I have a confession to make.

On the UDs of lightly-loaded A380s, the green lights of unoccupied CW seats stay on. Once the cabin lights are switched off for everyone to sleep, the low height of the undersides of the overhead bins means that the lights in effect create a sea of green ceiling, and a surprisingly bright one. So I have sometimes gone through the cabin moving the unoccupied seats just enough to get the green lights to switch off and make the cabin as dark as it ought to be during a true nighttime flight.

I suspect that lightly-loaded A380s have been a rarity recently.