TV Power Consumption Measured - CNET
CNET have published the results of their power consumption tests carried out on eighty television sets. 'There are four basic technologies that TVs use to produce a picture, and technology type has a large influence on power consumption per inch of screen. The traditional cathode-ray tube (CRT) blasts electrons onto chemical phosphors embedded on the inside of the tube, while plasma sets ionize gas to create colors in a million or more tiny pixel cells. SpongeBob or American Idol then show up on the other side of the glass, and both require more electricity to create a brighter image.
On the other hand, flat-panel LCDs and rear-projection microdisplays use a powerful fluorescent backlight or bulb that either punches through an LCD panel with its three color filters or that reflects off of a digital-light-processing chip that has a million miniature mirrors and a spinning color wheel. Either way, they consume the same power, regardless of the brightness of the image. That's because the primary light source--the backlight or the bulb--is essentially always running at maximum power. Note that many flat LCDs actually have adjustable backlights that you can turn down to consume less power and produce a dimmer image.'
Read: The basics of TV power - CNET