Green Light.

The green light event is when a room or multiple rooms are encapsulated by green light (the bulbs change from yellow/blue/white to green, a lamp changes to green, even fridge lights can be affected).

When a room is encapsulated by green light, that means that a spirit is ready to attack.

The green light phenomena can't happen if there are no lights present in the room.

The red light, on the other hand, is a good thing.

This behaviour can be seen here, here, and here.