The Natural Philosopher explained :
I think that is overblown.

All you need is something like a guitar pickup. Lots of turns round a magnet
close to where the blades are. Should be enough power to light a LED

Well I tried it and although the blown flap was able to operate a
micro-switch quite easily, the flap slowed the exit air flow and
quickly choked it up.

I'm not going to try attaching anything to the blades, I have in mind a
magnet on blade pulley, above the deck. It should be fairly easy to
then make a bracket to mount a coil.