Abstract:
A light engine has a pillar with first and second ends; a circuit board on the first end of the pillar, a light source mounted on the circuit board encircling the pillar and facing towards the second end of the pillar, and a surface extending from the second end of the pillar, that surface and the exterior of the pillar between that surface and the circuit board being coated with a reflective remote phosphor that is excited by light from the light source. The light engine may be used in a light bulb, with a frosted globe enclosing the circuit board and mounted round the outer edge of the phosphor-coated surface, and an Edison screw or other standard base connected to the second end of the pillar.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of: U.S. Provisional Application 61/279,586 filed Oct. 22, 2009 titled “Lamp” by several of the inventors; U.S. Provisional Patent Application 61/280,856, filed Nov. 10, 2009, U.S. Provisional Patent Application 61/299,601, filed Jan. 29, 2010, and U.S. Provisional Patent Application 61/333,929 filed May 12, 2010, all titled “Solid-State Light Bulb With Interior Volume for Electronics,” all by some of the same inventors; and U.S. Provisional Application 61/264,328 filed Nov. 25, 2009 titled “On-Window Solar-Cell Heat-Spreader” by several of the inventors. All of those applications are incorporated herein by reference in their entirety. 
         [0002]    Reference is made to co-pending and commonly owned U.S. patent application Ser. No. 12/378,666 (publication no. 2009/0225529) titled “Spherically Emitting Remote Phosphor” by Falicoff et al., Ser. No. 12/210,096 (publication no. 2009/0067179) titled “Optical Device For LED-Based Lamp” by Chaves et al, and Ser. No. 12/387,341 (publication no. 2010/0110676) titled “remote phosphor LED downlight.” All of those applications, which have at least one common inventor to the present application, are incorporated herein by reference in their entirety. Reference is made to co-pending U.S. patent application Ser. No. 12/778,231 titled “Dimmable LED Lamp,” filed May 12, 2010, Ser. No. 12/589,071 (publication no. 2010-0097002), titled “Quantum Dimming via Sequential Stepped Modulation” filed Oct. 16, 2009, and Ser. No. 12/______ (docket no. 047654-0041-00-US (460054)), titled “Solid state light bulb,” filed Oct. 22, 2010, all by several of the inventors. All of those applications, which have at least one common inventor to the present application, are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The term ‘solid state lighting’ (SSL) is more than just a synonym for the use of light-emitting diodes, since it also comprises circuit boards, dimming and color control, power supplies, heat sinks, and secondary optics. In large installations, the lights are spread out with controls and power supply separately located, typically without tight volume-constraints. In a retail lighting product, however, all the subsystems must fit within a standard envelope, meaning very tight constraints on weight and cost but most importantly on volume. In particular, a lamp that is intended to substitute for a conventional incandescent light bulb in existing fittings, such as the A-19 light bulb with medium Edison screw fitting that is common in the U.S.A., has relatively severe geometric constraints, on top of the generic difficulty of generating spherical output with inherently planar LED emission. One objective of the present invention is to provide a complete solid-state light bulb, within an Edison-base A-19 envelope, a PAR-lamp, or comparable envelopes that are used in other territories or for other purposes. 
       SUMMARY OF THE INVENTION 
       [0004]    Due to their high filament temperatures, the exterior of incandescent A-19 light bulbs is entirely made of glass, typically diffuse, except for the metallic base. However, glass is brittle, and the thin envelope of a conventional light bulb is somewhat fragile. Except for their base, embodiments of the lamps of the present invention can have a plastic exterior, which can be tougher than glass, and so can be inherently rugged. Embodiments of the present invention produce white light by a combination of blue LED chips and a geometrically separate reflective remote phosphor that converts most of the blue light to yellow. 
