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 the results of interim assessment from October 2015 to October 2016. It has been reported that the ban would be complete by October 2016. While not a complete ban, the UJALA plan in India sought to replace 770 million incandescent light bulbs with LED bulbs by 2019. This was expected to reduce energy consumption by over 100 billion kWh annually and reduce annual electricity bills by . As of April 2017, 229 million LED bulbs had been distributed across the country. The states of Tamil Nadu , Kerala and Karnataka in India have banned the use of incandescent bulbs in