The DisplayLink study measured the power needed for a desktop PC to run one to four LCD monitors. Two identically configured systems were used; one equipped with DisplayLink-enabled USB-to-DVI adapters and software, and another with dual-DVI discrete graphics cards, which DisplayLink said is the most common type of dedicated multi-display board. Power consumption was measured at the entry of the computer power supply to gauge total system power usage under different system loads.

The study found that by adding a display with a USB adapter it incurred an average increase of only 4 watts per display, or a 7 percent increase in power consumption.

However, the discrete graphics solution used considerably more power due to the necessary installation of dedicated hardware inside the computer, said DisplayLink. When driving a single display, the discrete card used, on average, an additional 34 watts of power, or a 67 percent increase in power consumption without the benefit of any additional displays, according to the study. When the system was configured to drive four displays (which required the installation of a second card), the power consumption jumped to an average of 117 watts, or an increase of 132 percent compared to the single-display configuration.

A key finding of the study revealed that an USB graphics solution used up to 80 percent less power to drive an extra display than a discrete graphics solution, while the discrete graphics solution consumed as much, if not more, power than an extra LCD monitor. This causes the overall system power consumption to more than double if three or more displays are used, or an increase of 128 percent, according to DisplayLink.

Another finding showed that when three additional displays were connected to the system using USB adapters (for a total of four displays), the system used only 22 percent more power (a total of 62 watts) than needed to drive a single display.

In addition, USB multi-display technology works with notebooks and small form-factor PCs, where a discrete graphics solution is not possible, allowing multiple display users to use more power-efficient notebook PCs in the place of traditional desktop PCs, said DisplayLink.

Click the link to download a copy of DisplayLink's white paper, Multiple Monitor Energy Use. To view a DisplayLink "Green IT" product demo, visit www.youtube.com/watch?v=GmTM2p5798U.