The world's top five cell phone makers have launched a common energy rating system for chargers, making it easier for us to compare and choose the ones consuming the least energy.

The new rating system developed and supported by LG, Motorola, Nokia, Samsung Electronics and Sony Ericsson, ranges from five stars for the most efficient chargers down to zero stars ranging from the most energy effecient to the least.

Many people may not know that when you leave your charger plugged into the socket, even if the phone is disconnected, it stil uses energy. Around two-thirds of the electricity used by cell phones are wasted this way.

"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.

See More: Green Charger Rating System