When you have rats in your home the rats will usually wait to come out and roam about your house when the lights are turned off.
That is usually because the rat believes everyone has went to bed and the house is safe for them to roam around.
I noticed when I had rats in my house that when I had the lights on the rats would not come out but as soon as I turned the lights off the rats would come out and start getting into things.
Rats usually sleep during the day and come out at night.
If you have rats you should get some rat poison to put out so that the rat eats it and then dies because rats can be hard to catch in traps.
Rats can do a lot of damage to your home such as chewing wires, tearing up papers etc.