Why can't I reflect light infinitely?

I put a LED night light in the bathroom so I don't have to turn the light on every time I go in there.
I have noticed that the light reflects in the mirror so I can see 2 night lights.
Hmmm, why can't I put mirrors on every wall (other than it would look like a whorehouse) and reflect the light over and over and over again infinitely?
Something tells me there is a basic law of physics that would prevent this - something like laws against perpetual motion.
So college kids (I rank this a little above high school physics and I hope I'm right because I don't remember learning it in high school) - why can't I put mirrors all over the walls and ceiling and magnify a 3w night light into 300 watts?
I have noticed that the light reflects in the mirror so I can see 2 night lights.
Hmmm, why can't I put mirrors on every wall (other than it would look like a whorehouse) and reflect the light over and over and over again infinitely?
Something tells me there is a basic law of physics that would prevent this - something like laws against perpetual motion.
So college kids (I rank this a little above high school physics and I hope I'm right because I don't remember learning it in high school) - why can't I put mirrors all over the walls and ceiling and magnify a 3w night light into 300 watts?