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 electricity savings would pay for the initial cost of CFLs four times faster than in Vancouver, where incandescent lighting contributes to space heating. In all climates, there is a net cost saving from changing to compact fluorescent lighting. The cost of CFL and LED bulbs has declined greatly since 2008, which shortens the time needed to pay off their initial cost. While the excessive heat produced by incandescent light bulbs is frequently seen as a drawback, in certain applications it is seen as an advantage. For example, automotive applications in cold climates benefit from the radiated heat as it melts