Patent Publication Number: US-2007114549-A1

Title: Light-emitting diode

Description:
1. FIELD OF THE INVENTION  
      The present invention relates generally to light-emitting devices and more particularly to a light-emitting diode (LED)  
     2. DESCRIPTION OF RELATED ART  
      At present, fluorescence lamps are popularly used as illumination tools. However the mercury used in the fluorescence lamps represents a great danger to environment when the fluorescence lamps are damaged and/or reclaimed, and many researchers have suggested using LEDs to replace them. This would also have the advantage of greater convenience as the lifespan of the LEDs is longer than that of the fluorescent lamps and the LEDs would therefore not need to be replaced so often. Therefore using LED light sources to replace fluorescent lamps has become seen as the way of the future.  
      The LEDs are semiconductor devices that can convert electrical energy directly into light, due to the nature of the recombination of electrons and holes that occurs in the semiconductor solid. The LEDs rely on this recombination process to emit light.  
      Generally, a LED has a hemispherical lens of a type well known in the art. However, the hemispherical surface of the lens can lead to optical aberration. When observed along a package axis the light emitted from the LED chip is dispersed. As a result, the intensity and the utility of such an LED cannot satisfy the needs of illumination.  
      Therefore, what is needed, is a light-emitting diode with a high light utilization ratio.  
     SUMMARY OF THE INVENTION  
      A light-emitting diode includes a base, an LED chip and a single-piece enclosure. The LED chip is electrically mounted on the base, and configured for emitting light beams. The single-piece enclosure attaches to the base and encloses the LED chip therein. The enclosure includes a central convergent lens portion configured for converging the light beams from the light-emitting diode chip. A peripheral portion surrounds and extends from the central convergent lens portion to the base. The central convergent lens has an outer aspheric surface and is aligned with the LED chip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Many aspects of the present light-emitting diode can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present light-emitting diode. Moreover, in the drawing like reference numerals designate corresponding parts throughout.  
       FIG. 1  is a schematic, cross-sectional view of a light-emitting diode in accordance with a preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Reference will now be made to the drawings to describe in detail the preferred embodiments of the present light-emitting diode.  
       FIG. 1  illustrates an exemplary light-emitting diode  20  in accordance with one embodiment. The light-emitting diode  20  includes a base  22 , an LED chip  24 , and a single-piece enclosure  26 . The LED chip  24  is electrically mounted on the base  22 , and configured for emitting light beams. The single-piece enclosure  26  is light-permeable, and preferably transparent. The single-piece enclosure  26  attaches to the base  22  and encloses the LED chip  24  therein. The enclosure  26  includes a central convergent lens portion  260  configured for converging the light beams from the LED chip  24 . A peripheral portion  262  surrounds and extends from the central convergent lens portion  260  to the base  22 . The central convergent lens portion  260  has an outer aspheric surface  264  and is aligned with the LED chip  24 . The light-emitting diode  20  defines a longitudinal axis  30  passing through the center of the base  22 , the LED chip  24  and the enclosure  26  in turn.  
      The central convergent lens portion  260  faces the LED chip  24  and the peripheral portion  262  is coupled to the base  22 . The central convergent lens portion  260  includes an outer aspheric surface  264  and an incident surface  266 . The incident surface  266  faces the LED chip  24  and the outer aspheric surface  264  faces outside of the light-emitting diode  20 . The aspheric surface mainly includes a quadric surface and a highly curved surface. Radius of curvature of the aspheric surface is changeable with positions of points on the aspheric surface. The aspheric surface can be a hyperbolic surface, an ellipse surface, a parabolic surface, and etc. In the illustrated embodiment, the aspheric surface is an ellipse-shaped surface. Lenses with aspheric surface can reduce optical aberration, so that imaging and spotlighting using the aspheric lens is better than that of a spherical lens. It is to be noted that although only outer aspheric surface  264  is exemplarily illustrated herein, the incident surface can also be an aspheric surface, which can be alternatively selected according to practical application within the spirit of the present invention.  
