Abstract:
A cylindrical light source comprises multiple LEDs mounted on either the exterior or interior surface of the cylinder, with heat-sink fins respectively on its interior or exterior. The LEDs emit radially, but their emission is redirected along the cylinder axis by individual ellipsoidal reflectors.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit of U.S. Provisional Patent Applications No. 61/132,258, filed Jun. 16, 2008, and No. 61/212,694, filed Apr. 15, 2009, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     In the ongoing endeavor to use multiple light emitting diodes (LEDs) in commercial lighting fixtures, there are two primary aspects, optical and thermal, that require careful consideration. Several US patents disclose reflective types of LED combiners. In U.S. Pat. Nos. 7,246,919 B2; 6,846,100 B2; 6,598,996 B1; and 6,364,506 an array of LEDs is mounted on a planar base, attached to an Edison screw connector. That approach, however, enlarges the emitting area and complicates thermal management. U.S. Pat. Nos. 7,249,877 and 6,682,211 B2 put an LED array at a location corresponding to the filament location of a corresponding incandescent bulb, but cooling is adequate only for low-power LEDs. What is needed is a fresh approach to multiple-LED employment, offering both superior cooling and compact beam-forming optics. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is a complete light source, comprising multiple LEDs, their optics, drive electronics, and integral cooling via a cylindrical housing. The LEDs are either mounted on the interior surface of the cylinder, facing radially inwards or optionally are mounted on the exterior of the cylinder, facing radially outwards. The cylinder is preferably metallic, or a composite material with adequate thermal conductivity, with external or internal fins for convective cooling. Alternatively, the cooling can be accomplished using the novel approach described in U.S. Provisional Application 61/205,390 titled “Heat Sink with Helical Fins and Electrostatic Augmentation” by several of the same inventors. This application is incorporated herein by reference in its entirety. 
     Each LED, or group of LEDs, has its own reflector, which forms an output beam running along the cylinder axis. A plurality of such LEDs, preferably four or more, and their reflectors are nested outside and/or inside the cylinder, with the light coming out one end of the reflector. The electrical power cabling and mechanical supports may come out the other end of the reflector. The combined light output of the four or more reflectors forms a typical PAR-type flood pattern. The advantage of this approach is multi-fold. The optical efficiency of the system is very high as the only losses come from absorption losses of light striking the reflectors. As such the intercept efficiency is typically at 90% (amount of light from the LED that gets to the target, with optical efficiency=reflectivity*intercept efficiency). In addition, the design may be made extremely compact allowing the system to operate inside a conventional 6 inch (15 cm) diameter ceiling can of conventional downlights. 
     Furthermore, the architecture aids in the creation of thermal cooling via convection loops even inside an insulated can. Using state-of-the-art white LEDs, the system can safely handle 15 watts of electrical power input to the LEDs (of which about ¾ is converted into heat) even with the system installed in an insulated can, as long as the room temperature is 35° C. or less. For example, using five CREE Corporation (of North Carolina) model MC-E white LEDs, flux levels of well over 1400 lumens (cool white) can be projected onto the floor. Using warmer color LEDs from the same manufacturer and others, the system can output approximately one thousand lumens with a color temperature under the 3000° K of incandescent light bulbs. This can be achieved with a sizable temperature safety margin for the system components. Thus this new approach makes it possible to produce solid state replacement lamps for the most popular PAR 20 and PAR 30 lamps, and even some PAR 38 lamps. 
