When it comes to energy consumption, you might be surprised how much more expensive a plasma TV can cost compared to an LCD. It’s a fact Consumer Reports knows well. Our lab techs measure the energy consumption of each TV we test. How? With a nifty little device called a “watt-ammeter,” at right. (Click to zoom in.)

One of our testers, Chris Andrade, rigged one to a 46-inch, 1080p LCD for me. The box on the bottom (with the gauge) provides a controlled voltage. The left number on the top box—the watt-ammeter—indicates the energy consumption of the TV, about 177 watts. A typical 1080p plasma of the same size would average about 400 watts.

How much will each set you back? Depending on how much you TV watch, the LCD could average more than $50 a year. The plasma, more than $120. For more sizes, see our chart on what it costs to run a big-screen TV. Fortunately, it’s likely those numbers will come down. Energy consumption should probably drop in TV models released later this year, as editor Paul Reynolds discusses in our video from CES 2009.

(If you really want to see how much juice your appliances are quaffing, check out our claim check on plug-in energy monitors.)

Energy costs shouldn’t be the only deciding factor when buying a TV. Big-screen plasmas do tend to cost less than similar-sized LCDs, and are generally better for theater-like viewing. There are plenty of other considerations before buying. Check out our TV Buying Guide for more on TV types, brand profiles, and shopping tips. —Nick K. Mandle