Abstract:
A lamp cover includes an array of lenses. Each lens includes an incidence surface for receiving light, and an emitting surface opposite to the incidence surface. One of the incidence surface and the emitting surface is a convex surface. Each lens includes a first end and an opposite second end in a column direction, a third end and an opposite fourth end in a row direction. The lenses in each row, a thickness difference between the first end and the second end of each lens is greater than a thickness difference between the third end and the fourth end thereof. An illumination lamp is also provided in this invention.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to commonly-assigned copending applications entitled, “lampshade and illumination lamp having the same”, filed on Jan. 25, 2008 (application Ser. No. 12/019,908). Disclosures of the above identified application are incorporated herein by reference. 
   BACKGROUND 
   1. Field of the Invention 
   The present invention generally relates to an illumination lamp, and particularly to a lamp cover of the illumination lamp. 
   2. Description of Related Art 
   In recent years, light emitting diode (LED) as a highly efficient light source is widely used in such fields as automobiles, display screens, and traffic lights. 
     FIG. 9  shows a simulated view of a light field of the LED. The light field of the LED is approximately circular. An intensity of the light field of the LED gradually decreases outwardly along a radial direction. Thus, the light field intensity near the LED is higher, and the light field intensity far from the LED is lower. However, in some cases, when the LED is adopted for a street lamp, the shape of the circular-shaped light field is often different from that of the street. As a result, a lighting area of such LED projected on the street is small. Thus, more LEDs are required for lighting the street, resulting in high cost and inefficient of energy. 
     FIG. 10  shows a light field of a street lamp  20  using LEDs as light source. The street lamp  20  is always positioned at one side of a street  22 . Because of the circular-shaped light field of the LED, some of light emitted from the LEDs only covers a portion of the street  22 . Thus, the street lamp  20  has a low utilization efficiency of the light emitted from the LEDs. 
   For the foregoing reasons, there is a need in the art for an illumination lamp which overcomes the above-described shortcomings. 
   SUMMARY 
   A lamp cover includes an array of lenses. Each lens includes an incidence surface for receiving light, and an emitting surface opposite to the incidence surface. One of the incidence surface and the emitting surface is a convex surface. Each lens includes a first end and an opposite second end in a column direction, a third end and an opposite fourth end in a row direction. The lenses in each row, a thickness difference between the first end and the second end of each lens is greater than a thickness difference between the third end and the fourth end thereof. 
   Other advantages and novel features of the present invention will be drawn from the following detailed description of a preferred embodiment of the present invention with attached drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many aspects of the present lamp cover and illumination lamp can be better understood with reference to the following drawings. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present lamp cover and illumination lamp. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is an explored, abridged general view of an illumination lamp in accordance with a first exemplary embodiment of the present invention. 
       FIG. 2  is an abridged general view of a light pervious lamp cover of the illumination lamp in  FIG. 1  viewed from another aspect. 
       FIG. 3  is an isometric view of one lens of the lamp cover of  FIG. 2 . 
       FIG. 4  is shows a simulated view of a light field of the illumination lamp incorporating the lamp cover of  FIG. 1 . 
       FIG. 5  shows a light field of the illumination lamp of  FIG. 3 , which is arranged at one side of a street. 
       FIG. 6  is an explored, abridged general view of an illumination lamp in accordance with a second exemplary embodiment of the present invention. 
       FIG. 7  an abridged general view of a light pervious lamp cover of the illumination lamp in  FIG. 6  viewed from another aspect. 
       FIG. 8  is an explored, abridged general view of an illumination lamp in accordance with a third exemplary embodiment of the present invention. 
       FIG. 9  shows a simulated view of the light field of a related illumination lamp. 
       FIG. 10  shows a light field of the related illumination lamp, which is arranged at one side of a street. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The detailed description of a light pervious lamp cover and an illumination lamp according to the present invention will now be made with reference to the attached drawings. 
   Referring to  FIG. 1 , the illumination lamp  40  includes a plurality of lighting members  41 , a plurality of circuit boards  410 , a reflecting board  42  and a light pervious lamp cover  10 . 
   The reflecting board  42  is wave-shaped. A cross section of the reflecting board  42  along the X-direction (i.e., column direction) is wave-shaped, which includes a plurality of horizontal flat sections  420  and a plurality of serrate sections  422  each interconnects with two neighboring horizontal flat sections  420 . A trapezoid-shaped interspace (not labeled) is thus defined among each horizontal flat section  420  and two neighboring serrate sections  422 . 
   Each circuit board  410  is arranged on a corresponding horizontal flat section  420 , and is received in a corresponding interspace. The lighting members  41  are arranged on the circuit boards  410  and are electrically connected to the circuit board  410 . Thus, when electric currents are applied to the lighting members  41  through the circuit board  410 , the lighting members  41  radiate light. In this embodiment, the lighting members  41  are light emitting diodes (LEDs). The lighting members  41  are arranged on the reflecting board  42  spaced evenly from each other. 
