Abstract:
An LED illumination device includes a polygonal reflector and a plurality of LEDs received in the reflector. The reflector includes multiple sidewalls connecting with each other. Each LED is located adjacent to at least one corresponding neighboring sidewall. The polygonal reflector can have a shape of a square, a rectangle, an octagon etc. Light generated by the LEDs has at least a part reflected by the reflector to radiate out of the LED illumination device upwardly. The LED is a top view LED. A top of an LED die of the LED is no higher than a bottom of the sidewalls of the reflector.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to illumination devices and, more particularly, to an LED illumination device having a reflector capable of producing a circular or square light pattern. 
     2. Description of Related Art 
     LEDs, available since the early 1960&#39;s and because of their high light-emitting efficiency, have been increasingly used. According to Illuminating Engineering Society of North America (IESNA), illumination distribution of lighting used in some occasions, such as squares, sidewalks, yards, parks, or parking lots must meet the standards of Type IV or Type V. These two types of standard require that the light illuminating on the site has a circular or square pattern, in which the light source is located at a center of the pattern. However, the light directly emitted from the LEDs usually cannot meet such a requirement. To meet the requirement, a lens which can modulate the light distribution of the LEDs may be used. However, the lens is expensive and when light travels through the lens the intensity of the light is significantly reduced. A reflector is cheaper than a lens and the light intensity will not be significantly reduced when the light is reflected by a reflector. 
     What is needed, therefore, is an illumination device having a reflector which can modulate the light generated by the illumination device so that the light pattern can meet the standards of IESNA Type VI and Type V. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is an isometric view of a reflector of an LED illumination device of a first embodiment of the present disclosure. 
         FIG. 2  is a top view of the LED illumination device of  FIG. 1 , including the reflector of  FIG. 1  and four LEDs placed within the reflector. 
         FIG. 3  shows a cross-section of the reflector with the four LEDs of  FIG. 2 . 
         FIG. 4  is similar to  FIG. 3 , wherein two opposite sidewalls of the reflector are curved inwardly. 
         FIG. 5  shows the reflector of  FIG. 1  stretched along a direction. 
         FIG. 6  is an isometric view of a reflector of an LED illumination device of a second embodiment of the present disclosure. 
         FIG. 7  is a top view of the LED illumination device of  FIG. 6 , including the reflector of  FIG. 6  and four LEDs surrounded by the reflector. 
         FIG. 8  shows the reflector of  FIG. 6  stretched along a direction. 
         FIG. 9  shows the reflector of  FIG. 6  stretched along another direction. 
         FIG. 10  shows photometric curves of an LED lamp including the LED illumination devices of the first and second embodiments arranged in a matrix. 
         FIG. 11  shows an illumination distribution of the LED lamp of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIGS. 1-2 , an LED illumination device of a first embodiment of the present disclosure is disclosed. The LED illumination device includes a reflector  20  and four LEDs  10  received in the reflector  20 . The reflector  20  has a square configuration constructed by four vertical sidewalls  22 . A symmetrical axis I is defined in the reflector  20  to divide the reflector  20  into two symmetrical parts. Left and right sidewalls  22  of the reflector  20  each define a zero angle with respect to the symmetrical axis I; in other words, the left and right sidewalls  22  are parallel to the symmetrical axis I. Front and rear sidewalls  22  of the reflector  20  each define an angle of 90 degrees with respect to the symmetrical axis I. In other words, the front and rear sidewalls  22  are perpendicular to the symmetrical axis I. Each LED  10  is located near a corner of the reflector  20 . Referring to  FIG. 3 , a guidance of the reflector  20  to the light emitted from an exemplary LED  10  located at a left and rear corner of the reflector  20  is illustrated. A first part of the light emitted from the LED  10  (such as light a shown in  FIG. 3 ), which is oriented towards a left direction with an emergent angle less than or equal to a critical angle α, would directly radiate out of the reflector  20  towards the left side of the reflector  20 . A second part of light emitted from the LED  10  (such as light c shown in  FIG. 3 ), which is oriented towards the left direction with an emergent angle larger than the critical angle of α, would be reflected by the adjacent left sidewall  22  towards the right side of the reflector  20 . A third part of light emitted from the LED  10  (such as light b shown in  FIG. 3 ), which is oriented towards the right direction with an emergent angle less than or equal to another critical angle of β, would directly transmit out of the reflector  20  towards the right side of the reflector  20 . A forth part of light emitted from the LED  10 , which is oriented towards the right direction with an emergent angle larger than the critical angle of β, would be reflected by the right sidewall  22  towards the left side of the reflector  20 . Since the critical angle of β is larger than the critical angle of α, an amount of the output light towards the right direction is larger than that towards the left direction (i.e., intensity of the first part of light plus the forth part of light being smaller that of the second part of light plus the third part of light). Therefore, the light emitted by the exemplary LED  10  is mainly guided by the reflector  20  towards the right direction. On the other hand, since the exemplary LED  10  is also located near the rear sidewall, the light emitted thereby would be mainly guided by the reflector  20  towards a front direction as well. Light emitted from the other three LEDs  10  is also guided by the reflector  20  in a manner similar to that of the exemplary LED  10 . The light directed by the reflector  20  from the four LEDs  10  overlaps with each other, to thereby form a symmetrically distributed light pattern, which is approximately square. 
