iPhone 5 flashlight strength
My apologies for not being able to give you a 100% answer. But I did find a informative post about the LED strength of an iPhone 4 (should be the same for the 5 - not the 5S).

Using a combination of direct and reflection lux meter readings, and comparing the same readings to lights of known lumen output, I'd roughly estimate the iPhone 4 LED is about 5 to 10 lumens in normal continuous use.
It briefly gets significantly brighter when used as a camera flash, but it's too brief to measure with my lux meter. I'd estimate it's about 4x brighter, which is around 40 lumens, but only for about 1/4 second.

Source
I hope this helps!