Nearly half of all office computers in the United States are left on overnight. And why? To save a few minutes of re-booting in the morning? The PC Energy Awareness campaign is here to tell us that this is some crazy stuff.

Here are the somewhat staggering stats: - Out of 104 million office PCs in the US, at least 31.2 million are left on all night.

• Turning off every work computer in the United States every night would save as much CO2 emissions as taking every car in the state of Maryland off the road.

• The simple step of shutting computers down each night can save a 10,000 PC enterprise more than $165,000 a year in energy costs. Across the US, this adds up to more than $1.72 billion dollars and almost 15 million tons of CO2 emissions.

Don’t believe the hype - computers don’t need to be left on overnight to receive security patches and software updates. And sleep mode does not save the energy one might think it does. Turn those computers off! But not before playing this fun energy awareness game.