         [0005]    A “remote” phosphor is one that is spaced apart from the LED or other excitation light source, in contrast to the common conformal phosphor, coated onto the encapsulant immediately covering the actual LED chip. Various benefits of the remote phosphor approach are taught in earlier U.S. patents and applications by several of the same inventors, including U.S. Pat. No. 7,286,296 to Chaves et al. There are two primary types of remote phosphor: transmissive and reflective. In a “transmissive” phosphor, the useful light emerges on the side of a phosphor layer away from the excitation light source. In a “reflective” phosphor, the useful light emerges on the side of the phosphor layer towards from the excitation light source. A reflective phosphor may be of similar composition to a transmissive phosphor, and may both transmit and reflect unconverted blue light, and may emit converted yellow light both forwards and backwards. The reflective phosphor is then typically applied as a coating on a highly reflective substrate, either diffuse or specular, that returns transmitted and forward emitted light back through the phosphor layer. Solid state lights based on the transmissive remote phosphor approach have been commercialized but the reflective approach has up to this time not made it to the marketplace. In U.S. Pat. No. 7,665,858, by several of the same inventors as this one, a reflective remote phosphor is shown that is color temperature tunable. Although the approach works it is also expensive and fairly complex to build. The present invention provides alternative approaches which are less expensive and more commercially viable for a wider range of applications. 
         [0006]    With currently available blue LEDs and yellow phosphors, the phosphor by itself will reflect about 10% of the blue light hitting it, whereas about 25% of the final white light must be the original blue wavelengths. It is possible, though exacting, to adjust the thickness of a reflection-mode phosphor on a reflective backing to get the proper amount (−15%) of unabsorbed blue light scattered out from within it. Instead, for some embodiments of the present invention it is advantageous to apply the phosphor in patches so as to leave uncovered white surface between them, as taught in co-pending application Ser. No. 12/387,341. 
         [0007]    One embodiment of the present invention comprises an LED light engine, to be utilized with either of two secondary optical elements. The shape of the optic can be either a conventional A-19 frosted light bulb or a PAR-19 lamp, either of which can be on an Edison-style screw-in base or other conventional base. The LEDs are on a circuit board facing this base, with the reflective remote phosphor receiving all of the light from the LEDs, with none of the LED&#39;s light directly shining upon the secondary optic. The remote phosphor is on a surface that is a part or all of a hemispheric cavity, depending upon the secondary optic. The remote phosphor and the white surface upon which it is deposited are both highly diffuse reflectors, with much of their emission falling on other parts of the remote phosphor. This self-illumination and the resulting light-mixing will help assure uniform luminance and chrominance of the white light coming off the remote phosphor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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: 
           [0009]      FIG. 1  is a cross-sectional view of a first preferred embodiment of a remote-phosphor light engine. 
           [0010]      FIG. 1A  is a close up of dispersed phosphor patches. 
           [0011]      FIG. 2  is a cross-sectional view of a lamp based upon the light engine of  FIG. 1 . 
           [0012]      FIG. 3A  shows a perspective exploded view of a lamp similar to that of  FIG. 2 . 
           [0013]      FIG. 3B  shows another perspective exploded view of the lamp of  FIG. 2 . 
           [0014]      FIG. 3C  shows an Isocandela plot of an embodiment of the lamp of  FIG. 2 . 
           [0015]      FIG. 4A  shows an exploded perspective view from the rear of a second preferred embodiment of a light engine. 
           [0016]      FIG. 4B  shows an assembled cross-section side view of the light engine of  FIG. 4A . 
           [0017]      FIG. 4C  shows a perspective front view of the light engine shown in  FIG. 4B . 
           [0018]      FIG. 5  shows a cross-sectional side view of a lamp with the light engine of  FIG. 4B . 
           [0019]      FIG. 6  shows a cross-sectional side view of a PAR lamp with the light engine of  FIG. 4B . 
           [0020]      FIG. 7  shows a graph of light intensity against distance off axis for a lamp similar to that of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    A better understanding of various features and advantages of the present invention may be obtained by reference to the following detailed description of embodiments of the invention and accompanying drawings, which set forth illustrative embodiments in which certain principles of the invention are utilized. 
