There's a multitude of emulsions available, even after a lot of them have been discontinued. Each one reacts a little differently to light, both in terms of requiring more or less light, but also in terms of reacting in various unique ways to light.
I like to view what people are hitting my site about so that I can make the content of my site more useful. Sometimes, I'll notice a search that seems to ask a question but I'm not sure if I've got a great answer for it, so here's some short answers...