I have two 'emergency' white led flashlights which are human-powered. They make a sound of a small generator which is probably a dc motor.
a) The squeeze light must be worked rapidly. It's always jittery since my hand is moving around. It goes dim as soon as you stop.
b) The windup light has a crank (similar to jack-in-the-box). After several seconds of rapid turning, you can stop and it stays lit for about a minute, gradually going dim. Tutorials suggest power comes from a capacitor rather than a battery.