Shape: Light and Distance

I'm doing the Strobist Lighting 102 course / exercises, and I the distance exercise is really valuable, I recommend everyone go read the post and do the exercise. The direct link is here.

So the exercise to the reader here is: what color is the actual background material? That's right, it's white foam core, and it's only 5 feet behind the vase. But (and here's the a-ha moment), the light is only 18 inches from the vase. So the light it casts on the background is much less intense than the light it casts on the subject (insert inverse square law here).

You can click on this image if you want all the lighting details.