The 'big three' of TV power: Size, type, and settings
The power used by an active television is determined by three factors: screen size; technology type, such as plasma or LCD; and picture brightness, which nearly always depends on user-selected picture settings.
Screen size: Bigger TVs use more power. A 32-inch LCD uses about half as much power as a 52-inch LCD. Of course, the 52-incher's screen is nearly three times as large as that of the 32-inch model, so the efficiency payoff for going down in screen size does tend to taper off. However, the chances are your new flat-screen TV will use more power than your old tube TV--if the new set is significantly larger.
Technology type: Plasma TVs use more power than LCD TVs. In our tests of TVs since the beginning of 2008 plasmas consume, on average, roughly two to three times more electricity to produce an image of the same brightness as LCD. In the last couple of years, plasma TV makers have made some progress--Panasonic claims improvements of 30 percent yearly, for example--but they still can't compete with LCD for energy efficiency. One problem is that in plasma TVs, each pixel is a discrete light source (think of it as a tiny light bulb), so when resolution increases, say from 720p to 1080p, power use goes up as well. The intensity of light from each pixel must be increased to brighten the picture as a whole.
With LCD-based TVs, on the other hand, a backlight shines through an LCD panel to create the image. Since the pixels reside in the panel, and not the backlight, the TV's power use is largely independent of resolution. Many LCDs can conserve additional power by automatically turning the backlight down during dark scenes and up during bright scenes. Some models use a different backlight technology, such as LEDs, which are inherently more efficient than standard fluorescent backlights. And some "local dimming" models can even control the brightness of different parts of the LED backlight independently.
Old CRT-based TVs are relatively inefficient, especially compared with LCD TVs; however, since CRT screen size is limited, they often don't use as much power as big flat-screen models. Rear-projection HDTVs are actually the most energy efficient per square inch of the TV technologies, but they're rare nowadays.
Picture settings: Brighter pictures consume more power, and since light output is primarily a function of the picture settings available on all TVs, this is the one factor that any user can control regardless of television. Reducing the light output of your TV can cut power use by as much as half, and as long as you don't overdo it, you'll still enjoy excellent picture quality.
The principal settings that matter are contrast (aka "picture") and backlight (or "cell light" on Samsung plasmas). Both directly control light output. Nearly every TV has a contrast control, but backlight is generally restricted to LCD models--and not every LCD has it. In LCDs with both backlight and contrast controls, backlight is the main determinant of light output and power use. Counterintuitively, the brightness control has less of an impact on TVs light output than the other two settings do.
Other controls are also often available, such as energy saver modes, which typically limit peak light output, dynamic settings that raise or lower the light output depending on the brightness or darkness of the picture being displayed, and room lighting sensors that increase light output in dark rooms and lower it when the lights dim. Engaging any of these controls will generally reduce the TVs power use, but it will often sacrifice image fidelity. Automatic adjustments can be distracting, for example, and aggressive energy saver modes can make images too dim.
But you're right, it could be a factor for some.
But now I'm a little devided...
