This is a General Electric, "War Dept. Standard" Indoor Blackout Bulb, shown with its original sleeve. It was used during WWII. This is an American bulb, but European blackout bulbs also exist (in Germany they were called Air Raid Lamps, "Luftschutz Lampen"). Their purpose was to create a minimal light source to be used inside homes during air raid alert "blackouts", in which there was reason to believe there was danger of an air raid. When this happened, all normal bulbs had to be turned off, and these bulbs had to be used instead. The idea was to make it more difficult for enemy aircraft to locate their targets. I heard a story about these bulbs from an eBay seller, he said that if patrolling troops saw light coming from your home during a "blackout", they could shoot out the source. (I haven't verified this). This bulb was made by General Electric, however there is also a version by Wabash, which is shaped like a radio tube. A very similar bulb was produced by the SAVE electric company. G.E. chose the regular appliance bulb shape for their Blackout bulbs (A-17 shape). Blackout bulbs were not the only "blackout" accessory produced; Plastic covers for essential lights such as car and bicycle headlights were also made, as well as black curtains for windows.