I've always wondered with flashlight apps, especially ones that use the LED light(s): Is there any risk of shortening the life of the LEDs? I noticed one app ("ASettings") gives a warning that doing so can "harm your phone"... which to me sounds even more ominous than burning out the bulb. I thought LEDs had a crazy long lifespan to begin with, so do I need to worry?
There's a really good thread of discussion about this on AndroidForums here.
In short, LEDs have a long life span (20k+ hours?). So the concern isn't really the LEDs burning out (although after a long period of time, they will eventually start losing the amount of output and their brightness will dim).
The real concern is to not apply too much voltage to the LED and overheat it. Another concern would be overheating your battery (due to heat dissipation from draining the battery from powering the LED).
In short, if you're only using the LED for time periods less than half an hour, you should be okay. If you need to use it longer, go get a real flash light. :)
LEDs do have a long lifespan (35K-50K hrs depending on the type of LED) but the issue is heat. The LEDs are intended to be used as a flash (ultra short duration) and probably don't have very robust heat managment systems if they have any at all. Each phone is going to be different. I would say that using it as a flashlight for a couple minutes tops is fine, but beyond that you run the risk of overheating which, depending on the type of LED and where it's positioned in the phone in relation to other hardware could damage the LED and possibly other components.