Backlight module

A backlight module, comprising:

• a plurality of first light-emitting elements;
• and
• a light guide plate, comprising:
• a light-emitting surface;
• a bottom surface opposite to the light-emitting surface;
• a first light-incident side connecting the light-emitting surface and the bottom surface, and the first light-emitting elements are disposed at the first light-incident side along a first direction;
• a plurality of first columnar microstructures extending along a second direction perpendicular to the first direction and disposed on the light-emitting surface;
• and
• a plurality of columnar microstructure groups disposed between the first columnar microstructures on the light-emitting surface, each columnar microstructure group comprises a plurality of second columnar microstructures extending along the second direction,
• wherein a number of the second columnar microstructures of each columnar microstructure group is 1-15 times a number of the adjacent one of the first columnar microstructures,
• wherein each first columnar microstructure has a first width along the first direction, each columnar microstructure group has a second width along the first direction, the first width is larger than or equal to the second width,
• wherein a first height of each first columnar microstructure is larger than a second height of each columnar microstructure group.