Abstract:
This invention discloses an optical device for a semiconductor based lamp, the optical device comprising a base for mounting a semiconductor based light-emitting device thereon, a transparent body encapsulating the semiconductor based light-emitting device, and a reflective surface covering a predetermined region on a top of the transparent body, the reflective surface having an opening exposing the transparent body, wherein light emitted from the semiconductor based light-emitting device transmits through the opening of the reflective surface.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to electrical lighting devices, and, more particularly, to an electrical lighting device utilizing light emitting diodes (LEDs). 
         [0002]    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. 
         [0003]    However, LED as 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, i.e., 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 has 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. 
         [0004]    As such, what is desired is a LED light bulb that can uniformly emit light in most directions from the LED chip. 
       SUMMARY 
       [0005]    This invention discloses an optical device for a semiconductor based lamp, the optical device comprising a base for mounting a semiconductor based light-emitting device thereon, a transparent body encapsulating the semiconductor based light-emitting device, and a reflective surface covering a predetermined region on a top of the transparent body, the reflective surface having an opening exposing the transparent body, wherein light emitted from the semiconductor based light-emitting device transmits through the opening of the reflective surface, meanwhile the reflective surface redirects some of the emitted light to lateral downward and in between directions. 
         [0006]    The construction and method of operation of the invention, however, 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 
         [0007]    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. 
           [0008]      FIG. 1  is a cross-sectional view of an optical device  100  for a semiconductor based lamp according to an embodiment of the present invention. 
           [0009]      FIG. 2  illustrates the working mechanism of the optical device shown in  FIG. 1 . 
           [0010]      FIG. 3A  illustrates light travel paths in the optical device  100  shown in  FIG. 1 . 
           [0011]      FIG. 3B  illustrates an addition to the optical device  100  shown in  FIG. 1  and associated light travel paths therein. 
           [0012]      FIGS. 4A and 4B  illustrate some design variations from the optical device  100  shown in  FIG. 1 . 
           [0013]      FIGS. 5A-5D  illustrate simulation results of the LED lamps of the present invention. 
       
    
    
     DESCRIPTION 
       [0014]    The present invention discloses an optical device for a 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. 
         [0015]      FIG. 1  is a cross-sectional view of an optical device  100  for a semiconductor based lamp according to an embodiment of the present invention. The optical device  100  comprises a semiconductor based light emitting device  110  mounted on a base  120 . A common type of the semiconductor based light emitting device  110  is light-emitting diodes (LEDs). The light emitting device  110  can be formed by either one LED or an array of LEDs. The light emitting surface of the light emitting device  110  is encapsulated by a transparent body  130 . A reflective surface  140  is then formed on the top of the transparent body  130 . The reflective surface  140  may have a slanted region  142  at an outer ring of the reflective surface  140 . Optimally the reflective surface  140  is part of the top surface of the transparent body  130  that mirror reflects light from the light-emitting device  110  to a wide angle with high light intensity. The reflective surface  140  can be formed by plating a metal layer or by adhering a thin layer of sheet metal on top of the transparent body  130 . 
         [0016]    Referring to  FIG. 1  again, the reflective surface  140  has an opening  145  that exposes approximately center portion of the transparent body  130  and hence center area of the light emitting device  110 . The opening  145  allows light from the light-emitting device  110  to shine directly out of the transparent body  130 . 
         [0017]    As shown in  FIG. 1 , a boundary  135  of transparent body  130  in the opening  145  area has a special concave contour, which is designed, together with the reflective surface  140 , to reflect some of the light from the light-emitting device  110  to lateral directions due to an optical phenomenon called “total internal reflection”. 
         [0018]      FIG. 2  illustrates the mechanism of the total internal reflection. When light crosses a boundary  202  between materials with different refractive indices (n 1  and n 2 ), the light beam  210  will be partially refracted  218  at the boundary surface  202 , and partially reflected  215 . However, if the angle of incidence θ2 is greater (i.e. the ray is closer to being parallel to the boundary) than a critical angle—the angle of incidence at which light is refracted such that it travels along the boundary—then the light  220  will stop crossing the boundary  202  altogether and instead be totally reflected back  225  internally, i.e. total internal reflection occurs. This can only occur where light travels from a medium with a higher (n 1 =higher refractive index) to one with a lower refractive index (n 2 =lower refractive index). For example, it will occur when passing from glass to air, but not when passing from air to glass. The material for making the transparent body  130  can be glass or transparent polymer, such as acrylics, polycarbonate, poly (vinyl chloride), polyethylene terephthalate (PET). 
