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 European Commission to take immediate measures to ensure that people who rely on incandescent light bulbs will be able to buy these bulbs until suitable alternative lighting technologies are available. There are also concerns about the risks to health from the high mercury content of the new bulbs. A campaign group called SPECTRUM was formed by the charities Lupus UK, Eclipse Support Group, ES-UK, XP Support Group and The Skin Care Campaign as an "alliance for light sensitivity" to oppose "UK and EU plans to phase out incandescent lightbulbs". Their campaign has been picked up and amplified by the British