My daughter knows of my interest in LED flashlights so she picked how does varying current change an LEDs brightness.

So I've been trying to bone up so I can explain principals to her.

I've read and halfway understand how a LED actually creates light-electrons falling into holes and giving off protons, but I can't find a good explanation of how increasing the current increases the brightness.

It doesn't help that I've heard most of our flashlights varying the brightness by the turning of the LED on and off really fast (PWM?)

So if anybody know of any sites or could explain how current increases, increase brightness I'd really appreciate it.