| 摘要 |
PROBLEM TO BE SOLVED: To overcome the problem such that it is difficult to provide water- proofing and dew condensation-proofing structure for an air layer without increasing the number of parts and an assembly work process in a light emitting device using a prism optical system having the oblique air layer inside. SOLUTION: This light emitting device is equipped with a light emitting tube 1, a reflection mirror 7 arranged along in the longitudinal direction of the light emitting tube and having a nearly semicircular or nearly semi-elliptic cross section, and the prism optical systems 6, 4 and 5 arranged in front of the light emitting tube. In the device, the air layer AIR extended obliquely to the longitudinal direction is formed in the prism optical system. The thickness G of the air layer is set to 0.03 mm<=G<=0.5 mm.
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