| 摘要 |
PROBLEM TO BE SOLVED: To make easily detectable a raindrop even in the case of a double- layered glass by arranging a light-guiding material or hologram at a hollow space part. SOLUTION: In an example where a light-guiding material 51 for introduction and a light-guiding material 52 for leading out are arranged at a hollow space part, if detection light is introduced to the double-layered glass as shown by an arrow when no rain is falling, the light passes through a prism 71 for introducing, indoor-side sheet glass 11, and the light-guiding material 51 for introduction and enters outdoor side sheet glass 12, is totally reflected for a plurality of times by the outdoor side sheet glass 12, passes through the light-guiding material 52 for leading out, the indoor-side sheet glass 11, and the prism 72 for leading out, and is received by a photo detector. In this case, nearly total quantity of detection light is received. On the other hand, when raindrops adhere to the outdoor side sheet glass 12, the detection light is scattered by the raindrops and the detection light being received drastically decreases. By comparing the quantity of received light with a reference amount value where no rain is falling, the raindrops can be accurately detected.
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