The green computing movement demands that all computer users shed the energy-wasting practices to which they've grown accustomed—so you decide that you're going to power down your PC at night, invest in an Energy Star–approved laptop, and only visit Web pages that eschew white space in favor of ostensibly more energy-efficient black backgrounds.

Before you tune out and turn off, you should know that black isn't necessarily the new green. Because computer monitors come in a variety of shapes and sizes, and not all monitors create black and white the same way, there's no proof that, on the whole, increased usage of black images would save more energy than the continued use of white ones. In fact in newer liquid-crystal display, or LCD, monitors white is actually slightly more energy efficient than black.

The notion that black screens save electricity certainly makes sense when you're talking about cathode-ray tube, or CRT, technology that works by moving an electron beam back and forth across the back of the screen. "The front screen is covered with red, blue and green phosphors," says Bill Schindler, vice president of electrical engineering for Panasonic Plasma Display Laboratory of America. To produce white, the electron beam is directed at the phosphors. However, "when the screen is black, you don't have to fire the beam," he adds.

CRT monitors, which until a few years ago were the predominant models among PC users, consume more power when a computer screen is white. To confirm this, Schindler measured the energy output of an 18-inch (45.7-centimeter) CRT monitor and found it used 102 watts when the screen was white but only 79 watts when the display was black.

This is not the case, however, with LCD monitors, which have no phosphors and represent the lion's share of every new monitored purchased in the developed world, including those used by laptops. Instead, LCD displays rely on an array of thin-tube fluorescent bulbs that provide a constant source of light to create a white screen. To make it black, LCDs rely on a diffuser to block this light. As a result, LCDs use more energy than CRTs to display a black screen. Measuring a 17-inch (43-centimeter) LCD monitor, Schindler found that white required 22.6 watts, while black came in a tad higher at 23.2 watts. With a 20-inch (50.8-centimeter) LCD, black required 6 percent more energy than white.

One of the most visible manifestations of the belief that black screens save energy is Blackle, an online search engine whose Web site is cast almost entirely in black. Created by Heap Media, Blackle exists "to remind people of the need to take small steps every day to save energy," says Blackle founder Toby Heap, who launched the site in January. "I do not expect the energy savings from Blackle to change the world on their own, but the point of Blackle is that every little bit counts."

One of the key arguments in favor of black screens is a 2002 research study produced by Lawrence Berkeley National Laboratory entitled "Energy Use and Power Levels in New Monitors and Personal Computers." The report indicates that "a given monitor requires more power to display a white (or light) screen than a black (or dark) screen." Indeed, that study reports that black screens consistently require less energy than white screens, regardless of whether the monitor is a CRT or LCD.

7 Comments

1. 1. thewebgarden 12:22 AM 3/29/08

   Wow! Quite an interesting debate, I'll have to get the power monitor out and check which way around my monitor is! You'd have thought that google could supply an option for a different colour page though!!

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2. 2. Leithauser 04:14 PM 4/5/08

   I have just developed an energy saving program for computers with CRT screens. It saves energy by blacking out areas of the screen that are not in use. The effect is small and ONLY on CRT monitors, but I offer the program free of charge. I would be delighted to have anyone evaluate the program and/or list it on their Web sites. The program is called CRT Energy Saver, and you can view the description and download the program from
   http://leithauserresearch.com/CRT-Energy-Saver.html

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3. 3. Bonney 04:48 PM 1/17/09

   Doing a quick calculation with Greenemeier's numbers, black backgrounds should save energy, even in the US. Assuming 75% of existing monitors in the US are LCD, (which is probably high, since "the market" refers to sales), and using a sample size of 100 monitors for ease of calculation and 17"-18" monitors, which seem to be the majority:
   With a white background: 75 17" LCD monitors using 22.6 watts each would use 1695 watts, and 25 18" CRTs using 102 watts each would use 2550 watts, for a total of 4245 watts;
   With a black background: 75 17" LCD monitors using 23.2 watts each would use 1740 watts, and 25 18" CRTs using 79 watts each would use 1975 watts, for a total of 3715 watts.
   As Greenemeier points out, the fact that the newer types of LCD's use less energy with a black background should continue to give black backgrounds the edge in energy savings as LCD's replace CRT's. And worldwide, there's a clear energy savings from black backgrounds. So those of us troglodytes still using CRT's should download Leithauser's free CRT Energy Saver (see comment #2) or something similar.

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4. 4. r52fn4 04:17 PM 4/23/09

   People would use more room lighting (or perhaps switch their room lights on five minutes earlier) if their monitor provides less light. This marginal increase in power used for room lighting might be the biggest factor and no-one has mentioned it!

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5. 5. LSBrew in reply to r52fn4 08:20 PM 5/25/09

   r52fn2
   That's real nice but you got it backwards. The darker the screen, the darker you need the room ambient light to be. So if your monitor monitor provides less light, you would actually be better off with less room light to compensate. This is so typical of so many "green arguments". Clueless. Go fill up on ethanol.

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6. 6. applebox 01:21 PM 10/19/09

   I have a load meter (in wattage) on my monitor, and when I look at black screens the load is definitely higher in comparison to when I view white screens. I have tested it several times. My LCD definitely uses more juice displaying black.

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7. 7. catooney 05:52 PM 12/14/11

   At the electron/bit level, black uses less energy over the network than white. Black as an rgb value is all zeros. White, all F's requires more energy to represent. (This does not relate to the energy used by your monitor to display said value)

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