| 摘要 |
PROBLEM TO BE SOLVED: To reduce uneven brightness due to reflection and to improve quality of the light emitting surface by forming the incident plane into a roughened surface within the range of specified arithmetical mean roughness and making the extent of roughness in the longitudinal direction of the incident plane rougher than the roughness in the thickness direction of the incident plane. SOLUTION: In the light transmission plate 12 an incident plane 12A is formed into a roughened surface within the range of 0.05-0.3 (μm) arithmetical mean roughness. Thereby the directivity of the incident irradiating light from the incident plane 12A is corrected and uneven brightness due to the reflection resulting from a change of the brightness level of the outgoing light is reduced. In the light transmission plate 12, the extent of roughness in the longitudinal direction X of the incident plane 12A is set to be rougher than the roughness in the thickness direction Y of the incident plane 12A in the roughening treatment. Namely, the light transmission plate 12 is formed with 0.10 (μm) arithmetical mean roughness in the thickness direction Y of the incident plane 12A, and on the other hand, is formed with 0.15 (μm) arithmetical mean roughness in the longitudinal direction X of the incident plane 12A. |