     Furthermore, each sidewall  22  of the reflector  20  can has its upper portion curvedly extending inwardly to enlarge an illumination area of the LED illumination device. Alternatively, the reflector  20  can only have two opposite sidewalls  22  or one sidewall  22  curved inwardly to just broaden the illumination at a corresponding direction. 
     The LED  10  has a flat light-emergent face in a top thereof. The LED  10  shown in  FIG. 3  includes a base  12  defining a cavity, an LED die  14  fixed in the base  12 , and an encapsulant  16  filling the cavity to form the flat light-emergent face in the top of the LED  10 . For such a top-view LED which has a flat light-emergent face, the LED  10  should be placed within the reflector  20  in a manner that the light-emergent face thereof levels with a bottom of the reflector  20  with the encapsulant  16  substantially located below the reflector  20 , thereby ensuring the light output from the light-emergent face to be effectively reflected by the reflector  20 . Alternatively, for another LED  10  which has a non-planar light-emergent face (such as the LED  10  shown in  FIG. 4 , the encapsulant  16  thereof being protruded upwardly to have an arced light-emergent face), the LED  10  should be placed within the reflector  20  in a manner that a top face of the LED die  14  flushes with the bottom of the reflector  20  with a top part of the encapsulant  16  being located in the reflector  20 .  FIG. 4  shows an alternative embodiment, wherein two opposite walls  22   a  of the reflector  20  are curved inwardly toward each other and toward the LEDs  10 . In particular upper portions of the two opposite walls  22   a  are bent toward each other and toward the LEDs  10 . 
     It is noted that the shape of the reflector  20  is not limited to the square as described above, but can include other polygons, such as rectangle shown in  FIG. 5  and octagons shown in  FIGS. 6-9 . Such alternative reflectors can also function to reflect the light generated by the LEDs  10  to have the desired light distribution pattern. The octagonal reflector  30  will be described below in more details. 
     Referring to  FIGS. 6-7 , the octagonal reflector  30  includes eight sidewalls  32  connected to each other successively to form a closed configuration. A symmetrical axis II is also introduced to the octagonal reflector  30  so that two parts of the reflector  30  divided by the axis II are symmetrical with each other. The eight sidewalls  32  of the reflector  30  define different angles from the axis II, wherein left and right sidewalls  32  each define an angle of zero degree from the axis II (i.e., parallel to the axis II), front and rear sidewalls  32  each define a 90 angle from the axis II (i.e., perpendicular to the axis II), and four diagonal sidewalls  32  each define an angle of 45 degrees from the axis II. The four LEDs  10  are received in the reflector  30  such that each LED  10  is located adjacent to a corresponding diagonal sidewall  32 . Like the square reflector  20 , the octagonal reflector  30  also reflects the light emitted from the four LEDs  10  to an overlapped pattern. The overlapped light pattern is a symmetrically distributed pattern which is approximately circular. Note that corresponding sidewalls  32  of the octagonal reflector  30  can also be curved inwardly to thereby broaden illumination at corresponding directions as desired. 
     Furthermore, the shape of the octagonal reflector  30  can also be varied to those shown in  FIGS. 8-9  according to different requirements. The reflector  30  of  FIG. 8  is stretched with respect to that of  FIG. 7  along the axis II, wherein the angle between each of the four diagonal sidewalls  32  and the axis II is changed to 22.5 degrees. The reflector  30  of  FIG. 9  is stretched with respect to that of  FIG. 7  along a direction perpendicular to the axis II, wherein the angle between each of the four diagonal sidewalls  32  and the axis II is changed to 67.5 degrees. By such variations of the shape of the reflector  30 , the light distribution pattern obtained by the LEDs  10  are changed from the circle shape to two ellipses which have major axes perpendicular to each other. 
     An LED lamp can have the LED illumination devices with the rectangular and the octagonal shapes arranged in a matrix to produce a more favorable light pattern.  FIG. 10  which is a Candela plot shows photometric curves  40 ,  50  of an LED lamp having the LED illumination devices of  FIG. 2  and  FIG. 7  arranged in a matrix (i.e., a four-column, eight-row matrix). The two photometric curves (i.e., the bold curve  50  and the thin curve  40 ) have similar shapes and are substantially overlapped, representing that the distribution of the light at the two orthogonal directions are approximate to each other. Thus, the light distribution of the LED lamp can have a desirable shape approximate to a circle as shown in  FIG. 11 , thereby meeting the Type IV and Type V illumination requirements of IESNA. 
     It is believed that the present disclosure and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the present disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments.