Abstract:
A lens includes a bottom face, a light incident face defined in the bottom face, a top face and four lateral faces interconnecting the top face and the bottom face. Each lateral face is perpendicular to two adjacent lateral faces, and parallel to an opposite lateral face. An LED unit incorporating the lens is also disclosed.

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to lenses, and more particularly to a lens having a rectangular light pattern and an LED (light emitting diode) using the lens. 
     2. Description of Related Art 
     Nowadays LEDs (light emitting diodes) are applied widely in various applications for illumination. The LED is a highly pointed light source. Thus, light directly emitted from the LED may form a small circular light spot. In order to achieve a large illumination area, a large number of LEDs are arranged in a matrix. However, dark areas may appear between peripheries of the circular light spots generated by the LEDs, whereby the illumination provided by the LEDs is not uniform enough. 
     What is needed, therefore, is a lens with a rectangular light pattern and an LED unit using the lens which can address the limitations described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present embodiments 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 embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the various views. 
         FIG. 1  shows a lens of an LED unit in accordance with an embodiment of the present disclosure. 
         FIG. 2  shows a cross section of the lens of  FIG. 1 , wherein an LED is placed below the lens. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-2 , an LED (light emitting diode) unit  100  in accordance with an embodiment of the present disclosure is shown. The LED unit  100  includes an LED  10  and a lens  20  covering the LED  10 . 
     The LED  10  may be made of GaN, InGaN, AlInGaN or other suitable semiconductor materials. The LED  10  can emit light when powered. Phosphor may be incorporated to the LED  10  for changing color of the light emitted from the LED  10 . Preferably, the LED  10  emits white light. 
     The lens  20  may be made of transparent material such as epoxy, silicone, glass or the like. The lens  20  includes a bottom face  21 , a light incident face  22  and a light emerging face  26 . The bottom face  21  is square and has four straight edges  210 . The light incident face  22  is formed in a central area of the bottom face  21 . The light incident face  22  is an elliptical face with a long axis perpendicular to the bottom face  21  and a short axis located within the bottom face  21 . The light incident face  22  encloses a cavity  25  in the lens  20 . The cavity  25  is depressed from the bottom face  21  towards the light emerging face  26  of the lens  20 . A diameter of the cavity  25  gradually increases towards the bottom face  21 . 
     The light emerging face  26  includes a top face  23  and four lateral faces  24 . The top face  23  is a smooth freeform face including a concave face  231  and a convex face  232  surrounding the concave face  231 . The concave face  231  is located at a central area of the top face  23  and just above the light incident face  22 . The convex face  232  smoothly connects the concave face  231 . The convex face  232  includes four sharp corners  234  extending outwardly and downwardly. Each corner  234  of the convex face  232  has a width gradually decreasing in a direction towards the bottom face  21 . A tip of each corner  234  of the convex face  232  directly connects a joint  212  of two adjacent edges  210  of the bottom face  21 . In other words, the top face  23  directly connects the bottom face  21 . The four lateral faces  24  are sandwiched between the top face  23  and the bottom face  21 . Each corner  234  of the top face  23  is located between and directly connects two adjacent lateral faces  24 . Each lateral face  24  is a flat face with a large amount of micro structures (such as protrusions or depressions). Thus, each lateral face  24  is rough for diffusing light passing therethrough. Each lateral face  24  is perpendicular to the bottom face  21 . Each lateral face  24  is perpendicular to two adjacent lateral faces  24 , and parallel to an opposite lateral face  24 . Each lateral face  24  connects a corresponding edge  210  of the bottom face  21 . That is to say, a boundary between each lateral face  24  and the bottom face  21  is a straight line. A boundary  240  between each lateral face  24  and the top face  23  is a curved line. Two adjacent curved lines connect the joint  212  of two corresponding adjacent edges  210  of the bottom face  21 . 
     A part of the light emitted from the LED  10  is refracted by the light incident face  22  and the top face  23  to be diverged out of the lens  20 , remaining part of the light emitted from the LED  10  is refracted by the light incident face  22  and diffused by the four lateral faces  24  out of the lens  20 . Thus, the light emerging from the lens  20  can form a substantially rectangular pattern. When a plurality of the LED units  100  are used together, peripheries of the rectangular patterns produced by the LED units  100  can be connected to or overlapped with each other, thereby eliminating dark areas between the peripheries of the light patterns. The LED unit  100  may be suitable for use in a backlight module of a display. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.