Originally Posted by
gulliBell
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.
A lighthouse doesn't shine through fog. That's why they are located with foghorns.