Abstract:
A luminaire takes the form of a bulb-shaped, LED-based lamp, which can replace a conventional incandescent bulb.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/177,834, filed on May 13, 2009, the entire disclosure of which is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    In various embodiments, the present invention generally relates to illumination devices, and in particular to replacement lamps, based on discrete light sources, for incandescent fixtures. 
       BACKGROUND 
       [0003]    Most household light fixtures utilize incandescent lightbulbs, which contain an incandescent filament inside a glass enclosure. These conventional light sources are fragile and have limited lifetimes, due primarily to increasing vulnerability of the filament to breakage as it ages. In practice, typical incandescent lightbulbs have a mean life of 500 to 4,000 hours. 
         [0004]    Light-emitting diodes (LEDs) represent an attractive alternative as light sources. Solid-state LEDs consume less power than incandescent lightbulbs and may have lifetimes in excess of 100,000 hours. Besides producing little heat and being energy-efficient, LEDs are smaller and less vulnerable to breakage or damage due to shock or vibration than incandescent bulbs. LED characteristics also do not change significantly with age. 
         [0005]    Widespread use of LED-based lighting systems has been limited, in part, because of the large installed based of incandescent fixtures and consumers accustomed to traditional bulb lights. 
       SUMMARY 
       [0006]    Embodiments of the present invention utilize LED-based illumination structures that can replace incandescent lightbulbs in existing fixtures. These structures can be shaped to resemble conventional lightbulbs, and can be equipped with appropriate power-conversion circuitry and a threadable base for compatibility with incandescent fixtures. The emitted light may be white or another color, and the illumination systems may incorporate a phosphor material for converting light emitted by an LED of one wavelength into light of another wavelength. The luminous efficacies of illumination systems in accordance with embodiments of the invention may be 90 lumens/watt or more. 
         [0007]    In an aspect, embodiments of the invention feature an LED-based illumination structure capable of replacing an incandescent bulb. The structure may include or consist essentially of a base for mating with an incandescent light socket, a rounded, bulb-shaped waveguide, and at least one LED. The waveguide includes or consists essentially of in-coupling, propagation, and out-coupling regions. The LED(s) are disposed for emission into the in-coupling region. Light from the LED(s) propagates (and/or mixes) through the propagation region and is emitted only from the out-coupling region. 
         [0008]    Embodiments of the invention may include one or more of the following features in any of a variety of combinations. The waveguide may include a base edge and a rounded crown portion opposite the base edge, and the in-coupling region may encompass the base edge, and the out-coupling region may encompass the crown portion. The out-coupling region may extend over at least half the length from the base edge to a peak point on the crown portion. A phosphor material for converting light to a different wavelength may surround (e.g., be present on the exterior of, or within) at least a portion of the out-coupling region. The illumination structure may include a heat sink between the base and the waveguide and/or power-conversion and drive circuitry for driving the LED from household current supplied to the base. 
         [0009]    A reflector may be disposed within and adjacent to the base edge. An inner reflector may be disposed over at least a portion of the inner surface of the waveguide, e.g., at least over the inner surface of the out-coupling region. The LED(s) may be embedded inside the base edge and/or may illuminate through the base edge. The illumination structure may include a plurality of LEDs evenly distributed circumferentially around the in-coupling region. At least one of the LEDs may emit light of a different color from that emitted by another one of the LEDs. The LED(s) may be bare light-emitting diode dies. 
         [0010]    The waveguide may surround a hollow interior space in the manner of an incandescent lightbulb. Light emitted from an exterior face of the out-coupling region may pass through the phosphor, and light emitted from an interior face of the out-coupling region may pass into the interior space and through an opposed portion of the out-coupling region. The phosphor may be outside a direct line-of-sight of the LED(s). The out-coupling region may include a plurality of optical elements, e.g., microlenses and/or scattering particles. 