      The peripheral portion  262  is coupled with the base  22  and is configured for refracting and bending light  28  so that the light  28  exits from the central convergent lens portion  260  as parallel to the longitudinal package axis  30  as possible. The peripheral portion  262  of the enclosure  26  tapers in a direction from the central convergent lens portion  260  to the base  22 . The interface between the enclosure  26  and the base  22  may be sealed using any sealant, such as a room temperature vulcanizing (RTV) sealant or the like. A first angle θ 1  between an outer surface  267  of the peripheral portion  262  and the base  22  is configured to be in the range from about 0 to about 90 degrees. A second angleθ 2  between an inner surface  268  of the peripheral portion  262  and the base  22  is in the range from about 0 to about 90 degrees. Preferably, the first angleθ 1  and the second angleθ 2  are in the range from 45 to 80 degree. The outer surface  267  of the peripheral portion  262  may be in contact with, or coated with, a reflective material so that the peripheral portion  262  can reflect light emitted from the LED chip  22  into the central convergent lens portion  260 .  
      The enclosure  26  may be manufactured as a separate component using a number of well-known techniques such as diamond turning (i.e. shaping the enclosure using a lathe with a diamond-bit), injection molding, and casting. The enclosure  26  can be made of a transparent material including but not limited to cyclic olefin copolymer (COC), polymethylmethacrolate (PMMA), polycarbonate (PC), PC and/or PMMA, and polyetherimide (PIE). The enclosure  26  includes an index of refraction (n) ranging from between 1.45 to 1.6, and preferably with a value of about 1.55, but with higher or lower values of index of refraction being possible based on the material used. In an alternative embodiment, the enclosure  26  may be formed onto the base  22  and the LED chip  24  by various techniques including but not limited to injection molding and casting.  
      As illustrated in  FIG. 1 , the base  22  supports the LED chip  24  for generating light. The base  22  is a flexible printed circuit board (FPCB). The LED chip  24  connects with the FPCB electrically. In the illustrated embodiment, the LED chip  24  is preferably a surface mount device (SMD) light-emitting diode chip with a power greater than one watt. The LED chip  24  may be one of any number of shapes, including but not limited to a cube, a rectangular solid, a truncated inverted pyramid (TIP) or a hemisphere. In the illustrated embodiment, the shape of the LED chip  24  is a rectangular solid. The LED chip  24  includes a bottom surface  240  that may be in contact with, or coated with, a reflective material. Although the LED chip  24  may emit light from all of its sides, the base  22  is generally configured to reflect emitted light upwards towards the enclosure  26  along the longitudinal axis  30  of the light-emitting diode  20 .  
      There is a volume  32  between the enclosure  26  and the base  22 . The volume  32  may be filled and sealed to prevent contamination of the enclosure  26  using silicone. The volume  32  may also be in a vacuum state, contain air or some other gas, or filled with an optically transparent resin material, including but not limited to resin, silicone, epoxy, water or any material with an index of refraction in the range of 1.4 to 1.6 may be injected to fill the volume  32 . The material inside the volume  32  may be colored to act as a filter in order to allow transmission of all or only a portion of the visible light spectrum. If silicone is used, the silicone may be hard or soft. The enclosure  26  may also be colored to act as a filter.  
      In operation, a part of light  280  emitted from the LED chip  24  passes through the central convergent lens portion  260 , and the central convergent lens portion  260  converges the light  280 . Another part of light  282  is incident onto the peripheral portion  262 , and is then reflected by the outer surface  267  of the peripheral portion  262  and spreads out from the outer aspheric surface  264  of the central convergent lens portion  260 .  
      While the present invention has been described as having preferred or exemplary embodiments, the embodiments can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the embodiments using the general principles of the invention as claimed. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and which fall within the limits of the appended claims or equivalents thereof.