         [0022]      FIG. 1  shows a somewhat schematic cross sectional view of light engine  10 , comprising circuit board  11  with LED chips  12  mounted on it, lateral light-shield  13 , vertical reflective remote-phosphor surface  14 , inner slanted reflective remote-phosphor surface  15 , outer slanted reflective remote-phosphor surface  16 , and electronics via  17 . There are eight LED chips  11  arranged in a circle surrounding a central hollow stalk, which has vertical remote-phosphor surface  14  on its outside and the hollow center of which forms electronics via  17 . The LED chips  11  emit blue light. The blue light falls on the remote-phosphor surfaces or on shield  13 , which is highly reflective, as are all exterior surfaces of light engine  10 . The lower edge of shield  13  is positioned so that it just prevents direct rays from LEDs  12  missing the outer edge of outer slanted remote-phosphor surface  16  and escaping. The remote phosphor surfaces have a microstructure shown in the close-up view of  FIG. 1A , with phosphor patches  18  on a highly reflective white substrate. The areas of white substrate exposed between the phosphor patches increase the proportion of blue LED light that is reflected without being converted to yellow by the phosphor. The overall color temperature of the light from the phosphor surfaces can thus be controlled by controlling the ratio of the areas of the phosphor patches and the exposed white substrate. It can be seen that each remote-phosphor surface shines onto the other two, helping to make them more uniform in brightness and color. 
         [0023]    In order to improve the color rendering, the LEDs  12  may include red or other colored LEDs mixed in with the blue LEDs. An alternative approach to achieving a high CRI is to use more than one phosphor, especially a tri-phosphor mix such as the one taught in co-pending application Ser. No. 12/______, (docket no. 047654-0041-00-US (460054)), titled “Solid state light bulb,” filed Oct. 22, 2010. This can be used in the above approach of  FIG. 1A  with a patterned phosphor layer, or where the phosphor layer is continuous. In the latter case, the thickness of the reflective remote phosphor must be controlled to allow the required amount of reflected unconverted blue to be mixed with the phosphor converted light. 
         [0024]      FIG. 2  shows lamp  20  in the A-19 configuration, with light engine  21  of the type shown in  FIG. 1 , frosted globe  22 , Edison-style screw-in base  24 , and electronics bay  23  in the lower part of the lamp between frosted globe  22  and screw-in base  24 . Globe  22  has a rough interior surface with a significant amount of backscattering, as well as diffusing outgoing transmitted light, a property that helps give the globe a uniform lit appearance. Edison-style screw-in base  24  serves in the conventional way for power supply and mechanical mounting of the lamp  20 , and can of course be substituted with a different sort of base to suit the receptacles available in a particular environment. Electronics bay  23  is connected to circuit board  11  through via  17 . 
         [0025]    The electronics and electrical wiring may be conventional, and in the interests of clarity are not shown in detail. The electronics serve at least to convert the power received through Edison-style screw-in base  24 , which in the U.S.A. is typically 110 V, 60 Hz AC, and in other parts of the world may be, for example, 220 V, 50 Hz AC, to the supply required for the LEDs, which is typically about 3 V DC, or 24 V for 8 LEDs wired in series, with regulated current. More sophisticated control of the LEDs may be provided, such as the traditional dimming approaches such as pulse width and current modulation and the novel approach taught in Ser. No. 12/589,071 which does so-called quantum dimming, where the LEDs are individually controlled. 
         [0026]    Because the physics of the Stokes shift in a phosphor inevitably produces significant waste heat, the body of the light engine on which the phosphor  14 ,  15 ,  16  is applied may be made of a heat-conducting metal or ceramic material that will conduct heat from the phosphor to the part of the exterior of the body exposed between the globe  22  and the base  24 . From there, the heat can be radiated or conducted to the surrounding air, and dissipated by convection. Similarly, the stalk or pillar can conduct heat away from the LEDs  12  on circuit board  11  to the body for dissipation. 
