In my last post I told you what I found out about the power consumption by our new TVs versus our old analog sets. It's not a very pretty picture. But what about plasma versus LCD? Is one of these more energy efficient than the other?

The prevailing wisdom is that plasma screens are the bigger consumers of power. That's because a plasma screen is made up of pixels, each of which has an individual light source that gets illuminated as needed. An LCD always has a backlight illuminating the entire screen. LCDs are sort of the reverse of plasma screens in that you create the picture not by illuminating the pixels, but by blocking light from getting through to certain pixels. The LCD backlight provides a steady source of power, while plasma pixels turn on and off. Because of this, energy consumption varies depending on what you're watching.

Call for Help, a TV show that covers technology, conducted a test that measured the electricity consumed by similar-sized plasma and LCD TVs. It found that most of the time LCD screens did, in fact, consume less power. However, that changed during certain conditions, such as when they displayed a solid color background on the screen or when there was static electricity. These situations taxed the LCD more heavily and resulted in more evenly matched results between LCD and plasma TVs.

It's not just what you're watching, either. Size has something to do with it as well. EfficientProducts.org, a site that rates energy-efficient products, recommends that for smaller screens (less than 40 inches), an LCD is generally more efficient than a CRT television. In large screen sizes (50 inches and above), the site reports that a projection TV is probably the most efficient TV you can buy. It consumes half as much electricity as comparably sized LCDs and plasmas. (But remember, the picture is not as bright.) At the intermediate sizes (40- to 50-inch range), things get even muddier in picking the winner, in part because the technologies are evolving so quickly and because of the difference in how they are used.

And if you think you can answer the question by heading over to the EPA's site on Energy Star ratings, well, you can't. The EPA's Energy Star program has been labeling energy-efficient TVs based on the amount of electricity they use in standby mode (when the user has turned off the TV, but the set is still plugged into an AC outlet). Currently, a TV receives an energy-efficient rating if it consumes less than one watt when switched off if it's an analog TV, and less than three watts if it's a digital TV. But it's really not enough to look at the ratings for TVs in the off mode. Many argue that to be meaningful at all, Energy Star ratings for TVs need to look at how efficient they are when they're active, too.

From my look at all the data across multiple sources, you're going to save electricity most of the time by buying an LCD. (You'll also spend more on the initial purchase.) Meanwhile, the one loud and clear takeaway is that no matter which flat-screen TV you've bought, you will save power if you unplug it from the wall when you're not using it. Those savings increase if you've got DVD players, tuners, and other systems hooked up to your TV since they typically remain in a low-powered but standby mode when you shut them off as well.