         [0019]      FIG. 3A  illustrates light travel paths in the optical device  100  shown in  FIG. 1 . Referring to  FIG. 3A , a light beam  310  emitted from the outer area of the light-emitting device  110  hits the boundary  135  with a small angle of incidence, some of the light  310  is refracted into a light beam  315 . Such refractive light  315  is the light that is transmitted directly from the light-emitting device  110 . 
         [0020]    Referring to  FIG. 3  again, another light beam  320  emitted from the center area of the light-emitting device  110  hits the boundary  135  with a large angle of incidence to incur total internal reflection. As a result, the light beam  320  bounces off the boundary  135  and then the reflective surface  140  and is transmitted out of the transparent body  130  in a lateral direction as a light beam  325 . Apparently the contour design of the boundary  135  along with the size of the opening  145  determines the amount of the light transmitted directly to the upright direction—represented by the light beam  315 , and the amount of the light transmitted to the lateral direction—represented by the light beam  325 . In general, the size of the opening  145  is smaller than that of the light-emitting device  110 . 
         [0021]      FIG. 3B  illustrates an addition to the optical device  100  shown in  FIG. 1  and associated light travel paths therein. Referring to  FIG. 3B , the light emitting device  100  is alleviated by a platform  360 . The platform  360  has slanted, reflective side walls  365 . A light beam  330  hitting the reflective surface  140  is reflected into a lateral lighting beam  335 . Another light beam  350  hitting the slanted region  142  of the reflective surface  140  is reflected downward thereby and then reflected again by the reflective side wall  365  of the platform  360 , and ends up with a lateral light beam  355  with less downward angle. 
         [0022]      FIGS. 4A and 4B  illustrate some design variations from the optical device  100  shown in  FIG. 1 . Referring to  FIG. 4A , an optical device  400  has the same light emitting device  110  as the optical device  100  of  FIG. 1 . But a transparent body  430  that encapsulates the light emitting device  110  has a center are protruding from an opening of a reflective surface  440 . A cross-section of the protruding center area presents two convex regions  432  bordered by boundaries  435  and  437 . The boundary  435  faces away from the center, and is exemplarily designed to be straight. The boundary  437  faces toward the center, and is exemplarily designed to be curved. A light beam  460  is total-internal reflected by the curved boundary  437  into a light beam  465  out of the transparent body  430 . Apparently, the curved boundary  437  functions the same as the concave boundary  135  as shown in  FIG. 3A . A light beam  450  is refracted through the straight boundary  435  into a light beam  455 . With both the boundaries  435  and  437  controllable, light emitting pattern of the optical device  400  can be more optimized. 
         [0023]    Referring to  FIG. 4B , the optical device  400  has a frosted semi-transparent cover  480  that encloses the entire optical device  400 . The frosted semi-transparent cover  480  enhances the uniformity of the emitted light. 
         [0024]      FIGS. 5A and 5B  illustrate simulation result of the LED lamp based on  FIG. 3B  of the present invention. Referring to  FIG. 5A , a 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 back to  FIG. 3B , a diameter of the LED device  110  is 20 mm. A diameter of the transparent body  130  is 38 mm. A distance between a top of the transparent body  130  and the surface of the LED device  110  is 8 mm. The far-field distribution  502  shows that light intensity below the LED device  110  has fairly large intensity. The far-field distribution  504  shows that light is also emitted to above the LED device  110 . 
         [0025]    Referring to  FIG. 5B , a far-field distribution  520  is obtained when a frosted cover similar to the frosted cover  480  shown in  FIG. 4B  is placed over the LED lamp of  FIG. 3B . 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. 
         [0026]      FIGS. 5C and 5D  illustrate simulation results of the LED lamps based on  FIGS. 4A and 4B  of the present invention. Referring to  FIG. 5C , circular polar plot  540  shows far-field distribution (light intensity distribution)  542  and  544  on circular angular scale  506 , with off-axis angle, with zero denoting the on-axis direction, and 180 degree the opposite direction, totally backward. Referring to  FIG. 4A , a diameter of the LED device  110  is 20 mm. A diameter of the transparent body  130  is 38 mm. A distance between a top of the transparent body  130  and the surface of the LED device  110  is 11.83 mm. The far-field distribution  542  shows that light intensity at about 135 and 225 degree angle above the LED device  110  is very high. The far-field distribution  544  shows that light is also emitted to above the LED device  110 . 
         [0027]    Referring to  FIG. 5D , a far-field distribution  560  is obtained when the frosted cover  480  is placed over the LED lamp as shown in  FIG. 4B . The far-field distribution  562  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. 
         [0028]    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. 
         [0029]    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.