| 摘要 |
PROBLEM TO BE SOLVED: To obtain a back light device in which emitted light beams are converged along the direction of the normal of a light guide plate to increase the directivity and to improve apparent luminance. SOLUTION: The device consists of a light guide plate 11 and a line shaped light source 12 arranged on the side of the plate 11. Plural grooves 15 are provided on a light emitting surface 21 of the plate 11. The cross section of each groove 15 is shaped into an approximate parallelogram and each of the grooves 15 is tilted with respect to the normal of the surface 21 so that it approaches the light source 12 as it extends toward the bottom of the plate 11. The plural grooves 15 are formed in parallel with the light source 12. The grooves 15 are filled in with the material having a refractive index less than the refractive index of the plate 11. Employing the total reflectivity of the grooved side surface, a back light having a high directivity is obtained. |
