Abstract:
An optical element for a lamp or lighting apparatus having at least one light emitting diode (LED) as a light source is provided. The optical element is positioned proximate to the LED and receives light rays therefrom. In turn, the optical element distributes the substantially unidirectional light output from the LED into an omnidirectional output with a controlled variance in light intensity at different directions about the LED. A diffuser can also be used around the optical element and LED to provide further distribution of the light rays by e.g., light scattering.

Description:
FIELD OF THE INVENTION 
     The subject matter of the present disclosure relates generally to lighting devices and, more particularly, to lighting devices using one or more LEDs as a light source and an optical element to provide an improved distribution of light. 
     BACKGROUND OF THE INVENTION 
     Conventional incandescent lamps such as the common A19 bulb size typically provide a relatively uniform distribution of light. Specifically, the intensity of light measured at a fixed distance but at different angles from a centerline axis through the bulb is relatively constant. In addition to consumer appeal, this uniformity may be necessary for certain applications. 
     As compared to incandescent lamps, other types of light emitting devices are available that have certain advantages. For example, light emitting diodes (LEDs) can provide a light output comparable to an incandescent lamp but at a significantly improved energy efficiency. Additionally, the lifetime of an LED lamp can be substantially longer than an incandescent lamp. 
     The LEDs can be configured in a lamp that includes a threaded base (sometimes referred to as an “Edison base”) such that it is interchangeable with conventional incandescent lamps. A diffuser can also be provided that, in addition to light scattering, can provide an LED lamp with a shape similar to that of conventional incandescent lamps. The color and intensity of light provided by the LED can also be similar to incandescent lamps. 
     However, certain challenges remain for the use of non-incandescent lamps. For example, LED lamps require an associated circuit board and generate significantly more heat than an incandescent lamp of comparable light output. In addition, LEDs act close to lambertian sources and thus they alone typically do not provide a uniformly distributed omnidirectional light output. LED devices are usually flat-mounted on a circuit board such that the light output is substantially along a line perpendicular to the plane of the circuit board. 
     As such, the circuit board and heat management features contribute to the optical losses different along each direction causing the non-uniformity of the light distribution from the LEDs. Providing more energy to the LEDs can increase the amount of light output, but still may not provide uniformity. However, this also increases the amount of heat generated, which will degrade LED performance unless additional thermal management is undertaken such as larger cooling features. Yet, the size of the overall lamp may be limited depending upon the intended application or conventional lamp form desired. 
     Accordingly, an optical element or lens for more uniformly distributing the light from a source that includes one or more LEDs or alternatively chip-on-board LED having tightly packed multiple chips together would be useful. More particularly, an optical element that can provide lighting having smaller variations in light intensity but varying angles from the LEDs would be beneficial. A lighting apparatus or lamp incorporating such an optical element would also be useful. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention provides an optical element for a lamp or lighting apparatus having at least one light emitting diode (LED) as a light source. Alternatively the source could be a Chip-On-Board (COB) LED which has closely packed multiple LED dies. The optical element is positioned proximate to the LED and receives light rays therefrom. In turn, the optical element distributes the substantially unidirectional (lambertian) light output from the LED into an omnidirectional output with a controlled variance in light intensity at different locations about the LED. A diffuser can also be used around the optical element and LED to provide further distribution of the light rays by e.g., light scattering. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention. 
     In one exemplary embodiment, the present invention provides a lighting apparatus that includes at least one light emitting diode and an optical element positioned adjacent to the at least one light emitting diode. The optical element defines a central axis and a lateral axis that is substantially orthogonal to the central axis. The optical element extends circumferentially about the central axis and includes a convex light receiving surface that is substantially symmetrical about the central axis and positioned adjacent to the at least one light emitting diode; a frustoconical light projecting surface positioned laterally outside of the convex light receiving surface and substantially symmetrical about the central axis; and an arcuate light reflecting surface positioned laterally inside of the frustoconical light projecting surface and substantially symmetrical about the central axis, the arcuate light reflecting surface spaced apart along the central axis from the convex light receiving surface. 
