You don't really need to be a rocket scientist to know that big screen TVs use more electricity than small screen TVs. The Christian Science Monitor has an article that pretty much states the obvious:

Already, televisions account for about 4 percent of annual residential electricity use in the United States - enough to power all of the homes in the state of New York for a year, according to a new NRDC study. Today there are about 266 million TVs, and that number is growing by 3.5 million per year. By 2009, when half of all new TV sales are expected to be extended- or high-definition digital sets with big screens, TV energy use will reach about 70 billion kilowatt-hours per year nationwide - about 50 percent higher than at present. Throw in a DVD and VCR player, a pair of high-definition set-top boxes, and other household TVs, and the total TV-related energy use for the home rises to about 10 percent, the NRDC estimates.

Insert loud "DUH" here. The thing to remember is that TVs and high tech devices are always becoming more energy efficient and the reason is pointed out in the article:

A solution may happen without federal intervention, industry officials say. "Consumer electronics are vastly different from electromechanical devices like refrigerators and dishwashers," says Douglas Johnson, senior director of technology policy at the Consumer Electronics Association (CEA), an industry trade group based in Arlington, Va. "There's already a great focus on efficient design and minimizing excess energy usage that produces heat, which is the enemy of long life for electronics. So there's already a built-in incentive for efficiency."

Read As TVs grow, so do electric bills