To carry out changeover of wavelength without deteriorating uniformity of luminance in an ultraviolet surface light source having a structure in which a plurality of straight-tube ultraviolet lamps are arranged and sufficiently use only one kind of the ultraviolet fluorescent lamp to be a base and to eliminate the need of using an expensive ultraviolet transmitting filter when used in a fluorescent transilluminator.
The ultraviolet light source is composed of an UV-B light source 1 irradiating the UV-B, an ultraviolet wavelength converter 2A absorbing the UV-B and emitting only UV-A, a lighting means for the UV-B light source 1 and a means for moving the ultraviolet wavelength converter 2A and inserting the ultraviolet wavelength converter 2A into an illuminating optical path of irradiated light from the UV-B light source 1 or taking out the ultraviolet wavelength converter 2A from the illuminating optical path. The ultraviolet wavelength converter 2A is composed of an ultraviolet transmitting glass plate 4 transmitting light at ≥300 nm wavelength and a layer 5 of an europium (Eu)-activated chloride ultraviolet phosphor represented by compositional formula Ba1-xEuxCl2 (wherein, 0.005≤x≤0.3) and formed on the surface thereof.
Kawai Nobuaki
Yasuhisa Tanizawa
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