Originally Posted by
cncpc
..How much cloud depth, i.e. ceiling lower than the light itself, will result in the light not being visible?
The light wouldn't be visible unless you were looking outside and saw it. They weren't expecting to see a lighthouse, and presumably the only person looking outside was the FLIR operator, who just happened to notice the rock, but with no mention of a lighthouse being planted on top of it. The cloud could be a pea-souper fog down to surface level and you should still be able to see the lighthouse light from a mile away through the fog and pitch blackness of the night.