Patent Document

[0001]     This application is a continuation-in-part of Application No. ______, filed Mar. 30, 2004, which is incorporated herein by reference in its entirety.  
         [0002]     The present embodiments may be further understood and/or can also be utilized with the embodiments described in co-pending U.S. Provisional Patent Application No. 60/470,691, filed May 13, 2003, U.S. patent application Ser. No. 10/461,557, filed Jun. 12, 2003, and U.S. Provisional Patent Application No. 60/520,951, filed Nov. 17, 2003, each being incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates to light-emitting diodes (LEDs), particularly optical means for producing various far-field light intensity distributions for LEDs.  
         [0004]     Conventional incandescent lamps of less than 100 lumens output can be matched by the latest white LEDs, albeit at a higher price. At this low end of the lumen range, the majority of incandescent applications are battery-powered. It is desirable to have an LED suitable for direct installation in the place of a burnt-out flashlight bulb.  
         [0005]     LED&#39;s can offer superior luminous efficacy over the conventional incandescent lamps used in battery-operated flashlights. Moreover, LEDs are far more tolerant of shock, vibration, and crush-stress. Although they currently cost more to produce than the incandescents, their lifetimes are ten thousand times longer. For the sake of efficacy flashlight bulbs are run hot so they typically last only a few hours until filament failure. Also, the prices of LEDs continue to fall, along with those of the control-electronics to handle variations in battery voltage.  
         [0006]     Indeed, LED flashlights are commercially available already, but their optics have to be adapted to the geometry of light-emitting diodes, which only emit into a hemisphere. Conventional LED lamps are unsuitable for direct installation into conventional flashlights, both electrically and optically. LED lamps are electrically unsuitable because they are current-driven devices, whereas batteries are voltage sources. Typical variations in the voltage of fresh batteries are enough to exceed an LED&#39;s tolerable operating-voltage range. This causes such high currents that the Ohmic heating within the die exceeds the ability of thermal conduction to remove it, causing a runaway temperature-rise that destroys the die. Therefore, a current-control device must accompany the lamp.  
         [0007]     Conventional LED lamps are optically unsuitable for direct installation into the parabolic reflectors of flashlights. This is because their bullet-lens configuration forms a narrow beam that would completely miss a nearby parabola. Using instead a hemispherically emitting non-directional dome, centered on the luminous die, gives the maximum spread commercially available, a Lambertian pattern, with a sin 2 θ dependence of encircled flux on angle θ from the lamp axis. Since θ for a typical parabolic flashlight reflector extends from 45° to 135°, an LED with a hemispheric pattern is mismatched because it&#39;s emission falls to zero at only θ=90°. This would result in a beam that was brightest on the outside and completely dark halfway in. Worse yet, even this inferior beam pattern from a hemispheric LED would require that it be held up at the parabola&#39;s focal point, several millimeters above the socket wherein a conventional incandescent bulb is installed.  
         [0008]     Another type of battery-powered lamp utilizes cylindrical fluorescent lamps. Although LEDs do not yet offer better luminous efficacy, fluorescent lamps nonetheless are relatively fragile and require unsafely high voltages. A low-voltage, cylindrical LED-based lamp could advantageously provide the same luminous output as a fluorescent lamp.  
         [0009]     Addressing the needs above, U.S. patent application Ser. No. 10/461,557, OPTICAL DEVICE FOR LED-BASED LIGHT-BULB SUBSTITUTE, filed Jun. 12, 2003, which is hereby incorporated by reference in its entirety, discloses such LED-based lamps with which current fluorescent and incandescent bulb flashlights can be retrofitted. It often desirable, however, for LED lamps such as those described in U.S. patent application Ser. No. 10/461,557 to have other far-field intensity distributions of interest. Also, U.S. patent application Ser. No. 10/461,557 touched on the function of color mixing, to make the different wavelengths of chips  23 ,  24 , and  25  of FIG. 2 of U.S. patent application Ser. No. 10/461,557 have the same relative strengths throughout the light coming out of ejector section  12 . This assures that viewers will see only the intended metameric hue and not any colors of the individual chips. Previously, rectangular mixing rods have been used to transform the round focal spot of an ellipsoidal lamp into a uniformly illuminated rectangle, typically in cinema projectors. Generally, polygonal mixing rods worked best with an even number of sides, particularly four and six. With color mixing for LEDs, however, such rods are inefficient because half of an LED&#39;s Lambertian emission will escape from the base of the rod.  
         [0010]     There is thus a need in the art for effective and optically suitable LED lamps with various far-field intensity distributions and have proper shaping of their transfer sections enabling polygonal cross-sections to be used.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention advantageously addresses the needs above as well as other needs by providing an optical device for LED-based lamps with configurations for various far-field intensity distributions.  
