[sakuna]

Bioluminescence is probably the most efficient naturally occurring light source.
Think fireflies. In NZ we have an insect commonly known as a glow worm (arachnicampa luminosa) or cannabilistic maggots with shiny **** which is more accurate as they are larvae & not actually a worm. They predominately live in dark, damp, & drafty areas specifically caves, where they spin vertical silk feeding lines to catch their prey, utilising their glowing excrement as a lure.
My point is, that in areas heavily populated with glow worms, they collectively emit enough light that, you could almost read a book. Perhaps you could breed a colony then populate your living areas as required.
Impractical i know, but i thought it worth mentioning.
A couple of free energy hydraulic devices for consideration/research are the self acting water ram & the vortex generator, both can provide mechanical advantage in numerous applications and/or generate electricity.
Best regards