Abstract:
In accordance with certain embodiments, an illumination device includes a light-emitting diode and a light-guiding optical component comprising a channel therethrough.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/333,043, filed May 10, 2010, the entire disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to optics for lighting systems, and more specifically to optics facilitating thermal dissipation. 
       BACKGROUND 
       [0003]    Discrete light sources such as light-emitting diodes (LEDs) are an attractive alternative to incandescent light bulbs in illumination devices due to their smaller form factor, longer lifetime, and enhanced mechanical robustness. For a wide variety of lighting applications, the light from one or more LEDs is frequently diffused and directed by optics such as total-internal-reflection (TIR) optics. Thus, even though LEDs are effectively omnidirectional point sources of light, the light from LEDs may be propagated through a large area and/or in specific directions. 
         [0004]    Traditionally, optical engineers have designed lenses to obtain a desired illumination pattern from an LED or LED system. Lenses, however, can only collect light within their diameters; light outside the diameter of lens is lost, resulting in the need for further optics to capture such light. TIR optics utilize the principle of total internal reflection—whereby light is reflected at the boundary (or boundaries) of the optic and retained therein—and typically encompass the entire light source, thereby reducing or eliminating optical loss. 
         [0005]    However, the utilization of optics such as TIR optics for LEDs is not without its drawbacks. In addition to light, LEDs typically generate heat during operation, and increased operating temperatures may have negative impacts on the lifetime and/or performance of the LEDs. Furthermore, any light scattered back to the LED by a TIR optic may generate additional heat as it is absorbed by the LED, exacerbating these thermal reliability issues. Since the small form factor of LEDs causes heat to be concentrated in a small area (smaller than, e.g., the surface area of a typical incandescent light bulb), there is a need for methods of cooling and ventilation that facilitate the reliable functioning of illumination devices based on solid-state light sources such as LEDs. 
       SUMMARY 
       [0006]    In accordance with certain embodiments, LED-based illumination devices having ventilated optics are provided. Each optic may be associated with one or more LEDs and contains at least one channel extending therethrough. The channel(s) facilitate the flow of air around and/or past the LED, cooling the LED and substantially eliminating pockets of “dead” (i.e., stagnant or uncirculating) air near the LED. In this manner, deleterious increases in the LED&#39;s operating temperature are avoided and the lifetime and reliability of the LED are enhanced. 
         [0007]    In an aspect, embodiments of the invention feature an illumination device including or consisting essentially of a light-emitting diode and a light-guiding optical component disposed over the light-emitting diode for propagating and directing light from the light-emitting diode. The optical component includes a channel therethrough fluidly connecting the light-emitting diode proximate one end of the channel to an outside ambient at the other end of the channel. 
         [0008]    Embodiments of the invention may include one or more of the following, in any of a variety of combinations. The optical component may be a total-internal-reflection optic. At least a portion of light emitted by the light-emitting diode may propagate directly through the channel without reflection or refraction. At least a portion of light emitted by the light-emitting diode may propagate through the channel via total internal reflection. The non-channel portion of the optical component may conduct, with total internal reflection, at least a portion of light emitted by the light-emitting diode to the emission surface of the optical component opposite the light-emitting diode. Heat produced by the light-emitting diode may convect through the channel into the surrounding ambient. Air drawn in from the surrounding ambient through the channel may convect heat produced by the light-emitting diode. The optical component may be substantially optically transparent. 
         [0009]    The light-emitting diode may be disposed within a cavity in the optical component, and the cavity may have a cross-sectional area larger than the cross-sectional area of the channel. The cavity may include, between the light-emitting diode and the optical component, a gap for enabling flow of air past the light-emitting diode to the surrounding ambient through the channel. The channel may flare outwardly from one end to the other end. At least portions of the light-emitting diode and the optical component may be disposed within a housing. The housing may include a threaded base compatible with an incandescent light fixture (i.e., a fixture for incandescent light bulbs). A diffusive cover may be disposed over at least a portion of the optical component. At least one additional light-emitting diode and associated additional optical component may be disposed in the housing, and the optical component and the additional optical component may direct light out of the housing in substantially the same direction. 
         [0010]    In another aspect, embodiments of the invention feature a method of illumination. Simultaneously, from a light source (e.g., one or more light-emitting diodes) and in an emission direction, a first light portion is propagated through a light-guiding optic, and a second light portion (i.e., different from the first light portion) is propagated through free space. 
