I think most OSR-ish people would agree that resource management is a fairly essential part of the game. That running out of light or spells or needing to rely on wits rather than something on the character record sheet is one important aspect of making D&D more fun, exciting, scary and “realistic” (only in as far as realism adds to the fun and does not detract from it).
Having watched the videos below and a bunch more:
I came to the following conclusions:
All my real world research indicates that PCs have the choices between:
A. Torches, that burn half an hour each and with good amount of smoke and of which they can only carry a limited amount due to bulk/size and also weight. (I will be tying this to STR and statur/encumbrance)
B. Oil lamps, which gave very little light, rather easy to either break or snuff out. Required you to carry vegetable oil.
C. Beeswax candles, likely in a lantern in order that they stay lit/are more portable and don’t get snuffed out by a draft or wind. But, in (pre) medieval beeswax candles were very expensive indeed, on the order of Silver pieces (maybe even a GP?) per each candle and the alternatives (rush lights, cheaper tallow instead of wax “candles”, which burned faster, sputtered, gave less light and were unreliable (snuffed out easier, wick needed trimming).
D. Ropes used to be hard and costly to make, were thick and heavy and would be substantially weaker when wet. So not every player can just carry 3 coils of 20 meters at all time, not even close. It depends on strength and how much other kilos they are carrying.
So the upside is that darkness will be scary again, players will have to absolutely resource manage/hurry through or make several trips to a dungeon and/or spend quite a bit of cash to even have a reliable light source in order to go down a (every) dungeon and to poke around without being literally 100% in the dark. They may have to climb without the safety of a rope or simply spend money on new rope with some frequency.
Now I just have to conclusively figure out a “realistic” (good) D&D cost per candle and also how many hours each “standard” medieval candle would burn.