Subject: Could you trap light in a perfect mirror-box and release it later?

I always thought it an interesting question.  Perhaps because I'm not 
a physics man.

Suppose we had a "perfect" mirror substance that would reflect light 
perfectly.  

If we made a cube of this with a lid, took it out into the sunshine, 
opened it, then closed it.  Could we capture some sunshine?  Then take 
the box to a dark room and open it and experience a brief flash of 
light as the trapped sunshine escaped?

Re: Could you trap light in a perfect mirror-box and release it later?