         [0012]     In some embodiments, an optical device for use in distributing radiant emission of a light emitter is provided. The optical device can comprise a lower transfer section, and an upper ejector section situated upon the lower transfer section. The lower transfer section is operable for placement upon the light emitter and further operable to transfer the radiant emission to said upper ejector section. The upper ejector section can be shaped such that the emission is redistributed externally into a substantial solid angle. In some preferred embodiments, the transfer section is a solid of revolution having a profile in the shape of an equiangular spiral displaced laterally from an axis of said solid of revolution so as to place a center of the equiangular spiral on an opposite side of the axis therefrom.  
         [0013]     In some embodiments, an optical device for distributing the radiant emission of a light emitter is provided. The optical device can comprise a lower transfer section, and an upper ejector section situated upon the lower transfer section. The lower transfer section can be operable for placement upon the light emitter and operable to transfer the radiant emission to the upper ejector section. The upper ejector section can be shaped such that the emission is redistributed externally into a substantial solid angle. The ejector section can further comprise lower and connecting upper portions.  
         [0014]     Some preferred embodiments provide an optical device for distributing radiant emissions of a light emitter. The optical device can comprise a transfer section, and an ejector section situated upon the transfer section. The transfer section is operable for placement adjacent with a light emitter and operable to transfer radiant emission from the light emitter to the ejector section. The ejector section is shaped such that the emission is redistributed externally into a substantial solid angle. In some embodiments, the ejector section has an upper surface with a profile of an equiangular spiral with a center at an upper edge of said transfer section. Some embodiments further provide for the ejector section to include a surface comprised of a radial array of V-grooves. Still further embodiments provide that a surface of said transfer section is comprised of an array of V-grooves. Further, the transfer section can be a polygonal, can be faceted and/or have other configurations.  
         [0015]     In one embodiment, the invention can be characterized as an optical device for distributing radiant emission of a light emitter comprising a lower transfer section and an upper ejector section situated upon the lower transfer section. The lower transfer section is operable for placement upon the light emitter and operable to transfer the radiant emission to the upper ejector section. The upper ejector section is shaped such that the light within it is redistributed out an external surface of the upper ejector section into a solid angle substantially greater than a hemisphere, and approximating that of an incandescent flashlight bulb. The ejector section is positioned at the same height as the glowing filament of the light bulb it replaces. It is easier to optically move this emission point, using the transfer section, than to put the LED itself at such a height, which would make heat transfer difficult, among other problems that the present invention advantageously addresses.  
         [0016]     In another embodiment, this invention comprises a multiplicity of such transfer sections joined end-to-end, with two LED sources at opposite ends of this line-up. These transfer sections have slightly roughened surfaces to promote diffuse emission, so that the entire device acts as a cylindrical emitter, and approximating the luminous characteristics of a fluorescent flashlight bulb.  
         [0017]     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 an illustrative embodiment in which the principles of the invention are utilized. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:  
         [0019]      FIGS. 1   a  through  38   b  are cross sectional views of LED lamps having various configurations of transfer and ejector lens sections (hereafter called virtual filaments) according to the present invention, with each cross sectional view accompanied, respectively, by the individual configuration&#39;s far field pattern.  
         [0020]      FIG. 39  is a perspective view of a linear array of V-grooves.  
         [0021]      FIG. 40  is a diagram of the angles reflected by a linear V-groove array.  
         [0022]      FIG. 41  is a perspective view of a radial array of V-grooves.  
         [0023]      FIG. 42   a  is a perspective view of the configuration of  FIG. 37   a  according to the present invention.  
         [0024]      FIG. 42   b  is a perspective view showing the vector triad on the configuration of  FIG. 42   a  according to the present invention.  
         [0025]      FIG. 43  is a perspective view of the construction of a V-groove on a curved surface according to the present invention.  
         [0026]      FIG. 44  is a perspective view of a virtual filament with a curved radial V-groove array on top according to the present invention.  
         [0027]      FIG. 45  is a perspective view of a virtual filament with a linear V-groove array on its transfer section according to the present invention.  
         [0028]      FIG. 46  is a perspective view of a six-sided barrel-shaped virtual filament according to the present invention.  
         [0029]      FIGS. 47   a  and  47   b  is a side and perspective view, respectively, of a sixteen-sided virtual filament according to the present invention.  
         [0030]      FIG. 47   c - e  show blue (465 nanometers), green (520 nanometers) and red (620 nanometers) emission patterns, respectively, of the embodiments of  FIGS. 47   a - b , at the various cylindrical azimuths.  
         [0031]      FIGS. 48   a  and  48   b  is a side and perspective view, respectively, of another sixteen-sided virtual filament, with a slotted ejector section according to the present invention.  
         [0032]      FIG. 48   c  depicts a 300° emission pattern produced by the collar of  FIG. 48   a.    
         [0033]      FIGS. 49   a  and  49   b  is a side and perspective view, respectively, of a faceted virtual filament that mixes the disparate wavelengths of a tricolor LED according to the present invention. 
     
    
       [0034]     Corresponding reference characters indicate corresponding components throughout the several views of the drawings, especially the explicit label in  FIG. 1   a  of LED package  20  being implied throughout  FIG. 2   a  to  FIG. 38   a.    
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     The following 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 scope of the invention should be determined with reference to the claims.  
         [0036]     The present embodiments provide light sources with predefined far-field intensities. The present embodiments can be utilized in numerous applications. For example, in some applications, the embodiments can be utilized to replace and/or substitute for other types of light sources, such as compact light sources, incandescent light sources, florescent light sources and other light sources. As a further example, the present embodiments can be utilized in replacing incandescent light sources in flight lights and other devices using incandescent light sources.  
         [0037]     The present embodiments can also be utilized with the embodiments described in co-pending U.S. Provisional Patent application No. 60/520,951, filed Nov. 17, 2003, incorporated herein by reference in its entirety. The surface faceting configuration presented herein in  FIG. 49A  and  FIG. 49B , and in co-pending U.S. Provisional Patent Application No. 60/520,951, filed Nov. 17, 2003, can be employed in variations of all of the non-faceted embodiments shown herein in order to achieve the color mixing and other benefits thereof.  
         [0038]     The present embodiments can further be utilized with the embodiments of and in the applications described in U.S. Provisional Patent Application No. 60/470,691, filed May 13, 2003, and U.S. patent application Ser. No. 10/461,557, filed Jun. 12, 2003, incorporated herein by reference in their entirety. For example, the present embodiments can be utilized in the light sources described in U.S. Provisional Patent Application No. 60/470,691, filed May 13, 2003, and U.S. patent application Ser. No. 10/461,557, filed Jun. 12, 2003.  
         [0039]      FIGS. 1   a  through  38   b  are cross sectional views of LED lamps having various configurations of transfer and ejector lens sections (hereafter called virtual filaments) according to some present embodiments, with each cross sectional view accompanied, respectively, by the individual configuration&#39;s far field pattern.  
         [0040]     Only  FIG. 1   b  has the labels that are implicit in all the output patterns of the preferred embodiments in the figures that follow: semicircular polar plot  2700  shows normalized far-field distribution  2701  on semi-circular angular scale  2702 , with off-axis angle, with zero denoting the on-axis direction, and 180° the opposite direction, totally backward. This is possible for those preferred embodiments having some sideways extension so that 180° is unimpeded by the source.  
         [0041]     In  FIG. 1   a  only, the light source is designated as LED package  20  with LED chips  22 ,  23 , and  24 , but the same package-outline is depicted without labels in all subsequent figures of virtual filaments. This LED package represents but one possible way for the present invention to utilize multiple light emitters. Such multiple chips can have identical or different wavelengths. For example, the different wavelengths can be red, green, and blue wavelengths that span a chromaticity gamut for human color vision, or amber, red, and infrared wavelengths for night-vision devices, or other combinations of different wavelengths.  
         [0042]     Similarly in  FIG. 1   a  only, the position of the focus of ellipse segment  271  is shown by star  271   f . In all subsequent figures, the focus of the profile of the transfer section is also near the bottom point of the same curve on an opposite side of a central axis.  
         [0043]      FIG. 1   a  shows virtual filament  270  comprising compound elliptical concentrator (hereinafter CEC) transfer section  271 , and an ejector section comprising outward slanting lower cone  272  and inward slanting upper cone  273 .  FIG. 1   b  shows that the far-field distribution of this preferred embodiment peaks in the forward direction with a ±20° extent.  
         [0044]      FIG. 2   a  shows virtual filament  280  comprising CEC transfer section  281 , multiple stacked toroids  282 , and ejector section  283 , shaped as an equiangular spiral with origin at point  283   f .  FIG. 2   b  shows that the maximum far-field intensity of this preferred embodiment lies on angles from about 500 to 600 off-axis, a so-called bat-wing distribution.  
         [0045]      FIG. 3   a  shows virtual filament  290 , comprising CEC transfer section  291 , cones  292  and  293 , and equiangular spirals  294  and  295 . Predominantly horizontal equiangular spiral  294  has its center at central point  294   f . Equiangular spiral profile  295  has oppositely situated center  295   f .  FIG. 3   b  shows the far-field distribution of this preferred embodiment, peaking at 40° off-axis and mostly confined to the range of 10-700, also with a secondary lobe from 150-170°.  
         [0046]      FIG. 4   a  shows virtual filament  300  comprising CEC section  301 , flat  302 , sideways equiangular spiral  303  with center at point  303   f , and top equiangular spiral  304  with center at point  304   f .  FIG. 4   b  shows a subtle tuning of the far-field resulting from the noticeable profile-modification, as shown in  FIG. 4   a , of the preferred embodiment shown in  FIG. 3   a .  FIG. 4   b  shows that the far-field distribution of this preferred embodiment has a primary maximum on a main lobe between 400 and 600 off-axis, and a secondary maximum on a secondary rear lobe extending between 160° and 170°, nearly backwards. The next preferred embodiment is a modification of this one.  