     Other aspects of the invention provide reflector and cylinder sub-assemblies around which the complete light source may be built. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the present invention will be apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  is a bottom plan view of a light source with four LEDs mounted internally on a cylindrical heat sink. 
         FIG. 2  is a perspective view of the light source shown in  FIG. 1 . 
         FIG. 3  is a perspective view of the light source shown in  FIG. 1 , showing light output, both reflected and unreflected, from one LED. 
         FIG. 4  is a perspective view of the light source shown in  FIG. 1 , showing unreflected light output from one LED. 
         FIG. 5  is a perspective view of the light source shown in  FIG. 1 , showing the entire output of the light source. 
         FIG. 6  shows the illuminance pattern of the light source of  FIG. 1 . 
         FIG. 7  shows the far-field intensity pattern of the light source of  FIG. 1 . 
         FIG. 8  shows a perspective view of a 5-LED light source. 
         FIG. 9  is a contour graph of illuminance when one LED of the 5-LED light source of  FIG. 8  is emitting. 
         FIG. 10  is a contour graph of illuminance when all LEDs of the 5-LED light source of  FIG. 8  are emitting. 
         FIG. 11  shows an isometric view of the illuminance when all LEDs of the 5-LED light source of  FIG. 8  are emitting. 
         FIG. 12  shows a perspective view of a light source with 10 LEDs and reflectors, mounted externally on a cylindrical heat sink. 
         FIG. 13  shows a perspective view of a light source with five LEDs, along with primary and secondary reflectors. 
         FIG. 14  is a close-up perspective view of one of the LEDs and its reflectors, showing light rays. 
         FIG. 15  is an isometric view of the illuminance distribution produced by the light source of  FIG. 12 . 
         FIG. 16  is an illuminance contour graph for the 10-LED system of  FIG. 12  with one LED emitting. 
         FIG. 17  is an illuminance contour graph for the system of  FIG. 12  with all 10 LEDs emitting. 
         FIG. 18  shows an isometric view of the illuminance when all LEDs of the 10-LED light source of  FIG. 12  are emitting. 
         FIG. 19  shows an isometric view from the same 10-LED light source when the LEDs are moved away from their nominal position. 
         FIG. 20  shows a modified form of the design of  FIG. 12  with both smooth and faceted sections for simplified molding. 
         FIG. 21  shows a peened 5-LED reflector system with the reflectors facing inwards. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description of the invention and accompanying drawings, which set forth illustrative embodiments in which various principles of the invention are utilized. 
     Referring to the drawings, and initially to  FIGS. 1 through 5 ,  FIG. 1  shows a plan view of an embodiment of a light source, indicated generally by the reference number  100 , comprising LED packages  101 , ellipsoidal reflectors  102 , mounting cylinder  103 , and convective fins  104 . The ellipsoidal reflectors  102  are mounted on the inside of the cylinder  103 , with each LED package  101  mounted centrally within a respective reflector  102 . The fins  104  extend axially along, and project radially from, the outside of the cylinder  103 . When the light source  100  is mounted in a ceiling can, the view shown in  FIG. 1  is the view of the light source  100  as seen looking up from the floor. 
     The downward intensity of the direct light from the LEDs is very low, one of the advantages of this design. Also, the area of the images of the LED sources seen from below is very small. Each LED appears to the observer as two small point like sources. One apparent source is the actual LED, which is the source of the portion of the light that exits the device without reflection. The other apparent source is the virtual source of the portion of the light that is reflected from beam forming optics before exiting. (In a more general case, the virtual source could appear as more than one apparent point-like source.) Thus, the bulb (light source  100  as a whole) in a direct view appears as a compact “stars” field. This is advantageous as it reduces the glare compared with light sources that are extended in area, which is the case for most current solid state light products. The reason for this advantage is that the human eye has adapted over thousands of years to be comfortable seeing many small bright objects on a dark background (the stars) but has not adapted as well for large area sources (a more recent phenomenon). An illuminating apparatus intended to simulate the appearance of a starry sky is described in U.S. Pat. No. 5,219,445 to Bartenbach. 
