If you are talking about the "lighting effects" filter, it should be under Filters>Render>Lighting Effects, if it is where it was in CS3.
It’s not there. I googled, and apparently they decided not to put it in. There was a big forum discussion about it, and now I can’t recall exactly what they said. You can still use it if you run it at 32 instead of 64 or something. It’s not he end of the world, I only used it on occasion, but I’m not sure why they would dump it.
However, it does some other things I really like and i still have 7 on my PC laptop so if I just HAD to have it for something I could still do it. I’m still getting used to the ins and outs, it’s quite a jump up from 7.