You will need to make a small modification to the expression. At the very end, instead of random(0,100), you might want to change that to random(30,100). Play around with it and see. This will effect how dark the light goes when it flickers. You may also want to tweak some of the other parameters to make it look more natural.
Modern televisions work much differently than the old CRTs we grew up with. The conventions of clicking remotes and snow between channels are still expected by most audiences but they are anachronisms. It is very easy to over-work this effect by adding way too much activity.
Even in the olden days, we found it was much more interesting and satisfying to play a videotape through a TV on the shooting set than it was to try to fake it.
Forget After Effects and start thinking about renting or borrowing some hardware. A practical effect will be the most convincing BY FAR. You won't get AE to realistically follow lighting contours on a human face without a TON of work... and I somehow think that's something you're trying to avoid.
Put the video you want on tape or DVD.
Include Channel Changes.
Play it back through a video projector.
Aim it at the part of the room you want to light up.
Tweak the room lighting until it's the way you want it.
Roll the camera and the video.
Get a few takes... or several, depending on your needs.
Poof! You're done! No AE necessary!
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA