A lot of my postwar pictures show some mercury vapor street lights within the "Vintage Photos" section. Here we see a rather revolutionary lamp developed by Westinghouse and was commercially available commencing in 1947. The first ones were 400 watts (as seen here) followed by a somewhat similar but smaller 250-watt version. Advantages of these newly designed mercury lamps included much more light per watt than previous ones and that this design (owing to its quartz arc tube) could be operated in any position (the predecessor ones were vertical only). These energy-efficient bulbs were pretty much a Westinghouse exclusive until late 1949 or early 1950 when GE started making them. The slim bulb as shown was soon thereafter replaced (in 1951) by a larger one (BT-37) for the practical application of diffusing color-corrected phosphors on their insides (like a fluorescent bulb). This also allowed better heat disappation and longer lamp life. Mercury vapor lamps typically deliver twice the same amount of light (albeit, bluish-green to bluish-white) than filament bulbs and have been known to last many times longer than their incandescent counterparts. The average life of these of these were a few years in street lighting service opposed to once or twice-a-year replacement when using incandescents. Subsequent mercury lamps lasted much longer, typically around 20 years with only a rather small amount of light-output depreciation in many instances. These and the early 250W lamps provide almost as much light as today's equivalents! PS..Hint, Hint! ...I collect old mercury lamps like this one, working or not. If you run across anything like this during your hunts I'd appreciate a note.