Every readout here is an object in the world, not an overlay: oxygen on the suit forearm, temperature on a gauge bolted by the hatch, power as a lamp that actually lights the room, and the wreck log on a screen you have to walk over to. Drag power down and the pod genuinely gets darker. Drag damage up and the instruments start to flicker.
Drawn by src/diegetic.js. Each function takes a context and a world position and returns nothing — except drawPowerLamp, which returns the light radius so the caller can feed it into its own lighting pass. That is why low power darkens the room instead of displaying a number telling you it is dark.