Patent ID: 8136975

Claim:
An optical film, applied in a side-emitting backlight module, having a light guide plate for guiding a chief light beam, which has a light emitting surface to define a normal direction thereof, the optical film comprising: a lower prism structure, disposed on the light emitting surface and comprising a plurality of first prisms, wherein each of the first prisms has a first flat surface and a second flat surface, and the first flat surface and the second flat surface form a vertex angle between a range from 30 to 70 degree; an intermedium layer comprising a diffusing agent mixed with a glue layer, connected to the lower prism structure and disposed on the lower prism structure; and an upper prism structure, connected to the intermedium layer and disposed on the intermedium layer and comprising a plurality of second prisms, wherein each of the second prisms has a vertex angle between a range from 70 to 110 degree, the intermedium layer is located between the lower prism structure and the upper prism structure, as a continual entity, wherein after the chief light beam exits from the light emitting surface of the light guide plate and goes through the lower prism structure, the chief light beam is capable of being refracted on the first flat surface, reflected on the second flat surface via total reflection, and then emitted towards the upper prism structure, or the chief light beam is capable of being refracted on the first flat surface and emitted towards the upper prism structure directly, the chief light beam goes through the intermedium layer along a changed traveling direction, and after the chief light beam exits from the intermedium layer and goes through the upper prism structure, the chief light beam is turned from the changed traveling direction to the normal direction.