     In another exemplary embodiment, the present invention provides a lighting apparatus that includes at least one light emitting diode and an optical element positioned adjacent to the at least one light emitting diode. The optical element defines a central axis and a lateral axis that is substantially orthogonal to the central axis. The optical element extends circumferentially about the central axis and includes a light receiving surface that is substantially symmetrical about the central axis and positioned adjacent to the at least one light emitting diode, the light receiving surface forming an acute angle with the central axis; a light projecting surface that is substantially symmetrical about the central axis and spaced apart from the light receiving surface along the central axis; a frustoconical surface connected with the light projecting surface and substantially symmetrical about the central axis; and an arcuate light reflecting surface positioned laterally inside of the frustoconical surface and substantially symmetrical about the central axis, the arcuate light reflecting surface spaced apart along the central axis from the light receiving surface. 
     In still another exemplary embodiment, the present invention provides an optical element for a lighting apparatus having at least one light emitting diode. The optical element for positioning adjacent to the at least one light emitting diode. The optical element defines a central axis and a lateral axis that is substantially orthogonal to the central axis. The optical element extends circumferentially about the central axis. The optical element includes a light receiving surface that extends circumferentially about the central axis and is configured for positioning near the at least one light emitting diode. A frustoconical surface is spaced apart from the light receiving surface along the transverse direction and extends circumferentially about the central axis and is substantially symmetrical about the central axis. An arcuate light reflecting surface is positioned laterally inside of the frustoconical surface and extends circumferentially about the central axis and is substantially symmetrical about the central axis. The optical element is configured so that light from the at least one light emitting diode is emitted from the optical element with variation in light intensity measured at a fixed distance from central axis CA over the range of zero to 135 degrees that is not more than±twenty percent from the average light intensity measured from zero to 135 degrees. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  provides a perspective view of an exemplary embodiment of an optical element of the present invention. 
         FIG. 2  provides a cross-sectioned, perspective view of the exemplary embodiment of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the exemplary embodiment of  FIG. 1  taken along line  3 - 3  of  FIG. 1 . 
         FIG. 4  is a schematic view, along one side of central axis CA, of the exterior surface for the exemplary embodiment of  FIG. 1 . 
         FIG. 5  is a schematic view representing the effect of the exemplary optical element of  FIG. 1  on light rays from certain light sources as further described herein. 
         FIG. 6  is a graph depicting light intensity as a function of position for the exemplary embodiment of  FIG. 1  as will be further described herein. 
         FIG. 7  is a perspective view of another exemplary embodiment of the present invention. 
         FIG. 8  is a perspective view of another exemplary embodiment of an optical element of the present invention. 
         FIG. 9  provides a cross-sectioned, perspective view of the exemplary embodiment of  FIG. 8 . 
         FIG. 10  is a cross-sectional view of the exemplary embodiment of  FIG. 8  taken along line  10 - 10  of  FIG. 10 . 
         FIG. 11  is a schematic view of the exterior surface for the exemplary embodiment of  FIG. 8 . 
         FIG. 12  is a schematic view representing the effect of the optical element of  FIG. 8  on light rays from certain light sources as further described herein. 
         FIG. 13  is a perspective view of the exemplary optical element and LEDs of  FIG. 5  with an exemplary diffuser. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     An exemplary embodiment of a lens or optical element  100  of the present invention is shown in  FIGS. 1 through 4 . The optical element  100 , including certain surfaces as will be further described, is substantially symmetrical about a central axis CA and extends along circumferential direction C about central axis CA. For purposes of further describing this exemplary embodiment of the invention, optical element  100  defines a lateral direction L that extends substantially orthogonal to central axis CA. Optical element  100  may comprise a light transmissive material such as e.g., a glass, a polymer such as polycarbonate or an acrylic, or other light transmissive materials. 
     Optical element  100  includes a convex light receiving surface  102 . In a lighting apparatus such as a lamp, convex light receiving surface  102  would be positioned adjacent to, or in close proximity to, one or more LEDs and would allow light rays from such light source(s) to travel into optical element  100  ( FIG. 5 ). Convex light receiving surface  102  extends circumferentially, and is substantially symmetrical about, central axis CA. As indicated in  FIG. 4 , for this exemplary embodiment, convex light receiving surface is defined by a radius R 1  of about 11.75 mm. Other values for radius R 1  may be used as well. 
     Convex light receiving surface  102  is part of a cylindrical portion  110  of optical element  102 . Cylindrical portion  110  includes a cylindrically-shaped surface  108  that is linear when viewed along the cross-section shown in  FIG. 3 . The length of cylindrical portion  110  along central axis CA may be varied to yield still other embodiments of the present invention. 
