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 has an exchange program to replace incandescent bulbs. Tunisia is reported to have a partial ban on incandescent light bulbs. Since January 2016 the importation of incandescent light bulbs has been banned in Zambia. Zimbabwe has banned incandescent light bulbs. Bahrain has banned incandescent light bulbs. Bangladesh has an exchange program. China will ban imports and sales of certain incandescent light bulbs starting October 2012 to encourage the use of alternative lighting sources such as light-emitting diodes (LEDs), with a 5-year plan of phasing-out incandescent light bulbs over 100 watts starting 1 October 2012, and gradually extend the ban to