       FIG. 2  shows a perspective view of the light source  100  of  FIG. 1 , also showing a better view of a mounting wedge  101   w . The mounting wedges  101   w  are interposed between LED packages  101  and cylinder  103  so that package  101  faces slightly downwards, at a 10° angle from the wall of cylinder  103 . Wedge  101   w  is preferably composed of a highly thermally conductive material such as copper. 
       FIG. 3  shows a different perspective view of the same light source  100 , also showing rays  105   r  that, after being emitted by one of the LEDs  101 , are reflected by the ellipsoidal mirror  102  into a caustic at the second focus of ellipsoid  102 . As may be seen from the pattern of rays  105   r  in  FIG. 3 , the LED  101  is approximately at the first focus of the ellipsoid  102 , and the second focus is approximately vertically below the first focus, and below the bottom rim of reflector  102  and mounting cylinder  103 .  FIG. 3  also shows direct rays  105   d , which are rays emitted straight out from the same one LED  101  without meeting mirror  102 . 
       FIG. 4  shows a different perspective view of the same light source  100 , showing only direct rays  105   d.    
       FIG. 5  shows a further perspective view of the same light source  100 , showing light emission  105  of all four LEDs  101 . (The LEDs themselves are not visible in  FIG. 5  because of the angle of view). 
       FIG. 6  shows an isometric view of a normalized illuminance graph  200 , having a horizontal X axis  201  and horizontal Y axis  202 , with scales in millimeters, and vertical intensity axis  203 , running from 0 to 1. Graphical surface  204  represents the spatial distribution of light 3 meters from the light source. The Z axis in  FIG. 6  is assumed to be the axis of symmetry of light source  100  (vertically downwards for a ceiling can light) and the mounting cylinder  103  with its cooling fins  104  is assumed to fit within a 6″ (15 cm) diameter ceiling can. 
       FIG. 7  shows a normalized intensity graph  300 , comprising horizontal axis  301  representing emission angle in degrees of arc from the axis of cylinder  103  of  FIG. 1  and vertical axis  302  representing azimuthally integrated relative output in percent. Curved line  303  shows the angular intensity of light source  100  of  FIG. 1 , relative to 100% on axis, falling to zero at about 60° off axis. Dotted curve  304  is a cumulative energy curve that shows as a function of angle off axis the energy of the part of the intensity distribution of light source  100  within a cone having the specified half-angle centered on the axis. Although the half-power point is at 20° off-axis, half the total energy is within 18° off-axis, a characteristic of a ‘peaky’ distribution, which is typical of commercial incandescent PAR lamps. 
     In case a light source with five LEDs is desired,  FIG. 8  shows a perspective view of a further embodiment of light source  400 , comprising five LED packages  401 , toroidal reflectors  402 , mounting cylinder  403 , and convective fins  404  (not shown to scale). Coordinate triad  405  has its Z axis along the center axis of mounting cylinder  403 , and is aligned with the particular reflector  406  which is numbered, that is to say, with the negative direction of the Y axis radially outward through the center of the particular reflector  406 . The toroidal reflector differs subtly from an ellipsoidal shape. In a local coordinates system with the origin at the reflector apex, the toroid is described by the equation:
 
