We've all had a time or too two that when you really needed light, and I mean need it immediately, and you flip on the switch, and with a pop and a bright flash, your incandescent is toast. However, I am wondering why this happens.

I know all things will break eventually during use and it's impossible for it not to break over millions of years, but really, why does it happen so shortly? I have concluded that the heating and cooling of the filament so fast is damaging to it, and it just gets to a point where the filament becomes fragile and snaps. But will they not burn out if you leave them on constantly? I don't really mean forever, but I'm mostly asking if it will have 5-6 times longer life than before, not if it will last indefinitely. Just for completeness since we're talking about burning out and the filament expanding due to sudden temperature changes: Will dimming it slowly over a few seconds before turning it off/on help too? (Letting it cool down/warm up slowly and not a sudden reaction.)


1 Answer 1


See the world's oldest light bulb; over 110 years old!

However, that's carbon-filament rather than the modern tungsten filament, and it's not very bright. Tungsten filament bulbs are nice and bright but do evaporate over time; they will die after a decade or so, even if on continuously.

You're absolutely right about the surge behaviour with temperature and the benefits of slowly warming it up.

You could choose LED lights for longevity, but the driver circuitry has questionable lifetime, especially in electrolytic capacitors, and they need to be kept from overheating.

  • \$\begingroup\$ Clear, simple and precise. +1 And the light bulb? Wow. \$\endgroup\$ Aug 18, 2013 at 19:18
  • \$\begingroup\$ Even a tungsten-filament lamp could probably last an exceptionally long time if operated at a temperature where it's barely glowing. Many kind of lights (incandescent, LED, fluorescent, etc.) can operate for a very long time without failure at low intensity, but can glow more brightly if one is willing to tolerate a reduced lifetime. In some cases, a bulb that glows dimly for twenty years may be preferable to a bulb that glows brightly for one. In other cases, a bulb may only need to glow for a couple hours, but if it didn't glow brightly would be useless no matter how long it could last. \$\endgroup\$
    – supercat
    Aug 18, 2013 at 20:34
  • \$\begingroup\$ @supercat post above is good advice. Lowering the voltage by two bulbs in series greatly extends the reliability of light output. ie: a 40 watt and 100 watt bulbs in series. \$\endgroup\$ Aug 19, 2013 at 7:02

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