TV power consumption

In accordance with new Energy Star standards for HDTVs, we have changed our testing methodology somewhat, so our results should jibe more closely with those of other publications that use the new standards. The standard itself is known as IEC 62807, the gist of which is summed up at Energy Star's site (pdf).

To collect the data, we use a Watts Up? electricity meter (pictured). We retired our old Extech 380083 meter after working with Ecos Consulting, who told us that the Watts Up? is a more-accurate meter for our purposes. We're considering getting a more-expensive meter, primarily for proper measurement of small wattages found in standby mode, but it's not in the budget yet.

The basic test procedure goes as follows:

• Plug the television into the meter and the meter into a wall outlet.

• Connect a DVD player via an HDMI input.

• Insert the IEC 62087 test DVD, which contains a specific 10-minute clip of program material, into the player.

• Turn on the television.

• If the TV has a "home" mode available as a choice during initial setup, choose it and go through the rest of the initial setup process, making sure to not change any of the picture settings. This ensures the closest to "default" picture setting.

• Run the IEC test DVD for an hour by setting the 10-minute clip to repeat 6 times. This warms up the TV and stabilizes its power consumption.

• Default test: After the warmup period is over, run the test DVD for the official 10-minute clip, making sure to increase the volume to a moderate level the tester can hear clearly.

• Power saving mode test: If the TV has a power saver mode, engage that mode in its most-efficient setting, the one that uses the least power, and repeat the 10 minute clip.

• Post-calibration test: Repeat the 10 minute clip again in the calibrated picture settings.

• Standby test: Turn the TV off and observe the meter's readout after it settles down into a steady standby power draw, typically after a minute or two.

• Upload the results to a PC, average out the 1-second interval wattage readings, and report the results. The last three 10-minute clip tests, along with the reading from standby power, are reported in the Juice Box attached to every TV review (see below).

It's worth noting that IEC and Energy Star don't report on power saver or post-calibration numbers. The latter are particularly useful to CNET readers, since we publish our post-calibration picture settings with every HDTV review. Users who own the TV reviewed and use our settings can expect similar power consumption to the "calibrated" results we report, and in general their TVs will use less power than the default settings.

Our methodology differs from Energy Star in one more important way: we don't currently account for any room lighting sensors in our testing. Even if the TV ships with a room lighting sensor engaged by default, we turn it off for our default mode testing. Energy Star, on the other hand, dictates leaving room lighting sensors engaged in default modes, and includes an appropriate test procedure. We do intend to follow that procedure at some point in the future, but at the moment we do not have the proper equipment.

About the Juice box

In the spirit of the Geek box, which collects some of the numerical findings regarding the objective performance of TVs, the Juice box included in TV reviews collects data about TV power consumption. Here's a rundown of the terms used and how we achieve the results.

Picture settings
Because picture settings usually affect the amount of power a TV consumes, we list up to three different picture-setting scenarios for each TV we test. Power consumption is almost always related to the TV's light output--generally, the brighter the TV, the more power it uses--and the Calibrated and Power Save picture settings usually attenuate light output significantly, thus using less power.

Default
This column lists results we measure when the TV's settings are in the default position, right out of the box. Typically the default picture settings represent "torch mode," with high light output and correspondingly high power consumption (examples include "Dynamic" or "Vivid" picture modes), but some new models default to a more efficient picture mode when the user indicates a "home" rather than a "store" environment during initial setup. In these cases we'll use the "home" setting for the default measurement. The Default settings are also the only ones used to arrive at the TV's power consumption scores (see below).

Calibrated
This column lists results we measure after the picture has been adjusted, or calibrated, for optimal home theater picture quality in a dark room. This adjustment is part of every TV review, and the individual picture settings are always linked from the Performance section of the review.

Power Save
Many televisions have a mode designed to cut down on power consumption. In the final column, we list results measured when this mode is engaged while the other picture settings remain in Default. If the set has multiple power-saving modes, like "Low" and "High," we use the one that saves the most power. If the TV lacks a power saving mode, we list "N/A" in this column.

Picture on (watts)
This row lists the raw average wattage the TV consumes while the picture is on.

Picture on (watts/sq. inch)
This row lists the result of dividing the Picture on (watts) number by the area of the TV's screen. Larger TVs typically consume more power, so this number allows approximate comparisons between TVs of different sizes. In general, plasmas consume the most energy per square inch, flat-panel LCDs are about average, and rear-projection sets consume the least.

Standby (watts)
This row lists the raw average wattage the TV consumes while turned off but plugged in. This number does not depend on picture settings, so it's the same in all three columns. The exception is when a TV has a "Standby power saver mode," in which case we test and list its wattage in the Power Save column. Note: The Watts Up meter we currently use to test power consumption usually indicates a standby wattage of 0. The TV is still consuming some power in standby, but the amount is too small to register on the meter, and is generally insignificant to total power use.

Cost per year
This row lists the amount of money the TV would cost to run over one year, assuming it's turned on for 8 hours a day and off for 16. We use the average price of energy in the U.S. during 2007, which is about 10.6 cents per kilowatt-hour according to the Energy Information Administration.

Scores
In these two rows, we rate the TV's general power consumption efficiency against other TVs we've tested, specifically including sets from this list and all TVs that include a Juice box in the review. In an attempt to keep things simple, the only possible scores are Good, Average, and Poor, and TVs that consume less power receive a better score. The list of TVs we've tested is simply divided into thirds; the top third earns "Good," the middle third earns "Average," and the bottom third earns "Poor." We use only the Default picture setting numbers at the moment, but we plan to add Calibrated and Power Saving scores when we accumulate enough data in those categories.

Important Note: This simple scoring method has some drawbacks. Adding each new TV modifies the list slightly, and as a result the same number can (rarely) be "Average" for one TV and "Poor" for another reviewed a couple months later (and no, we don't update old Juice boxes to keep up with these changes). Also, the difference between the high end of Average and the low end of Good, for example, can be as small as one one-thousandth of a watt, which is insignificant to even the staunchest greenie. Given these caveats, if you're really particular about power consumption it's best to compare the actual wattage numbers, listed above, instead of the scores.

Score (considering size)
In this row we score the TV's power consumption in watts per square inch against all other TVs we've tested. This rating does not take technology type into account. Smaller TVs often score poorly on this test because they can consume more watts per square inch, comparatively, than larger sets, despite consuming less total power. We'd assume that's because there's a minimum amount of power that TVs consume that does not vary with screen size. On the other hand, most big-screen rear-projection TVs will score a "good" in this category because they're significantly more efficient per square inch than flat-panel TVs. With that in mind, this score is useful for people comparing TVs of different sizes.

Score (overall)
In this row we score the TV's power consumption in watts versus all other TVs we've tested. We ignore screen size and technology type, so generally smaller TVs score better, as well as TVs that use more-efficient technologies. This score is useful for people interested in the most power-saving TVs, period.

For a look at our power testing methodology, click here to go to the top of this page.