Patent ID: 7160003

Claim:
An illumination device comprising: a light source; and a light guide plate for receiving light from said light source on a light incident plane thereof and emitting the light from a light emission plane thereof, wherein: said light guide plate includes a light distributor disposed on said light emission plane, and a prism section disposed on said light incident plane, said light distributor is configured to cause part of the light incident from said light source to emit from said light guide plate as it is, and to reflect at least part of remaining light toward said prism section, said prism section is configured to refract and reflect the light incident thereon from said light distributor and the light incident thereon directly from said light source to guide at least part of the light to said light emission plane, and said illumination device satisfies the following equation: D ≤ P < 2 ⁢ ( r + d ) tan ⁢ { 90 ⁢ ° - sin - 1 ( 1 n ) } + D where r represents a distance between said light source and said light incident plane; d represents a thickness of said light guide plate; D represents a width of said light source in a direction parallel with said light emission plane; P represents a width of said light distributor in a direction parallel with said light emission plane; and n represents a relative refractive index of said light guide plate to air.