Image if all the computers in the world magically were able to use a lot less electricity. There are so many computers in use, the energy saving would really add up. So it's an area that we should really get in the habit of thinking about. When we look for a computer, we shouldn't just buy the most powerful one on our budget. But, instead, we should think about what strikes a good balance between power consumption and computing power.

One desktop computer that stands out is the Dell Studio Hybrid. This uses a processor from Intel's mobile line. Since these processors are designed to be used in laptops, they have to be very energy efficient. It also uses a very efficient power supply. If you've ever noticed how warm the external power supply on a laptop computer gets, that warmth shows how power supplies waste electricity. The net result is that Dell says the Studio PCs use about 70% less power than a typical desktop.

When it comes to monitors, Lenovo is a good brand to consider. CNET.com is a good place to find power consumption for monitors; manufactures seem to make this information really hard to find. The Lenovo L1940p tested at only 18 watts. By comparison, other 19 inch monitors might use about 70 percent more electricity. Given how many hours a day people use computers, this difference can really add up. A good 24 inch model is the Dell G2410.

And if low energy consumption is your top priority, a laptop is pretty hard to beat. If you use a PC for hours at a time and don't like the idea of using a laptop because you don't like the screen, you can plug an external monitor into most laptops. Usually, the laptop's screen will automatically turn off when a monitor is plugged in. You still should end up with a more efficient arrangement than using a desktop computer.

Some laptops that stand out in terms of energy efficiency include:

Lenovo Thinkpad SL500 (about $500-900, depending on configuration)

HP ProBook 4510s (about $530-950, depending on configuration)

Acer Aspire 3935 (about $900)

Apple MacBook (13 inch, about $1300)

Your computer's power settings can make a big difference in how much electricity it uses. You can manually choose power settings in Windows by clicking "Start", "Settings", "Control Panel", then clicking on "Power Options". Or, if you prefer, you can try free software that automates the process by downloading Verdiem's Edison.

One trick to saving energy with a laptop is not to leave it plugged into the charger after the batteries are fully charged. You'll find that the charger stays warm even after the laptop is charged; that means energy is being wasted. Also, if you aren't using a wireless connection, turning off Wi-Fi on your laptop will save energy. The Wi-Fi card is a radio, that is both broadcasting and receiving, even if you aren't using it.

Another way to save electricity is to watch TV on your PC. If you would normally leave your PC on while you are watching TV, you could put a TV tuner card in your PC and not have two devices on at the same time, just your PC. These run about $60; and USB models are available if you don't want to open your computer's case. Some new PCs are coming with TV tuners built in.

Looking to the future - There are some technologies that are starting to be used that will be good for reducing energy use in computer equipment. These include monitors and laptop screens with LED backlighting, solid state hard drives (SSD), and the use of processors that use less electricity (such as Intel's Ultra Low Voltage (ULV) processors). These are available now on some products, but, in the case of LED backlighting and SSD's, can be expensive. Microsoft has done tests on their upcoming Windows 7, and found that a laptop playing a DVD can run up to an hour longer on batteries, compared to Vista. The longer runtime is great, but it also shows improved energy efficiency.

For many people, a computer is very important. So finding an efficient one is worth the effort.