     Optical element  100  also includes a trumpet-shaped portion  112  that is adjacent to cylindrical portion  110  along the direction of central axis CA. Trumpet-shaped portion  112  includes frustoconical light projecting surface  104  that is positioned laterally outside of convex light receiving surface  102 . Surface  104  extends circumferentially around, and is substantially symmetrical about, central axis CA of optical element  100 . As shown in  FIG. 4 , for this exemplary embodiment, frustoconical light projecting surface  104  forms an acute angle with central axis CA and forms an angle θ 6  with respect to lateral direction L. In one exemplary embodiment, angle θ 6  form an angle in the range of about 50 degrees to about 70 degrees from lateral direction L. In another exemplary embodiment, angle θ 6  is about 60 degrees. 
     Trumpet-shaped portion  112  also includes an arcuate light reflecting surface  114  that is positioned laterally inside of frustoconical light projecting surface  104 . Surface  114  extends circumferentially around, and is substantially symmetrical about, central axis CA of optical element  100 . Although shown as free form curve, arcuate light reflecting surface  114  can also be described with reference to angles θ 1 , θ 2 , θ 3 , θ 4 , and θ 5  of  FIG. 4 . Each such angle θ i , represents the angle relative to lateral direction L of a line tangent to surface  114  at locations  10 ,  20 ,  30 ,  40 , and  50 . Locations  10 ,  20 ,  30 ,  40 ,  50  lie in a plane that includes central axis CA and lateral direction L and are spaced apart from each at equal distances along surface  114 . 
     For one exemplary embodiment, θ 1  is about 63 degrees, θ 2  is about 38 degrees, θ 3  is about 24 degrees, θ 4  is about 19 degrees, and  74   5  is about 14 degrees. In still another exemplary embodiment, θ 1  is in the range of about 50 degrees to about 70 degrees, θ 2  is in the range of about 30 degrees to about 50 degrees, θ 3  is in the range of about 20 degrees to about 30 degrees, θ 4  is in the range of about 10 degrees to about 30 degrees, and θ 5  is in the range of about 10 degrees to about 30 degrees. Other shapes may be used for arcuate light reflecting surface  114  as well. 
     As shown in  FIGS. 1 through 3 , optical element  100  also includes a planar light projecting surface  106  that lies in a plane substantially perpendicular to central axis CA and substantially parallel to lateral axis L. Planar light projecting surface  106  is connected with frustoconical light projecting surface  104  at an edge  116  that extends circumferentially about central axis CA and is substantially symmetrical about central axis CA. Planar light projecting surface  106  is also connected with arcuate light reflecting surface  114  at an edge  118  that extends circumferentially about central axis CA, is substantially symmetrical about central axis CA, and is positioned laterally inward of edge  116 . Edge  118  is coincident with location  50  ( FIG. 4 ). 
     Optical element  100  includes a conically-shaped surface  122  that is configured in a substantially symmetrical manner about central axis CA and is connected to arcuate light reflecting surface  114  at edge  124 . As shown, surface  122  opens along central axis CA in the direction of zero degrees. Edge  124  is coincident with location  10 . 
     Arcuate light reflecting surface  114  may be covered or coated with a highly reflective material different than the material used for the construction of body  120  of optical element  100 . For example, surface  114  may be metallized or covered with a coating of e.g., aluminum, silver, or other reflective metal. Other materials and/or techniques may be used as well. Similarly, conically-shaped surface  122  may also be covered or coated with a highly reflective material different than the material used for the construction of body  120 . 
       FIG. 5  represents the simulated results obtained by placing optical element  100  closely adjacent to three light sources comprising LEDs  115 ,  117 , and  119 . Alternatively, multiple light sources can be replaced by a chip-on-board (BOC) LED having multiple dies. By way of example, light rays  126  pass through convex light receiving surface  102 , pass through the material of body  120 , and are reflected off of arcuate light reflecting surface  114  at different angles. Light rays  128  pass through convex light receiving surface  102  and then pass through conically-shaped surface  122  at different angles. Some light rays  130  pass through convex light receiving surface  102  and then exit optical element  100  through planar light projecting surface  106 . 
