Optical plate and backlight module using the same

A backlight module comprising:

• a housing having a base and a plurality of sidewalls extending around a periphery of the base, the base and the sidewalls cooperatively forming an opening;
• at least one point light source disposed on the base, each point light source having a light-emitting portion;
• at least one reflective member positioned above the top of the light-emitting portion;
• an optical plate positioned in the housing, the optical plate including at least one transparent plate unit having:
• a first surface;
• a second surface opposite to the first surface;
• a plurality of enclosing V-shaped protrusions formed on the first surface;
• a plurality of microstructures formed in the second surface, wherein each microstructure has circular cross-section taken along a plane parallel to its base surface thereof, a diameter of the circular cross-section decreasing along a direction away from its base surface thereof, and at least a lamp-receiving portion defined in at least one of the first surface and the second surface, wherein the light-emitting portion of the at least one point light source is inserted in the lamp-receiving portion correspondingly;
• and
• a light diffusion plate disposed on the housing over the opening.