Sag=( v   x   x   2   +v   y   y   2 )/(1+sqrt{1−(1+ k   x ) v   x   2   x   2 −(1+ k   y ) v   y   2   y   2 }),
 
where v x , v y  are sagittal and meridional curvatures and k x , k y  are conic coefficients. Each reflector is oriented with the y axis of the sag coordinate system radial to the mounting cylinder  403 , in the 0YZ plane of triad  405 . The sag describes the axial position z of the point with coordinates (x,y). The following table provide k x , k y , v x , and  v   y  coefficients for two preferred embodiments for the 5-LED light source of  FIG. 8 . Embodiment #1 uses a CREE MC-E LED and Embodiment #2 uses a Nichia NCSL 136 LED.
 
     
       
         
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Parameters 
               
             
          
           
               
                   
                 k x   
                 k y   
                 v x   
                 v y   
                 A 
               
               
                   
                   
               
             
          
           
               
                 Embodiment #1 
                 −0.56 
                 −0.49 
                 1/9.10 
                 1/9.42 
                 16°   
               
               
                 Embodiment #2 
                 −0.57 
                 −0.49 
                 1/7.65 
                 1/7.85 
                 15.8° 
               
               
                   
               
             
          
         
       
     
     Starting from the coordinate system  405  shown in  FIG. 8 , the sag-axis coordinates of the reflector as described above are shifted in the −Y direction of coordinate system  405  by 28.3 mm for embodiment #1 and by 28.5 mm for embodiment #2 and then rotated through the angle A counter-clockwise relative to the positive X direction (that is to say, angling the sag-axis of the toroid towards the center of the illuminated area beyond the exit end of the light source  400 ), around the point with coordinates shown in the table of rotation points below. 
     For the two embodiments the coordinates of the points of rotation on angle A are 
                                                               Y/mm   Z/mm                                        Embodiment #1   −28.3   7.2           Embodiment #2   −28.5   6                        
in the coordinate system  405  with its origin at the center of cylinder  403 .
 
     The source center positions are 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Y/mm 
                 Z/mm 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Embodiment #1 
                 −28.4 
                 7.434 
               
               
                   
                 Embodiment #2 
                 −29.7 
                 6.195 
               
               
                   
                   
               
             
          
         
       
     
     The foci of the toroid are the following positions 
                                                                                                     Meridional       Sagittal                    Y/mm   Z/mm   Y/mm   Z/mm                            Embodiment #1   −28.542   6.356   −28.67   5.88           Embodiment #2   −28.701   5.287   −28.807   4.912                        
The tolerances for foci positions with respect to the source positions are 0.1 mm in x,y,z directions.
 
     The inside diameter of the cylinder  403  is designed for the mounting of LEDs and equal to 56.8 mm for Embodiment #1 and 59.4 mm for Embodiment #2. Thus, the LED sources are approximately flush with the inner face of the mounting cylinder  403 . Attaching the LED sources to the face of the mounting cylinder  403  is in practice sufficiently close to flush. The minimum length of the cylinder  403  and reflectors  402  for Embodiment #1 is 27 mm and for Embodiment #2 is 22 mm. The length can be extended away from the exit end to provide space and support for LED drivers and other electronics. Both Embodiment #1 and Embodiment #2 produce a ±30° output beam. 
     The toroidal reflectors  402  are double ellipsoids having an aspheric modification that induces tailored aberrations. The aberrations&#39; function is to remove source irregularities from the beam pattern output. That assists in producing a uniform circular output (as the combined output from all the light sources) for the central part of the pattern. 
     For the lux values projected by a single LED of  FIG. 8 ,  FIG. 9  shows contour graph  500  with lux values listed and lined up with their corresponding contours. This is based on the output of Embodiment #1.  FIG. 10  shows contour graph  550  for all LEDs of  FIG. 8 , also with lux values listed, of course much higher than in  FIG. 9 .  FIG. 11  is an isometric view of illuminance at the plane 3 meters from the bulb, in which graph  600  has a surface  601  representing the lux values at each X, Y point under the lamp. The X and Y coordinates are in meters. The pattern for the case when all five LEDs are turned on is circular to a good approximation. The output pattern from a single LED is asymmetric. This is a novel approach as the prior art requires that each of the five beam outputs have circular symmetry. One benefit of this new approach is that the dimensions of the lamp can be reduced (versus the prior art), especially the diameter. This allows the lamp to be small enough to fit into a standard can while still achieving high flux. 
     For most purposes, the output pattern when all LEDs are turned on is sufficiently close to circular that any trace of polygonal pattern can be ignored. However, in special situations the number and orientation of the LEDs (four as shown in  FIG. 1 , five as shown in  FIG. 8 , or another number) may be chosen to provide a desired illumination pattern and/or a desired appearance when the light source  100 ,  400 , etc. is viewed directly. In such cases, it may be appropriate to configure the light source with a more pronounced polygonal light distribution that would usually be regarded as non-optimal. 
       FIG. 12  shows a perspective view of a further embodiment of a light source  700 , comprising ten LED packages  701 , their ten reflectors  702 , mounting cylinder  703 , and convective fins  704 . Interior convective fins  704  are diagrammatic rather than representative of actual designs. Typically, the surface area of the fins will be 10 square inches (65 cm 2 ) or more for each watt of heat from the LEDs. Also, in order for the convective loop to function properly in an insulated can, the distance between the fins should be approximately 10 mm. As described, the light source  700  shown in  FIG. 12  has a mounting cylinder  703  approximately 33 mm in radius, implying a circumference of 20 cm, so about 20 fins instead of the 80 fins shown. If the total heat dissipation is about 10 Watts thermal, which is a reasonable target for an LED downlight, each fin might then be around 1 cm (0.4 inches) in radial width and 16 cm (6.5 inches) in axial length, which is feasible within the dimensions of a conventional ceiling can. However, smaller fins may be preferred, for aesthetic reasons, where a lower thermal load permits. A more efficient cooling system uses the helical vanes of U.S. Provisional Application 61/205,390, or better still, the helical vanes with electro-static augmentation described in that application, which is incorporated herein by reference. Using the helical fins of that application, the length of the thermal management device can be reduced to 5 cm (2 inches), or only about one third of the length of the vertical system mentioned above, without reduction in cooling capacity. 
     With ten of the current Cree XP-E LED&#39;s this embodiment can provide 800 to 1000 lm light output (warm white). The following table provides k x , k y , v x , and v y  coefficients for a preferred embodiment for the 10-LED light source of  FIG. 12 . 
     