         [0011]    These and other objects, along with advantages and features of the invention, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. As used herein, the term “substantially” means±10%, and in some embodiments, ±5%. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
           [0013]      FIG. 1  is a schematic elevation of an exemplary replacement lamp in accordance with various embodiments of the invention; and 
           [0014]      FIGS. 2A and 2B  are schematic elevations of embodiments having, respectively, a bottom reflector and an inner reflector; and 
           [0015]      FIG. 3B  is a sectional view of the embodiment shown in  FIG. 1 , taken along the line A-A shown in  FIG. 3A . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Refer first to  FIG. 1 , which illustrates an exemplary replacement lamp  100 . The lamp  100  includes a mechanical and electrical interface  110 , driver circuitry  115 , a heat-sink element  120 , and a bulb-shaped waveguide  125 . In some embodiments, the interface (or base)  110  is a coupling for standard incandescent fixtures with a conductive threaded cap or sleeve and an electrical contact  130 . It should be understood, however, that the interface  110  may be tailored to mate with any type of lamp socket. 
         [0017]    Driver circuitry  115  is conventional and converts a household AC line voltage into a DC voltage suitable for powering one or more LEDs. For example, circuitry  115  may include a capacitor and a diode bridge, where the capacitor functions to limit current within the circuit  115  and the diode bridge converts the AC line voltage to DC (and provides a full-wave mode of operation); see, e.g., U.S. Pat. No. 5,463,280, the entire disclosure of which is hereby incorporated by reference. In some embodiments, the LED(s) may be driven directly by AC voltage, and the driver circuitry  115  connects the LED(s) to the AC line voltage. The circuit  115  is connected in a conventional fashion to the conductive cap and the electrical contact of interface  110  (in the manner of an incandescent bulb filament). Heat sink  120  has vanes, as illustrated, that promote convective dissipation of heat. Desirably, heat sink  120  is capable, for example, of dissipating at least 10 watts of consumed power. 
         [0018]    Waveguide  125  has a rounded shape and includes a base edge attaching to heat sink  120  and an opposed crown portion; the overall shape of the waveguide  125  desirably conforms to that of a conventional incandescent lightbulb. The waveguide  125  surrounds a hollow interior region  132 , and includes an in-coupling region  135  for receiving light from one or more discrete light sources  140 , which may include or consist of, e.g., one or more LEDs. In a preferred embodiment, discrete light sources (hereinafter referred to, for convenience, as LEDs)  140  are embedded within in-coupling region  135  near the base edge, so that heat is efficiently transferred from the LEDs  140  to heat sink  120 . The illumination of the LEDs  140  is aligned in the direction of, or perpendicular to, the waveguide propagation direction, or at any suitable angle consistent with proper in-coupling. As shown in  FIG. 3B , waveguide  125  may have a circular base edge, and a plurality of discrete light sources may be embedded within in-coupling region  135 . In such embodiments, the discrete light sources may be evenly distributed circumferentially around in-coupling region  135 . 
         [0019]    Waveguide  125  also includes a propagation region  145 , distal to in-coupling region  135 , for retaining and spreading light from in-coupling region  135  until it is emitted from an out-coupling region  150 . The out-coupling region, in turn, is located distal to propagation region  145  and spans the crown portion of the waveguide  125 . Propagation region  145  enables the light to disperse uniformly (e.g., in color and/or intensity) prior to entering out-coupling region  150  to promote uniform illumination from the lamp&#39;s surface. 
         [0020]    Waveguide  125  typically includes or consists essentially of a waveguide material having a refractive index greater than 1. Representative examples of suitable waveguide materials include, without limitation, a thermoplastic such as a polycarbonate, polymethyl methacrylate (PMMA), and/or polyurethane (TPU) (aliphatic) with a refractive index of about 1.50, TPU (aromatic) with a refractive index of from about 1.58 to about 1.60, amorphous nylon such as GRILAMID supplied by EMS Grivory (e.g., GRILAMID TR90 with refractive index of about 1.54), polymethylpentene, e.g., TPX supplied by Mitsui with a refractive index of about 1.46, polyvinylidene fluoride (PVDF) with a refractive index of about 1.34, or other thermoplastic fluorocarbon polymers, and/or STYROLUX (UV stabilized) supplied by BASF with refractive index of about 1.58. 
         [0021]    To facilitate emission of the light, out-coupling region  150  includes a plurality of optical elements therein or disposed on its top surface. The optical elements serve as scatterers and typically scatter light in more than one direction. When light is scattered by an optical element such that the impinging angle is below the critical angle for internal reflection, no total internal reflection occurs and the scattered light is emitted through the inner or outer surface of out-coupling region  150 . Additional details regarding optical elements, their function, and their placement may be found in U.S. Patent Application Publication Nos. 2009/0161341, 2009/0161369, and 2009/0161383, the entire disclosures of which are incorporated by reference herein. 
