Abstract:
An LED unit includes an LED and a lens mounted on the LED. The lens includes a light-incident face adjacent to the LED, a light-emergent face remote from the LED, and a light-reflecting face between the light-incident face and the light-emergent face. The light-incident face includes a first light-incident face faces the LED, and the light-emergent face having includes a first light-emergent face located opposite to the first light-incident face. The first light-emergent face is a continuously curved face which has a curvature, along a top-to-bottom direction of the lens, firstly increasing gradually, then decreasing gradually and then increasing gradually again.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a light emitting diode (LED) unit and, more particularly, to an LED unit having a lens which can produce an effectively converged light beam. 
         [0003]    2. Description of Related Art 
         [0004]    LEDs, available since the early 1960&#39;s and because of their high light-emitting efficiency, have been increasingly used in a variety of occasions, such as residential, traffic, commercial, and industrial occasions. Conventionally, light directly output from the LED does not have a desirable pattern; therefore, a light-adjusting element, such as a lens, is used with the LED to modulate the light pattern thereof. However, a typical lens generally has a limited light-converging capability; that is, the light passing through the lens cannot be effectively converged to have a small light-emergent angle. Thus, the light pattern output from the lens may have a yellow annulus or shining annulus appearing at a periphery thereof, adversely affecting illumination effect of the lens. 
         [0005]    What is needed, therefore, is an LED unit which can overcome the limitations described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    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. 
           [0007]      FIG. 1  is an isometric view of an LED unit of the disclosure. 
           [0008]      FIG. 2  is an inverted view of a lens of the LED unit of  FIG. 1 . 
           [0009]      FIG. 3  shows a cross-section of the LED unit of  FIG. 1 , with a printed circuit board on which the LED unit is mounted. 
           [0010]      FIG. 4  shows a curve of curvatures of a first light-emergent face of the lens of  FIG. 1  at different points along a top-to-bottom direction of the lens. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0011]    Referring to  FIGS. 1-3 , an LED unit of the present disclosure is illustrated. 
         [0012]    The LED unit comprises an LED  10  and a lens  20  mounted on the LED  10 . The LED  10  comprises a heat-conducting base  12 , an LED die  14  mounted on a top of the base  12 , and an encapsulant  16  covering the LED die  14  and fixed on the top of the base  12 . The base  12  of the LED  10  is soldered on a printed circuit board  100  to conduct heat generated by the LED die  14  to the printed circuit board  100 . In addition, the LED die  14  is electrically connected with the printed circuit board  100  via the base  12 . The LED die  14  may be an InGaN chip, an InGaAs chip, a GaP chip or other suitable chips which could generate visible light with a desirable color. The encapsulant  16  is made of epoxy, silicon, glass or other transparent materials which have good light-permeable and water-proof capabilities. Phosphor may be doped within the encapsulant  16  to adjust the color of the light emitted from the LED die  14 . The encapsulant  16  is shaped like a dome so as to collimate the light from the LED die  14  into a converged beam. The LED  10  has an optical axis I, around which the light emitted from the encapsulant  16  is symmetrical in a surrounding space. 
         [0013]    The lens  20  is made of transparent materials such as PC (polycarbonate) or PMMA (polymethyl methacrylate). The lens  20  comprises an optical member  22 , two opposite substrates  24  extending downwardly from a bottom face of the optical member  22  for supporting the optical member  22 , and a flange  26  extending outwardly from a circumference of a top of the optical member  22 , for being pressed by a clip (not shown) against the printed circuit board  100  to thereby secure the lens  20  on the printed circuit board  100 . A cavity  220  is defined in an interior of the lens  20 , recessed upwardly from a bottom thereof. The cavity  220  defines an opening (not labeled) at the bottom face of the optical member  22 . When the lens  20  is assembled to the LED  10 , the LED die  14  and the encapsulant  16  are received in the cavity  220 , and the base  12  is sandwiched between the two substrates  24 . The cavity  220  has a shape like a round column. An inner face of the lens  20  facing the encapsulant  16  of the LED  10  functions as a first light-incident face  2201  of the lens  20  to receive the light emitted from the LED  10  with a small light-emergent angle (such as light A shown in  FIG. 3 ). Another inner surface of the lens  20  surrounding the encapsulant  16  of the LED  10  functions as a second light-incident face  2202  of the lens  20  to receive the light emitted from the LED  10  with a large light-emergent angle (such as light B shown in  FIG. 3 ). The first light-incident face  2201  is curved and slightly protrudes downwardly towards the LED  10 , and the second light-incident face  2202  is a circumferential face of a column. In the embodiment of this disclosure, the first light-incident face  2201  is a spherical surface and has a curvature of 0.04 mm −1 . The first light-incident face  2201  and the second light-incident face  2202  cooperatively form a light-incident face  200  to refract all of the light of the LED  10  into the lens  20 . 
