Abstract:
A lens array for a lamp directs light to a light conduit such as an optical fiber or light pipe for guiding light to a remote location. An array of LED serve as light sources. The lens array includes an integrally formed member having a number of collimator lenses positioned in the lens array so that each lens can operate as a collimator for a corresponding LED to produce a respective collimated beam of light. The lenses have optical properties that are optimized according to where their corresponding LED are positioned in the LED array, so that the lens array is provided with lens prescriptions that produce refraction of the collimated beams of light toward an entrance aperture of the light conduit.

Description:
RELATED APPLICATIONS 
     Commonly-assigned, Netherlands application, Ser. No. PHN 17 233, filed Dec. 17, 1998, and Netherlands application, Ser. No. PHN 17607, filed Sep. 19, 1999 both relate to light generators having one-piece lens arrays for collimating light. 
     FIELD OF THE INVENTION 
     This invention relates to lenses used for collimating and focusing light in LED light generators and in particular, to one-piece lens arrays for collimating and focusing light and LED light generators that use such lens arrays. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Present LED light generator designs collect light from an array of separate LED sources, and focus the light at a target, such as the entrance aperture of an optical fiber. A critical aspect in most of these designs is the collimation and focusing of the separate LED sources in order to create a useable light beam. 
     Many LED light generator designs employ a plurality of separate and distinct primary optical elements (collimators) each of which efficiently captures the widely divergent light generated by a respective one of the LED sources. For practical reasons, the collimators are identical, and thus have parallel optic axes which produce collimated light beams which are parallel to one another. A second lens (collection lens) focuses the parallel collimated light beams at the desired target. The second lens must have relatively high-angle refraction to focus the light beams generated by the LED sources at the periphery of the array. 
     The use of a separate and distinct collimator for each LED source of the array undesirably increases the size, complexity and cost of the light generator design. This is because the collimators must be individually mounted and aligned using bulky mounting hardware and spacers that require expensive handling and alignment steps during assembly. 
     Additionally, the high-angle refraction of the collection lens reduces total collection efficiency due to Presnel loss and beam spreading at the higher refraction angles. 
     Accordingly, lenses which collimate and/or focus light in LED light generators are needed that reduce handling and alignment during light generator assembly and allow more compact light generator packaging with substantially identical optical function. 
     In one aspect of the invention, a lens array for a lamp directs light to a light conduit such as an optical fiber or light pipe for guiding light to a remote location. An array of LED serve as light sources. The lens array includes an integrally formed member having a number of collimator lenses positioned in the lens array so that each lens can operate as a collimator for a corresponding LED to produce a respective collimated beam of light. The lenses have optical properties that are optimized according to where their corresponding LED are positioned in the LED array, so that the lens array is provided with lens prescriptions that produce refraction of the collimated beams of light toward an entrance aperture of the light conduit. 
     In another aspect of the invention, a light generator for a lamp uses an array of LED as light sources. Each LED generates diverging light. An integrally formed member defines a number of collimator lenses positioned in a lens array so that each of the lenses operates to collimate the diverging light generated by corresponding one of the LED into a respective collimated light beam. The lenses have optical properties that are optimized according to where their corresponding LED are positioned in the LED array. A collection lens is used for focusing the collimated light beams at an entrance aperture of a light conduit such as an optical fiber or light pipe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages, nature, and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with accompanying drawings wherein: 
     FIG. 1 is a diagrammatic view of a lens array according to an embodiment of the invention as used in a typical light emitting diode (LED) light generator; 
     FIG. 2 is a diagrammatic view of an LED light generator having a collection lens especially adapted for use with the lens array of the invention; 
     FIG. 3A is a diagrammatic view of a reference system that was used in a calculation performed with an optical ray-tracing program to illustrate the performance of a conventional lens system used in a typical LED light generator; 
     FIG. 3B is a diagrammatic view of a system that was used in a calculation performed with an optical ray-tracing program to illustrate the performance of the lens system of the invention; 
     FIG. 4A is a graphical illustration of the angular distributions and integral distributions for the reference system; 
     FIG. 4B is a graphical illustration of the angular distributions and integral distributions for the improved system; and 
     FIG. 5 is a schematic diagram of an LED light generating system of the invention including a light pipe extended into a signage configuration. 
    
    
     It should be understood that the drawings are for purposes of illustrating the concepts of the invention and are not to scale. 
     DETAILED DESCRIPTION 
     FIG. 1 is a diagrammatic view showing a lens array  10  according to a first embodiment of the invention as used in a typical light emitting diode (LED) light generator  16  comprises of an array  17  of LED sources  18   a  through  18   e . The lens array  10  integrates a plurality of collimator lenses  14   a  through  14   e  into a single unitarily formed member  12  which can be inexpensively manufactured from plastic using known conventional optical plastic molding methods. The lenses  14   a  through  14   e  are positioned in the array  10  in a predetermined manner so that each LED source  18   a  through  18   e  has its own collimator. Each lens  14   a  through  14   e  this array  10  is optically optimized according to where its corresponding LED source  18   a  through  18   e  is positioned in the LED array  17 . A planar collection lens  20  such as a Fresnel lens, is provided after the lens array  10  for focusing the light beams Ba through Be at a desired target  22  such as the entrance apertures of a light conduit such as an optical fiber or light pipe of a signage or illumination system. The collection lens  20  has a lens prescription that is selected to permit it to operate effectively with the optically optimized lenses  14   a  through  14   e  of the lens array  10 . 
     As stated earlier, each lens  14   a  through  14   e  of the array  10  is optically optimized for the positioning of its corresponding LED source  18  in the LED array  17 . For example, the lenses  14   a  through  14   a  located at the periphery  24   a  and  24   e  of the lens array  10  which collimate the LED sources  18   a  through  18   e  located at the periphery  26  of the LED array  17  is provided with their own specific lens prescriptions. Such a lens prescription can define a refractive surface  28   a  through  28   e  that enables the lens  14   a  through  14   e  to refract or “steer” the collimated beam Ba through Be of light partially toward the selected target  22 . Because the lenses  14   a  through  14   e  are an integral molded one-piece member, virtually no additional manufacturing costs will be incurred as the individual lens prescriptions can be easily provided in the plastic molding tooling. Accordingly, the inventive lens array  10  permits the use of a variety of LED packages, size requirements, total-lumen requirements, etc. The data provided further on shows the results of a simplified calculation that illustrates this principle. 
     The ability to optically optimize each individual lens  14   a  through  14   e  in the lens array  10  by providing them with their own specific lens prescription advantageously permits variable spacing of the LED sources  18  in an LED light generator  16 . This is important for the following reason. For all designs, there is a tradeoff between the collimator&#39;s efficiency and its size. A smaller collimator is less efficient, but it improves the collection lens efficiency, since the focusing angle is smaller (larger collimators are more efficient but increase the focusing angle because they can be farther from the central axis of the light generator). Restated, there is a tradeoff between collimator efficiency and collection lens efficiency. In conventional light generator designs, the collimator efficiency (i.e., size of the collimator lens) decision can only be made once, globally, for all the LED sources. However, the collimator efficiency of each lens  14   a  through  14   e  of the lens array  10  of the present invention, can be specifically matched (a prescription which varies the “size” of the lens  14 ) for the position of its corresponding LED source  18 . Since the collection efficiency of the collection lens  20  varies across its radius, matching can be accomplished by inversely varying the collimator efficiency of the of the lenses  14  of the array  10  according to how its corresponding LED source  18  is positioned relative to the collection lens  20 . Hence, the use of the lens array  10  of the present invention can lead to higher total LED light generator efficiency. For example, the lenses  14   a  through  14   e  at the periphery  24   a  through  24   e  of the lens array  10  can have lens prescriptions that call for an increased exit aperture size. This would provide more collimation of light at the periphery of the lens array  10  thereby matching the lower collection efficiency at the periphery of the collection lens  20 . 
