[The evolution of artificial sun lamps in Japan between the two World Wars].

This paper depicts the historical evolution of ultraviolet devices in Japan during the interwar period. The outbreak of the First World War spurred the development of the glass industry in Japan, being triggered by the military demand on optical instruments in particular. Meanwhile, physicists needed special glass which could cut off ultraviolet radiation to protect the eyes during spectroscopic experiments. Furthermore, as the effects of the invisible rays on human health came to intrigue the medical and lay audience introduced by the works of Niels Ryberg Finsen, artificial sun lamps for actinotherapy were devised. In Japan, Tokyo Electric (a forerunner of Toshiba) together with the physicist, Nagaoka Hantaro, promoted the development of anti-ultraviolet glass. A national institute based in Osaka chased the project. Eventually, with the advent of knowledge regarding the glass which was practically transparent to ultraviolet rays, the electric company launched a commodity for lay consumers in 1930. The electric device manufacturer produced ultraviolet radiators as a "load builder," during the times when the supply of electricity in Japan exceeded its demand. Ultraviolet radiators, used as tools for hygiene and public welfare as well as for medical treatment, thus trickled onto Japanese soil by the next World War.