Optical film having linear protrusions with inwardly curved ridges and back light module with the optical film

A backlight module, comprising:

• a set of light sources;
• a light guide plate, having a light incidence surface and a light-emitting surface connecting the light incidence surface, wherein the set of light sources is located beside the light incidence surface;
• an optical film, disposed on the light-emitting surface and comprising:
• a body, having a first surface and a second surface opposite thereto;
• and
• a plurality of first linear protrusions, disposed on the first surface, wherein each of the first linear protrusions is extended along a first direction and has a first curvy ridge line which is curved inward into the first surface, and when the first curvy ridge line is located on a first suppositional plan, the first suppositional plan is not parallel to the first surface;
• and
• a reflective plate, disposed under the light guide plate, wherein the light guide plate is located between the reflective plate and the optical film.

An optical film, comprising:

• a body, having a first surface and a second surface opposite thereto;
• a plurality of first linear protrusions, disposed on the first surface, wherein each of the first linear protrusions is extended along a first direction and has a first curvy ridge line which is curved inward into the first surface, and when the first curvy ridge line is located on a first suppositional plan, the first suppositional plan is not parallel to the first surface;
• and
• a plurality of second linear protrusions, disposed on the second surface, wherein each of the second linear protrusions is extended along a second direction different from the first direction and has a second curvy ridge line which is curved inward into the second surface, and when the second curvy ridge line is located on a second suppositional plan, the second suppositional plan is not parallel to the second surface.