It really depends on what you want to say. This is mostly the same abstract difference between "I think" and "I believe". About "Lorsque" and "Quand" there is a very mathematic difference. "Lorsque" can be used about both of past and future, "Quand" can be use about the only future. If you want to use "Lorsque" about the future, it pictures a very precise moment like talking about what someone will do right after being here, or the precise moment you can take off the bag of tea from boiling water.

Haha! Thankyou Chris I thought not, as in lorsque and quand for when. How about pour for to and for...why.and when are they both used?

I was going to say that there is a difference, but it's so subtle that it vanished before my eyes! So would say that no, there is no difference.