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 those over 15 watts on 1 October 2016. Another source, however, has indicated that by 1 October 2016, all incandescent light bulbs will be banned. According to this source, 1 November 2011 to 30 September 2012 will be a transitional period and as of 1 October 2012, imports and sales of ordinary incandescent bulbs of 100 watts or more will be prohibited. The first phase will be followed by a ban on 60-watt-and-higher incandescent light bulbs starting in October 2014. By October 2016, all incandescent light bulbs will be banned in China. The final phase may be adjusted according to