         [0047]      FIG. 5   a  shows virtual filament  310  with CEC transfer section  311 , planar annulus  312 , equiangular spiral  313  with center at axial point  313   f , and upper equiangular spiral  314  with center at opposite point  314   f . In addition to elements in correspondence with those of  FIG. 4   a  are inward slanting steep cone  315 , upward slanting shallow cone  316 , and upper flat circle  317 . The normalized far-field pattern of this preferred embodiment differs significantly from the previous, as shown in  FIG. 5   b , with a fluctuating forward lobe and a half-strength rear lobe.  
         [0048]     Delving further on the theme of minor modifications,  FIG. 6   a  shows virtual filament  320  comprising CEC transfer section  321 , planar annulus  322 , equiangular spiral  323  with axial position of its center as shown by star  323  f, upper equiangular spiral  324  with center at opposite point  324   f , and a new element—central upper equiangular spiral  327 , also with center at  324   f . In similarity to  FIG. 5   a , virtual filament  320  also comprises inwardly slanting steep cone  325  and upward shallow cone  326 . The normalized far-field pattern of the preferred embodiment of  FIG. 6   a  is shown by  FIG. 6   b  to be mainly between 30° and 50° off axis, with a rear lobe from 120° to 170°, with reduced forward emission as compared to  FIG. 5   b.    
         [0049]      FIG. 7   a  depicts a preferred embodiment that is the result of small modifications of virtual filament  320  of  FIG. 6   a .  FIG. 7   a  is a cross-section of virtual filament  330 , comprising CEC transfer section  331 , slanting conical section  332 , horizontal equiangular spiral  333  with center at axial point  333   f , steep conic edge  335 , vertical equiangular spiral  334  with oppositely situated center  334   f , and central cone  336 .  FIG. 7   b  shows its far-field intensity concentrated in a forward lobe within ±200 of the axis, with a strong rearward lobe peaking at 150°.  
         [0050]     Continuing the theme of component modifications,  FIG. 8   a  depicts virtual filament  340  comprising CEC transfer section  341 , planar annulus  342 , inwardly slanting steep cone  335 , downward slanting shallow cone  346 , outer edge  348 , horizontal equiangular spiral  343  with center at off-axis point  343   f , vertical equiangular spiral  344  with center at opposite point  344   f , and upper equiangular spiral  347 , also with center at opposite point  344   f .  FIG. 8   b  shows that its far field pattern has a collimated anti-axial beam and a broader ±30° forward beam.  
         [0051]      FIG. 9   a  depicts virtual filament  350  comprising CEC transfer section  351 , dual conical flanges  352 , and upper conic indentation  353 .  FIG. 9   b  shows that its far-field pattern has strong forward and rear lobs, but some side emission.  
         [0052]      FIG. 10   a  depicts virtual filament  360  comprising CEC transfer section  361 , conical flange  362 , upper equiangular spiral indentation  363  with center at proximal point  363   f , and cylindrical flange  364 .  FIG. 10   b  shows how the rearward emission of  FIG. 9   b  has been eliminated.  
         [0053]      FIG. 11   a  depicts another variation of  FIG. 10   a . Virtual filament  370  comprises CEC transfer section  371 , dual conic flanges  372 , central conic indentation  373 , set into central cylinder  374 . The far field pattern of  FIG. 11   b  shows a forward ±30° main lobe and a small secondary lobe at 125°.  
         [0054]      FIG. 12   a  depicts a variation of component proportions in the preferred embodiment of  FIG. 11   a . Virtual filament  380  comprises CEC transfer section  381 , dual conic flanges  382 , and central conic indentation  383 . The far field intensity pattern of  FIG. 12   b  shows the same overall forward and backward emphasis of  FIG. 9   b , with differing details.  
         [0055]      FIG. 13   a  depicts virtual filament  390  comprising CEC transfer section  391 , spheric section  392 , and central conic indentation  393 . In similarity to spheric ejector section  72  of FIG. 7 of U.S. patent application Ser. No. 10/461,557, both surfaces  392  and  393  are diffusing, in that rays from within and going through them are scattered diffusely into air.  FIG. 13   b  shows a strong forward lobe of ±40° superimposed on a weaker emission that is nearly omnidirectional.  
         [0056]      FIG. 14   a  depicts virtual filament  400  comprising CEC transfer section  401 , steeply slanting cone  402 , outer equiangular spiral  403  with axially located center  403   f , and inner equiangular spiral  404  with center at proximal point  404   f . As shown in  FIG. 14   b , its far field intensity pattern has no rearward energy, and somewhat approximates a Lambertian pattern.  
         [0057]     In a variant of the previous figure,  FIG. 15   a  depicts virtual filament  410  comprising CEC transfer section  411 , cylindrical stack  412  of multiple toroidal sections  412   t , inner equiangular spiral  414  with center at proximal point  414   f , and upper curve  413  tailored to refract rays coming from  414   f  and being reflected at  414  and direct them tangent to  413 .  FIG. 15   b  shows the resultant far-field pattern to be mostly forward, within ±30°.  
         [0058]      FIG. 16   a  depicts virtual filament  420 , comprising CEC transfer section  421 , cylinder  422 , conical indentation  423  in shallower top cone  424 .  FIG. 16   b  shows its far-field pattern is mostly between 10° and 20° off axis.  