   As shown in  FIGS. 2 and 3 , the lamp cover  10  is arranged over the lighting members  41 . The lamp cover  10  includes a plurality of lenses  11 . The number of the lenses  11  is the same as that of the lighting members  41 . Each lighting member  41  is arranged corresponding to one lens  11  or each lens  11  is arranged corresponding to one lighting member  41 . In this embodiment, the lenses  11  are formed separately and then assembled together. Alternatively, the lenses  11  can be integrally formed. 
   Each lens  11  includes an incidence surface  110  facing the corresponding lighting member  41 , and an emitting surface  112  opposite to the incidence surface  110 . The incidence surface  110  is a concave surface configured for receiving the light of the lighting member  41 . The emitting surface  112  is a convex surface configured for emitting light from the lamp cover  10  into ambient. The concave surface  110  and the convex surface  112  are column-shaped. The concave surface  110  extends along the X-direction. The convex surface  112  extends along the Y-direction (i.e., row direction). In this embodiment, the Y-direction is perpendicular to the X-direction. Each lens  11  forms a micro-structure  111  thereon. The micro-structure  111  is a long and narrow protrusion, and extends outwardly from the lens  11  along the X-direction. A cross section of micro-structure  111  along the Y-direction is triangle. 
   Each lens  11  has a first end surface  114  and a second end surface  116  facing away from the first end surface  114 . The first end surface  114  and the second end surface  116  are both parallel with the Y-direction and adjacent to both of the concave surface  110  and the convex surface  112 . A cross section of each lens  11  taken along a direction perpendicular to the Y-direction has two sides  118  and  120 , which belong to the first end surface  114  and the second end surface  116 , respectively. A length L 1  of the side  118  is larger than a length L 2  of the side  120 . 
   During operation, when the electric currents are applied to the lighting members  41  through the circuit board  410 , the lighting members  41  radiates light. The reflecting board  42  reflects part of the light to the lamp cover  10 . Thus, approximately all of the light generated by the lighting members  41  enters into the lamp cover  10  through the incidence surface  110 . The micro-structure  111  can increase radiating range of the light along the Y-direction when the light enters into the lamp cover  10  through an outer surface of the micro-structure  111 . Conversely, the convex surface  112  is used for contracting radiating range of the light along the X-direction. Thus, the area which the illumination lamp  40  illuminates along the Y-direction is increased, and the area along the X-direction is decreased. The circular-shaped light field of the lighting members  41  is thus elongated. 
   Referring to  FIG. 4 , a light field adopting the lens  11  is shown. The light field along the Y-direction is increased and the light field along the X-direction is decreased. The shape of the light field is approximately the same as that of the street, thus all of the light radiating by the lighting members  41  can be utilized. In addition, because the cross section of the lens  11  has two sides  118  and  120  with different lengths, the center of the light field is off the center of the lens  11  along the X-direction. Thus, the radiating range of the lighting members  41  integrally translates a distance relative to the radiating range of the relate illumination lamp  20  along the X-direction. As shown in  FIG. 5 , almost all of the light emitted from the illumination lamp  40  is utilized to illuminate a street  400 . Thus, the street lamp  40  has a high utilization efficiency of the light emitted from the lighting members  41 . 
   It is to be understood that the micro-structures  111  are configured for increasing radiating range of the lighting members  41 , and the number, the arrangement of the micro-structures  111  can be changed according to the shape or the size of the illumination lamp. 
   Referring to  FIGS. 6 and 7 , an illumination lamp  60  according to a second embodiment of the present invention is shown. The illumination lamp  60  includes a plurality of lighting members  41  arranged on a reflecting board  42 , and a light pervious lamp cover  50  arranged over the lighting members  41 . The lamp cover  50  is constructed by a plurality of lenses  51 . Each lens  51  includes an incidence surface  510  facing the lighting members  41 , and an emitting surface  512  opposite to the incidence surface  510 . Each lens  51  has a first end surface  514  and a second end surface  516  facing away from the first end surface  514 . The first end surface  514  and the second end surface  516  are both parallel with the Y-direction and adjacent to both of the incidence surface  510  and the emitting surface  512 . A cross section of each lens  51  taken along a direction perpendicular to the Y-direction has two sides  518  and  520 . The sides  518  and  520  belong to the first end surface  514  and the second end surface  516 , respectively. A length L 3  of the side  518  is larger than a length L 4  of the side  520 . The difference between this embodiment and the first embodiment is that the incidence surface  510  is a planar surface, and the emitting surface  512  is a convex surface. 
     FIG. 8  shows an illumination lamp  80  in accordance with a third embodiment of the present invention. The differences between this embodiment and the first embodiment are that the incidence surface  710  is a convex surface, and the emitting surface  712  is a concave surface. The micro-structure  711  is formed on the concave emitting surface  712 . 
   It can be understood that the above-described embodiment are intended to illustrate rather than limit the invention. Variations may be made to the embodiments and methods without departing from the spirit of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.