Patent ID: 7819560
Filing Date: 2010-10-26
Classification: F21V,F21Y,G02B,H01L

Abstract:
1. An illumination device, comprising: a point-like light source emitting light; and a lens receiving the light emitted from said point-like light source and emitting the light as illumination light illuminating a region-to-be-illuminated, said lens having a flat incidence face directed to said point-like light source and a light control emission face that is located opposite to said flat incidence face, the lens emitting rays which reach said light control emission face after being emitted from said point-like light source, the rays entering into said lens through said flat incidence face and travelling only within said lens without undergoing inner-reflection at any surface of said lens as said illumination light, said light control emission face having a configuration such that no crossover is given by rays included in said illumination at least before said illumination light reaches said region-to-be-illuminated, said light control emission face including a first emission face and a second emission face connected continuously with and surrounding the first emission face, the first emission face being smoothly concavely curved from a connection portion between the first emission face and the second emission face, the second emission face being smoothly convexly curved from the connection portion to an outer edge of the light emission face, and light flux density of said illumination light is lower in a direction-range-near-to-optical-axis including a direction of an optical axis of said point-like light source as compared with that in a direction range outside of said direction-range-near-to-optical-axis, the first emission face smoothly concavely curved and the second emission face smoothly convexly curved providing curvature such that the emission direction characteristics are expressed by the following formula, where θ1 is an incidence angle within the half-intensity-angular-range, the incidence angle θ1 being an incidence angle defined as an angle made by light from a light emitting element and an optical axis, θ5 being an emission angle defined as an angle of light being emitted from the light control emission face, θ′ being an angle giving the maximum of θ5, and k being a constant larger than 1 for expressing a difference in illuminance between a center portion and a periphery portion of the region-to-be-illuminated.