These energy criteria have been taken considerable time to develop and finalise due to several factors:

- The complexity of creating criteria relevant to companies that make different products in different ways.
- Developing criteria that as accurately as possible allow companies efforts to be compared across sectors.
- Consulting with leading independent energy experts such as the US EPA Energy Star and the Wuppertal Institute for Climate, Energy and Environment.

Invaluable advice from independent climate and energy experts has helped create an accurate, holistic and robust set of criteria that reflect how each company is responding to the vital need to tackle global warming by improving the efficiency of their products and cutting their over all emissions.

Here is a brief explanation of why we chose these specific criteria. If you're not an energy nerd now's probably a good point duck out before we get all heavy on the details.

Support for global mandatory reduction of GHG emissions - Does the company publicly support the emissions cuts needed to prevent dangerous global warming?

Disclosure of carbon footprint (GHG emissions) of company's own operations and two stages of the product supply chain - Does the company audit and publish the emissions it is responsible for to the international ISO standards? If not, any claimed reductions cannot be independently verified.

Companies covered in the guide differ widely in the scale of their operations. Some like Dell, and HP, don't do much (if any) manufacturing, mainly assembly. Other companies like Samsung and Sony may make components for other companies. That's why we are asking for figures from 2 stages of the product supply chain. We are not comparing the size of the carbon footprints of the companies (that will obviously vary widely) but checking if and how companies are auditing their emissions.

Commitment to reduce GHG emissions from a company's own operations with timelines - Which companies are serious about tackling their emissions?

Amount of renewable energy used as proportion of total electricity use in own operations - Do claims of solar panels here or buying some green energy there stack up to a significant amount of the a company's power use?

Energy efficiency of new models of specified products - Do all a company's products meet the latest relevant EPA Energy Star standard as a minimum. How many of a company's products significantly exceed Energy Star by more than 50 percent?

The energy efficiency criterion was probably the hardest to devise as the ranking covers companies who make very different things. Nokia makes just a few types of products where as Panasonic makes thousands of different products. To ensure a manageable scope our assessment will only cover battery chargers, computers (desktops, laptops, games consoles) and TVs as defined by Energy Star. As the clearest example of a companies commitment to saving energy this criteria scores double points.

We also left out things from the criteria. Carbon offsetting is not included because emissions reductions are what's needed now. If you have any questions leave a comment below: