A single incandescent 100-watt light bulb left on around the clock for a year costs more than US$80 to power. Generating that power releases about 1,350 pounds of carbon dioxide emissions into the atmosphere — a major contributor to global warming.

According to Dean DeWhitt, director of Microsoft’s Windows Kernel team, that is about the same amount of power many PCs consume while not in use. Yet, while few people would leave a light bulb on for a year, many people keep their PCs running with screen-savers at all hours, which actually consumes more energy than an idling PC. What’s more, many large organizations constantly leave their PCs running so they are available to receive security patches and updates.

“While education may be the key for many consumers, businesses are forced to balance cost and environmental impact against their own security and operations requirements,” says DeWhitt. “New power management features in Windows Vista are designed to help them with this challenge.”

In fact, Microsoft today announced the results of an independent study from UK-based PC Pro Labs, which looks at the energy consumption of Windows Vista and the potential reduction in carbon dioxide emissions. "Power Consumption, Windows Vista versus Windows XP" compared energy usage between Windows XP and Windows Vista, clearly showing that the power management features in Windows Vista could help reduce the carbon dioxide generated in an organization, equal to 45 tonnes per year for a 200-seat business. In addition, the study found that these features could also deliver savings on energy bills of up to £46 per desktop PC per year.

The study is based on real-world usage of desktop computers in the work environment of 800 desktop PC users. The cost savings and reduction in carbon dioxide emissions are due to the “Sleep” mode in Windows Vista, which automatically activates after one hour of non-use.