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Parameters 
               
             
          
           
               
                 k x   
                 k y   
                 v x   
                 v y   
                 A 
               
               
                   
               
               
                 −0.57 
                 −0.54 
                 1/7.55 
                 1/6.9 
                 16° 
               
               
                   
               
             
          
         
       
     
     Starting from the central axis of mounting cylinder  703  shown in  FIG. 12 , the sag-axis coordinates of the reflector as described above are shifted radially outward by 35.5 mm and then rotated through the angle A counter-clockwise relative to the positive X direction. The angle of rotation for reflector  706  in  FIG. 12  is in the direction of arrow  707  for coordinate system  705  for  FIG. 12 . 
     The coordinates for the center of rotation for angle A are: 
                                             Y/mm   Z/mm                           35.5   6                        
in the coordinate system  705  with its origin at the center of cylinder  703 .
 
     The source center position is 
                                           Source center position                Y/mm   Z/mm                       33.8   5.425                        
and the axis of the LED is orthogonal to the axis of the cylinder  703 .
 
     The positions of the foci of the reflector nearest the source are: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Meridional 
                   
                 Sagittal 
                   
               
             
          
           
               
                   
                 Y/mm 
                 Z/mm 
                 Y/mm 
                 Z/mm 
               
               
                   
                   
               
               
                   
