Luke 11,33-36  

33    " One who lights a lamp does not put it in the cellar or under a bushel basket ,
but rather on a lampstand , so that they who come in may see the light.
34  The eye is the lamp of your body .
When your eyesight is sound , your whole body is lighted up ;
but when your eyesight is bad , your body is in darkness.
35  Take care , then , that your light is not darkness.
36  If your whole body is lighted up and not partly in darkness ,
it will be as fully illumined as when a lamp shines brightly for you. "