Erica Ogg has an interesting story on the future of plasma displays on how companies are trying to improve the brightness and energy efficiency of plasma display technology. A few months ago when Samsung was showing off some of their new products in San Francisco, I checked out some of their new HDTVs and got a bit of a shock hearing about the power consumption of plasma versus LCD displays. The 50" plasma displays used anywhere from 450 to 550 watts of power depending on the brightness of the image being displayed. On the other hand, LCD displays of similar size only used half the energy yet they seem just as bright or brighter and this was one of the reasons I didn't rate plasma displays very high in my HDTV buying guide.
70" rear-projection displays are also in the 250 watt range but they're not nearly as bright compared to plasma or LCD so that may not be a fair comparison, but they do use a lot less energy for a given size. The latest 70" LCD Samsung showed off takes around 500 watts of power to operate because the power consumption grows proportionally to the display surface area. If it were a 70" plasma display then the power consumption would be much higher.
A 500 watt device if left on for 12 hours a day will cost $219 a year based on 10 cents per kilowatt*hour energy rates and that could be doubled if you need to run air conditioning. While that may not be a lot of money relative to the cost of the display, buyers need to factor power consumption costs in their buying decisions not to mention the pollution implications. According to Ogg's story, companies like Panasonic, Hitachi and Pioneer have banded together to double the efficiency of plasma displays. But until that time comes, plasmas will be energy hogs and that neutralizes the slightly lower purchase cost over LCD displays. For now, the plasmas will still have better contrast ratios while the LCDs will have better brightness and energy efficiency.