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
Longest-lasting light bulbs Longest-lasting light bulbs This is a list of the longest-lasting incandescent light bulbs. The world's longest-lasting light bulb is the Centennial Light located at 4550 East Avenue, Livermore, California. It is maintained by the Livermore-Pleasanton Fire Department. The fire department claims that the bulb is at least 117 years old (installed 1901) and has only been turned off a handful of times. The bulb has been noted by The Guinness Book of World Records, Ripley's Believe It or Not!, and General Electric as being the world's longest-lasting light bulb. While it might seem astonishing that so many longest-lasting light bulbs