I would need help from more experienced with this:
— Is the LED life affected by using PWM? For example flashlight with 2.8A nanjg driver - 2.8amp impulses on lower than 100% mode.
— Does amperage matters? ie. is PWM with lower current impulses better for LED than high current impulses?
— Are there some other advantages/disadvantages or differences using pwm vs. current regulated driver?
Good question. With PWM the led isn’t technically on as much, but it’s constantly turning on and off which usually isn’t good for things.
Manufacturers don’t seem to be worried with PWM. Many cars have PWM leds on position lights. Even bedside digital clocks use PWM dimming at night and the illumination of those displays is the lest thing that fails.
Leds have extremely long lifespan I wouldn’t worry if it PWM cuts it in half (not that it does)
PWM can be good - turning on at higher amp seem to help LEDs maintain their tint better. By using high enough, say 2kHz above, you get good compromise between flicker and modulating brightness.
Current regulated sometimes shift the LED tint to yellow/green at very low current.
I haven't read anywhere that switching affects the led life at all. What does happen is that in a PWM controlled light the led always gets high currents (but in the lower modes in a on-off cycle). So if the led is overdriven in max mode (2.8A for xml is pretty overdriven already), it also receives that current in the lower modes, but in strobe form. But still then, I think a led suffers the most from the overheating that comes with continious high currents, not so much from high current alone.
Disadvantage of PWM control, apart from the fact that some people are sensitive to low frequency PWM, is that also in low modes the led suffers the same inefficiency that comes with the overdriven current that is used on the max setting. But then again, a lot of the inefficiency that is measured at high currents is again caused by overheating of the led and that does not occur in low modes.
Personally I like a light that uses PWM to be not too much overdriven, because that also affects runtime in the lower settings . But a current controlled light I like to have with a ridiculously overdriven turbo setting 
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Disadvantage of current control (if you think that it a disadvantage) is that the led tint is affected by current, especially noticable in very low currents.
LEDs aren't like incan lights. Switching on and off doesn't shorten their life span. Incans hate it because they use a filament and create light by heating until they glow. THe heating and cooling cycles on the filament create expansion and contraction in the metal causing it to weaken far more quickly than if simply left on. Like bending a paperclip back and forth until it weakens and breaks, turning an incan off and on does the same and eventually the filament fatigues and breaks.
If anything, I'd imagine PWM will increase the lifespan of an LED. If an LED would last 100,000 hours if left on in continuous regulation, it may just live 200,000 hours left on using PWM with 50% duty cycle. It's overdriving an LED that will shorten it's lifespan.
Heat is the big worry for the LED. Driving at lower current is generally more efficient (except at the super low levels.) In theory you could get the same light levels with less total heat generated using a constant current instead of a PWM. Not sure it would be more than a trivial difference though because we are already talking about lower levels not the max where heat is less of an issue.
Let’s be honest even a 20k hour lifespan on an LED in a flashlight used on average an hour a day is 54.8 years of usage. Lifespans are usually rated to 70% output as well not death. That light would still be useful, if dimmer, long after that period.
Well, that sucks. I was planning to continue using my lights well into my two hundreds.
Thanks all for answers, so this could be the result:
- pwm doesn't affect led life
- then I suppose amperage of PWM pulses doesn't matter also, as long as LED has good cooling and is not suffering from heat
with current regulation there is a little tint change in low levels, which doesn't happen with high current PWM pulses at low output
- and of course low PWM frequency is not wanted
Any tips to live that long? :-)
1. Be a turtle.
2. Stay away from Asia and the bikini atoll.