         [0011]    Embodiments of the invention may include one or more of the following, in any of a variety of combinations. The first light portion may be refracted or reflected within the light-guiding optic. The first and/or second light portions may be diffused prior to being propagated to the surrounding ambient. Heat from the light source may be convected through the free space through which the second light portion is emitted. Air may be conducted through the free space through which the second light portion is emitted, thereby convecting heat from the light source. The free space through which the second light portion is propagated may include or consist essentially of a channel through the light-guiding optic. The light-guiding optic may include or consist essentially of a total-internal-reflection optic. 
         [0012]    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 
         [0013]    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: 
           [0014]      FIG. 1  is a schematic illustration of a prior-art illumination device incorporating an optic; 
           [0015]      FIG. 2  is a schematic illustration of an illumination device having an optic with a channel therethrough, in accordance with various embodiments of the invention; and 
           [0016]      FIGS. 3 ,  4 , and  5  are, respectively, a perspective view, a front view, and a cross-sectional schematic view of an illumination system in accordance with various embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  depicts a prior-art illumination device  100  that includes an LED  110  and an optic  120 . The LED is typically a packaged LED that includes the LED chip, associated electronics, and a package featuring a lens surrounding the chip. Optic  120  includes a cavity  130  into which the LED  110  is positioned such that substantially all of the light emitted by LED  110  propagates into optic  120  and is confined therein until emerging out its top surface  140 . Problematically, air is generally trapped inside cavity  130  between LED  110  and optic  120 . During operation of LED  110 , the temperature of LED  110  and the trapped air increase dramatically, since air flow out of cavity  130  is difficult or impossible, and the lifetime and reliability of LED  110  are negatively impacted. 
         [0018]      FIG. 2  depicts an illumination device  200  in accordance with embodiments of the present invention. Illumination device  200  includes a discrete light source  210  (interchangeably referred to herein as LED  210 ), which may be one or more packaged LEDs, bare LED chips, LED chips each capped with one or more lenses, packaged or bare laser chips, and/or other solid-state light sources. LED  210  may even include a plurality of any of the foregoing examples together in a single package. LED  210  may emit substantially white light; for example, LED  210  may have a colored output that mixes with a phosphor to produce a white output or may be a combination of colored LEDs (e.g., red, green, and blue) whose emitted light mixes to form substantially white light. In other embodiments, LED  210  emits non-white light, e.g., red, amber, blue, or green light. 
         [0019]    An optic  220  is disposed over LED  210 ; typically, LED  210  is positioned within a cavity  230  formed by a surface of optic  220 . Optic  220  may be a TIR optic, is generally solid (i.e., not hollow except for the presence of one or more channels therewithin, as described below), and may include or consist essentially of a substantially transparent polymeric material (e.g., polycarbonate). Preferably, optic  220  is not completely sealed to LED  210 . Rather, there is preferably at least one opening or gap therebetween to facilitate airflow around and/or past LED  210  (as detailed below). The gap may be created by posts or other spacers (not shown) that elevate optic  220  above LED  210 , or, depending on the design of the illumination system, by the larger fixture retaining both the optic  220  and the LED  210 . 
         [0020]    Optic  220  advantageously features at least one channel  240  that extends through optic  220  from cavity  230  to a top surface  250 . Channel  240  enables the flow of air (or another cooling fluid) past LED  210  through optic  220  and into the surrounding ambient (or vice versa). This convection airflow  260  (depicted in  FIG. 2  as arrows) draws heat away from LED  210  during operation, thus maintaining LED  210  at a lower temperature and enhancing its lifetime and reliability. Although airflow  260  is depicted as flowing upward from LED  210  through channel  240 , it may alternatively or additionally flow in the opposite direction. Airflow  260  may result from natural convection and/or may be driven by one or more active cooling mechanisms such as fans (not shown). During operation of illumination device  200 , the temperature of LED  210  may be between approximately 1° C. and approximately 5° C. cooler due to the presence of channel  240 . In preferred embodiments, channel  240  has a smaller cross-sectional area than that of cavity  230 , and no portion of LED  210  is disposed within channel  240 . Furthermore, preferably (but not necessarily) substantially all of optic  220  is optically transparent, e.g., no reflective or mirror coatings are present on optic  220 . 
