Live shadow effects on an element

So I got this idea while I was working on a site that used some parallax effects. I thought, “wouldn’t it be cool to be able to change the box-shadow on an element as you scroll past it?” It would give the illusion of the users point of view being a light source that was shining on the page. Well I told a talented friend about this idea and before I could even grasp how to achieve this, he had it all whipped up! But he did it in an even better way than I had previously thought. Take a look at the jsfiddle and see for yourself.