| 摘要 |
PROBLEM TO BE SOLVED: To increase the exit light quantity of a lamp and to obtain the lamp having high luminance and low electric power consumption by providing the outer peripheral surface of a glass tube with an antireflection film specified in refractive index. SOLUTION: The antireflection film 1 consisting of a prescribed dielectric film, etc., is formed on the outer peripheral surface 3a of the glass tube. The light generated by a phosphor film 7 is prevented for being reflected on the outer peripheral surface 3a of the glass tube by this antireflection film 1. The material of the antireflection film 1 formed on the outer peripheral surface 3a of the glass tube 3 is adequately a material having the refractive index between the refractive index of the glass tube 3 and the refractive index of air in a range of visible light (wavelength 350 to 780 nm). Namely, the antireflection film 1 having the refractive index of at least one component material larger than the refractive index of the air and smaller than the refractive index of the glass material constituting the glass tube 3 is disposed on the outer peripheral surface 3a of the glass tube 3. As a result, the surface reflection on the outer peripheral surface of the glass tube 3 of the lamp 2 is suppressed and the light generated from the lamp 2 may be emitted outside without being returned to the lamp 2.
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