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 quality of products. Those CFLs with a recent Energy Star certification start in less than one second and do not flicker. In January 2011, the province of British Columbia banned retailers from ordering 75- or 100-watt incandescent bulbs. Canada's Energy Efficiency Regulations are published on the Natural Resources Canada website. The Canadian federal government banned the import and sale of 75- and 100-watt incandescent bulbs, effective 1 January 2014. On 1 January 2015, 40- and 60-watt bulbs were also banned. Retailers will be allowed to sell their existing inventories imported before the bans. Cuba exchanged all incandescent light bulbs for