A friend of mine pointed me to a bizarre site called Blackle which is, essentially, Google with a black background. Blacke claims that:
Blackle saves energy because the screen is predominantly black. “Image displayed is primarily a function of the user’s color settings and desktop graphics, as well as the color and size of open application windows; a given monitor requires more power to display a white (or light) screen than a black (or dark) screen.” Roberson et al, 2002 (…) We encourage you to set Blackle as your home page. This way every time you load your Internet browser you will save a little bit of energy. Remember every bit counts! You will also be reminded about the need to save energy each time you see the Blackle page load.
Which seems to be a ludicrous attempt to capitalize on web audience based on the fact that people tend to believe in the strangest things if they’re told it’s for some noble cause. While it is actually true for CRT monitors, the first thing that popped in my mind is that the effect should be exactly the opposite in LCD displays. From Wikipedia:
In a twisted nematic device (still the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular, and so the molecules arrange themselves in a helical structure, or twist. (…) When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field, distorting the helical structure (this is resisted by elastic forces since the molecules are constrained at the surfaces). This reduces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules are completely untwisted and the polarization of the incident light is not rotated at all as it passes through the liquid crystal layer. This light will then be polarized perpendicular to the second filter, and thus be completely blocked and the pixel will appear black.
So in most LCD displays, the amount of energy applied to produce a black pixel is actually larger than producing a white pixel. No wonder screen savers in Nokia and Sony Ericsson cell phones are mostly white. But one doesn’t even need to gather information elsewhere about power usage in LCD devices, a quick look at the paper cited as reference in Blackle itself reveals that:
Among CRTs, maximum on power appears to be associated with a white display, or a maximum-sized application window (which approximates a white display). Among the few LCD monitors in the table, the power used to display a white screen is indistinguishable from power used to display the desktop. Thus, it appears that display color is a significant determinant of on power for CRTs, but not for LCDs.
If you want to be a nice person and save the planet, do it the right way. Research. Check if your acts actually have some significance. Don’t believe something just because someone told it’s a good thing. If you are actually concerned and want to help, good. Buy a less power-hungry CPU. Install cpufreq. Use power management. Reduce brightness or intensity of the backlight. Turn off lights you don’t need. Use Blackle you find it funny and amusing, but don’t do that thinking you’re doing any good — especially if you use an LCD monitor. It’s plain stupid.
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