Abstract: According to an embodiment, a backlight device includes a plurality of light guide plates, a plurality of light sources and a light-source substrate. The light guide plates overlap each other with a same light output direction; each of the light guide plates includes a plurality of stripe-shaped projections aligned on a light output face and a light output pattern. Each of the light sources emits light incident into any one of the light guide plates and propagating in an extending direction of the stripe-shaped projections. The light-source substrate includes a plurality of interconnections, a turning-on signal is selectively supplied via the interconnections to at least one of light source groups, and each of the light source groups includes at least one of the light sources. At least one part of a light emission face, including the light output faces, emits light output from the light source group receiving the turning-on signal.

Abstract: A light reflection surface member (2) is arranged on the bottom surface of a hollow unit case (1), a light emitting surface member (3) is arranged on the upper surface side of the unit case to face the light reflection surface member, and a hollow light guide region (10) is formed by being sandwiched by the light reflection surface member and the light emitting member. On the side surface of the unit case, an LED light source (5) is arranged. The LED light source has many LEDs (7R, 7B, 7G) in rows, and each LED emits single color light of red or green or blue. On two strips of light reflection surface member in the unit case (1), a color sensor is arranged for measuring illuminance of each color light entered the hollow light guide region from the LED light source (5).