     A lighting apparatus incorporating optical element  100  and one or more LEDs  115 ,  117 , and  119  positioned adjacent thereto may also include a diffuser  136  as shown in  FIG. 13 . More particularly, diffuser  136  may be placed around optical element  100  to provide further scattering of the lights rays from the LED(s) and optical element  100  as will be understood by those skilled in the art. Diffuser  136  may, for example, by a constructed from a diffusive plastic material with low light absorption losses or as a glass bulb containing a phosphor and positioned around optical element  100  and one or more LEDs. Diffuser  136  may e.g., connect to heat sink and/or threaded (e.g., Edison) base (not shown). 
     Optical element  100  is configured to provide a more uniform distribution of light than is available from an LED light source, which provides substantially a single direction light output. More specifically,  FIG. 6  provides a simulated plot of light intensity (e.g., in candela) as a function of vertical angle from central axis CA for optical element  100 . Using lamp  133  for example, the plot represents the light intensity at angles from zero degrees to 180 degrees from central axis CA as shown (zero degrees and 180 degrees being coincident with central axis CA). As depicted in  FIG. 6 , for the exemplary embodiment of optical element  100 , the surfaces described above are configured so that the variation in light intensity measured at any distance from central axis CA over the range of zero to 135 degrees is not more than±twenty percent from the average light intensity measured from zero to 135 degrees. In another exemplary embodiment, such variation in light intensity is not more than±ten percent from the average light intensity at angles measured from zero to 150 degrees. 
       FIG. 7  provides a perspective view of another exemplary embodiment of an optical element  200  of the present invention similar to the exemplary embodiment of  FIGS. 1-4  in that it includes convex light receiving surface  102 , frustoconical light projecting surface  204 , and arcuate light reflecting surface  214 . However, optical element  200  includes curved flutes  232  on light projecting surface  206  that extend in a substantially symmetrical manner about central axis CA and are circumferential about central axis CA. Additionally, a circular surface  236  located at central axis CA also includes a plurality of flutes  238  that extend in a substantially symmetrical manner about central axis CA and are circumferential about central axis CA. Flutes  232  and  238  provide additional light scattering. Other surface features such as e.g., pillows may also be used to provide additional light scattering. 
     Another exemplary embodiment of an optical element  300  of the present invention is shown in  FIGS. 8 ,  9 ,  10 , and  11 .  FIG. 12  illustrates this exemplary embodiment in conjunction with LEDs  315 ,  317 , and  319 . Optical element  300 , including certain surfaces as will be further described, is substantially symmetrical about a central axis CA and extends along circumferential direction C about central axis CA. For purposes of further describing this exemplary embodiment of the invention, optical element  300  also defines a lateral direction L that extends substantially orthogonal to central axis CA. Optical element  300  is constructed from a light transmissive material such as e.g., a glass, a polycarbonate, an acrylic, or other light transmissive materials. 
     Optical element  300  includes a disc-shaped portion  310  and a trumpet-shaped portion  312 . Disc-shaped portion  310  includes a light receiving surface  302 . As shown, surface  302  is conical in shape and forms an acute angle with the central axis CA. However, light receiving surface  302  could also be curved in a convex manner. In a lighting apparatus such as a lamp, light receiving surface  302  would be positioned adjacent to, or in close proximity to, one or more LEDs and would allow light rays from such light source(s) to travel into optical element  300  ( FIG. 12 ). Light receiving surface  302  extends circumferentially, and is substantially symmetrical about, central axis CA. 
     Disc-shaped portion  310  includes a cylindrically-shaped surface  308  that is linear when viewed along the cross-section shown in  FIG. 10 . The length of disc-shaped portion  310  along central axis CA may be varied to yield still other embodiments of the present invention. A light projecting surface  338  is connected to surface  308  and spaced apart from light receiving surface  302  along the direction of the central axis CA as shown. For the exemplary embodiments shown, light projecting surface  338  is frustoconical in shape. However, surface  328  may also be arcuate or convex in other embodiments of the invention. As shown in  FIG. 11 , for this exemplary embodiment, surface  338  forms an obtuse angle with central axis CA and forms an acute angle α 8  with respect to lateral direction L. In one exemplary embodiment, angle α 8  is about 25 degrees. In another exemplary embodiment, angle α 8  is in the range of about 20 degrees to about 30 degrees. 
