Abstract:
An optical device for a semiconductor based lamp comprises a semiconductor based light-emitting device and a light-redirecting member. The light-redirecting member has a reflective surface that redirects at least some of the light emitted from the semiconductor-based light-emitting device ambiently, away from the lamp, and into the surrounding environment in divergent lateral and at least partially downward directions, without further reflection. A frosted semi-transparent cover encloses the light-emitting device and light-redirecting member. A gap between the semi-transparent cover and an outer edge of the light-redirecting member passes some of the light emitted from the semiconductor-based light-emitting device upwardly into a surrounding environment.

Description:
RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. patent application Ser. No. 13/665,281, filed Oct. 31, 2012 and entitled “Optical Device for Semiconductor Based Lamp,” which is a continuation of U.S. Pat. No. 8,324,645, issued Dec. 4, 2012, also entitled “Optical Device for Semiconductor Based Lamp,” both of which are herein incorporated by reference for all purposes. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to electrical lighting devices, and, more particularly, to an electrical lighting device utilizing light emitting diodes (LEDs). 
         [0003]    A light-emitting diode (LED) is a semiconductor diode based light source. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. When used as a light source, the LED presents many advantages over incandescent light sources. These advantages include lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. 
         [0004]    However, the LED as a light source has its disadvantages. One of the disadvantages is that the light emitted from a LED chip concentrates in a direction normal or perpendicular to the surface of the LED chip. That is, LED light is strong in the upright direction and drastically diminished in the sideway directions. In order to make a LED light more like a traditional incandescent light source with uniform light emitting intensity in all directions, reflectors have been used to redirect the LED beam from upright to sideways. However, redirecting light merely sacrifices light in the upright direction in favor of sideway directions and may not be an efficient uniform wide-angle light source. 
         [0005]    As such, what is desired is a LED light bulb that can uniformly emit light in most directions from the LED chip. 
       SUMMARY 
       [0006]    One embodiment of an optical device for a semiconductor based lamp comprises a semiconductor based light-emitting device and a light-redirecting member. The light-redirecting member has a reflective surface that redirects at least some of the light emitted from the semiconductor-based light-emitting device ambiently, away from the lamp, and into the surrounding environment in divergent lateral and at least partially downward directions, without further reflection. The light-redirecting member also passes some of the light emitted from the semiconductor-based light-emitting device upwardly into a surrounding environment. 
         [0007]    In one embodiment, the reflective surface is approximately conical and has an opening, where the approximately conical reflective surface surrounds the opening. A vertex angle defined by the approximately conical reflective surface is relatively narrower for a first portion of the light-redirecting member near a base of the light-redirecting member than for a second portion of the light-redirecting member far from the base of the light-redirecting member. In another embodiment, both vertical and horizontal cross-sections of the approximately conical reflective surface are curved. 
         [0008]    In yet another embodiment, a frosted semi-transparent cover enclosing the light-emitting device and light-redirecting member. A gap between the semi-transparent cover and an outer edge of the light-redirecting member passes some of the light emitted from the semiconductor-based light-emitting device upwardly into a surrounding environment. 
         [0009]    Another embodiment of an optical device for a semiconductor based lamp comprises a semiconductor based light-emitting device and a light-redirecting member. The light-redirecting member has a reflective surface that redirects at least some of the light emitted from the semiconductor-based light-emitting device ambiently, away from the lamp, and into the surrounding environment in divergent lateral and at least partially downward directions, without further reflection. A frosted semi-transparent cover encloses the light-emitting device and light-redirecting member. Furthermore, a gap between the semi-transparent cover and an outer edge of the light-redirecting member passes some of the light emitted from the semiconductor-based light-emitting device upwardly into a surrounding environment. The optical device radiates light broadly and divergently about the optical device into the surrounding environment, including generally upward, lateral, and at least partially downward directions. 
         [0010]    In one embodiment, the reflective surface is approximately conical. The light-redirecting member has an opening. The approximately conical reflective surface surrounds the opening. In another embodiment, both vertical and horizontal cross-sections of the approximately conical reflective surface are curved. A vertex angle defined by the approximately conical reflective surface is relatively narrower for a first portion of the light-redirecting member near a base of the light-redirecting member than for a second portion of the light-redirecting member far from the base of the light-redirecting member. 
