Differences between heavy and light whipping cream?
Heavy Whipping Cream (at least in the States I believe) has a fat content of 36% or greater. Light Cream generally sits between 30% and 36%. Heavier cream generally will have a "richer" taste. Light Cream will also not whip quite as thick and not hold it's form as well. That said, for most cases, I've successfully managed to use them interchangeably. I guess it might make a difference if you were doing something where holding a rigid structure for extended periods of time was important.

Note: What various grades of cream/dairy are called varies by region... Here in Canada we have Whipping Cream 35% and Heavy Cream ~40%. If I were somewhere where "Light Whipping Cream" sat closer to 30%, I might grab something a little higher.

More info.