Prices for flat-screen TVs are falling fast and with the January sales in full swing, it's a great time to find a bargain. On the high street this month, a quality 42" plasma TV can cost as little as £500 and an LCD of the same size will set you back only £600.

Almost all new TVs sold in the UK now are flat-screen, and when buying a new TV most consumers upgrade not just in style and technology, but also in size. The Energy Savings Trust says that the average flat-panel is now 50% larger than the TV it replaces.

Although prices on new TVs have never been lower, the running costs are much higher than their old-school predecessors. Most consumers aren't aware of the extra energy expense when shopping for a new TV but upgrading to flat-panel could cost you more than three times more to run than your old TV.

How much more energy does a new TV actually use?
A conventional 28" TV uses about 100 watts of electricity. A new 42" LCD TV will use about twice that, but it's the plasma TV that's the real energy-hog. An efficient 42" plasma TV will use about 300 watts and if the display is set to high and bright, it will use much more - up to 500 watts - making it the SUV of TVs.

Most TVs are on for about five hours a day and with a standard old TV, that would account for about 3% of annual household energy usage. A plasma will increase its share of your household electricity bill to about 10%. But it's not just new TVs that are adding to our energy bills. Xboxes, Playstations and set-top-boxes will add to that again. In fact, an Xbox 360 uses almost as much electricity when played as a plasma TV. When put together, your new TV and games console could add £100 a year to you electricity bill.

Legislation in the US
Across the pond in California, the extra energy used by flat-screens is causing such a worry to legislators that they are planning to pass laws banning retailers from selling all but the most efficient models. The new laws set to come into effect in 2011 are part of a larger plan to ease pressure on California's ageing grid. With an ageing grid here as well, it can only be a matter of time before MPs start looking at our TVs too.

To reduce the effect you new TV has on your pocket, look at the energy ratings before buying. Plasma TVs use much more energy, but they are becoming more efficient. And if you don't need a monster TV, go for an LCD.

Of course, you can compensate for the added usage of your new TV by cutting consumption elsewhere in your home such as shutting off standby gadgets, using efficient lighting and adding power-saver plugs. But if you've already taken these steps, the easiest way to offset the inevitable increase in cost is to switch energy suppliers to the cheapest deal. If you haven't switched for a while, you could save 15% so even with your new TV; you'll still come out ahead.

This article also appeared on MSN