Prism sheet, surface light source device, image source unit, and liquid crystal display device

A prism sheet which changes directions of incident lights to emit the incident lights, the prism sheet comprising:

• a body portion formed in a sheet, having a light transmitting property;
• a unit prism portion arranged on one face side of the body portion, having a plurality of unit prisms each having a convex shape and arrayed in a direction along a sheet face;
• and
• a light diffusing layer arranged on the other face side of the body portion, wherein:
• one side across a tip of the convex shape is a light input face of each of the unit prisms, the other side is a reflection face, and the reflection face consists of three faces each having a different inclination angle;
• and
• Ra≦−0.0263·P+2.0537 is satisfied wherein P (μm) is a pitch of the plurality of unit prisms and no less than 10 μm, and Ra (μm) is a surface roughness of the light diffusing layer and no less than 0.035.

A prism sheet which changes directions of incident lights to emit the incident lights, the prism sheet comprising:

• a body portion formed in a sheet, having a light transmitting property;
• a unit prism portion arranged on one face side of the body portion, having a plurality of unit prisms each having a convex shape and arrayed in a direction along a sheet face;
• and
• a light diffusing layer arranged on the other face side of the body portion, wherein:
• the unit prism is formed in a symmetrical shape and a vertex angle at a tip of the convex shape of each of the unit prisms is no more than 80°;
• and
• Ra≦−0.0208·P+2.0223 is satisfied wherein P (μm) is a pitch of the plurality of unit prisms, and Ra (μm) is a surface roughness of the light diffusing layer.