Roman plasterwork was applied in layers, and in first layer (which is quite rough) a diamond pattern is scratched. This is to increase the adhesion of the next layer (also known as the key). This is also true of lime plasterwork done through the ages.
As far as I can see only the first layer with the diamond pattern is visible one the left wall. The other layers may have not survived. Why would you bother to create a diamond pattern if you're not going to put more layers on?
In fact, the wall at the far end does show more layers, and also some decoration right in the the middle.
I wonder how they came up with that 1750 BC figure of 400 hours of work for one hour of light. Any ideas? It sounds ridiculously high, so I assume I'm missing something. What are they even talking about? Olive oil or tallow lamps? Firewood? Something else?
"One hour of light (referred to as the quantity of light shed by a 100 watt bulb in one hour) cost 3200 times as much in 1800 in England than it does today"
Oil lamps are not so bright, and you would need lots of them to reach the same brightness as a 100 watt bulb.
In other words, they still had light, but not so much and not so often.
Roman salves in some case could become full citizens. Slavery was different for different cultures treatment varied greatly from situation to situation. The closer the slave was to the rich the better they were treated in general
So even slaves at Pompeii had a window to get light from, we see.