         [0027]      FIG. 3A  shows a perspective exploded view of a lamp  30  similar to that shown in  FIG. 2 , comprising screw-in Edison base  31 , frosted globe  32 , lower body containing electronics bay  33 , circuit board  34  bearing LED chips  35 , and light shield  36 . 
         [0028]      FIG. 3B  shows another perspective exploded view of lamp  30 , also showing remote phosphor surfaces  37  and  38 . As may be seen from  FIG. 3B , lamp  30  does not have a distinct inner slanted remote-phosphor surface between vertical remote-phosphor surface  14  and outer slanted remote-phosphor surface  16 . Other configurations are of course also possible. 
         [0029]      FIG. 3C  shows a simulated isocandela plot  38  for an embodiment of lamp  30  with plot contour  39 . This plot was generated by the Inventors using the commercial ray-trace package TracePro. The simulation assumed the phosphor layers completely covered the exposed surfaces  14 ,  15 , and  16  of  FIG. 1 . A tri-phosphor formulation comprising:
       Epoxy matrix: Masterbond UV 15-7, specific gravity of 1.20   And per gram of Masterbond UV 15-7 epoxy:   red phosphor (PhosphorTech buvr02, a sulfoselenide, mean particle size less than 10 microns, specific gravity of about 4): 21.1±0.03 mg.   yellow phosphor (PhosphorTech byw01a, a Ce-YAG, mean particle size 9 microns,   specific gravity 4): 60.7±0.3 mg.   green phosphor (Internatix g1758, an Eu doped silicate, mean particle size 15.5 microns, specific gravity 5.11): 250.6±1.3 mg,
 
(taught in the afore-mentioned co-pending patent application Ser. No. 12/______ (docket no. 047654-0041-00-US (460054)), titled “Solid state light bulb,” filed Oct. 22, 2010) was used to determine the bulk scattering coefficient and other required parameters in the simulation. The isocandela plot is sufficiently uniform to meet current US Energy Star standards.
       
 
         [0036]    It is possible to alter the light engine of  FIG. 1  or  FIG. 3B  by laterally extending the remote-phosphor surfaces  13 ,  14 , and  15  or  37  and  38  with more remote-phosphor surface that extends outward back up to make a complete cup and reduce or eliminate any need for the light shield  13  or  36 .  FIGS. 4A ,  4 B, and  4 C, collectively  FIG. 4 , show various views of this concept. 
         [0037]      FIG. 4A  shows an exploded view of light engine  40 , comprising circuit board  41  with a ring of eight LEDs  42 , pillar  43  with reflective remote phosphor on its exterior, and hemispheric cup  44  with reflective remote phosphor on its interior and aperture  45  at its bottom, receiving pillar  43 . 
         [0038]      FIG. 4B  is a lateral cross-section of light engine  40 , showing circuit board  41 , LED chips  42 , pillar  43 , hemispheric cup  44 , and electronics via  46  within pillar  43 . As is best seen from  FIG. 4B , the rim of cup  44  is flush with the lower or rear face of circuit board  41 , on which the LEDs  42  are mounted. Assuming a hemispherical emission from LEDs  42 , cup  44  just intercepts all of the direct rays from LEDs  42 , so that no light shield  13 ,  36  is required. 
         [0039]      FIG. 4C  is a perspective front view of light engine  40 , showing circuit board  41 , pillar  43 , and the remote-phosphor surface of cup  44 . The view around circuit board  41  is only of remote-phosphor surfaces. 
         [0040]      FIG. 5  shows a cross section of lamp  50 , comprising frosted globe  51 , light engine  52  of the type shown in  FIG. 4 , and Edison-style screw-in base  53 . The light engine  52  shines from a chord of frosted globe  51 , assuring that it globe  51  is comparatively uniformly illuminated. Although globe  51  still needs to be diffusely transmitting, globe  51  need not have any backscattering, unlike the frosted globe of  FIG. 2 . The light engine of  FIG. 4  needs no further mixing, unlike that of  FIG. 1 , in which the uniformity of the output can be improved by some modest mixing by backscattering off the inside of its globe. 