         [0059]      FIG. 17   a  depicts virtual filament  430 , comprising CEC transfer section  431 , outer cone  432 , and inner conical indentation  433 . In spite of the small differences from FIG.  16   a , the far-field pattern of  FIG. 17   b  is considerably different from that of  FIG. 16   b.    
         [0060]      FIG. 18   a  depicts virtual filament  440 , comprising CEC transfer section  441 , outer cone  442 , and inner conical indentation  443 . In spite of the small differences of this preferred embodiment from that of from  FIG. 17   a , the far-field pattern of  FIG. 18   b  is narrower than that of  FIG. 17   b.    
         [0061]      FIG. 19   a  depicts virtual filament  450  comprising CEC transfer section  451 , spline curve  452 , central equiangular spiral  453  with center at proximal point  453   f , and surrounding top conic indentation  454 .  FIG. 19   b  shows its far-field pattern is predominantly forward, with ±20° at the half-power point.  
         [0062]      FIG. 20   a  depicts virtual filament  460  comprising CEC transfer section  461 , spheric section  462  with radius  462   r  that equals 0.38 times the height of section  461 , and central equiangular spiral  463  with center at proximal point  463   f .  FIG. 20   b  shows its far-field pattern to lie between 100 and 600 off axis.  
         [0063]      FIG. 21   a  depicts another similar configuration, virtual filament  470  comprising CEC transfer section  471 , spheric section  472  with radius  472   r  that is 0.7 times the height of section  471 , and central equiangular spiral  473  with center at proximal point  473   f .  FIG. 21   b  shows that the far-field pattern has significantly narrowed from the previous one.  
         [0064]      FIG. 22   a  depicts another similar configuration, virtual filament  480  comprising CEC transfer section  481 , spheric section  482  with radius  482   r  that is 0.8 times the height of section  481 , and central equiangular spiral  483  with center at proximal point  483   f . Spheric section  482  is partially covered with multiple convex toroidal lenslets  482   t .  FIG. 22   b  shows that the far-field pattern undergoes only minor change from the previous one, with narrowing of the central beam compared to that seen in  FIG. 21   b.    
         [0065]      FIG. 23   a  depicts virtual filament  490  comprising CEC transfer section  491 , spheric section  492  with radius  492   r  that is 0.62 times the height of section  491 , section  492  being fully surfaced by multiple toroidal lenslets  492   t , and central equiangular spiral  493  with center at proximal point  493   f .  FIG. 23   b  shows how these lenslets greatly broaden the far-field pattern over that of  FIG. 22   b.    
         [0066]      FIG. 24   a  depicts virtual filament  500  comprising CEC transfer section  501 , spheric section  502  with radius  502   r  that is 0.76 times the height of section  501 , section  502  being surfaced by multiple convex toroidal lenslets  502   t , and central equiangular spiral  503  with center at proximal point  503   f .  FIG. 24   b  shows that the far field pattern is not greatly changed from that of  FIG. 23   b , by section  502  having a somewhat larger radius than that of section  492  of  FIG. 23   a.    
         [0067]      FIG. 25   a  depicts virtual filament  510  comprising CEC transfer section  511 , spheric section  512  with radius  512   r  that is equal to the height of section  511 , section  512  surfaced by multiple convex toroidal lenslets  512   t , and central equiangular spiral  513  with center at proximal point  513   f .  FIG. 25   b  shows that the far field pattern is now considerably changed from that of  FIG. 24   b , due to the larger radius of section  512  than that of section  502  of  FIG. 24   a.    
         [0068]      FIG. 26   a  depicts virtual filament  520  comprising CEC transfer section  521 , lower spline section  522 , central equiangular spiral  523  with center at proximal point  523   f , and outer cylindrical section  524  covered with multiple convex toroidal lenslets  524   t .  FIG. 26   b  shows a very broad pattern that does not vary much until 130° and is only reduced by half at 180°.  
         [0069]      FIG. 27   a  depicts virtual filament  530  comprising CEC transfer section  531 , conical section  532 , central equiangular spiral  533  with center at proximal point  533   f , and cylindrical stack  534  surfaced by multiple convex toroidal lenslets  534   t .  FIG. 27   b  shows that this substitution of a cone for a tailored spline causes the far-field pattern to drop in the near-axis angles, as compared to  FIG. 26   b . In the following FIGURE there are no such lenslets.  
         [0070]      FIG. 28   a  depicts virtual filament  540  comprising CEC transfer section  541 , conic section  542 , central equiangular spiral  543  with center at proximal point  543   f , and outer cylinder  544 .  FIG. 28   b  shows that the far-field pattern of this preferred embodiment is much narrower without the lenslets  534   t  of  FIG. 27   a.    
         [0071]      FIG. 29   a  depicts virtual filament  550  comprising CEC transfer section  551 , shallow upward cone  552 , central equiangular spiral  553  with center at proximal point  553   f , and outer concave spline  554 .  FIG. 29   b  shows its far-field pattern, with substantial axial emission.  
         [0072]      FIG. 30   a  depicts virtual filament  560  comprising CEC transfer section  561 , planar annulus  562 , central equiangular spiral  563  with center at proximal point  563   f , and outer cylinder  564 .  FIG. 30   b  shows its far-field pattern  FIG. 31   a  depicts virtual filament  570  comprising CEC transfer section  571 , planar annulus  572 , central equiangular spiral  573  with center at proximal point  573   f , and outer conical edge  574 .  FIG. 31   b  shows that far-field emission is predominantly forward.  
