That is perfect, yes, that makes sense with my understandings. No one seemed to mention the change of light and dark spots, or interference either, so now that I know where to go it's a big help, thank you Ibix.
I have a question that I haven't found any information elsewhere on how to approach. Just because yahoo answers seemed particularly keen to sniff out homework and mock those asking questions by it, just to clarify this is for my own knowledge not for any project for school or anything. Anyway, I...