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 directive EC 1194/2012 relates to mains voltage directional halogen lamps and means many common halogen reflector lamps such as D rated GU10's are affected. Iceland is following the same route as the EU. Montenegro banned incandescent bulbs over 100W from 1 July 2018, part of a phased ban. Norway has implemented the EU directive for the phase-out of incandescent light bulbs and has followed the same phase out route as the EU. There was a half-year delay in implementing the directive compared to the EU, but the phase out occurred at the same time since the affected light bulbs