                 35.08 
                 4.54 
                 35.103 
                 4.846 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 16  shows contour graph  1000  of the illuminance values in lux projected by a single XPE LED for the embodiment of  FIG. 12 .  FIG. 17  shows illuminance contour graph  1050  with all ten XPE LEDs of  FIG. 12  emitting.  FIG. 18  is an isometric view of illuminance for the ten-LED lamp on a plane 3 meters from the lamp. The X,Y coordinates at the illuminated plane are shown in mm. The pattern for the case when all ten LEDs are emitting is circular to a good approximation. The output pattern from the single LED is asymmetric. This is a novel approach as the prior art requires that each of the ten beam outputs have circular symmetry. In  FIG. 16  the maximum intensity from the single LED spot is shifted away from the central axis of the lamp. Superposition of all ten LEDs creates the circular spot with the extended flat plateau shown in  FIGS. 17 and 18 . 
       FIG. 19  shows an illuminance contour graph  1200  for a spot located at 3 meters from the lamp of  FIG. 12  with 10 XPE LEDs all illuminated, with the LEDs shifted out of the nominal position 0.3 mm in the axial lamp direction (Z direction in  FIG. 12 ) and 0.3 mm in lateral −X,Y direction. Contours are at steps of 14 lux from 0 lux to 112 lux. The size of the spot is the same as in  FIG. 17 . The central part of the pattern with a flat plateau is transformed to a Gaussian type distribution. This elevates the illumination level at the center of the spot to 112 lux. Such performance tolerances are acceptable for typical illumination applications. Therefore, the lamp can be said to have a ±0.3 mm tolerance for positioning of the LEDs, an acceptable dimensional tolerance for volume manufacturing. 
       FIG. 13  shows a further embodiment of a luminaire  800 , comprising five lamps, with LEDs  801 , each located off the focus of a respective cutaway paraboloidal primary reflector  802 . The LEDs and reflectors are mounted on chimney  803 , having interior fins  803   f . The paraboloidal primary reflectors  802  face upwards and outwards. Struts  804  are connected to chimney  803  to support toroidal secondary reflectors  805 , above the primary reflectors  802 , which serve to spread out the light onto the floor below. The radial curvature of reflector  805  sends some of the light back under the associated primary reflector  801  so it can reach the part of the floor directly below the luminaire. The azimuthal curvature spreads the light out so the five patterns suitably overlap.  FIG. 13  is a close-up perspective view of one of the LEDs  801  and its associated reflectors  802  and  803  of luminaire  800 , showing light rays  801 R. 
       FIG. 15  shows an isometric view of an illuminance graph  900  with surface  901  representing strength of illumination over the x and y axes on the floor under light source  800  of  FIG. 13 . A smooth, nearly circular pattern results from the superposition of the five patterns of the individual secondary reflectors. The two curvatures of toroidal secondary reflector  805  of  FIG. 12  can be adjusted for different illumination patterns. In fact, the reflector  805  could have two surfaces of different shapes back to back, for example, two toroidal surfaces that differ in one or both of their primary curvatures, for different patterns. The two-surface reflector  805  would then be mounted so it can be rotated (not shown) around strut  804  so either of two toroidal surfaces could be selected. 
     Although the embodiments described herein use reflectors that are smooth and specular, the invention also includes embodiments where the reflectors make use of spreading surface features such as faceting, peening or mild diffusers (including kineform or holographic structures). Using spreading features on the reflectors homogenizes the beam more than specular reflectors but has the effect of spreading the beam output angle and tends to eliminate the sharp cut-off at the periphery of the beam. This may be desirable in some lighting applications. The effect of spreading features (faceting, peening, etc.) on beam output is described in the book “The Optical Design of Reflectors” by William B. Elmer, on pages 27 thru 29, which is incorporated herein by reference. In particular, equations 1, 2 and 3 in Elmer provide a way of quantitatively predicting the effect of spreading features based on the average diameter of the peened spots, their radius and the radius of curvature of the reflector. Elmer also provides a simplified equation for the special case of flat facets. Of course the range of possible spreading surfaces is not limited to those described by Elmer. It should be evident to those skilled in the art how such spreading features can be applied to the designs of the present application to achieve a required or desired beam output. 
     In some cases it is desirable to have a hybrid reflector where a portion of the reflector is specular and another portion uses spreading features. That can be useful for eliminating artifacts in a beam pattern where the artifacts stem from a particular segment of the reflector. In that situation the reflector can be shaped so that only the segment causing the problem has spreading features on it. 
