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
Phase-out of incandescent light bulbs less than 100 watts, nightlights and shatter resistant bulbs. This effectively banned the manufacturing or importing of most incandescent bulbs of that time. The timeline for these standards was to start in January 2012. By 2020, a second tier of restrictions would become effective, which require all general-purpose bulbs to produce at least 45 lumens per watt (similar to current CFLs). The United States Environmental Protection Agency's Energy Star program in March 2008 established rules for labeling lamps that meet a set of standards for efficiency, starting time, life expectancy, color, and consistency of performance. The intent of the program