Well the app I used to use had several variable output levels, and it was very handy when you really needed it, but high drained battery quickly. Of course that was before I switched to LED flashlights, now its a pretty weak light 
Any light is 100% better than no light. As I understand it many backlit PDA and phones provided enough light for some to get out of the World Trade Center. My ancient Nokia 3200 has a small built in flashlight, but no flash for the camera, good hear new phones have a light I was going to miss it when upgrading someday. Almost bought the Nexus4 during the recent $199 unlocked sale, but too slow to act, so waiting on Nexus5 and BF (black Friday after Tday sales).
What app? I dont know any app with variable output
I thought most had variable output, the basic ‘flashlight’ app that came on my HTC Desire S has 3 levels. I measured them at 8, 12 and 16 lumens so not great spacing though.
Just an HTC flashlight app has 3 modes, not infinitely variable.
If you have an apple product the “Flashlight” app has a slider bar, compass, on/off button, 18 speeds of strobe, and SoS.
Edit: In the pitch black of night the lowest setting of flash…light is a bit too bright indoors; I usually just flip the phone over and occasionally press the home or sleep button to keep the lock screen open and illuminating the floor with the screen on ~40% brightness.
its a fine device, but battery life is not good enough, hopefully nexus 5 fixes that, but i am doubtful
really?
anybody could try to use the phone as a flashlight for more than 1 hour and would it burn out?
There are LEDs made specifically for camera flash applications. Also driver chips designed for LED flashes. Many of the flash LEDs have a rather limited lifetime spec (like 10,000 flashes).
Semiconductors usually have some kind of heat cycle life rating, so many times at X temp and so many die. With a camera and a LED light source I can see a designer playing some games, intensity vs duration and matching the chosen capture time with the camera sensor, maybe even something fancy like flash duration and intensity to suit ambient light, motion in the frame, with the sensor telling the driver when it has enough light for a good capture.
With a cellphone I can’t see a designer not erring on the safe side for LED flashlight use regards heat etc.
OTOH, as long as no more than X fail under warranty, I doubt they care, if not actually wanting some number to fail post warranty or contract time.
My ancient Nokia 3200 flashlight mode is similar to a keyring device with a dime battery, very low, but you can find a keyhole or watch your step.
camera flash led, interesting concept that i never considered, what is different about it vs a regular LED?
My guess, nothing with the emitter, maybe a slight difference in heatsink/mount, and a special driver with a burst mode.
possibly, but 10,000 flashes is very low, a 105C driver oscillates 4500 times per second
The phone manufacturer did not design the driver chip. The chip has 2 distinct modes.
Here is an example of 1 such chip:
Here is a good explanation of a mobile phone camera flash:
http://wiki.maemo.org/N900_Hardware_Flash_Torch
The more features you supply as standard, the less opportunity people have to develop for your platform. The fewer people developing, the less mass you have. Less mass==less money.
Its been awhile, but as I recall its junction temperature and heat cycles, even in the slow strobe modes I don’t think significant heat cycling occurs, but it would need to be something like that where the temperature change at the junction is fairly large.
They are designed to take momentary high current pulses for producing bright flashes. They still have a limited lifetime due to being severely overdriven in flash mode.
Cut and paste of the specs for a couple from texaspyro’s link.
Part
Typ Flux (lm)
Typ Vf (V)
Typ CCT (K)
Off-State Appearance
Test Current (mA)
Datasheet
LXCL-EY17 260 3.2 6000 White 1000 DS121
LXCL-LW07 500 3.25 4500 White 2000 DS122
thanks for posting that