Optical film applied to a side-emitting backlight module

A side-emitting backlight module, comprising:

• an optical film, comprising
• a lower prism structure, 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;
• a light guide plate, disposed under the lower prism structure of the optical film, and comprising a light incident surface and a light emitting surface, wherein the light emitting surface faces the lower prism structure and defines a normal direction vertical to the light emitting surface;
• and
• a light source, disposed by side of the light incident surface of the light guide plate;
• wherein after the light source emits a chief light beam, the chief light beam enters the light guide plate through the light incident surface, exits from the light emitting surface, subsequently, and then 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 after passing through the lower prism structure, and after the chief light beam exits from the intermedium layer and then goes through the upper prism structure, the chief light turns from the changed traveling direction to the normal direction.