Reader Question: How Green is My HDTV?

Q: Some weeks ago, I heard you mention thedifference in power consumption between LCD and plasma televisions on The Personal Computer Show. I have found that Crutchfield provides a comparison option which includes their own testing of TVs. When you have some time, could you compare the four 46″ models I have listed below, using Crutchfield.com. From what I can determine there does not seem to be a great deal of difference of power consumption in actual real world use. Thank you.
David Whitfield, Ohio

A: Thanks for the question, David. As with most technical issues, the generalities are sometimes contradicted by specific instances. This is a complex topic, but let me take a stab at it.

First and foremost, I commend Crutchfield for putting in the time and effort to measure power consumption for their televisions. A review of the four models you cite does show a plasma unit scoring slightly lower than an LCD unit using the Crutchfield measurements. Unfortunately, I cannot find any details on the Crutchfield Web site about how they got these results, so there has to be some question about how to interpret them.

The problem is that LCD and plasma screens consume power differently. Plasmas draw the most power when displaying a white screen at full brightness, because plasma power consumption is a direct result of how much light is needed to create the image on the screen. A picture of a snowy mountain top in daylight is going to draw much more power than a shot of a bad guy lurking in the shadows of a Gotham City alley. This is why it would be helpful to know how Crutchfield tested, because the images you put on the screen will affect the results.

LCDs, on the other hand, change their consumption little as the image changes. For most, they have fluorescent tubes as backlights, which remain on at full brightness whenever the set is on. The LCD layer blocks or transmits the light as needed to create the image, but the backlight stays on. The backlight is more efficient than the plasma panel, however, which is why the LCDs use less power than the plasma maximum.

And there’s one more factor that Crutchfield does not report, and that’s the brightness of the display. In general, LCDs are capable of producing a brighter image than a plasma. I expect that if the brightness on these LCDs was dialed back down to match the output of the plasmas, the power consumption advantage of the LCDs would show more clearly.

Note that some new LCD TVs are using LED backlights instead of fluorescent. Not only do these tend to give better color performance and consume a bit less power, they also make it possible to dim the backlight in darker regions of the image on the screen. This can cut power consumption in half.

Finally, it’s worth considering how significant the savings are. If you leave a single 100 watt light bulb burning while you watch TV instead of turning it off, you will wipe out the difference between the most power hungry model and the least on your list. Using Crutchfield’s estimate of 6 hours a day and $.10 per kilowatt hour, that difference is just $2 a month. So it may not be worth spending hundreds of dollars more just to get a set with lower power consumption.

Do you have questions about HDTVs? Write me at alfred@hdtvprofessor.com and I’ll do my best to help.