         [0073]      FIG. 32   a  depicts virtual filament  580  comprising CEC transfer section  581 , planar annulus  582 , upper equiangular spiral  583  with center at proximal point  583   f , outer cylinder  584  surfaced with concave toroidal lenslets  584   t , and central upper cone  585 .  FIG. 32   b  shows that its far-field pattern is predominantly forward, with full intensity within ±30°.  
         [0074]      FIG. 33   a  depicts virtual filament  590  comprising equiangular-spiral transfer section  591  with center at opposite point  591   f , outward cone  592 , central indentation  593  shaped as a higher-order polynomial, and steep outer cone  594 , and surfaces  595 ,  596 , and  597  forming a slot. Its far-field pattern is shown in  FIG. 33   b , with a sharp cutoff at 1500 off-axis and only 2:1 variation from uniform intensity at lesser angles.  
         [0075]      FIG. 34   a  depicts virtual filament  600  comprising equiangular-spiral transfer section  601  with center on opposite point  601   f , protruding cubic spline  602 , and central equiangular spiral  603  with center at proximal point  603   f . Its far field pattern is shown in  FIG. 34   b , and is to be compared with those of the following two preferred embodiments, in which the cubic spline protrudes more.  
         [0076]      FIG. 35   a  depicts virtual filament  610  comprising equiangular-spiral transfer section  611  with center at opposite point  611   f , protruding cubic spline  612 , and central equiangular spiral  613  with center at proximal point  613   f .  FIG. 35   b  shows that its far field pattern has reduced on-axis intensity compared with  FIG. 34   b.    
         [0077]      FIG. 36   a  depicts virtual filament  620  comprising equiangular-spiral transfer section  621  with center at opposite point  621   f , protruding cubic spline  622 , and central equiangular spiral  623  with center at proximal point  623   f .  FIG. 36   b  shows that its far field pattern has reduced on-axis intensity compared with  FIG. 35   b.    
         [0078]      FIG. 37   a  depicts virtual filament  630  comprising equiangular-spiral transfer section  631  with center at opposite point  631   f , planar annulus  632 , central equiangular spiral  633  with center at proximal point  633   f , and outer cylinder  634 .  FIG. 37   b  shows that its far field pattern has no on-axis intensity.  FIG. 37   b  can be compared with  FIG. 30   b , given the similarity of  FIG. 37   a  to  FIG. 30   a.    
         [0079]      FIG. 38   a  depicts virtual filament  640  comprising equiangular-spiral transfer section  641  with center at opposite point  641   f , lower conical section  642 , upper conical section  643 , and outer spline curve  644 .  FIG. 38   b  shows the far-field pattern. Cone  642  is a white diffuse reflector with Lambertian scattering, so that unlike the diffuse transmissive surface  392  of  FIG. 13   a , it only reflects light falling on it.  
         [0080]     Previous embodiments have complete circular symmetry, since they are formed by a 360° cylindrical profile-sweep. Thus they have no azimuthal shape variation, only the radial variation of the profile. This is because real-world 360° output patterns do not call for azimuthal variation. There is one type of azimuthal shape variation, however, having no azimuthal intensity variations in its light output. This is the V-groove.  
         [0081]     The geometry of a linear array of V-grooves is shown in  FIG. 39 . Reflective 90° V-groove array  650  is bordered by x-z plane  651  and y-z plane  652 . Incoming ray  653  is reflected at first groove wall  650   a  become bounce ray  654 , then reflected at second groove wall  650   b  to become outgoing ray  655 . Incoming ray  653  has projection  653   yz  on border plane  652  and projection  653   xz  on border plane  651 . Bounce ray  654  has projection  654   yz  on border plane  652  and projection  654   xz  on border plane  651 . Outgoing ray  655  has projection  655   yz  on border plane  652  and projection  655   xz  on border plane  651 .  
         [0082]      FIG. 39  also shows macrosurface normal N lying perpendicular to the plane of V-groove array  650 , which in the case of  FIG. 39  is the xy plane. The directions of projected rays  653   xz  and  655   xz  obey the law of reflection from a planar mirror with the same surface normal. But on yz plane  652 , outgoing projection  655   yz  has the opposite direction of incoming projection  653   yz , which has in-plane incidence angle ψ. Thus linear V-groove array  650  acts as a combination of retroreflector and conventional reflector. That is, when incoming ray  653  has direction vector (p,q,r), then outgoing ray  655  has direction vector (p,−q,−r). This condition, however, only holds for those rays undergoing two reflections. Of all possible input-ray directions, the fraction that is reflected twice is 1−tan(ψ).  
         [0083]     The configuration pertinent to the present invention is when surface  650  is the interface between a transparent dielectric, such as acrylic or polycarbonate, lying above the surface (i.e. positive z) and air below it. The particular case shown in  FIG. 39  is also valid for total internal reflection, which occurs whenever the incidence angle  0  of a ray on the dielectric-air interface exceeds the local critical angle 
        θ c =arcsin(1/n) for refractive index n. Since the unitary normal vectors on the 2 sides of the grooves are (0, 0.5, 0.5) and (0,−0.5, 0.5), the condition for total internal reflection can be vectorially expressed as 
 
