You do not want enemy bombing aircraft to see a light and give away your position but how do you get around in a blackout?
Using a 3 watt Argon gas lamp which puts out 1 candlepower of light (concealed in oblong Admiral's hat type reflector to point visible light rays downward) and sending invisible light rays (ultraviolet) to road signs with reflective fluorescent paint. Enough illumination for drivers or pedestrians but not seen from plane.