         [0022]    The optical elements may include or consist essentially of light-scattering particles such as, e.g., beads, glass beads, or other ceramic particles, rubber particles, silica particles, particles including or consisting essentially of inorganic materials such as BaSO 4  or TiO 2 , particles including or consisting essentially of a phosphor material, and the like. In an embodiment, the light-scattering particles are substantially or even completely non-phosphorescent. Such non-phosphorescent particles merely scatter light without shifting the wavelength of any of the light striking the particles. The term “optical elements” may also refer to non-solid objects embedded in the waveguide, provided that such objects are capable of scattering the light. Representative example of suitable non-solid objects include, without limitation, closed voids within the waveguide, e.g., air bubbles, and/or droplets of liquid embedded within the waveguide. The optical elements may also be organic or biological particles, such as, but not limited to, liposomes. In some embodiments, optical elements such as microlenses are utilized in conjunction with, or even instead of, light-scattering particles. In other embodiments, optical elements include or consist essentially of structures such as hemispheres or diffusive dots. 
         [0023]    In accordance with various embodiments of the invention, the size, type, and/or density of optical elements is selected to provide illumination that is substantially uniform in intensity across the out-coupling region  150  to faciliate omnidirectional light distribution. This need not be the case, however. For example, the density of the optical elements may increase toward the crown of waveguide  125 . 
         [0024]    In various embodiments, at least a portion of the light emitted from LEDs  140  is stimulated by a phosphor or other photoluminescent material disposed within or adjacent out-coupling region  150 . In some embodiments, the optical elements incorporate the phosphor material, and in other embodiments, the phosphor material is present as a discrete layer or region within out-coupling region  150  through which the light propagates prior to being emitted. The phosphor material may even be present within a layer disposed directly on the interior or exterior surface of out-coupling region  150  such that light emitted therefrom is shifted as it passes through the layer. For ease of illustration, the figures show the phosphor  160  as a discrete layer over out-coupling region  150 . As used herein, however, references to a phosphor “surrounding” the out-coupling region connote disposition within and/or on that region—that is, a phosphor embedded within the thickness of out-coupling region  150 , disposed on the interior and/or exterior surface of out-coupling region  150 , or both. 
         [0025]    As used herein, the term “phosphor” refers to any material for converting at least a portion of the light from LEDs  140  into a different color (i.e., changing its wavelength). For example, part of the light from a blue LED may be shifted to yellow light, which mixes with the remaining blue light to provide white output illumination. Additional details regarding phosphor materials and their placement may be found in U.S. Patent Application Nos. 2009/0161341, 2009/0161369, 2009/0161383, 2009/0129115, 2009/0141476, and 2010/0002414, the entire disclosures of which are incorporated by reference herein. Thus, particularly in white-light embodiments, it is ordinarily important for only some of the light from LEDs  140  to interact with the phosphor, so that some unshifted light exists to mix with the wavelength-shifted (converted) light. The ratio between the shifted light and the unshifted light is determined by the phosphor concentration or layer thickness (for a given phosphor material). So long as the concentration or thickness is correctly chosen, proper mixing will occur. In particular, some of the light exiting the exterior surface of light-coupling region  150  will have interacted with the phosphor  160 , and some will not have. Light emitted from the interior surface of light-coupling region  150 —which may be partially shifted or entirely unshifted, depending on where the phosphor  160  is disposed with respect to the in-coupling region—traverses the hollow interior region  132  of lamp  100  and passes through an opposed portion of the out-coupling region (and the phosphor  160  associated therewith). 
         [0026]    As shown in  FIGS. 2A and 3B , a specular or diffusive reflector  200  may be placed across the narrow end of the waveguide  125 , i.e., in the illustrated embodiment, the reflector  200  spans the circular region defined by the base edge of the waveguide. This reflector  200  prevents scattered light from entering and being lost in the lamp base. Alternatively or in addition, a specular or diffusive reflector  210  may cover all or a portion of the interior surface of waveguide  125 . This reflector  210  prevents back-scattered light from the out-coupling region  150  from reaching and passing through the interior region  132  of the lamp  100 , ensuring that all light is emitted directly through the outer surface of out-coupling region  150 . 
