I was recently watching this American WW2 propaganda video about the Japanese people and their culture. The scene in question (running from 51:18-51:22) came up in the part where they explain the military training that young children undergo. It lasts only about 5 seconds and depicts several naked boys with tinted goggles in what almost appears to be a room with radiation of some sorts. If any one could provide any insight to what is occurring and if it actually did occur in Japan (as this is a propaganda video and what they are doing almost seems sinister in nature).
It looks sinister in the movie perhaps, but it is simply UV light therapy. It was common to do it like this in Scandinavia too, but now tanning salons serve the same purpose.
Vitamin D production is dependent on sun, and during dark winters of the north, it is necessary to supplement the UV radiation from natural sources. Vitamin D is added to milk in Scandinavia for this reason, but tanning is also a way to achieve this. This is also said to help with seasonal affective disorder/winter depression.