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 an accommodating portion. The accommodating portion defines at least one receiving hole ( 320 ) for receiving at least one light source. A thickness of the light guide gradually reduces from the accommodating portion to surrounding portions of the light guide along at least one direction.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to light guides, and particularly to a light guide for illuminating a keypad or keyboard uniformly.  
       DESCRIPTION OF RELATED ART  
       [0002]     It is common to illuminate a keyboard or keypad 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.  
         [0003]     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. 6 , 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 .  
         [0004]     Therefore, a heretofore unaddressed need exists in the industry to overcome the aforementioned deficiencies and inadequacies.  
       SUMMARY OF INVENTION  
       [0005]     In an exemplary embodiment, a light guide for illuminating a keypad including a plurality of keys, comprises a plurality of apertures corresponding to the keys, and an accommodating portion. The accommodating portion defines at least one receiving hole for receiving at least one light source. A thickness of the light guide gradually reduces from the accommodating portion to surrounding portions of the light guide along at least one direction.  
         [0006]     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 DRAWINGS  
       [0007]      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;  
         [0008]      FIG. 2  is an enlarged, inverted, isometric view of the light guide of  FIG. 1 ;  
         [0009]      FIG. 3  is a cross-sectional view along line IV-IV of  FIG. 3 ;  
         [0010]      FIG. 4  is a schematic diagram of the light reflecting in the light guide of  FIG. 1 ;  
         [0011]      FIG. 5  is an inverted, assembled view of  FIG. 1 ; and  
         [0012]      FIG. 6  is a plan view of a conventional light guide. 
     
    
     DETAILED DESCRIPTION  
       [0013]     Referring to  FIGS. 1 and 5 , an electronic device  1   0  of an exemplary embodiment of the present invention comprises a keyboard  20  and a light guide  30 .  
         [0014]     The keypad  20  has a generally rectangular profile. The keypad  20  comprises a plurality of keys  22 . Each of the keys  22  comprises a key column  220 .  
         [0015]     Referring also to  FIGS. 2 and 4 , the light guide  30  can be mounted on a circuit board comprising a light source, for example, a light-emitting diode (not shown). The light guide  30  is a transparent plate. Lengthwise, in cross section, the light guide  30  is generally wedge-shaped. The light guide  30  comprises a first end portion  32  and a second end portion  34 . A thickness of the light guide  30  gradually reduces from the first end portion  32  to the second end portion  34 . The light guide  30  further comprises an accommodating portion disposed in the first end portion  32 . A receiving hole  320  is defined in the accommodating portion, for receiving the light source.  
         [0016]     Referring also to  FIG. 3 , the light guide  30  comprises a plurality of apertures  300  corresponding to the keys  22  of the keypad  20 . The key columns  220  of the keys  22  are received in the corresponding apertures  300 . Each of the apertures  300  is a tapered through-hole. A radius of an end portion of each aperture  300  adjacent to the circuit board is greater than that of the other end portion of each aperture  300  adjacent to the keypad  20 , thereby the light from the light source can be easily introduced into the keys  22 , and illuminate the keys  22  uniformly.  
         [0017]     The light guide  30  also comprises a plurality of holes  302  each disposed near each aperture  300 . Each hole  302  is tapered and triangular shaped. A width of an end portion of each hole  320  adjacent to the circuit board is greater than that of the other end portion of each hole  320  adjacent to the keypad  20 , thereby, the light from the light source can be easily introduced into the keypad  20  along all directions, and can illuminate the keypad  20  uniformly.  
         [0018]     In assembly, the key columns  220  of the keypad  20  are received in the corresponding apertures  300  of the light guide  30 .  
         [0019]     In use, the light from the light source received in the receiving hole  320  is introduced into the light guide  30 , and an angle of incidence is designated as θ 1 . After the light first reflects within the light guide  30 , a second angle of incidence is designated as  02 . Because of the wedge shape of the light guide  30 , and the light source being received in the receiving hole  320  of the first end portion  32  having the greater thickness, the angle θ 1  is greater than the angle θ 2 . After each reflection of the light, the incident angles becomes more acute and the distance between deflection points reduces gradually from the first end portion  32  to the second end 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 source 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.  
         [0020]     In an alternative embodiment, the light guide  30  may be mound-shaped with the accommodating portion defining the receiving hole  320  disposed in a middle portion of the light guide  30 , which has a greater thickness than surrounding portions. As above, the angle of incidence of the light reflecting within the light guide  30  becomes more acute gradually as it travels away from the light source in the middle portion of the light guide  30  to the surrounding portions. Thus, uniform illumination by the light source is achieved.  
         [0021]     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.