Abstract:
A light guide ( 30 ) for illuminating a keypad ( 20 ) including a plurality of keys ( 22 ) includes a plurality of apertures ( 300 ) corresponding to the keys, and a plurality of projecting portions ( 340 ). The projecting portions protrude from a face of the light guide away from the keypad.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This present application is related to two co-pending U.S. patent applications entitled “LIGHT GUIDE FOR ILLUMINATING KEYPADS,” recently filed with Attorney Docket Nos. US9499 and US9503, and assigned to the same assignee as that of the present application. 
     
    
     1. FIELD OF THE INVENTION 
       [0002]    The invention relates to light guides, and particularly to a light guide for illuminating a keypad or keyboard uniformly. 
       2. DESCRIPTION OF RELATED ART 
       [0003]    It is common to illuminate a keypad or keyboard of an electronic device, such as a mobile telephone, to facilitate nighttime use. Each individual key may be illuminated by a respective light source located directly behind the key. This arrangement is, however, very expensive since a separate light source is required for each key. Furthermore, the power dissipation of the mobile telephone is increased, and the standby time of the mobile telephone is shorter. 
         [0004]    A more economical approach utilizes fewer distributed light sources and the light is directed towards the keys with the aid of a light guide in the form of a transparent plate. Referring to  FIG. 5 , a plan view of a conventional light guide  50  is shown. The light guide  50  comprises a plurality of V-shaped notches  52  defined at a periphery thereof, and an array of apertures  520  arranged in four rows and three columns. The apertures  520  are rectangular with rounded corners, corresponding to keys  60  of a keypad. Four light sources, such as light-emitting diodes, are located behind the light guide  50 . In a vicinity of each of the light sources, the light guide  50  comprises a respective convex lens  70  formed integrally therewith. Aligned with the lens  70 , adjacent to a front face of the light guide  50 , there is provided a prismatic indentation  72 , which offers four reflecting surfaces each having a triangular outline. The light from the light source is collimated by the lens  70  into a beam traveling transversely into the light guide  50 , then the prismatic indentation  72  serves to direct the beam into a plane of the light guide  50  by means of total internal reflection to illuminate the keys  60 . However the number of the light sources is four, and the power dissipation of the mobile telephone is still too great. In addition, the illumination is not uniform as the brightness of the keys  60  adjacent to the light source is greater than that of the keys  60  away from the light source, and the cost of manufacturing the light guide  50  is greater because the lens  70  is formed integrally with the light guide  50 . 
         [0005]    Therefore, a heretofore unaddressed need exists in the industry to overcome the aforementioned deficiencies and inadequacies. 
       SUMMARY OF THE INVENTION 
       [0006]    An aspect of the invention provides a light guide for illuminating a keypad including a plurality of keys. The light guide includes a plurality of apertures corresponding to the keys, and a plurality of projecting portions. The projecting portions protrude from a face of the light guide away from the keypad. 
         [0007]    Another aspect of the invention provides an electronic device. The electronic device includes a keypad, a light guide disposed under the keypad, and at least one light source. The keypad includes a plurality of keys. The light guide includes a plurality of apertures corresponding to the keys, at least one receiving hole defined in an end thereof, and a plurality of projecting portions protruding therefrom. Density of the projecting portions increases along a direction away from the at least one receiving hole. The at least one light source is received in the at least one receiving hole of the light guide. 
         [0008]    Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an exploded, isometric view of an electronic device of an exemplary embodiment of the present invention, the electronic device comprising a keypad and a light guide; 
           [0010]      FIG. 2  is an enlarged, inverted, isometric view of the light guide of  FIG. 1 ; 
           [0011]      FIG. 3  is an enlarged view of a circled portion III of  FIG. 2 ; 
           [0012]      FIG. 4  is a schematic diagram of light reflecting in the light guide of  FIG. 1 ; and 
           [0013]      FIG. 5  is a plan view of a conventional light guide. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIG. 1 , an electronic device  10  of an exemplary embodiment of the present invention is shown. The electronic device  10  comprises a keyboard  20  and a light guide  30 . 
         [0015]    The keypad  20  has a generally rectangular profile. The keypad  20  comprises a plurality of keys  22 . 
