| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to reduce the thickness of the above device and to permit the easy and rapid execution of work for replacing a display board and fluorescent tubes. SOLUTION: This device consists of the display board 4 which is disposed in an aperture 9 of a box-shaped frame 5 opened on one side, the fluorescent tubes 3 which are light sources disposed within the frame 5 and a luminance regulation film 2 which regulates the quantity of the light radiated from the fluorescent tubes 3. The light transmittance of the luminance regulation film 2 changes at a specified ratio in proportion to the distance L between the fluorescent tubes 3 and the display board 4 to 40 to 60% within the perpendicular projection range X of the fluorescent tubes 3 and up to 95% off the perpendicular projection range X (a range Y) in the luminance regulation range.
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