The Egyptians used copper and bronze mirrors to reflect the ample sunlight available outside.
The cave paintings were lit by some sort of firelight, and it wouldn’t surprise me to learn they’d figured out candlemaking that long ago, they certainly had enough fat available from megafauna kills.
That theory about mirrors has been demonstrated to be false. The laws of physics on light simply don’t permit the theory to work to any distance within a tomb.
I’ve seen some small (around 4” in circumference)containers that were supposed to be oil lamps, but the length of time they would work would be very limited. And if you’ve ever been down deep into a pyramid (like the one at Chichen Itza that is open to tourists) you know that the supply of fresh air is limited as well.
Still, if you have unlimited time and shifts of workers, I suppose you can accept that. Dogged fellows those Egyptians.