         [0011]    The construction and method of operation of the invention together with additional objectives and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The drawings accompanying and forming part of this specification are included to depict certain aspects of the invention. A clearer conception of the invention, and of the components and operation of systems provided with the invention, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings, wherein like reference numbers (if they occur in more than one view) designate the same elements. The invention may be better understood by reference to one or more of these drawings in combination with the description presented herein. 
           [0013]      FIG. 1  is a perspective view of an optical device for a LED lamp according to an embodiment of the present invention. 
           [0014]      FIG. 2  illustrates the working mechanism of the optical device shown in  FIG. 1 . 
           [0015]      FIG. 3  illustrates dimensional considerations of the optical device for achieving a uniform light dispersion pattern. 
           [0016]      FIGS. 4A-4G  illustrate several alternative light redirecting features that can be applied to the LED lamp of  FIG. 1 . 
           [0017]      FIGS. 5A and 5B  illustrate simulation results of the LED lamps based on  FIG. 5C and 5D  of the present invention. 
       
    
    
     DESCRIPTION 
       [0018]    The present invention discloses an optical device for semiconductor based lamp. The optical device spreads semiconductor based lamp&#39;s directional light to directions of a wide angle, so that the light emitting pattern of the semiconductor based lamp resembles that of a traditional incandescent light bump. 
         [0019]      FIG. 1  is a perspective view of an optical device  100  for a LED lamp according to an embodiment of the present invention. The optical device  100  comprises a base  110  on which a LED device  115  is mounted. The LED device  115  can be formed in a single semiconductor substrate or by an array of LEDs. A cone-shaped light-redirecting member  120  is secured to the base  110  by three legs  130 . The legs  130  may be on the outside of or under the light redirection member  120 . The legs  130  may be knife-shaped with knife edge toward a central axis of the light redirection member  120  to avoid light shielding. Or, the legs  130  may be made of thin wires to avoid light shielding. Using metal to construct the light-redirecting member  120  and the mounting legs  130  has a benefit of better dissipating heat generated by the LED device  115 . 
         [0020]    Referring to  FIG. 1  again, the light-redirecting member  120  has an opening  125  in the center thereof. The opening  125  is positioned directly above the LED device  115 . 
         [0021]      FIG. 2  illustrates the working mechanism of the optical device  100  shown in  FIG. 1 . A diameter of the opening  125  is smaller than a diameter of the semiconductor device  115 . Light beams  210  emitted from the center of the LED device  115  goes right through the opening  125 . Light beams  221   a,    222   a,    223   a,    224   a  emitted from the peripheral area of the LED device  115  are reflected by the cone-shaped light-redirecting member  120  into lateral beams  221   b,    222   b,    223   b,    224   b.  Therefore, the optical device  100  allows both the upright light beams  210  and lateral beams  221   b,    222   b,    223   b,    224   b  to be emitted from the LED device  115 . 
         [0022]    Furthermore,  FIG. 2  shows the light beams  223   a  and  224   a  that in a normal angle to the surface of the LED device  115 . The LED device  115  also emits light beams  221   a  and  222   a  in off-normal directions albeit not as intense as the normal directional beams  223   a  and  224   a.  A sum of these light beams, both normal ( 223   a  and  224   a ) and off-normal ( 221   a  and  222   a ), provides a light source that has a relatively uniform dispersion pattern in more directions from the LED device  115 . 
