Hewlett-Packard has set ambitious goals to improve the energy efficiency of its printers and use more recycled materials in their manufacture -- and it intends to draw buyers' attention to the features with a new Eco Highlights labeling plan.

Despite all the work that HP is doing to reduce the environmental impact of its printers, though, the biggest problem is the paper itself, according to Klaus Hieronymi of HP's Environmental Business Management Organization.

Around two-thirds of the carbon-dioxide emissions caused by printing are due to the manufacturing of the paper, he said, suggesting that the simplest way to reduce greenhouse gas emissions from printing activities is to use less paper.

That's the motive for HP's focus on enabling duplex printing by default in its printer management software -- and for setting another ambitious goal of having 80 percent of printing in its own offices done on both sides of the paper, according to Bill DeLacy, general manager of HP's Imaging and Printing Group for Europe, Middle East and Africa.

HP still thinks that reducing the carbon emissions of the printers themselves can make a difference, and hopes to draw customers' attention to it with its Eco Highlights labels. Although these are intended to aid in comparison shopping for environmental benefits, this is solely an HP initiative: The company is not working with any other printer manufacturers to introduce comparable labeling, said DeLacy.

The company will introduce the labels on four printers: the Deskjet D2545 color inkjet and the LaserJet P4015x, P4515x and P4515xm black-and-white laser printers.

HP heralds the labels as clear and simple to read, but for the LaserJet P4515, that is likely to raise as many questions as it is answers. For example, shouldn't printing on both sides of the paper cut paper consumption by 50 percent, rather than the 25 percent claimed by HP? That depends on the proportion of single-page documents that you print.

The device's Instant-On technology is said to yield up to 50 percent energy savings -- but the little asterisk suggests that that, too, depends: in this case it's compared to products that use traditional fusing, but buyers will need to know whether their existing printers have a traditional fuser to figure out their savings.

Indeed, "It depends" is Hieronymi's stock answer to many questions, including whether it is more environmentally friendly to continue using an 11-year-old HP LaserJet 4 plus or to discard it, replacing it with a newer model.

What questions like that depend on is something HP plans to address with a carbon footprint calculator it will put online at the end of June. The calculator will take into account the new and old printers' electricity consumption, and also the source of the electricity: Norway's use of hydroelectric power means electricity consumed there generates only 100 grams of carbon dioxide per kilowatt-hour, compared to 850g/kW/h in China, where coal-fired generators are more common, said Hieronymi.

As it reduces its printers' energy consumption, HP wants to increase the level of recycled materials they contain three-fold by 2011, with those materials coming primarily from old HP printers.

That's now becoming possible because HP has spent the past four or five years redesigning its printers "for recyclability," as the Eco Highlights label of the P4515 puts it, using far fewer kinds of plastic. The new Deskjet D2545 is one of the first fruits of that work: Five-sixths of the plastic it contains is recycled.