I guess an ultraviolet lamp works also? )Or at least the Soviets thought it did). https://www.nationalgeographic.com/photography/photo-of-the-day/2009/10/ultra

I guess an ultraviolet lamp works also? )Or at least the Soviets thought it did). https://www.nationalgeographic.com/photography/photo-of-the-day/2009/10/ultraviolet-bath-mcnally-pod/ https://www.nationalgeographic.com/photography/photo-of-the-...