         [0023]      FIG. 3  illustrates dimensional considerations of the optical device  100  for achieving a uniform light dispersion pattern. A height H of the optical device  100  is measured from the top of the light-redirecting member  120  to the bottom of the LED device  115 . A width F of the optical device  100  is generally measured as a diameter of the light-redirecting member  120 . In order to retrofit the optical device  100  into a limited space of a traditional incandescent light bulb, a ratio of the height H to the diameter D of the LED device  115 , i.e., H over D, and the width F to the diameter D of the LED device  115 , i.e., F over D, must both be less than four. The above ratios can be more critical when the diameter D of the LED device  115  is equal to or above one forth of the bulb diameter. In generally, a ratio between a diameter F of the light-redirecting member  120  and a diameter D of the LED device  115  is between 0.7 and 2. A ratio between a diameter E of the opening  125  and the diameter D of the LED device  115  should be less than 0.7. Although not shown in  FIG. 3 ,  FIG. 1  shows that the LED device  115  is mounted on the base  110 . Preferably the dimension of the base  110  is larger than that of the LED device  115 . 
         [0024]      FIG. 4A-4G  illustrate several alternative light redirecting features that can be applied to the LED lamp  100  of  FIG. 1 . Referring to  FIG. 4A , the light-redirecting member  120  is comprised of a cone-shaped plate structure  410  made of a material of plastic, glass or metal. A reflective layer  412  is then plated on the bottom of the plate structure  410 . 
         [0025]    Alternatively,  FIG. 4B  illustrates a solid structure  420  with cone-shaped surface plated with a reflective layer  412 . The solid structure  420  preserve the opening  125  for allowing light to be directly emitted in the upright direction. 
         [0026]    Referring to  FIG. 4C , the light-redirecting member  403  comprises a flat ring  430  surrounding the center opening  125 . A reflective surface follows the contours of the bottom surfaces  412  and  430 . 
         [0027]    Referring to  FIG. 4D , the light-redirecting member  404  comprises a bottom facing reflective surface  440  as an outer ring of the reflective surface  412 . With the addition of the bottom facing reflective surface  440 , some of the light beams, such as  442 , is re-directed downward. As a result, light emitting pattern from such light-redirecting member  120  is more of a global pattern. 
         [0028]    Referring to  FIG. 4E , a main portion of the reflective surface  450  is approximately horizontally positioned, so that more emitted light will be reflected downward. Slanted surface  452  surrounding the horizontal reflective surface  450  makes more light to be reflected downward. 
         [0029]    Referring to  FIG. 4F , the LED device  115  is raised by a protruding member  460 . The protruding member  460  has side reflective surfaces  462 . A light beam  465  is reflected twice, once by the bottom facing reflective surface  440  and the other by the side reflective surface  462 . Such structure is also instrumental for achieving a more global light-emitting pattern. 
         [0030]    Referring to  FIG. 4G , a frosted semi-transparent cover  470  encloses a LED light source with the light-redirecting member  120  for further enhancing the uniformity of emitted light intensity. Such LED light source more resembles a traditional incandescent light bulb. Moreover, the light-redirecting member  120  passes light upwardly not only through the opening  125  but also through a space  126  between the distal edge of the light-redirecting member  120  and the frosted semi-transparent cover  470 . 
         [0031]      FIGS. 5A and 5B  illustrate simulation results of the LED lamps based on  FIG. 5C and 5D  of the present invention. Referring to  FIG. 5A , circular polar plot  500  shows far-field distribution (light intensity distribution)  502  and  504  on circular angular scale  506 , with off-axis angle, with zero denoting the on-axis direction, and 180 degree the opposite direction, totally backward. This is possible for those preferred embodiments having some sideways extension so that 180 degree is unimpeded by the source. Referring to  FIG. 5C , a diameter of the LED device  115  is 20 mm. A width of the light-redirecting member  405  is 32 mm. A diameter of the opening  125  of the light-redirecting member  405  is 12 mm. A distance between a top of the light-redirecting member  405  and the surface of the LED device  115  is 8 mm. The far-field distribution  502  shows that light intensity below the LED device  115  has fairly large intensity. The far-field distribution  504  shows that light is also emitted to above the LED device  115 . 
         [0032]    Referring to  FIG. 5B , far-field distribution  520  is obtained when a frosted cover  570  similar to the frosted cover  470  of  FIG. 4G  is applied as shown in  FIG. 5D . The far-field distribution  522  shows that the light emitting pattern is close to a circle which means that light is emitted from the LED lamp uniformly in all directions. 
         [0033]    The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims. 
         [0034]    Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims.