The Deep

Below the colony, below the bars, the farms glow. You are going east through them, and the crop is the only light there is.

In a closed ecosystem the light is alive. Darkness is not the absence of a lamp — it is the absence of something living, so every dark stretch is a place the system already failed. The thing that failed it is still down here, and it breathes what the plants do not.

Down into the farms

The light is alive, and it is the only thing keeping the dark off you.

Point and hold to walk. That is all there is.
The crop glows, so where the crop is living, you can see — and the meter top-left tells you whether you are standing in enough of it.
The plants make the oxygen. The thing down here breathes the other gas, so it will not follow you into living ground. In the dark it will.
Where it passes the crop dies, so the dark spreads behind it and the ground you were counting on stops being safe.
Go east, and keep to the green. There is a way up at the far end.

Where the rules come from

“The genetically modified plants let off a gentle green glow…”
“The light they emit actually contains enough energy to provide a photosynthetic process for the remaining plants.”
“The plants generated oxygen and pumped it through the caverns.”
“The farms, although rich and plentiful, looked like they had been largely abandoned.”
“A race capable of living on far less oxygen and far more carbon dioxide.”

All from Trials.