Why does a light bulb blow out when you turn it on.

by Alfredo on May 6, 2011

Ever have a lamp burn out the minute you turn it on? I think wéve all experienced that, why does that happen?  Turning on a lamp is the main cause of lamp failure. In fact if you leave a lamp on, it will last indefinitely.

The reason that lamps fail when you turn them on is that when you turn on the switch it  sends 120 volts of  electricity surging through this hair thin tungsten filament at a mere 186,000 miles a second. Its a wonder  lamps don’t burn out more often. The older the lamp the less tungsten on the filament ( it burns off)  making the filament weaker and more likely to snap when you turn it on.

There is a lamp in a Livermore fire station that was originally turned on around 1905 then given to the fire station in 1973.  It’s called the Centennial lamp, and its so famous that they have even set up a web cam  at so people can log on  to see that its still on.   http://www.centennialbulb.org/cam.htm.  I think the switch is under lock and key to prevent it from being accidently being turned off.

So how do you prevent a lamp from blowing out the filament when turned on?  Use a dimmer;  newer  dimmers have a soft start technology that helps preserve lamp life because instead of slamming the 120 volts through the filament.  the soft start  ramps up the voltage allowing the filament to pre heat a bit before hitting full intensity, and then cool the filament down a bit as it turns off.  Dimming lamps also prevents the filament from burning at full intensity helping preserve more  tungsten on the filament.

Dimming fluorescent lighting does not provide the same advantages because fluorescent lamps don’t have a filament and prefer full voltage to vaporize the amalgam to keep the phosphors excited to provide maximum lumen output.

Incandescent-Halogen lamps that are rated to last 3000 hours can last years longer when controlled by dimmers. We have projects in the field with lamps that I installed over 10 years ago. Granted the lumen output has greatly depreciated, but that’s a topic for another day.

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