         [0014]    The optical member  22  has an upwardly-expanding bowl shape. An outer circumference of the optical member  22  functions as a light-reflecting face  300  of the lens  20  to totally reflect the light transferred from the second light-incident face  2202  towards the top of the lens  20 . Alternatively, the light-reflecting face  300  can be further coated with a reflective layer (such as aluminum layer or silver layer) for promoting light reflection. The flange  26  is extended along the light-reflecting face  300 . The light-reflecting face  300  is divided by the flange  26  into a first light-reflecting face  2203  and a second light-reflecting face  2204 . The first light-reflecting face  2203  is conical and expands from the bottom towards the top of the lens  20 . The second light-reflecting face  2204  is vertical. 
         [0015]    The optical member  22  has a top face which is planar and circular. A center of the top face of the optical member  22  is concaved downwardly to form a columnar recessed portion  224 . The recessed portion  224  is rotationally symmetrical relative to the optical axis I of the LED  10 . The top face of the optical member  22  directly connects with the second light-reflecting face  2204 . A protrusion  228  is protruded upwardly from a central area of a bottom face of the recessed portion  224 . The protrusion  228  is shaped like a dome and has a continuously curved top face. The protrusion  228  is also rotationally symmetrical relative to the optical axis I of the LED  10 . The curved top face of the protrusion  228  is located just opposite to the first light-incident face  2201 . The curved top face of the protrusion  228  acts as a first light-emergent face  2205  and takes charge mainly for the light transmitted from the first light-incident face  2201 . The top face of the optical member  22  of the lens  20  acts as a second light-emergent face  2206  and takes charge mainly for the light totally reflected by the light-reflecting face  2203 . The curved top face of the protrusion  228  and the top face of the optical member  22  refract nearly all of the light from the LED  10  out of the lens  20  within a small light-emergent angle. In other words, the first light-emergent face  2205  and the second light-emergent face  2206  of the lens  20  cooperatively form a light-emergent face  400  to refract the light within the lens  20  towards a place above the lens  20 . 
         [0016]    Referring to  FIG. 4  also, a length of the first light-emergent face  2205  from a top to a bottom thereof is supposed to be 1L. The first light-emergent face  2205  has a curvature firstly increasing gradually from a top (i.e., first position) towards a bottom of the first light-emergent face  2205  of the protrusion  228 ; at a second position which is located away from the top of the first light-emergent face  2205  for about 45% of the length (0.45L), the curvature starts to decrease gradually; at a third position which is located away from the top of the first light-emergent face  2205  for about 70% of the length (0.7L), the curvature starts to increase gradually again; finally, at a fourth position which is located away from the top of the first light-emergent face  2205  for about 95% of the length (0.95L), the curvature starts to decrease gradually again, within a small range till a bottom (fifth position) of the first light-emergent face  2205  of the protrusion  228 , which is away from the top of the first light-emergent face for 100% of the length (1L). In the embodiment of this disclosure, the first light-emergent face  2205  has a curvature of 0.0083 mm −1  at the first position (the origin of the coordinate of  FIG. 4 ), a first curvature of 0.182 mm −1  at the second position (0.45L), a second curvature of 0.066 mm −1  at the third position (0.7L), a third curvature of 0.1964 mm −1  at the fourth position (0.95L) and a curvature of 0.1923 mm −1  at the fifth position (1L). The abscissa of the coordinate of  FIG. 4  represents the length of the first light-emergent face  2205  of the protrusion  228  measured from the top to the bottom of the first-emergent face  2205 . The ordinate thereof represents the curvatures of the first light-emergent face  2205  of the protrusion  228  along different points thereof. 
         [0017]    Being adjusted by the first and second light-incident faces  2201 ,  2202 , the first and second light-reflecting faces  2203 ,  2204 , and the first and second light-emergent faces  2205 ,  2206 , the light emitted from the LED  10  could be effectively converged within a small angle, thereby preventing a periphery of a light pattern output by the LED  10  via the lens  20  from being yellow or shining. 
         [0018]    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.