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 have banned incandescent light bulbs on 1 January 2014. As specified in Interministerial Ordinance 1,007 of 31 December 2010, incandescent light bulbs must perform according to certain levels of luminous efficacy in order to be produced, imported and sold in Brazil. Non-conforming light bulbs are being gradually phased out. As of July 2013, bulbs ranging from 61 to 100 Watts which do not perform accordingly can no longer be produced nor imported, but until mid-2014 they can still be sold. Since end of June 2016 it has been completely prohibited in Brazil. The Chilean government has prohibited the manufacture, import