A backlight module includes that of: a substrate; a plurality of light-emitting elements, disposed on the substrate along a first direction and a second direction; and at least one optical film, comprising: a first surface, having a plurality of microstructures, the microstructures being parallel to each other, every microstructure having a first ridge, and an angle being between the first ridge and the first direction; and a second surface, corresponding to the first surface and toward the substrate, the plurality of light-emitting elements being between the substrate and the second surface; wherein a distance X is between the light-emitting element and the other light-emitting element that is adjacent to the light-emitting element along the first direction, and a distance Y is between the light-emitting element and the other light-emitting element that is adjacent to the light-emitting element along the second direction, hence a range of the angle is: ( tan - 1 ⁢ Y X ) - 10 ⁢ ° ≤ θ ≤ ( tan - 1 ⁢ Y X ) + 10 ⁢ ° .