral reflector  22  and projector  24  components that cooperate in a highly efficient manner to gather the diffuse light output from a high intensity light source  28 . Further, the present invention operates in an efficient manner to collimate and homogenize the light output thereby forming a highly desirable uniform and circular far field beam image that has been previously unknown in the art. For these reasons, the instant invention is believed to represent a significant advancement in the art, which has substantial commercial merit. 
     While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.