The present invention improves the luminous efficiency of lamps that emit light
due to electric discharge, such as a fluorescent lamp and an HID lamp. The fluorescent
lamp includes a glass tube used as a fluorescent tube made of a glass material
containing an emissive element. When exposed to ultraviolet light (with the peak
wavelength of 251 nm) emitted due to mercury excitation, the emissive element emits
ultraviolet light having a longer wavelength than that. The HID lamp includes an
envelop made of a glass material that contains an emissive element. When exposed
to ultraviolet light emitted due to excitation of an emissive material enclosed
in an arc tube, the emissive element emits ultraviolet light having a longer wavelength
than that.