     For the embodiments described herein for the 5-LED and 10-LED systems, the reflectors are designed to wrap around the source and are considered re-entrant surfaces from the standpoint of molding technology. The molding of these parts is still possible for those skilled in the art of designing and manufacturing molds. Indeed it is possible even to mold multiple reflectors (10 in the case of  FIG. 12 ) at once. Alternatively, the array of reflectors (five or ten respectively for the embodiments of  FIG. 8  and  FIG. 12 ) can be molded in two halves with a draft angle at or near zero degrees for each half. Finally, it is also possible to simply remove the small portion of the reflector that is re-entrant. Removal of this small section of the reflectors has little effect on the illumination pattern from the light source, as was proven by extensive ray tracing modeling carried out by the inventors. 
       FIG. 20  shows one half of a mold  1300  for a hybrid version of the embodiment of  FIG. 12  combining triangular planar facets  1301  and smooth surfaces  1302  to make the 10-reflector part more easily moldable. No part of the 10-reflector array of  FIG. 20  is re-entrant, and therefore a single 10-reflector part comprising the mounting cylinder  703 , cooling fins  704 , and reflectors  706  can be molded in one piece using simplified molding techniques. The performance of the hybrid-reflector system is equal to the preferred embodiment previously described herein. 
       FIG. 21  shows a peened embodiment  1400  with 5 reflectors, wherein the reflectors are facing inwards, as in  FIG. 8 . The mounting cylinder is omitted from  FIG. 21  to allow a clearer view of the reflectors. The peening features are sections of a sphere such that each feature produces a very similar circular pattern in the far field, thereby creating the desired beam pattern by multiple overlapping of beams with the same angle and shape (as opposed to the other approach described in this application). The overall shape of the reflectors in  FIG. 21  is parabolic or it can also be compound parabolic. The peening features then convert the collimated beam from the original parabolic reflector into a uniform circular beam pattern with a desired divergence, controlled by the curvature of the individual peening features, that is wider than the pattern of the parent collimated beam. This is an alternative embodiment of the invention. This approach can also be used with other embodiments, including embodiments in which the reflectors facing outward as opposed to inward. 
     The preceding description of the presently contemplated best mode of practicing the invention is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The full scope of the invention should be determined with reference to the Claims. 
     Although various embodiments have been described, the skilled reader will understand how features of the different embodiments may be combined. 
     Various changes may be made in the described light sources without departing from the scope and spirit of the invention as claimed. For example, although the actual emitters of light are described as light emitting diodes (LEDs), other emitters, including emitters hereafter to be developed, may be used instead. Further, each LED package  101 ,  401 ,  701 ,  801  or other light emitter may comprise a plurality of LEDs mounted close together within a common modified or unmodified ellipsoidal reflector. The LEDs within each package may then be the same or different, and may be switched on or off together or separately. 
     The light sources shown in the drawings have been described as being used in ceiling can lights, but for convenience of illustration have in many cases been drawn with the exit end (which would be downwards in a ceiling fixture) facing upwards in the drawing. Terms of orientation such as “bottom” are used with reference either to the normal orientation of the light sources in ceiling fixture use or to the orientation shown in the drawings. However, these and other light sources according to the invention may of course be used, mounted, and stored in either of those orientations or in other orientations. 
     The light sources shown in the drawings have been described as being circular, with the LED packages and reflectors evenly spaced around the axis of the mounting cylinder. However, for some purposes, for example, a wall-sconce designed to match the embodiments shown, the LED packages and reflectors may form an incomplete ring. For example, a wall-sconce designed to match the embodiment shown in  FIGS. 13 and 14  might have the cylinder  803  mounted close to the wall, and only three of the five sets of components  801 ,  802 ,  803 ,  805 . A wall-sconce designed to match the embodiment shown in  FIGS. 1 to 5 , or  FIG. 8 , or  FIG. 12  might have an incomplete mounting cylinder mounted with its open side against the wall, or in the case of a semicircular mounting cylinder with its open side against a mirror, so that the real and mirror-image halves form a complete, circular luminaire. 
     The mounting cylinder  103 ,  403 ,  703 ,  803  has been shown in the drawings as a right circular cylinder. The circular cylinder is simple to design, simple to manufacture, robust, and aesthetically pleasing. Other shapes, including a polygon or a shape intermediate between a polygon and a circle, are of course possible. To avoid redesigning the optics, a shape that maintains the even positioning of the LED packages and optics on a notional circle is preferred. In a practical embodiment, the cylinder may have a slight conical draft for ease of molding.