DETAILED DESCRIPTION OF THE INVENTION

[0022] FIG. 1 shows a bottom view of a surface light source 30 , which has a light source 31 and a light guide plate 32 used to transmit light from the light source 31 .

[0023] FIG. 2 is a perspective view of the light guide plate 32 in the FIG. 1 , which is in a shape of a rectangular plate. It can instead have a shape of wedge-plate. The thickness thereof is generally approximately 1 mm to 10 mm. The light guide plate 32 includes a light incidence surface 321 , an emission surface 325 perpendicular to the light incidence surface 321 , and a bottom surface 323 opposite to the emission surface 325 . A groove array 328 and a plurality of reflection dots 329 are formed on the bottom surface 323 , wherein the groove array 328 is adjacent to the light incidence surface 321 .

[0024] In the present invention, a transparent glass or synthetic resin may be used to make the light guide plate 32 . Various kinds of highly transparent synthetic resins may be used, such as acrylic resin, polycarbonate resin, vinyl chloride resin, etc. These resins may be molded into a planar member using a normal molding method, such as an extrusion molding method, an injection molding method, or the like. Particularly, polymethylmethacrylate (PMMA) resin is excellent in light transmission, heat resistance, dynamic characteristics, molding performance and processing performance, etc. Thus, it is especially suitable as a material for the light guide plate 32 .

[0025] Further, inorganic fine particles, such as glass beads, titanium oxide particles or the like, or fine particles made of styrene resin, acrylic resin, silicone resin or the like, may be dispersed as light-scattering material in the light guide plate 32 .

[0026] The individual reflection dots 329 may have a shape of an ellipsoid, a cylinder, a cube, a pyramid, or another shape. To promote uniform emission of the light beams through the emission surface 325 , a size of the reflection dots 329 increases as a distance from the light incidence surface 321 increases.

[0027] The reflection dots 329 are made using a screen printing technique which uses a pale or white ink containing a white pigment such as titanium oxide, a mechanical shot blasting technique, a photo-sensing method using sensitized paper, an integral molding technique, or any other appropriate method.

[0028] The groove array 328 has a plurality of grooves 327 parallel to each other and arranged in a continuous band. The grooves 327 extend perpendicular to the light incidence surface 321 of the light guide plate 32 and each in cross-section has a hemicycle shape. Each groove 327 has a same curvature radius, and a pitch between grooves can be selected to meet requirement; normally the pitch is set between 20 millimeters and 5 mm. Each groove 327 is equal in width and depth, the maximum depth being 0.1 millimeter.

[0029] The grooves 327 maybe formed on the bottom surface 323 of the light guide plate 32 by injection molding, a tool cutting method, a laser processing method, or the like.

[0030] In operation, the light source 31 emits light beams into the light guide plate 32 . In this process, a part of the light beams is directly transmitted into the light guide plate 32 through the light incidence surface 321 , and another part of the light beams propagates into the grooves 327 . The light beams propagating into the grooves 327 are reflected in all directions by the grooves 327 , thereby enlarging the area of the light guide plate 32 which provides illumination. The light beams propagating in the light guide plate 32 are scattered and reflected upwardly to the emission surface 325 by the reflection dots 329 on the bottom surface 323 . Due to the design of the light guide plate 32 , illumination emitted from the emission surface 325 is fairly uniform over the entire emission surface 325 .

[0031] FIG. 3 is a bottom view showing a second surface light source 40 of the present invention similar to the surface light source 30 . The differences between the surface light source 40 and the surface light source 30 shown in FIG. 1 are described as follows: 1) the surface light source 40 has two light sources 41 ; 2) the light guide plate 42 has two light incidence surfaces 421 ; 3) two groove arrays 428 are formed on the bottom surface 423 . Each groove array 428 is adjacent to one light incidence surface 421 ; 4) a size of the reflection dots 429 is greater as the distance from the nearest light source 41 increases and becomes greatest in a middle area (not labeled) of the bottom surface 423 .

[0032] FIG. 4 is a perspective view showing a third surface light source 50 of the present invention similar to the surface light source 30 . The surface light source 50 comprises a plurality of LEDs 51 used as light sources and a wedge-shaped light guide plate 52 of the present invention.

[0033] The surface light source according to the present invention has some advantages as follows. Firstly, the light beams are reflected toward the emission surface 325 from the bottom surface 323 in a uniform manner, so no dark regions in the light guide plate 32 are apparent. Thus, the light beams are efficiently utilized and uniformly distributed. Secondly, since the size of the reflection dots 329 increases as a distance from the light incidence surface 321 increases and since the light beams decrease in intensity as they propagate in the light guide plate 32 , the amount of the light beams reflected by the reflection dots 329 are equal throughout the length of the light guide plate 32 . So, the surface light source 30 provides a highly uniform illumination.

[0034] In order to make the light beams emit more uniformly from the light guide plate 32 , a plurality of V-grooves or sawtooth-grooves can be defined in the emission surface 325 . A diffusing plate or a prism plate can also be disposed on the emission surface 325 . The method of forming the V-grooves or sawtooth-grooves may be a V-cut technique, a laser processing method, or a milling cutter method.

[0035] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, 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 invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.