How we test TV power consumption
CNET follows the standards outlined in IEC 62807, the same methodology employed by Energy Star, to test TV power usage. Per these methods, TV power draw is tested in the default picture setting and in standby mode. At CNET, we also test two additional picture-setting scenarios: post-calibration and power saver. Unlike Energy Star, we also disable room lighting sensors in default mode, if possible, before running the test. For the full details of Energy Star 3.0 testing requirements, click here (PDF).
To collect the data, we use a Chroma 66202 Digital Power Meter, which is designed to meet Energy Star/IEC 62301 measurement requirements. The meter automatically averages 1-second interval wattage measurements over the 10-minute test period, and is capable of accurate standby measurements. (We retired our old Watts Up meter, which was not capable of accurately measuring the fractional watts drawn by most new HDTVs' standby mode, in June 2009, so most measurements made before then showed standby consumption of zero watts.)
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.
- If the TV's default settings incorporate an automatic brightness control with a room lighting sensor, turn it off. If the control cannot be turned off, make sure the light level striking the sensor is as close to 300 lux as possible.
- Run the IEC test DVD for an hour by setting the 10-minute clip to repeat six times. This warms up the TV and stabilizes its power consumption.
- Default test: After the warm up 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, with a light output of 40 footlamberts measured on a specific window test pattern (more information).
- 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.
- The 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).
As we mentioned, Energy Star does not report on the effects of power saver or post-calibration picture settings. We chose to include these tests because they give a better overall picture of TV power use, rather than what you get simply with the default picture settings. The post-calibration results in particular are useful for leveling the field of comparison between different TVs. Default picture modes can vary widely in light output, and thus power use, but our calibration specifies a set light output.
The post-calibration setting is also useful to CNET readers because 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.
About CNET energy ratings
To supplement the information in the Juice box, CNET has instituted a series of simpler, graphical ratings, represented by the meter graphics at the top of every review. The three meters, labeled "Good," "Fair," and "Poor," appear in the margin to the right of the page. They're determined by the same methodology and data used in the Juice box.
The most-efficient HDTVs also earn our "power saver" badge. Here are the qualifications:
A TV must be a current model that was measured by CNET's reviews team to have a default picture mode that uses 0.2 watt per square inch or less and its overall wattage must be among the upper-third of TVs we've tested with an energy rating of Good, all while achieving a brightness level higher than 40 footlamberts.
Since we created the award in April 2009, most of the LCD TVs we've reviewed have qualified, so we'll probably make the qualifications stricter for 2010. *None of the plasma TVs we've reviewed since that date qualify.
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 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.
Default
This column lists results we measure when the TV's settings are in the default position, right out of the box. (See above for information on how this mode is determined.) 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 per square 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.
Cost per year
This row lists the amount of money the TV would cost to run over one year. Prior to April 10, 2009, we assumed the TV was turned on for 8 hours a day and off for 16, and based the cost on the average price of residential electricity in the U.S. during 2007, which is about 10.6 cents per kilowatt-hou,r according to the Energy Information Administration. On April 10, 2009, starting with the Samsung UNB7000 review, we updated our numbers for this calculation, using 5.2 hours on and 18.8 hours off--based on a 2007 PG&E study cited (PDF) by the California Energy Commission--along with 11.35 cents per kw/Hr, the average residential electricity cost for 2008. These updated 2009 numbers are reflected on the Annual Cost column in the big chart, but Juice boxes in individual reviews published prior to April 10, 2009, contain the old cost per year number.
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, Fair, 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 "Fair," 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. Through the end of 2009 these scores are determined by data drawn from every HDTV tested since 2006. For the 2010 models, we will revise the dataset and methodology to encompass only more recent HDTVs.
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 "Fair" 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 Fair 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.
Annual energy cost after calibration chart
Starting with the Sony KDL-52V5100 review published on June 19, 2009, we've included a comparison chart below the Juice box of every HDTV review. It lists the estimated annual energy cost after calibration (the same as "Cost per year" in the "Calibrated" column of the Juice box) for the reviewed TV and five other comparable models. Those models are chosen by CNET editors' based on screen size, technology, and other factors to give a good cross-section of where the reviewed TV stands among its peers in terms of power usage.
