A group of mobile manufacturers has launched a common energy rating system for chargers, making it easier for consumers to compare and choose the one that saves the most energy. The star rating system developed and supported by LG, Motorola, Nokia, Samsung Electronics and Sony Ericsson is one of a series of measures being taken by the industry to reduce the environmental footprint of its products.

Chargers consume electricity when disconnected from the phone but left plugged into the wall socket. Around two thirds of the energy used by mobile devices is wasted in this way. Manufacturers are addressing this by continually improving the efficiency of their chargers and in making it easier for consumers to pick the ones using the least energy.

The new rating system indicates how much energy each charger uses when left plugged into the wall socket after charging is completed. The ratings covers all chargers currently sold by the five companies, and range from five stars for the most efficient chargers down to zero stars for the ones consuming the most energy. "If the more than three billion people owning mobile devices today switched to a four or five star charger, this could save the same amount of energy each year as produced by two medium sized power plants," Nokia said in a statement.

People will be able to visit the websites of each manufacturer to view and compare the results for every charger. The ratings are based on the European Commission's energy standards for chargers and the internationally recognized Energy Star standards set by the Environmental Protection Agency in the U.S.

Many of the manufacturers are also working on other ways to reduce energy consumption. Most major producers have begun introducing visual alerts into their devices to remind people to unplug the charger from the mains when the battery is fully charged.