How CNET tests LCD monitor power consumption
CNET uses the Chroma Digital Power Meter 66200 Series to test the power consumption of LCD monitors.
We first connect the monitor to our test system via its DVI connection. We then plug the monitor into the meter and then plug the meter into the wall. If the monitor includes an ambient light sensor that automatically adjusts its luminance, we disable this.
Once we've set up the "Power" test on the meter, it conducts a reading of how many watts the monitor pulls over a 5-minute period. The meter then displays an average of that reading. We use this number as our result.
We test each monitor in five different states. Two of the tests (On and Sleep/standby) are conducted in accordance with the Energy Star 5.0 Displays Specification. Energy Star does not test monitors with their brightness level at their highest, lowest, or their default level; however, we felt these results would be helpful when choosing a display to purchase.
Our five tests
On
We set the monitor's luminance based on Energy Star's 5.0 Specification. This setting will be different depending on the screen size and resolution of the monitor.
Full brightness
The brightness dial on the monitor adjusted to its highest setting.
Minimum brightness
The brightness dial on the monitor adjusted to its lowest setting.
Sleep/standby
The monitor in sleep/standby mode. We induce sleep mode by setting the Power Option in Windows to put the monitor to sleep after 1 minute of being idle. The monitor is not powered off or unplugged.
Default
The factory settings of the monitor are restored.
CNET does not test the power consumption of monitors that are turned off because the amount of power drawn by a monitor when "off" is virtually the same as when it's in standby/sleep mode. Secondly, "off" for most monitors is not true a off. Unless there is a power switch (not power button) on your monitor that lets you switch it off, the monitor will draw power as long as it's plugged in.
Annual energy cost
We determine the energy cost of each monitor. This cost is calculated based on the U.S. average of $0.1135 cost per watt.
The formula for calculating the "weight" of each monitor state is based on Energy Star's desktop computer usage model. We only use the On and the Sleep/standby mode in our calculation. In our model we assume that a monitor is in Sleep/standby mode 70 percent of the time and on for 30 percent of the time. These numbers are weighed, and then averaged out over 365 days to get the final estimated cost.
Power Saver Seal Criteria
To qualify as a Power Saver, a monitor must be current (i.e., not yet replaced by another model) and measured by the CNET Reviews editors to have a default wattage of 20 or less and a Sleep mode wattage of less than 1.
