You can watch how depth changes light
intensity. Just Click
here and you will find a device such as this. Pull the lever
down to increase depth and you will see how the light intensity
is different. You must go to the site to use it.
This picture is from"Shedding
Light on the Subject". (Online) Available http://illuminations.nctm.org/imath/912/Light/index.html,
April 18, 2001.