( p,q,r )(0,±0.5, 0.5)&lt;cos θ c  
 
 which can be rearranged to yield 
 
| q|+( 1 −p   2   −q   2 )&lt;[2(1−1 /n   2 )]
       
 
         [0085]      FIG. 40  shows contour graph  660  with abscissa p and ordinate q. Legend  661  shows the fraction of rays that are retroreflected by total internal reflection. For p=0, the maximum q value for which there is total internal reflection for the 2 reflections is 
 |cos −1   q|&lt; 45°−θ c    
 which amounts to a vertical width of ±2.80 for acrylic (n=1.492) and ±60 for polycarbonate (n=1.585). These small angles are how much such incoming rays are not in plane  651 . 
 
         [0086]     More pertinent to the present invention is radial V-groove array  670  shown in  FIG. 41 . Crest-lines  671  and trough-lines  672  are the boundaries of planar triangles  673 , which meet at the crest-lines and trough-lines with 90° included angles  674 .  
         [0087]     In  FIG. 37   a , the genatrix curve of upper surface  633  has the form of an equiangular spiral. It is possible to impose a radial V-groove array on such a surface, so that crest-lines  671  of  FIG. 41  would become curved downward, depressing the center point.  
         [0088]      FIG. 42   a  is a perspective view of the preferred embodiment of  FIG. 37   a . Virtual filament  680  comprises equiangular-spiral transfer section  681 , equiangular-spiral top surface  683 , and cylindrical side surface  684 , the apparently polygonal shape of which is a pictorial artifact. Crest curves  683   c  are shown as twelve in number, to correspond with crest-lines  671  of  FIG. 41 .  
         [0089]      FIG. 42   b  is another perspective view of the same preferred embodiment, but with surfaces  683  and  684  of  FIG. 42   a  removed. Twelve crest-curves  683   c  are shown, one shown with tangent vector t, normal vector n, and their vector product the binormal vector b=t×n. If a crest-curve were the path followed at uniform speed by a particle, then its velocity vector lies along tangent vector t and its acceleration vector is the negative the normal vector n. The latter is so that it will coincide with the surface normal of the surface. Because each crest-curve lies in a plane, binormal vector b is constant, meaning the crest-curves have zero torsion.  
         [0090]      FIG. 43  is a perspective view of the construction of a V-groove on a curved surface according to the present invention.  
         [0091]     In modifying surface  683  of  FIG. 42   a  to become like radial-groove array  670  of  FIG. 41 , the curvature of the crest-lines would make the groove surfaces become non-planar. In fact, such surfaces would be the envelopes of elemental planes coming off each point on the curve at a 45° angle, as shown in  FIG. 43 . Incompletely swept equiangular spiral surface  690  is identical to surface  683  of  FIG. 42   a . Part of the sweep is unfinished so that crest-curve  691  can be clearly seen. Tangent to it are three elemental planar ridges  692  with 90° interior angles. Let a crest curve be specified by the parametric function P(t), where t is the path-length along said crest-curve, with normal vector n(t) and binormal vector b(t). Any point X on a 45° plane touching the crest-curve at P(t) is specified by 
 
( X−P ( t ))·( n ( t )± b ( t ))=0  (1) 
 
 with the ‘±’ referring to there being two such 45° planes corresponding to the walls of a 90 V-groove. Varying t gives a family of such planes. In order to calculate the envelope surface to this family of planes, differentiate Equation (1) with respect to parameter t, giving  
                   -       ⅆ     P   ⁡     (   t   )           ⅆ   t         ·     (       n   ⁡     (   t   )       ±     b   ⁡     (   t   )         )       +       (     X   -     P   ⁡     (   t   )         )     ·     (         ⅆ     n   ⁡     (   t   )           ⅆ   t       ±       ⅆ     b   ⁡     (   t   )           ⅆ   t         )         =   0           (   2   )             
 
 The orthogonal vector triad formed by the parametrically specified unit vectors t(t), n(t), and b(t) is called the Frenet frame of the curve it follows as t varies. Each of these three vectors has a definition based on various derivatives of the equation for P(t). Differentiating these definitions with respect to t gives the Frenet equations, well-known in differential geometry. A laborious combination of the Frenet equations with Equation (2), and eliminating t, finally yields 
 
( X−P ( t ))· t ( t )=0  (3) 
 
 Equation (3) and Equation (1) must be fulfilled simultaneously for each point X of the envelope surface. Equation (3) establishes that the same vector X−P is normal to tangent vector t, while Equation (1) implies that the vector X−P is normal to n±b. Thus X−P, for a point satisfying equations (1) and (3), must be in the direction n-b, because n and b are orthogonal unit vectors so that (n−b) ·(n+b)=0, i.e., 
 
 X−P ( t )= s (− n ( t )± b ( t ))  (4) 
 
 This is the parametric equation of the two envelope surfaces of the ridge. The radial parameter is t and transverse parameter is s, with one ridge for +b(t) and the other for −b(t). Curves  683   c  of  FIG. 42   b  will be crest curves if we take s&gt;0 for both ridges (with s=0 for the crest curves) and they will be trough curves if s&lt;0 (with s=0 for the trough curves in this case). More pertinently, 
 
 X ( t,s )= P ( t )+ s (− n ( t )± b ( t ))  (5) 
 
 is the equation of the envelope surface as a function of the crest equation P(t), and its normal and binormal vectors. The parameter s extends to the value of s that at the bottom of the groove, where it meets the corresponding point on the next ridge. 
 