         [0021]    In addition to facilitating the cooling of LED  210 , optic  220  enables more efficient light extraction from LED  210  than an optic without channel  240  (such as optic  120 ). With such prior-art optics, all of the light emitted by the LED must pass through the optic to be directed into the outside ambient. Some light may lost in such a process (e.g., due to reflection), decreasing the overall efficiency of the illumination device. In contrast, a portion  270  of the light emitted by LED  210  travels directly through channel  240  rather than the bulk of optic  220 , increasing the efficiency of illumination device  200 . Since channel  240  preferably defines a direct line-of-sight between LED  210  and the emission surface of optic  220  opposite LED  210 , portion  270  of the light emitted by LED  210  travels through channel  240  without reflection or refraction, and another portion of the light (not shown) typically also propagates through channel  240  via internal reflection from the inner surface of channel  240 . Additional light  280  (e.g., light emitted non-vertically in the arrangement of  FIG. 2 ) enters optic  220  and is emitted therefrom as it would from optic  120 . The extraction efficiency may increase (compared to an illumination device having an optic without channel  240 ) by between approximately 1% and approximately 5%. 
         [0022]    Although channel  240  is depicted as cylindrical in shape with a substantially smooth wall, the cross-section of channel  240  may have other shapes and may be nonuniform through its length. For example, channel  240  may flare outward at one or both ends (as shown in  FIG. 5 ). Moreover, there may be more than one channel  240  arranged in a pattern designed to balance the need for airflow against degradation of optical performance. Other configurations are possible and are encompassed by embodiments of the present invention. Furthermore, channel  240  may be utilized in conjunction with or instead of other ventilation paths that may be present in LED-based illumination devices (e.g., in the surrounding opaque housings of such devices). 
         [0023]    Embodiments of the present invention may be utilized in a variety of illumination systems. For example,  FIGS. 3-5  depict an illumination system  300  incorporating six LEDs  210 , each with an associated optic  220 , disposed in a housing  310 . Each optic  220  contains a channel  240 , as detailed above, and may be covered with a diffusive cover  320  (not shown in  FIG. 4 ). Diffusive cover  320  may be disposed over only the channel  240  of an optic  220 , the entire top surface of the optic  220  including the channel  240 , or over multiple (or even all) optics  220  in the illumination system. Preferably, at least in embodiments in which diffusive cover  320  is disposed over channel  240 , diffusive cover  320  is not in direct contact with channel  240 ; rather, there is preferably a gap therebetween, thereby enabling air flow into and/or out of channel  240  as described herein. The gap may be created by posts or other spacers (not shown) that elevate diffusive cover  320  above channel  240 , or, depending on the design of the illumination system, by the larger fixture retaining both the diffusive cover  320  and the channel  240 . In some embodiments, diffusive cover  320  is disposed over portions of one or more optics  220  other than their channel(s)  240 . The diffusive cover  320  may include or consist essentially of a substantially transparent or translucent material, e.g., a polymeric or plastic material, and may be textured (and/or incorporate a pattern of diffusive structures such as dots or hemispheres) in order to scatter and/or redirect light passing therethrough across a wider angle. 
         [0024]    Housing  310  may have the form factor of an incandescent bulb (e.g., the floodlight shape depicted in  FIGS. 3-5 ), e.g., a PAR form factor such as PAR-20, PAR-30, PAR-30S, PAR-30L, or PAR-38. Housing  310  typically also includes a threaded base  330  for compatibility with incandescent fixtures. Housing  310  may also include channels  340  therethrough that are in fluid connection with channels  240  of optics  220 . Thus, air flowing into channels  240  may advantageously flow through channels  340  (or vice versa) and back into the surrounding ambient, dissipating heat along the way. Housing  310  may also house various electronic circuits for control of or power supply to LEDs  210 , e.g., a dimmer, rectifier, and/or transformer, as well as electrical connections thereto. The electrical circuits incorporated within illumination system  200  or  300  may also include thermal foldback circuits such as those disclosed in U.S. patent application Ser. No. 12/881,764, filed Sep. 14, 2010 and/or U.S. patent application Ser. No. 13/092,445, filed Apr. 22, 2011, the entire disclosure of each of which is incorporated by reference herein. Such circuits may advantageously utilize and/or sample the temperature of one or more LEDs  210 , optics  220 , and/or of the air flow through one or more channels  240  or  340  in feedback-based control of the LEDs  210 . 
         [0025]    Illumination system  200  or  300  may be utilized as a replacement for one or more incandescent, halogen, or fluorescent light bulbs, particularly in applications and/or locations where heat dissipation (particularly lateral heat dissipation, i.e., perpendicular to the light-emission axis) is poor. Illumination system  200  or  300  may be utilized in systems utilizing solid-state and/or LED-based lighting, for example, the streetlight systems disclosed in U.S. patent application Ser. No. 12/977,901, filed Dec. 23, 2010, and/or the exterior illumination and/or emergency lighting systems disclosed in U.S. patent application Ser. No. 12/945,364, filed Nov. 12, 2010, the entire disclosure of each of which is incorporated by reference herein. 
         [0026]    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.