     Trumpet-shaped portion  312  is adjacent to disc-shaped portion  310  along the direction of central axis CA. Trumpet-shaped portion  312  includes frustoconical surface  304  that connected with light projecting surface  338 . Surface  304  extends circumferentially around, and is substantially symmetrical about, central axis CA of optical element  300  and is spaced apart along central axis CA from surface  338 . As shown in  FIG. 11 , for this exemplary embodiment, frustoconical surface  304  forms an acute angle with central axis CA and forms an angle α 7  with respect to lateral direction L. In one exemplary embodiment, angle α 7  is about 28 degree from lateral direction L. In another exemplary embodiment, angle α 7  is in the range of about 23 degrees to about 33 degrees from lateral direction L. 
     Trumpet-shaped portion  312  also includes an arcuate light reflecting surface  314  that is positioned laterally inside of frustoconical surface  304 . Surface  314  extends circumferentially around, and is substantially symmetrical about, central axis CA of optical element  300 . Although shown as free form curve, arcuate light reflecting surface  314  can also be described with reference to angles α 2 , α 3 , α 4 , α 5 , and α 6  of  FIG. 11 . Each such angle α i , represents the angle relative to lateral direction L of a line tangent to surface  314  at locations  10 ,  20 ,  30 ,  40 , and  50  as shown in  FIG. 11 . Locations  10 ,  20 ,  30 ,  40 ,  50  lie in a plane that includes central axis CA and lateral direction L and are spaced apart from each at equal distances along surface  314 . 
     For one exemplary embodiment, α 2  is about 51 degrees, α 3  is about 43 degrees, α 4  is about 33 degrees, α 5  is about 23 degrees, and α 6  is about 15 degrees. In still another exemplary embodiment, α 2  is in the range of about 46 degrees to about 56 degrees, α 3  is in the range of about 38 degrees to about 48 degrees, α 4  is in the range of about 28 degrees to about 38 degrees, α 5  is in the range of about 18 degrees to about 28 degrees, and α 6  is in the range of about 10 degrees to about 20 degrees. Other shapes may be used for surface  114  as well. 
     As shown in  FIGS. 10 and 11 , optical element  300  also includes a pair of adjacent frustoconical surfaces  340  and  342  that are substantially symmetrical about central axis CA and extend circumferentially about central axis CA. Surface  340  and  342  are connected between arcuate light reflecting surface  314  and frustoconical surface  304 . 
     Optical element  300  includes a conically-shaped surface  322  that is located in a substantially symmetrical manner along central axis CA and is connected to arcuate light reflecting surface  314  at edge  324 . As shown, surface  322  projects along central axis CA in the direction of zero degrees. Edge  324  is coincident with location  10 . 
     Arcuate light reflecting surface  314  may be covered or coated with a highly reflective material different than the material used for the construction of body  320  of optical element  300 . For example, surface  314  may be metallized or covered with a coating of e.g., aluminum, silver, or other reflective metal. Other materials and/or techniques may be used as well. Similarly, conically-shaped surface  322  may also be covered or coated with a highly reflective material different than the material used for the construction of body  320 . 
       FIG. 12  represents the simulated results obtained by placing optical element  100  closely adjacent to three light sources comprising LEDs  315 ,  317 , and  319 . By way of example, light rays  326  pass through light receiving surface  302 , pass through the material of body  120 , through surfaces  338  and  304 , and are reflected off of arcuate light reflecting surface  314  at different angles. Light rays  328  pass through light receiving surface  302  and then pass through conically-shaped surface  322  at different angles. Some light rays  330  pass through light receiving surface  102  and then exit optical element  300  through one or both of the pair of frustoconical surfaces  340  and  342 . 
     A lighting apparatus incorporating optical element  300  and one or more LEDs  115 ,  117 , and  119  positioned adjacent thereto may also include a diffuser similar to diffuser  136  shown in  FIG. 13  with the exemplary embodiment  100 . Optical element  300  is equipped with a plurality of legs  344  that may be used to position and support element  300 . 
     As with previous embodiments, optical element  300  is configured to provide a more uniform distribution of light than is available from an LED light source. In a manner similar to that discussed above using  FIG. 6 , optical element  100  and the surfaces described above are configured so that the variation in light intensity measured at different angles from central axis CA over the range of zero to 135 degrees is not more than±twenty percent from the average light intensity measured at such fixed distance from zero to 135 degrees. In another exemplary embodiment, such variation in light intensity is not more than±ten percent from the average light intensity. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.