Firing at night has some of it's own challenges...
If you can't see when the stack clears, there are other clues.
Steam gauge is one, as soon as it starts to drop a pound or two,
it's time to feed it again...If the engine is working steadily upgrade,
the time between fires will be about the same interval.
You also have to learn to peek at the fire without killing your night vision so you can see if there are light spots that need covering.
Early on, I was still learning this. On my first pay trip west
from Alamosa it was near midnight and I went to the gangway for some air. My night vision was affected by not keeping eyes near closed
to look into the firebox. As I reached for the grab irons on the right side, My left hand missed the iron and I swung out a bit and came
close to falling off the damn engine right there!
Only then did I discover we were right on the middle of the Cascade Trestle. It would have been a hell of a step, and the ol'm D&RGW
almost was short of a green fireman that night.