A lighting device includes a housing, a plurality of LEDs arranged on a base of the housing, and a first optical plate positioned above the LEDs. The first optical plate includes a light input surface, a light output surface opposite to the light input surface, and a plurality of V-shaped ridges aligned in at least two different directions formed on the light output surface. The V-shaped ridges aligned in different directions intersect with one another. The lighting device may be used as a backlight module.