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It can be difficult to calculate quite how much power your computer and its peripherals consume, so we've tested a range of equipment and power configurations to reveal how much energy your system may be gobbling up - even when it's switched off.

The three most power-hungry parts of a PC are the monitor, processor and graphics card. As a result, the energy demands of a top-of-the-range gaming PC can be much higher than a standard desktop. In our tests, the high-end Chillblast 8800GTX consumed a full 273W of power when running a 3D action game, whereas the Dell Dimension C521 consumed only 105W during the same 3D tests. Even when idle, the Chillblast used 183W compared to the Dell's 70W. The lesson? If you want to be environmentally friendly, don't buy a PC with a higher spec than necessary.

While such advice may be unattractive for many, there are easy ways to make power savings with your choice of screen. Naturally, the bigger the screen the more electricity it draws, but our tests reveal that it's the screen's native resolution rather than physical size that is the differentiator. Thus our tests reveal two 20in screens with a native resolution of 1,680 x 1,050 draw almost identical amounts of power as two 22in models of the same resolution (around 45W). Move up to 24in screens running at 1,920 x 1,200 and the power requirements rocket to around 75W. But don't be lulled into thinking that reducing your screen's resolution in Windows will save power - it's the physical number of pixels being illuminated that makes the difference.

However, there's an easy way to crank down your monitor's energy demands - reduce the brightness. Our measurements show that a monitor running at half brightness consumes only three quarters of the power, and many monitors still display a perfectly presentable picture at lower levels of brightness.

Printers are another peripheral where power consumption varies enormously. Laser printers are the energy villain of the piece - the Oki B2500 MFP consumed as much as 760W during operation (three times the drain of the gaming PC), with the HP LaserJet M1005 MFP eating through an average of 300W; the most power-hungry inkjet in our sample consumed a mere 20W. Yet, the green case for inkjets isn't as clear-cut as it first looks, with speed of printing and the environmental benefits of toners over ink cartridges providing some redemption for the lasers.

Perhaps the most surprising results are those for energy consumed when the PCs and peripherals are turned off at the power button. Unbelievable as it may seem, your devices continue to draw power as long as they remain plugged in. The high-end Chillblast PC drew 3W of power when off, HP's C5180 inkjet took 6W, while many of the monitors took a residual watt or two. These may sound inconsequential, but when you consider that all your devices added together could consume 25W simply by being plugged in, over the course of a year they could eat up around 220kwh of power, which adds about £20 to your electricity bill. In other words, that £10 power strip that turns off all your peripherals with your computer would repay the investment within six months.