I do not think I have ever seen a need to run a light for a continuous 24 hours. My multiple battery operated lights and a slew of new batteries would easily go for a week or more if needed. After that my crank-operated Eton radio-light thingie would continue to work, though a pain. Candles, open flame fire, and I suppose at last resort my camp stoves could sort of work.

I am a fan of going to sleep when it is dark and working when it is not.