Patent ID: 7434976

Claim:
A double-side display device comprising: a semi-transmissive liquid crystal panel comprising a liquid crystal layer sealed by sandwiching the liquid crystal layer between two glass substrates, the semi-transmissive liquid crystal panel having a reflecting region and a transmission region; and a surface light source device comprising: a light guide plate having a light outgoing plane in a principal plane thereof, the light outgoing plane facing the semi-transmissive liquid crystal panel; and a light source facing one end face of the light guide plate, wherein a plurality of deflection patterns are formed in a surface facing the light outgoing plane of the light guide plate, the deflection pattern including an inclined plane located on a light source side and a re-incident plane substantially perpendicular to the light outgoing plane; light emitted by the light source into the light guide plate is reflected by the inclined plane and then the light is outputted from the light outgoing plane; and a tilt angle (α) of the inclined plane satisfies: 45°−[Sin −1 (Sin θ/ n )]/2≦α≦45°+[Sin −1 (Sin θ/ n )]/2, where θ is an angle formed between a direction of peak brightness of the light outputted from the light outgoing plane and a direction perpendicular to the light outgoing plane, and n is a refractive index of the light guide plate.