Super Mario Boards

how else will he get that eerie ominous glow from the inside, perfect for setting the atmosphere

It's weird, doesn't Luigi first encounter many rooms inside with the lights off already?

he does. once luigi's in the mansion there's no need for the atmospheric setting from the outside, so turn it off until mr. green lights the place up

alternatively, perhaps the presence of ghosts suppresses light, and the presence of light suppresses ghosts. so king boo was able to empower them to make their way into the rooms and block out the light, but once caught they are no longer capable of doing so