Patent ID: 7815345

Claim:
A vehicle-purpose lighting tool, comprising: a light-conducting member having a front light-emitting plane, a rear plane having a concave/convex shape, and a side edge plane; and a light source arranged at a position opposite to the side edge plane, wherein external light which is entered via the front light-emitting plane into the light-conducting member, a portion of the external light which is directly traveled to the side edge plane is totally reflected on a boundary plane of a side edge plane portion, wherein a plurality of reflecting portions are formed on the rear plane and are coupled to each other via a coupling portion in such a direction that the reflecting portions are separated apart from the side edge plane-side, wherein distances between the plurality of reflecting portions and the front light-emitting plane are changed in a discontinuous manner along the separating direction, and wherein an angle “θ” defined between a plane defined by the reflecting portions and the side edge plane, another angle “θ 1 ” defined between the front light-emitting plane and the side edge plane, an incident angle “θ 2 ” of the light of the light source with respect to the side edge plane, and a refractive index “n” of the light-conducting member can satisfy the below-mentioned relative equation: θ=[180°−θ1−sin−1{sin(90°−θ1/ n )+sin−1{(sinθ2)/ n}} /2.