Global information technology firm 1E released on Tuesday its 2009 PC Energy Report which showed that office computers left open overnight cost American firms $2.8 billion yearly.

The amount is for 108 million unused PCs, which also discharge 20 million tons of carbon dioxide emissions annually. That is equivalent to tailpipe emissions of 4 million vehicles.

The research, prepared by 1E in partnership with the Alliance to Save Energy, surveyed adult professionals from various countries. It is part of 1E's mission to raise global awareness on the economic and environmental value of shutting off computers when not in use.

The same report said up to 50 percent of U.S. workers who use a computer in the office or at home, do not close their computers at the end of the day. The survey showed Europeans are more conscious about shutting down their PCs, with 56 percent of workers in the United Kingdom and Germany reporting they closed their computers at the end of the day.

1E, to provide a clearer picture of the amount of power wastage caused by PCs left open, estimated that if all of the 1 billion computers across the globe would close for only one night, the saved power would be sufficient to light up the Empire State Building inside and outside for more than 30 years.

1E chief executive officer Sumir Karayi challenged employers to use this time when many businesses are cutting corners to put in place energy saving measures like putting up processes that would lead to the closure of PCs at the end of business hours.

Karayi said in the report, "Every day that passes is a lost opportunity to save money and reduce your carbon footprint. We hope you'll act now to take this opportunity to make a difference."