[reed13k]

If I recall correctly there were often mirror systems - burnished copper/bronze I think - used to reflect lights into these as they were constructed as well. I’d imagine those were expensive and transported from place to place as needed.

and then the lamps and likely braziers.

[Covenantor]

I've often wondered how they provided sufficient light and air into the tombs for the elaborate wall decorations. And in the Lescaux caves as well.

Regardless of the type of available fuel of that era, all would have generated various quantities of soot or lampblack which could be expected to rise to the ceilings. Which is not evident in the highly decorated ceiling in the above photo.

It appears as the niche soffit in the image below which seems to show such lampblack, but absent a descriptor we're left to speculate.

Another example of what might be lampblack on a very low ceiling.

The other problem is getting sufficient air into the chambers to both feed the combustion and provide for the artisans breathing.

Any system of reflectors is limited in the distance between light source andcwork surface, light intensity drop off, square of distancecand all that. Try it with a candle and a silvered mirror, better than anything available then, and you'll understand the problem in the high spaces.

I find the cave drawings a far more interesting problem because aside from being in pitch black spaces, they are also high, beyond human reach without some aid, rude scaffold maybe. At any rate some construction skills seem necessary but not evident from the drawings themselves or recovered artifacts. Interesting points to ponder and chat about.