If you’ve been in web development for a long enough amount of time, you will have eventually come across information about the United States Department of Energy’s report on the colors displayed on one’s computer monitors and their impact on electricity consumption. That innocent little web page has sparked tremendous debate throughout the web development community, as well as a minor revolution in web design! It is a fabulous, fabulous wake-up call for many of us who design content for the Web. There is only one problem with that information: for roughly 75 percent of the monitors in use today, the information is outdated and no longer accurate.
What that Department of Energy web page fails to mention is the fact that the results that they are reporting related to electricity consumption and color pertain specifically to cathode-ray tube (CRT) monitors, even though CRT monitors only make up approximately 25 percent of the total monitors in use within developed nations in 2007. The remaining 75 percent of monitors are liquid crystal display (LCD), which process color completely different than their CRT counterparts.
CRT monitors function in a similar fashion to a light bulb on a dimmer switch: the “brighter” the bulb is, the more wattage it is consuming. CRT monitors, therefore, use fewer watts when displaying less-bright colors. LCD monitors, on the other hand, are back-lit displays that selectively block out certain wavelengths of light. Displaying an all-black background on an LCD monitor requires that monitor to devote more energy into blocking out most/all wavelengths in light…which will increase the amount of watts consumed in the process.
Two great articles on this particular subject can be found on Pablo Päster’s “Ask Pablo” blog and on Mark Ontkush’s ecoIron blog. It has really opened my eyes on this particular issue, and I will be doing my part to help spread the word related to the differences in power consumption with CRT and LCD displays.
One final thought on this subject: I use an LCD monitor in my daily work, and was recently trying to see if I could subsequently set my Windows XP screensaver to use a white background instead of black (for the reasons described above). I’ve tried and tried, without any luck. If anyone out there would know of a good way for me to accomplish this, or has any good reasoning behind why someone should NOT try and do this, I would be grateful. Thanks!
[...] As pointed out by Graphics Optimization, the technology in an LCD monitor is entirely different – the brightness is provided by a backlight of some description, and colours are produced by filtering that white backlight with liquid crystals. In this scheme the lowest energy consumption is for a white pixel, where nothing is filtered. Turning a pixel black requires filtering pretty much everything, so uses the most energy. [...]
Left by Go green by going black? …not convinced. : Roosenmaallen.com on December 23rd, 2007
I have one good reason why turning your screensaver background white is counterproductive and have also included a more general discussion of the issues involved.
Your LCD backlight consumes ~75% of total display power, so efforts made to reducing power should focus on minimizing backlighting. [http://techlogg.com/content/view/383/31/]
More savings can be achieved by using your screen at a reduced brightness, using a screen with an ambient light sensor, or making heavy use of power saving features.
Rather than worry about the relatively small difference pixel intensity makes to overall power usage, I find using power management features to turn off the monitor (in XP it is on the same dialog as screensaver) after just 3 minutes works much better than using a screensaver at all. It turns back on almost instantly when triggered by user input. Experiment with the value to find something that works well with your usage patterns and be sure the computer sleeps after a reasonable interval as well in case you leave your workstation unattended.
Left by Greg on January 4th, 2008
Thanks for sharing that comment, Greg! That is an excellent, excellent point. I usually will have my brightness rate set very high when I am doing image optimization work (making sure that no subtle differences are noticeable on a very-bright display that might not have been noticed with a lower brightness setting), then bump it down a few notches for typical word processing or web browsing tasks.
The trick with controlling LCD screen brightness is that it varies from computer to computer. On my Dell laptop (running Windows XP), I use the Function (Fn) key, and either the up or down arrow to adjust my brightness settings. Other computers, however, use different methods for adjusting brightness. You’re absolutely right though….LCD screen brightness will save a LOT more power in the long run over playing around with screensaver backgrounds. I was just looking for any “edge” I can find.
Another good link on the topic of LCD brightness is http://chris.pirillo.com/2007/07/31/lcd-screen-brightness/ Thanks again for that great comment!
Left by datonn on January 4th, 2008