Environmental group Greenpeace handed out grades Thursday to what it said were the world's "greenest" consumer electronics makers, as the annual gadget industry trade show opened here on Thursday.

Greenpeace released an update to its "Green Electronics Survey" at the Consumer Electronics Show (CES), which brings together the world's leading manufacturers of computers, mobile phones, televisions and other devices.

The Greenpeace product survey evaluated the "greenest" desktop computers, notebook computers, netbook computers, computer monitors, mobile phones, smartphones and televisions available in the first quarter of 2011.

"Our survey shows that electronics manufacturers have made demonstrable progress over the past few years by producing products that are free of the worst toxic chemicals, more energy efficient and more easily taken back for reuse or recycling," said Renee Blanchard, Greenpeace International Toxics Campaigner.

"Major brands are responding to consumer demand for greener gadgets, and we expect them to continue to innovate and make all their products, and not just a niche few, with these higher green standards," Blanchard said in a statement.

"The next challenge for the industry is to design green products that last longer and can be repaired rather than replaced every few years," Blanchard said.

Greenpeace said 21 leading electronics companies were invited to take part in the survey. Most agreed but Apple and Philips were among the companies which declined to participate, the environmental group said.

Greenpeace ranked the products according to various criteria including energy efficiency, product lifespan and energy used in production.

The VW-247H-HF computer monitor made by Asus scored the highest with 7.5 points on a 10 point scale and the Taiwan-based company had another winner in the notebook computer category with its Asus UL30A.

The TM8172 from Taiwan's Acer was the top-ranked netbook computer and the HP Compaq 6005 Pro was the leading desktop computer.

The LC-52SE1 from Japan's Sharp was the leader in the television category.

The Sony Ericcson Aspen rang up the highest score in the smartphone ranks and Samsung's GT-S75550 came out on top in the mobile phone space.

Other companies submitting products included Dell, Fujitsu, HCL, Lenovo, LG Electronics, Motorola, Nokia, Panasonic, Research In Motion, Toshiba and Wipro.