Subject: if light entered a light-proof box of mirrors- would the light intensify?

First of all - this is for personal curiousity, not any college assingment-
  I a wondering if fiber optics took light into a lght-proof box, with the 
inside enclosed with solar cells-   would the intensity of the light 
inside increase?    the inside of the box would completely be covered with 
solar cells and no light could escape the box- 

  My reason for asking is   a question of if light was fed into these 
boxes by fiber optics   and the intensity of the light did increase-  then 
more energy should be produced -making them more efficient than solar 
cells in the "open" where the light not "absorbed" escapes
   Thank You Greatly for any Help!  Extreme Thanks
Vegan Peace to you
Jon Janssen

Re: if light entered a light-proof box of mirrors- would the light intensify?