Why is there any >24hr requirement?

For years I used a cheap incandescent, battery munching, flashlight with 'heavy duty', low capacity chloride, cells and made it work. Even for a week out camping I seldom used more than one set of batteries. Most things can be done in the dark. When the sun goes down you park it and sleep. Total artificial light use each day was a few minutes. Mostly digging in backpacks and finding stuff I dropped. Most tasks can be done by moon/starlight and by feel.

This isn't without precedent. Historic anthropologists estimate that most farmers in the late 1700s were getting ten or more hours of sleep each night. More in winter; less in summer. This was motivated by the cost of lighting. Candles and oil were expensive. Tallow and rush lighting, the low cost alternatives, gave very poor light, smoked, smelled and were otherwise problematic.

Exactly what is the light needed for? How much light, duration and intensity, is really needed?

Back in the late 60s flashlights ate batteries, didn't produce much light by today's standards, and the lights were bulky and relatively expensive. Many a Boyscout troop had one flashlight for every second or third kid and but one set of batteries per light. You didn't use it when it wasn't needed, and you didn't leave it on for long.

About the only areas that might need extended lighting through the night would be something along the lines of a command center or casualty collection site. But both of those are pretty much beyond the scope of what an individual, or even a small group, needs to worry about.

Given this sort of need oil/kerosene lamps and slow-burn candles are suitable for low-area/ambient lighting. The advantage of oil and candles are that they are simple, reliable, and the energy sources store quite well.

There are several small LED lights that use larger batteries, in one case a standard 9v stack, and they can work well. LEDs are quite easy to rig into a wide variety of batteries so they are fairly easy to rig for anyone handy with basic electricity.

For higher intensity lighting, such as task lighting for reading and medical procedures, propane and white gas mantle lanterns are quite good. These burn through a night on low but need refilling on high.