LEDs 5 serving as light sources are arranged so as to face an incidence
surface 4 of a light guide plate 3. Light emitted from the LEDs 5
is incident on the incidence surface 4 of the light guide plate 3
to enter the light guide plate 3 to be propagated through the light
guide plate 3. When the angle of incidence of the light on an emission surface
6 of the light guide plate 3 is a critical angle or less while the
light is propagated, the light leaves the emission surface 6. On at least
one of the emission surface 6 of the light guide plate 6 and a surface
10 opposite to the emission surface 6 of the light guide plate 6,
a large number of prism protrusions 12 extending in parallel to such a direction
that a distance from the incidence surface 4 increases are formed along
the incidence surface 4. A side-face side portion 10b of the
prism protrusions 12 is formed so as to have a height gradually decreasing
as a distance from the incidence surface 4 decreases. With this construction,
even if the LEDs are used as light sources, abnormal emission can be suppressed
in the vicinity of the incidence surface of the light guide plate, and the luminance
of exiting light can be uniform.
