1.  Technical Field
The present disclosure relates to an optical plate and a backlight module using the optical plate. 
2.  Description of the Related Art
Referring to FIGS.  10 and 11, a direct backlight module 100 includes a frame 11, a plurality of light sources 12, a light diffusion plate 13, and a prism sheet 10.  The light sources 12 are positioned in an inner side of the frame 11.  The light diffusion plate 13 and the prism sheet 10 are positioned on the light sources 12 above a top of the frame 11 in that order. 
The light diffusion plate 13 includes a plurality of diffusion particles (not shown) to scatter light.  The prism sheet 10 includes a transparent substrate 101 and a prismatic layer 103 formed on the transparent substrate 101.  The prismatic layer 103 forms a plurality of elongated V-shaped protrusions 105. 
In use, light emitted from the light sources 12 enters into the light diffusion plate 13 and becomes scattered.  The scattered light leaves the diffusion plate 13 to the prism sheet 10.  The scattered light then travels through the prism sheet 10, and is refracted out of at the elongated V-shaped protrusions 105 and concentrated by the elongated V-shaped protrusions 105, thus enhancing an illumination of the backlight module 100 within a predetermined view angle. 
However, although light from the light sources 12 enters the diffusion plate 13 and becomes scattered, after the light leaves the prism sheet 10, strong light spots of the light sources 12 directly above the light sources 12 are often formed.  Therefore, an upper diffusion film 14 may be positioned on the prism sheet 10 to reduce or eliminate light spots of the light sources 12.  However, although the upper light diffusion film 14 and the prism sheet 10 are in contact with each other, a plurality of air pockets may still exist around the boundaries of the light diffusion film 14 and the prism sheet 10.  When the backlight module 100 is in use, light passes through the air pockets, and some of the light undergoes total reflection by the air pockets along one or more corresponding boundaries.  In addition, the upper light diffusion film 14 may absorb a certain amount of the light from the prism sheet 10.  As a result, a brightness of light illumination of the backlight module 100 is reduced. 
Therefore, an optical plate and a backlight module using the optical plate are desired in order to overcome the above-described shortcoming.