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 in times known as "blackouts", in which there was reason to believe there was danger of an airstrike. When this happened, all normal bulbs were turned off, and these bulbs were used instead. The idea behind this probably was to make it difficult for enemy airplanes to accurately locate cities to attack. 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, but it wouldn't surprise me if it's true). 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 car and bicycle headlights were also made.