A device used to provide illumination by means of an electric current which excites mercury vapor in a glass tube, producing short-wave ultraviolet light that then creates fluorescence, producing visible light.
Instant-start type bulbs required no starter switches, lowering the cost of maintenance. To allow for an instant start, the lamp bulb contained a loose overwind of fine (0.7 mil.) tungsten wire added to a coil of modified dimensions. The overwind performed a double function. First, it reduced sputtering time by rapidly reaching the emitting temperature when the arc first struck; and second, it acted as a 'basket' to hold a large quantity of emission material tightly. When the first lamps of this design were manufactured, they were affected by end discolouration. This problem was resolved in 1947 by using a cathode shield made of nickel or iron.
An example of a lamp bulb used in Canada, part of a large and varied collection of over 7500 electrical items acquired and documented by Ontario Hydro in the 1960s. The collection was thought to be the largest and most comprehensive of its kind in Canada and was donated to the Canada Science and Technology Museum in 1992
Glass tube coated with white phosphor/ metal parts/ synthetic parts
Number of Parts
White tube/ metallic and black end caps
Black lettering on glass reads 'WESTINGHOUSE/ 40 W COOL WHITE/ INSTANT START/ F40T12/CW/IS' and '37'