| 摘要 |
PROBLEM TO BE SOLVED: To improve the transmitted illumination efficiency and the illumination brightness quality by laminating a light guide plate on the whole rear surface of a dial, and forming V-shaped grooves on a rear surface of the light guide plate along a circular arc drawn on a light source position. SOLUTION: The light sources 22 are mounted on the outer edge surfaces of the light guide plates 21, 23 on which the rear surfaces of dials of a measuring instrument are laminated, and a number of V-shaped grooves 30 are formed on the rear surfaces of the light guide plates along a circular arc drawn on a position of the light source 22 from a position close to the light source 22 in the direction far from the same. Further a number of stepped parts 31 are formed after a group of V-shaped grooves 30 along the circular arc on the light source 22 from the light source 22 in the direction far from the same. The intervals among the V-shaped grooves 30 and the intervals among the stepped parts 31 are respectively gradually narrowed in the direction far from the light source 22, whereby the brightness of a part far from the light source 22 can be increased, and the surface illumination of approximately uniform brightness can be obtained by the surfaces of the light guide plates receiving the light by their outer side edge surface. |
