| 摘要 |
PROBLEM TO BE SOLVED: To provide a light guide plate which can easily control the intensity and directivity of projection light emitted from an arbitrary position of a light projection surface part, and to provide a plane illumination device using the light guide plate. SOLUTION: The plane illumination device is equipped with the light projection surface part 16 for projecting the light, a reverse-surface part which is positioned on the opposite side from the light projection surface part 16, flank parts 13a to 13d which cross the light projection surface part 16 at right angles, an incidence end part 14 which is formed at the flank parts 13a and 13b and where light from a light source 15 is made incident, a light guide plate 12 having a plurality of light deflecting elements 19 which are projected at the reverse- surface part and have ridges 20 extended radially from the incidence end part 14 so that the heights of the ridges 20 from the reverse-surface part gradually increase toward the incidence end part 14 and sectional shapes perpendicular to the ridges 20 are triangular, and a light reflecting sheet 17 which covers the light guide plate 12 except the incidence end part 14 and light projection surface part 16. |
