TV power consumption

The Extech 380803 power analyzer

The whole idea behind this project is to get a good idea of how much electricity a TV uses by recording the actual current flow into the set. We talked to consultants and engineers, both from the Environmental Protection Agency and from major TV makers, to come up with a reliable test procedure.

While manufacturers usually report TV power consumption data, they often report only peak usage or standby time. Our goal was to come up with a more real-world estimate of how much power TVs use under normal usage patterns. To collect our data, we used an Extech 380803 power analyzer connected to a laptop PC for data logging. We set it to record in 1-second intervals the power consumption, in watts, of all of the TVs we tested.

We performed two separate tests for each display. The first consists of one hour with the power on, where the screen displays an average TV show--in our case, we use two back-to-back episodes of That '70s Show (trust us, that $#@ show should have been canceled much sooner than it was), including commercials, recorded to a DVD. To maintain as level a playing field as possible, we connect each TV via HDMI to a DVD player playing the disc, we reduce the volume control all the way to "0" (but not muted), and we leave the picture settings in their default positions. The second test consists of one hour of standby, where the TV is left powered off but still plugged in. Updated 07-02-2007: For our Juice Box tests, as defined below, we use the same DVD but perform up to four separate measurements: Standby, Default, Calibrated, and Power Save. We've also shortened the measurement recording time to a half-hour for each test, because it turns out there's little statistical difference between the average power consumption over 30 versus 60 minutes.

It's interesting to note that the TVs' audio volume actually had little to no effect on power consumption, whereas picture settings usually had a big impact. With most TVs, the default, out-of-the-box picture settings are extremely bright, so our power on numbers generally represent the maximum power consumption of any TV over an hour of viewing. As soon as we started to reduce the light output (see TV power-saving tips), either by engaging a dimmer preset such as Cinema or Pro, or by simply reducing the contrast control, we noticed that power consumption decreased.

Using data from these two tests, we determine the watts per square inch (while powered on) and extrapolate the estimated annual energy cost, which is the price it costs to watch the TV for 8 hours per day and leave it turned off in standby mode for the remaining 16 hours per day. Believe it or not, according to Nielsen, the average household has a TV on for more than 8 hours a day, which means there's typically 16 hours of standby time as well. Note that Nielsen did not have the statistics for how long each TV is on during each day; obviously the annual power rating will be lower for TVs that are used for less than 8 hours, and higher for those used more. To calculate cost, we used the average price of energy in the U.S. during 2007, according to the Energy Information Administration.

If you want to test your own TV's power consumption, you can get a rough idea using less sophisticated tools than we did. For example, stores such as ThinkGeek sell inexpensive meters so you can have a better idea how much power your TV, and other appliances, actually use.

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, such as the Panasonic TH-50PZ800U, 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 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 listed in the "Tips & Tricks" 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: According to Extech, the manufacturer of the power meter we use for testing, readings of less than 1 watt may not be entirely accurate. We will still report the data the meter provides, but you should take results of less than 1 watt with a grain of salt.

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 kilowatthour according to the Energy Information Administration (see above).

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.

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