Energy Stars Burn Dimmer

The EPA (Environmental Protection Agency) awards an Energy Star label to monitors that use 30 W or less of power in their standby mode, and many of the monitors we tested carry the EPA's blessing (see the Roll Call on page 224). So far, no technology can dramatically reduce the current draw of monitors while they are fully active. But a power-down mode can drop current draw from approximately 100 W to less than 30 W. The EPA estimates that people use their monitors only 20 percent of the time the displays are on, so power-down savings could be considerable.

The EPA's guidelines cover only power-level targets, not the ways manufacturers can reach these levels, so manufacturers have created a number of different power management "standards." One of the first monitors with power conservation features came from Nanao. The F series of products feature a microprocessor-controlled system that watches Windows activity. If the monitor senses a blanked Windows screen, the control system initiates a partial shutdown of the high-voltage systems in the monitor, keeping only the CRT and microprocessor warm. When you press a key or move the mouse, the monitor turns on again. If no activity occurs within a user-definable period, the monitor enters a second level of power reduction, called the suspend state, which lowers power consumption to around 4 W. Standby mode refers to the intermediate shut-down level.

There are trade-offs between these states. While the suspend state uses very little power, the monitor requires 8 to 10 seconds to power back up. The standby state uses about 30 W, but the monitor returns to a full image in just a couple of seconds.

But implementations that require the monitor to constantly check on the CPU make it tricky to match monitors and computers. VESA has proposed DPMS (Display Power Management Signaling), a set of power management standards for communication between computers and monitors. DPMS governs the signals used to initiate power reduction in monitors. It relies on Intel and Microsoft's APM (Advanced Power Management) specification to define the names, broad definitions, and recovery times of reduced power levels. The chart below details the APM conventions, along with typical values for the monitors we tested.

APM STATE              ON          STANDBY
Power savings          None        Minimal (to under 40 W)
Recovery time          Not         Short recovery
                       applicable  (2 to 4 seconds)

APM STATE              SUSPEND                        OFF
Power savings          Substantial (to under 4 W)     Maximum
Recovery time          Longer recovery                System-
                       (8 to 12 seconds)              dependent

DPMS uses the presence or absence of sync and video signals to control power levels. Using these r ules as the common starting point, manufacturers of computers and monitors can use whatever technology is available to regulate the power consumption.

If you are considering purchasing a new monitor, an energy-saving display can offer real operational cost savings. Make sure that the monitor will function with your "green" PC or with an external software package such as Windows screen blankers. Our tests also showed that simply using the standard Windows utility to blank the screen (totally blank--no flying appliances) reduces power consumption by an average of 23 percent, even for monitors not equipped with power management systems.