         [0092]     The upshot of this differential-geometry proof is that each of the planes of  FIG. 43  contributes thick lines  693  to the envelope surface of the curved V-groove. Thick lines  693  of  FIG. 43  in fact represent the second term in Equation (5). If successive lines  693  cross as they issue from closely neighbouring points, then the resultant envelope surface may have ripples or even caustics (which are physically unrealisable). In the present invention, any such mathematical anomalies would be too far from the crest curve to be of relevance.  
         [0093]      FIG. 44  is a perspective view of virtual filament  700 , comprising equiangular-spiral transfer section  701 , radial V-grooves  702 , and cylindrical sidewall  703 . Only twelve V-grooves are shown, for the sake of clarity, but an actual device may have many more. The utility of such grooves is that they enable the designer to avoid the use of a coated reflector.  
         [0094]      FIG. 45  shows virtual filament  710 , comprising transfer section  711  with longitudinal V-grooves, and ejector section  703 . As shown in  FIG. 45 , V-grooves can also be used on the transfer section of the present invention, enabling a cylindrical shape to be used.  
         [0095]     The discussion of FIG. 2 of U.S. patent application Ser. No. 10/461,557 touched on the function of color mixing, to make the different wavelengths of chips  23 ,  24 , and  25  have the same relative strengths throughout the light coming out of ejector section  12 . This assures that viewers will see only the intended metameric hue and not any colors of the individual chips. Previously, rectangular mixing rods have been used to transform the round focal spot of an ellipsoidal lamp into a uniformly illuminated rectangle, typically in cinema projectors. Generally, polygonal mixing rods worked best with an even number of sides, particularly four and six. With color mixing for LEDs, however, such rods are inefficient because half of an LED&#39;s Lambertian emission will escape from the base of the rod.  
         [0096]     The following preferred embodiments of the present invention remedy this deficit by proper shaping of its transfer section. This shaping enables polygonal cross-sections to be used in the present invention.  
         [0097]      FIG. 46  depicts virtual filament  720 , comprising hexagonal transfer section  721  and hemispheric ejector section  722 . Within package  723  are red LED chip  723   r , green chip  723   g , and blue chip  723   b . Transfer section  721  comprises expanding bottom section  721   b , mid-section  721   m  with constant cross-section, and contracting upper section  721   u . The shape of sections  721   b  and  721   u  acts to prevent the escape of rays that a constant cross section would allow if it extended the entire length of transfer section  721 . Similar to the grooves of  FIG. 44  and  FIG. 45 , a polygonal transfer section would constitute a departure from complete rotational symmetry.  
         [0098]      FIG. 47   a  is a side view of virtual filament  730  comprising sixteen-sided off-axis ellipsoid  731 , conical ejector section  732 , and mounting feet  734 .  FIG. 47   b  is a perspective view of the same preferred embodiment, also showing spline top surface  733 .  FIG. 47   c  shows the blue (465 nanometers) emission pattern of this preferred embodiment, at the various cylindrical azimuths, 0° azimuth indicated by reference numeral  735 , 45° azimuth indicated by reference numeral  736 , 90° azimuth indicated by reference numeral  737 , and 135° azimuth indicated by reference numeral  738 , and as indicated in the legend at upper right.  FIG. 47   d  shows the green (520 nanometers) emission pattern of this preferred embodiment, at the various cylindrical azimuths  735 - 738  and as indicated in the legend at upper right.  FIG. 47E  shows the red (620 nanometers) emission pattern of this preferred embodiment, at the various cylindrical azimuths  735 - 738  and as indicated in the legend at upper right.  
         [0099]      FIG. 48   a  is a side view of virtual filament  740  comprising sixteen-sided off-axis ellipsoid  741 , conical ejector section  742 , conical collar  744 , and cylindrical connector  745 .  FIG. 48   b  is a perspective view of the same preferred embodiment  743 . The purpose of the narrowing by collar  744  is to produce the 300° emission pattern  747  shown in  FIG. 48   c.    
         [0100]      FIG. 49   a  is an exploded side view of faceted virtual filament  750  and tricolor LED package  755  being inserted into and optically coupled to the filament  750 . Beyond polygonally-shaped transfer sections are more complex departures from circular symmetry. Virtual filament  750  comprises an output section spanned by arrow  751 , transfer section  752 , and mounting feet  753 . Faceted virtual filament  750  is a single piece of plastic, such as acrylic, the surface of which is covered by planar facets  754 . The two mounting feet  753  are designed to be proximate to the outer surfaces of LED package  755 , to aid in alignment and bonding of virtual filament  750  to package  755 . In one embodiment of the invention, adhesive is applied to the inner sidewalls of feet  753  for bonding to LED package  755 . In this instance the inner sidewall of each leg  753  has a surface that is substantially parallel to the proximate edge surface of LED package  755 . Optical coupling of the bottom of virtual filament  750  to the top surface of LED package  755  can be achieved by several means, such as use of optical adhesives, non-curing and curing optical gels (such as available from Nye Optical Products of Fairhaven, Ma) or index matching liquids (such as available from Cargille Laboratories of Cedar Grove, N.J.).  
         [0101]      FIG. 49   b  is an exploded-part perspective view showing rectangular LED package  755  as removed from virtual filament  750 . Within reflector cup  757  are red chip  758   r , green chip  758   g , and blue chip  758   b . Cup  757  is filled with transparent epoxy (not shown) up to top  756  of package  755 . Top  756  is optically bonded to the bottom of faceted virtual filament  750 . This three-chip configuration is an example of the present invention incorporating multiple light sources. The three chips shown could also be amber, red, and infrared, suitable for illuminators compatible with night-vision devices, and other combinations.  
         [0102]     Typically the base of a mixing virtual filament is larger than the emitting surface of the RGB LED illuminating it. In one preferred embodiment the inner diameter of the sixteen-sided polygonal shaped base of the mixing optic  750  is 20% larger than the diameter of the circular exit aperture of the RGB LED  755 . In the case where the RGB LED  755  has a non-circular exit aperture, the base of the virtual filament is made sufficiently large to completely cover the exit aperture of the LED.  
         [0103]     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention as set forth in the claims.

Technology Category: 2