Incandescent light bulb Small variations in resistivity along the filament cause "hot spots" to form at points of higher resistivity; a variation of diameter of only 1% will cause a 25% reduction in service life. These hot spots evaporate faster than the rest of the filament, which increases the resistance at that point—this creates a positive feedback that ends in the familiar tiny gap in an otherwise healthy-looking filament. Irving Langmuir found that an inert gas, instead of vacuum, would retard evaporation. General service incandescent light bulbs over about 25 watts in rating are now filled with a mixture of mostly argon and
Hammer Historical Collection of Incandescent Electric Lamps William Joseph Hammer started to collect incandescent light bulbs from 1879 while they were being developed in the Edison laboratory in Menlo Park, New Jersey. He was an associate of Thomas Edison and in his engineering career he was able to collect early filament electric light bulbs from Edison and others because of his association in the field. The Hammer collection is the most comprehensive collection of incandescent electric light bulbs known in the world. It shows the technology development of the filament electric light bulb during Thomas Edison's lifetime. Hammer's incandescent light bulb collection from around the world was