Originally Posted by
Ziemas
The real question is how much of that four hours is usable light? I'd be interested in the runtime to 50% output, which is how lights are usually rated.
Well, it has a driver so the light output is very nearly constant.
As the battery voltage drops the current draw increases so that the watts supplied to the LED remains the same.
With a fresh battery the voltage is high and the current draw is low.
With a tired battery the voltage is lower and more amps are taken from it to compensate.
This enables the driver to keep the current (and therefore the voltage) at the LED the same.
Having said that, before the LED went out I shone it on a white surface, then when it went out I did the same immediately after fitting a fresh battery and it was a little brighter.
Maybe the when the battery is nearly depleted it can't supply enough amps to keep the wattage the same and then the output drops ? I don't know for sure, more run tests and measurements required.
I'd say that if the light output did drop as low as 50% before going out, it must have been in the last 2 or 3 minutes.
Hope this helps....