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 potentially visually-obstructive snow and ice on warning lights and signs. The heat is also used to melt the wax inside lava lamps. Some CFLs may not be compatible with existing dimming circuits such as those using TRIACs, although more dimmable CFLs are expected to become available as the phase-outs continue. Mains voltage halogen bulbs provide a somewhat more efficient dimmable alternative to common incandescent bulbs and are readily available, although they too will be phased out in the EU from September 2018. Dimmable LED lamps are available from several vendors, although not all LED lamps are compatible with dimmers and