         [0016]    Referring also to  FIGS. 1-3 , the light guide  30  can be mounted on a circuit board comprising a pair of light sources, for example, two light-emitting diodes (not shown). The light guide  30  is a transparent plate. The light guide  30  comprises a first end portion  32 , a second end portion  34  opposite to the first end portion  32 , and a middle portion  36  connecting the first end portion  32  with the second end portion  34 . A pair of spaced receiving holes  320  is defined in an end of the first end portion  32  away from the middle portion  36 , for receiving the light sources. The light guide  30  further comprises a plurality of projecting portions  340  protruding from the second end portion  34  and the middle portion  36 . The projecting portions  340  are away from the keypad  20 . The projecting portions  340  absorb light from the light sources, and then diffuse the light within the light guide  30 . Meanwhile, the projecting portions  340  prevent total reflection, thereby the light is uniformly thrown from a surface of the light guide  30  adjacent to the keypad  20 . In the exemplary embodiment, the projecting portions  340  are made of print material comprising Silicon Dioxide (SiO2) and Titanium Dioxide (TiO2). A diameter of each projecting portion  340  arranged on the middle portion  36  is slightly greater than that of each projecting portion  340  arranged on the second portion  34 . A distance between every two adjacent projecting portions  340  arranged on the middle portion  36  is slightly greater than that between every two adjacent projecting portions  340  arranged on the second portion  34 . In this way, density of the projecting portions  340  arranged on the middle portion  36  is less than that of the projecting portions  340  arranged on the second portion  34 . 
         [0017]    The light guide  30  comprises a plurality of apertures  300  corresponding to the keys  22  of the keypad  20 . The apertures  300  are generally positioned in three columns. One of the columns of the apertures  300  is positioned in a lengthwise central line of the light guide  30 . The receiving holes  320  are symmetrically positioned to either side of an end of the central column of the apertures  300  in the first end portion  32 . The light guide  30  further comprises two apertures  300  defined in the second end portion  34  and respectively positioned in the same lengthwise lines as the receiving holes  320 . Thus, the keys  22  of the keypad  20  are positioned in an illumination range of 120° corresponding to that of the light sources. In the exemplary embodiment, the light sources are light-emitting diodes. A preferred illumination range within which power of illumination from the light-emitting diode is greatest is 120° centered about an axis of each receiving hole  320 . Thus, at least one portion of each key  22  of the keypad  20  is positioned in the illumination range of 120° corresponding to that of the light sources. 
         [0018]    The light guide  30  also comprises a plurality of holes  302 . Some of the holes  302  are disposed near the apertures  300  adjacent to the receiving holes  320 , and two of the holes  302  are positioned in the same lengthwise line as the receiving holes  320 . That is, the holes  302  are disposed near the keys  22  where illumination is greatest. Each hole  302  is triangular shaped. Thereby, the light from the light sources illuminates the keypad  20  uniformly. 
         [0019]    In assembly, the keys  22  of the keypad  20  are received in the apertures  300  of the light guide  30 , respectively, thereby the keypad  20  and the light guide  30  are mounted together. 
         [0020]    In use, the light from the light sources received in the receiving holes  320  is introduced into the light guide  30 , and reflects within the light guide  30 . Because the projecting portions  340  are arranged on the second end portion  34  and the middle portions  36 , and the light sources being received in the receiving holes  320  of the first end portion  32  having no the projecting portions  340 , the number of reflections that the light reflects within the first end portion  32  is less than that of the second portion  34  and the middle portion  36 . Meanwhile, because the density of the projecting portions  340  arranged on the second portion  34  is less than that of the projecting portions  340  arranged on the middle portion  36 , the number of reflections that the light reflects within the middle portion  36  is less than that of the second portion  34 . In this way, the loss of illuminating power as the light travels through the light guide  30  is compensated for by the increase in density of the number of reflections over distance. Thus, a brightness of the portion of the light guide  30  away from the light sources is comparable to a brightness of the portion of the light guide  30  near the light source, so that a uniform brightness is obtained. Furthermore, the number of the light sources used in the electronic device  10  is reduced, and the standby time of the electronic device  10  is prolonged. 
         [0021]    In an alternative embodiment, the projecting portions  340  may be defined in the first end portion  32 , the middle portion  36  and the second end portion  34 . Density of the projecting portions  340  reduces gradually from the first end portion  32  to the second end portion  34 . Alternatively, density of the projecting portions  340  arranged on the middle portion  36  may be slightly greater than that of the projecting portions  340  arranged on the first end portion  32 , but less than that of the projecting portions  340  arranged on the second end portion  34 . 
         [0022]    While exemplary embodiments have been described above, it should be understood that they have been presented by way of example only and not by way of limitation. Thus the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.