I think LED lights are the way to go! Way less complex than a
generator, very low power use, life near forever, no extra drag for
horses to pull. simple straighforward change.

even if you have a generator you will still need a battery for non
motion times.

LED should cost less too.

just go look at some current LED lanterns, WOW was my first thought.

If you REALLY want a generator get a small hand crank one the amish
kids can wind to keep the battery charged!