Backlight for a display having an optical film with first and second prism structures disposed on opposing optical surfaces thereof, or backlight for a display having an optical film set with first and second prism structures disposed on opposing optical films

An optical film set, comprising a first film and a second film, wherein:

• the first film has a first optical surface and a plurality of first prism structures, wherein the first prism structures are disposed on the first optical surface, and each of the first prism structures has a first extending direction;
• the second film has a second optical surface and a plurality of second prism structures, wherein the first optical surface and the second optical surface respectively face opposite directions, the second prism structures are disposed on the second optical surface, and each of the second prism structures has a second extending direction;
• and
• wherein the first extending direction is different from the second extending directions;
• wherein after a light enters the main body from one of the first optical surface and the second optical surface, and is emitted from another one of the first optical surface and the second optical surface, a portion of the light is emitted along a front view direction, another portion of the light is emitted along a side view direction, wherein a ratio of a light luminance from the side view direction to a light luminance from the front view direction is greater than 0.4, comprising an endpoint value.