     Other advantages are realized with the lens array  10  of the invention. For instance, the lens array  10  also reduces the light generator&#39;s  16  manufacturing cost because it requires substantially less handling and alignment during assembly as compared to conventional separate collimator lens elements. Additionally, the inventive lens array  10  permits a more compact light generator design with substantially the same optical function as larger conventional designs, because the mounting lips and spacers associated with conventional separate collimator lens elements are not needed. 
     The collection lens  20  used with the lens arrays  10  that have lenses with “beam steering” lens prescriptions require modification to operate effectively with the lens array  10 . The lens array  10  depicted in FIG. 1 provides only a small amount beam steering thus the curvature of the collection lens  20  can be modified from that of a simple spherical lens in order to more efficiently refract the “steered” beams B of the light from the lens array  10 . 
     When the lenses  14   a  through  14   e  of the lens array  10  are provided with optical prescriptions that produce a substantial amount of beam steering, the collection lens can be constructed as a curved one-piece array  30  of Fresnel lenses as shown in FIG.  2 . Because the collection lens  30  is single unitarily formed member it can also be inexpensively manufactured from plastic using known conventional optical plastic molding methods. In addition, the Fresnel lenses of the collection lens array  30  can have different focal lengths. The collection lens  30  can also include other modifications which optimize light gathering. 
     As should now be apparent, the lens array  10  of the invention has two separate advantages. The first is cost. The single unitarily formed member part is less expensive to manufacture than the many parts that it replaces in conventional light generator designs. The second advantage is performance. The integration permits a more complex optical design at virtually no additional manufacturing cost, leading to improved light collection as the lens array  10  collimates and also partially steers the light towards the light generator exit aperture and the collection lens then completes the task of focusing. By splitting the refraction angle burden between two elements, the total efficiency is improved. 
     As mentioned earlier, a simplified calculation was performed to demonstrate the higher performance of the inventive lens array  10 . The calculation was performed using an optical ray-tracing program known as ASAP™. The calculation was performed for a conventional light generator lens system with a non-beam steering collimator (reference system), and a light generator lens system using a beam steering lens array of the present invention (improved system). 
     As depicted in FIG. 3A the reference system  40  used a parallel plate  42  and single wedge  44  to deflect the beam B. The improved system  50  depicted in FIG. 3B used two wedges  52 ,  54 . All plates and wedges had an index of refraction of 1.5. The wedge and total refraction angles were chosen arbitrarily, and there was no particular significance to the specific values other than convenience. The results are a general feature of the comparison between using one wedge and two wedges for beam deflection. The parallel plate was included to represent a collimator with no steering function, but the Fresnel losses of its two surfaces were included to approximate the reference collimator Fresnel loss. The single wedge of the reference system had an angle of 39.53°, resulting in a total refraction angle of 33.18°. The two wedges of the improved system each had an angle of 25°, which also resulted in a total refraction angle of 33.18°. All wedges had their entrance surfaces perpendicular to the initial beam direction. Again, this is for computational convenience only, and does not represent any essential feature of the calculation. 
     The results of the calculations show that the improved system was superior in two ways. First, where the reference system transmitted only 64% of the input beam (a truncated Lambertian of cone angle 2×4°), the improved system transmitted about 80%, or 25% more light than the reference system (i.e. 80/64=1.25). The second advantage is a bit subtler, but of comparable importance. The beam exiting the reference system was broader (and therefore of a lower intensity per unit of total flux) than the improved system beam. The numerical value of the advantage that this represents depends on the specific geometry of the application, but the magnitude of the broadening can be at least quantified. 
     Since both beams were broadened asymmetrically, with the asymmetry being much worse for the reference system, the integral of the total flux is considered, and the angle from the 10% point to the 90% point (i.e. the central 80% of the beam) is measured. Those angles were 13.7° and 10.4° for the reference and improved systems respectively. Graphics of the angular distributions and integral distributions for the reference system and the improved system are shown in FIGS. 4A and 4B, with cursors (“+”) marking the range of measurement on the integral distributions. 
     While the foregoing invention has been described with reference to the above embodiments, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.