Hey, I´m surely not the best person to help you out, but given that you've got no reply so far, I'll throw in a few comments on the meantime...
I think that this is a pretty advanced question and not many people other than the ones that designed lightnig in Away3dLite can give you a direct answer. The best thing for you to do is dive into the engine's source and try to understand how it works. Once you've got an idea of the general architecture, you can focus on the specifics of lighting. Many optimization techniques are used in the engine and not only in the lighting features but in clipping, sorting, caching, etc, so all those combined might be the answer to your question.
