In terms of getting the TV screen lit, yor best bet is to plug the image on the screen into the ambient, rather than the diffuse, channel. Then, for lighting the room around it, you could go for the gather node - but that can be tricky, and works best for objects that are closer to the screen. Better bet would be to place a spotlight inside the TV screen (or just outside, if you prefer). Use a blueish colour (TVs rarely project an accurate light based on the image on them, but it tends to be an all-over blueish colour instead - in my experience, anyway). If you put the spot inside the Tv, make sure you have the 'cast shadows' unchecked in the TV's properties tab.

jonthecelt