         [0041]      FIG. 6  shows PAR lamp  60 , comprising conical mirror  61 , with a 23° opening half-angle, light engine  62  similar to that shown in  FIG. 4 , Edison-style screw-in base  63 , and heat-dissipating fins  64 . 
         [0042]      FIG. 7  shows the exemplary illumination performance of the PAR lamp of  FIG. 6 , with graph  70  of lux at a distance of 3 meters, comprising abscissa  71  in mm off-axis and ordinate  72  in lux per lumen of lamp output. The curve in  FIG. 7  was calculated using TracePro. Curve  73  is quite smooth, corresponding to a full width  74  at half-maximum of 50°, typical for a PAR lamp. 
         [0043]    Although the reflective remote-phosphor surfaces of the present invention are much larger than the LED chips illuminating them, their cost is modest in comparison to the eight LEDs. For 18 square centimeters of phosphor area, a YAG-only phosphor with a color-rendering index around 75 costs only US$0.20 while a high-CRI triple-species phosphor with a color-rendering index of 92 costs about US$1.20, roughly the cost of a single LED chip, and considerably less than the cost of the high-flux packages LEDs commercially available at the time of this invention, typically US$2 to US$4 in high volume. 
         [0044]    Although specific embodiments have been described, the skilled reader will understand how features of different embodiments may be combined, and how features of various embodiments may be modified or varied. 
         [0045]    For example, the bulb  20  shown in  FIG. 2  has a substantial body with an electronics compartment  23  between the frosted globe  22  and the connector base  24 . The bulb  50  shown in  FIG. 5  does not have an electronics compartment  23 , but the interior  46  of the pillar  43  and the interior of the Edison screw base  53  are available for electronics. Either configuration of space for electronics, or anything in between, may be used in any of the embodiments. The optimum choice will be guided by the compactness of the available or required electronics and the available space within a light fitting into which the bulb  20 ,  50 , etc. is to be fitted. However, embodiments of the invention comply fully with the external dimensions specified in the standard for the A19 bulb. 
         [0046]    The diameter of the hollow interior  46  of the pillar  43  may also be varied within limits but in general it is preferred, as shown in  FIG. 4B , for the height of the pillar between the circuit board  41  and the inside of the bowl  44  to be at least equal to the diameter of the ring of LEDs  42 , to allow space for the light from the LEDs to spread out and illuminate the phosphor relatively evenly. Another approach that is possible is to have the driver electronics in a package remote from the lamp or downlight. This is certainly possible in a downlight and is currently an approach used in many solid state products currently on the market. For example, the Edison screw base of the bulb of  FIG. 5  can be replaced by a mounting feature and the driver/power supply can be located in a remote location. This would be useful for a candelabra where the driver/power supply provides power for more than one lamp. Alternatively, the Edison screw base of  FIG. 6  can be replaced by a GU24 or other connector to meet the requirements of certain municipality, state or Federal regulations. (The GU24 “twist and lock” connector is being promoted in the U.S.A. as a successor to the Edison screw. The intention is that it shall be a general standard for self-contained high-efficiency lamps, but that incandescent bulbs and other low efficiency lamps shall not be available with the GU24 fitting.) 
         [0047]    For example,  FIGS. 2 and 3B  show a succession of convex cylindrical or frustoconical phosphor coated surfaces.  FIG. 4B  shows a cylindrical phosphor coated surface  43  on the pillar and a concave, hemispherical phosphor coated surface on the bowl  44 . Other configurations are possible, such as a bowl  44  with two or more distinct surfaces, which may comprise flat surfaces, concave frustoconical surfaces, and/or surfaces curved as seen in axial cross-section. 
         [0048]    For convenience of description, terms of relative orientation have been used in the description, with the end of the bulb having the mounting screw generally referred to as the base, bottom, or rear. However, all of the lamps shown in the embodiments may of course be used, mounted, or stored in any orientation. 
         [0049]    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.