Why do light bulbs burn out when turned on, but not while shining?

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SUMMARY

Electric light bulbs typically burn out at the moment they are turned on due to the rapid thermal expansion of the filament, which can lead to breakage from small imperfections. Once the bulb reaches a steady-state temperature, the filament no longer experiences significant expansion. The risk of burnout increases with the use of low-quality dimmer switches, which deliver power in a choppy manner, causing the filament to oscillate and potentially fail. High-quality dimmers incorporate chokes and capacitors to smooth the signal and reduce this risk.

PREREQUISITES
  • Understanding of thermal expansion and its effects on materials
  • Knowledge of electric light bulb components, particularly filaments
  • Familiarity with dimmer switch technology and its variations
  • Basic principles of electrical circuits and power delivery
NEXT STEPS
  • Research the thermal properties of tungsten filaments used in light bulbs
  • Learn about the differences between standard and advanced dimmer switches
  • Explore the impact of electrical signal quality on filament longevity
  • Investigate alternative lighting technologies, such as LED and their dimming capabilities
USEFUL FOR

Electrical engineers, lighting designers, and anyone interested in the longevity and performance of electric light bulbs, particularly in relation to dimming technology.

9danny
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Why does an electric light bulb nearly always burns out just as you turn on the light, but almost never while the light is shining? :confused:
 
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The filament is rapidly becoming hotter, and thus rapidly undergoing thermal expansion. During this expansion, any small imperfection may cause it to break.

Once the bulb is in steady-state, the filament no longer grows hotter, and no longer expands.

- Warren
 
The effect is much worse if your bulb is being dimmed by a cheap dimmer switch, because even though the filament is getting less power, it's getting it in a very choppy form that often causes the filament to oscillate and buzz. Better dimmers have a choke and some capacitors to help smooth out the choppy signal coming from the triac.
 

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