We talked again. Lets say you have a totally concealed room made up of all mirrors. The only thing is that there is a hole in the wall. If you shine a light through that hole into the room full of mirrors and then have a device that slides in a small mirror shaped as the hole instantaneously as soon as you take the light away. Will that room always be lit up?
I'm gonna have to guess no. Not all light incident on the mirror will be reflected. Some of the light will be used to heat up the mirrors. So I'd say the light will slowly fade and you'll end up with a room full of warm mirrors.
I do not quite remember the name of the law but When light comes in contact with any object part of it passes through it. Light even passes through the earth, albeit in a non noticeable way.