Patent ID: 8780419

Claim:
A light guide, comprising: a rod-like main body which is capable of guiding light in a longitudinal direction; an input surface which is provided on one end of the main body and on which the light is inputted; an output surface which is provided on the main body, from which the light is emitted in a direction intersecting with the longitudinal direction and which is long in the longitudinal direction; a reflecting surface which is a surface provided on the main body and opposite to the output surface; a first diffusing portion which is formed on a part of the reflecting surface closer to the input surface than a preset reference position and diffuses light; and a second diffusing portion which is formed on a part of the reflecting surface closer to a side opposite to the input surface than the reference position and diffuses light; wherein: the first diffusing portion has a first length in a direction orthogonal to the longitudinal direction, the first diffusing portion includes a plurality of recesses disposed at intervals along the longitudinal direction, each recess in the first diffusing portion extending in a direction perpendicular to the longitudinal direction and functioning as a prism; the second diffusing portion has a second length in the direction orthogonal to the longitudinal direction, the second diffusing portion includes a plurality of recesses disposed at intervals along the longitudinal direction, each recess in the second diffusing portion extending in the direction perpendicular to the longitudinal direction and having a shorter length in the direction perpendicular to the longitudinal direction than the recesses in the first diffusing portion; each of the plurality of recesses has a first prism surface on the input surface side and a second prism surface on a side opposite to the input surface; an angle formed by the second prism surface of each recess included in the second diffusing portion and the longitudinal direction on the side opposite to the input surface is smaller than an angle formed by the second prism surface of each recess in the first diffusing portion and the longitudinal direction on the side opposite to the input surface; and the first length is longer than the second length.