Patent ID: 8177380

Claim:
A light-emitting device having an improved light scattering property on a planar display surface, comprising: a light-emitting element; and a light flux controlling member for controlling light emitted from the light-emitting element, the light flux controlling member having (i) a light-incoming surface from which the light emitted from the light-emitting element enters the light flux controlling member and (ii) a light-outgoing surface from which the light being incident on the light-incoming surface is emitted from the light flux controlling member, wherein the following equation is satisfied: ∫ P ⁡ ( ϕ 1 ) ⁢ sin ⁢ ⁢ ϕ 1 ⁢ ⅆ ϕ 1 = - A ⁢ ⁢ ⅇ - r 2 2 ⁢ σ 2 + C where the planar display surface is orientated perpendicular to the reference light axis of the light-emitting device, is provided at a certain distance from the light flux controlling member, and has a length (r) from the reference light axis of the light-emitting device, φ 1 is an angle between the light emitted from the light-emitting element and the reference light axis, P(φ 1 ) is a light distribution property of the light-emitting element, C is a constant defined to satisfy φ 1 =0 when r=0, σ is a constant indicative of a scattering property, and A is obtained by the following equation: A = ∫ 0 π 2 ⁢ P ⁡ ( ϕ 1 ) ⁢ sin ⁢ ⁢ ϕ 1 ⁢ ⅆ ϕ 1 .