# Does on/off affect an L.E.D's life span?



## Light-Headed (Nov 6, 2002)

*Does on/off affect an L.E.D\'s life span?*

I understand that, unlike incandescent flashlights, L.E.D. flashlights are good for supposedly several thousand hours of usable life without having to worry about a bulb burning out.

However, I'm curious about turning an l.e.d. flashlight on and off. Does turning an l.e.d. flashlight on and off repeatedly adversely affect the life span of the l.e.d. in the way it most likely would with an incandescent bulb?


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## Wits' End (Nov 6, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

I'm pretty sure not. Some lights, most noteably IMHO, the Eternalight. Use PWM (pulse width modulation?) to dim the LED's. Basically it strobes the LED's very fast to give the impression of being dimmer. If the on off cycle lessened the life, the lights that use this technique would die quickly.
Hope that helps


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## Saaby (Nov 6, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

It doesn't affect the life at all. If it does it's hardly at all--maybe trims 10 hours out of that 100,000






Here's why: The reason turning on a bulb affects it's life is because when you turn it on that wire (fillament) inside sparks to life and heats up so hot that it turns white--when you turn it off it cools down (quite quickly) and the fillament shrinks. Turning it on causes the violent heating and expansion of the fillament again. This extreme expansion and contration is what kills the bulb.

LEDs have no fillamant. Turn the electricity on and light comes out. Turn the electricity off and light stops.


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## Harrkev (Nov 6, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

If anything, it should help, as when the LED is first turned on, it is cold. Heat is the big enemy of LEDs.


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## Jonathan (Nov 6, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

One of the things that contributes to lumen reduction over the life of an LED is small cracks forming in the semiconductor, and cracks in the epoxy, as well as changing the bonding to the lead frame. Thermal cycling can accelerate this cracking. So I would bet that turning on and off an LED that is being driven quite hard (and thus getting quite hot) will accelerate lumen reduction.

On the other hand, if the LED is gently driven, or the 'on and off' is PWM where the temperature is essentially constant, then I wouldn't expect it to change life at all.

-Jon


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## RonM (Nov 6, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

Sometimes the "laser" used in fiber optic communications and data systems is actually an LED. Just think about how fast that thing is being turned on and off. Hundreds of thousands of times a second?


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## Mrdi (Nov 6, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

Yes,
It depletes the estimated life expectancy from 900 to 848 hours.


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## MicroE (Nov 6, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

Ron M. wrote 
"Sometimes the "laser" used in fiber optic communications and data systems is actually an LED. Just think about how fast that thing is being turned on and off. Hundreds of thousands of times a second?"

Actually, it millions or billions of pulses per second. Those LEDs are low power (compared to a Luxeon or even a Nichia) and they are very well heat-sinked. Some even include thermoelectric (Peltier) coolers. 
Jonathan was exactly right on thermal cycling causing failures in LEDs. It's the total change in temperature that matters (highest temp to lowest temp.) Big swings in temp will eventually an LED.--Marc


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## camisdad (Nov 6, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

It also depends upon the circuitry around it if any - a current spike on on/off could have significant effect on life time cycles.


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## Light-Headed (Nov 7, 2002)

*Re: Does on/off affect an L.E.D\'s life span?*

Thanks for the answers guys. Very helpful.


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