         [0027]    Various embodiments of the present invention feature one or more phosphor materials  160  surrounding out-coupling region  150  outside of the direct “line-of-sight” from LEDs  140 . That is, in such embodiments, there is no direct, straight-line optical path between any LED  140  and the phosphor material; rather, light emitted from LEDs  140  reflects from a reflector, a surface, or an interface within the lamp  100  before reaching the phosphor material. Thus, any light striking and being back-reflected from phosphor material  160  will not propagate directly back into a LED  140  (where it could be absorbed, thus reducing overall light output and efficiency of lamp  100 ). Rather, light reflecting from the phosphor material  160  will tend to remain within waveguide  125  until it is emitted through out-coupling region  150 . In some embodiments, there is substantially no direct line-of-sight between any of LEDs  140  and the phosphor material  160 , i.e., less than approximately 5% of the light from LEDs  140  has a direct line-of-sight to the phosphor material; any losses thereof are therefore negligible. 
         [0028]    Whether or not the phosphor material is within a direct line-of-sight of LEDs  140 , the phosphor material  160  may advantageously be located remotely in relation to LEDs  140 . The quantum efficiency (or other performance metric) of the phosphor material may degrade when the material is exposed to elevated temperatures, e.g., temperatures greater than approximately 50° C. Remote placement of the phosphor material  160  prevents the temperature of the material from rising during operation due to, e.g., heat given off by LEDs  140 . Instead, the temperature of remotely placed phosphor material will generally remain at the ambient temperature of the surroundings of lamp  100 . Generally, the temperature of the phosphor material may remain at least approximately 30° C., or even up to approximately 100° C. less than the maximum temperature of LEDs  140  during operation. 
         [0029]    As previously mentioned, discrete light sources  140  may include or consist essentially of one or more LEDs, each of which includes the bare die and all the additional components packed in the LED package. More preferably, LEDs  140  may include or consist essentially of the bare die, excluding one or more of the other components (e.g., reflecting cup, substrate, LED package, and the like). In preferred embodiments of the invention, bare LED dies do not include a phosphor or other photoluminescent material as a portion thereof (e.g., on a common substrate therewith or incorporated into or onto the LED semiconductor layer structure). 
         [0030]    As used herein “bare die” refers to a p-n junction of a semiconductor material. When a forward bias is applied to the p-n junction through electrical contacts connected to the p side and the n side of the p-n junction, the p-n junction emits light with a characteristic spectrum. Thus, in various exemplary embodiments of the invention, LEDs  140  include or consist essentially of only the semiconductor p-n junction and the electrical contacts. Also contemplated are configurations in which several light sources are LEDs, and several light sources are bare dies with electrical contacts connected thereto. 
         [0031]    One advantage of using a bare die rather than a packaged LED is that some of the components in the LED package, including the LED package itself, may absorb part of the light emitted from the p-n junction and therefore reduce the light yield. Another advantage is that the use of a bare die reduces the amount of heat generated during light emission, because heat is generated via absorption of light by the LED package and reflecting cup. The consequent increase in temperature of the p-n junction causes a thermal imbalance that may reduce the light yield. Since the bare die does not include the LED package and reflecting cup, the embedding of a bare die in the waveguide reduces the overall amount of heat and increases the light yield. The elimination of the LED package permits the use of many small bare dies instead of large packaged LEDs. Such a configuration allows the operation of each bare die at low electrical current while still producing a sufficient overall amount of light, thus improving the p-n junction efficacy and/or the lifetime of the LED. 
         [0032]    LEDs  140  may include or consist essentially of multiple LEDs (or bare LED dies), each of which may emit substantially the same or a substantially different color. In the latter case, the light from each of the LEDs may mix within propagation region  145  to form light having a desired color gamut that is emitted from out-coupling region  150 . For example, LEDs  140  may include or consist essentially of one or more red LEDs, one or more green LEDs, and one or more blue LEDs, and the light emitted from out-coupling region  150  may be substantially white. LEDs  140  may also include one or more amber LEDs in such embodiments. 
         [0033]    In one embodiment, the lamp has a luminous flux performance of over 900 μm at a power consumption less than 10 watts, meaning that the lamp&#39;s luminous efficacy is better than 90 lm/w. 
         [0034]    The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.