Well, "sound" could be classified better as "Sonic" type, but that would sound like copyright infringement. As Colcolstyles said,
Coolboyman gave me the idea, and I started thinking about how it could be a really interesting "abstract" type to throw in that could be whatever you wanted it to be.
As for Light type, I still stand behind it. Dark needs a parallel, because with its super-effectiveness against Ghost and its immunity to Psychic, it is really strong. The only reason it's not superpowered is because there are so few pure Dark types. Now, people are thinking of "Light" as in physical light, but maybe it would be helpful to throw in a distinguishing factor. The Japanese for "Dark" is "aku" (あく - 悪), which means "evil" when translated. I am thinking of light as a Nintendo-censorship-standards-safe way of saying "holy", which in Japanese is "Sei" (せい - 聖). That should help to distinguish it from Fire, Electric, and Psychic in peoples' minds.
The type chart could be as follows:
Could non-haters check that out and see if you spot any imbalances? :)
There are only a few pokemon which I could see being re-typed as Light-types:
Blissey (and possibly Chancey)
Mawile (to make it an appropriate parallel to Sabeleye)
Hopefully that helps clarify why some of us want Light type.