There's a real simple, cheap, and easy way to add ambient lighting to your existing large television. Just mount a small light bulb behind the television set. It's that simple.
Step 2: Diagonals
Different CFLs have different color temperatures (not the amount of power needed for the bulb but how “cool” or “warm” the color is of the white bulb) and you may want to experiment with different bulbs to see what bulb reflects best off of your wall.
For my setup I've run an extension cable to a switched outlet so I can turn the ambient light off when I don't want it. I could have used a colored bulb for different moods.
Step 3: Horizontals
With a TV parallel to the wall you'll want to mount something on each side of the television (speakers, bookcases, or cabinets) to prevent spillover light when somebody walks on the side of the television.
Step 4: Conclusions
I decided to use this approach because it's so simple, I had all of the parts already (net cash outlay – zilch) and it only took 15 minutes to install.
If I wanted to get fancy I could have made a small controller with three different color bulbs so I could change the ambient light color.
These views show a commercial HDTV with a built in ambient back light and my HDTV without and with the ambient back light in action.