A mold frame contains a lamp shade and a light source, a light guide being erected at the open end and secured in place on one side of the lamp shade; streams of light from the light source entering into from one side of the light guide plate to project in the direction as expected; and a mask device being disposed on the mold frame at where close to the joint edge of the light guide plate so to weaken the reflection rate of the light that leaves the light guide plate, to reduce the interference of the light in the light guide plate, and to diminish the phenomenon of ripples.