Does a webpage with a black background save energy?

Question

Blackle is a search engine that claims to save energy because it uses a black background. Is there any evidence to back up their claim that a website using a black background will save energy, and if so, how much energy will be saved?

Answer 1

Blackle actually cite a real reference to backup their claims. Credit to them!

On their About page they quote a line from a Energy Use and Power Levels in New Monitors and Personal Computers, Roberson et al, Environmental Energy Technologies Division, Ernest Orlando Lawrence Berkeley National Laboratory, UCLA.

The quote is:

"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."

That line does actually appear in the report, and is backed by the following data:

The reports goes on to conclude:

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.

Clearly, in LCD technology terms, 2002 is a long time ago. I have no knowledge of any power-saving innovations in the meantime.

Answer 2

LCD panels make black pixels by blocking the colour filtered back-light from exiting the panel. It therefore uses a little more power to make black than to make white

See http://electronics.howstuffworks.com/lcd2.htm

LCD TV's sometimes have "dynamic contrast" LED back-lighting which should save power in black. This feature is sometimes found on high end IPS LCD monitors, though is useless for general computer use as the LED back-light resolution does not match the actual LCD resolution

OLED panels use power to make each individual coloured pixel, so black would save power. Who uses a couple of 24" OLED's yet?

See http://electronics.howstuffworks.com/oled2.htm

And more interestingly http://www.popsci.com/scitech/article/2009-09/mit-scientist-explains-oled-function-glowing-pickle

Answer 3

When blackle came out (2007) the majority of users still had CRT monitors. There's a nice discussion of this here http://ecoiron.blogspot.com/2007/08/history-in-january-2007-mark-ontkush.html

From the above link:

---

Criticisms There has been both praise and criticism for this initiative, with its supporters citing it as a great example of environmental thinking, and its detractors pointing out usability and aesthetic problems, as well as questions about the scientific validity of the claims. Some of the issues are listed below.

• Since the technique is most effective on CRT monitors, some proxy sites have been criticized for not mentioning this fact. In particular, the Blackle site has been heavily criticized, as it is probable that they are generating an substantial Adsense revenue stream from implementing the concept.
• CRT monitors are being phased out; about 75% of monitors in active use worldwide are LCDs. Additionally, countries with a high percentage of CRT are replacing them rapidly; for example, Display Search projects that only 18% of the monitors in China will be CRTs by the end of 2007. Therefore, although the technique would be effective for a limited period, it is questionable whether the disruption would be beneficial.
• CRTs are generally darker than LCDs, and the text on many of the proxy sites is barely readable on monitors of this type. For example, Blackle uses a small grey font on an all black background. It is possible that these 'all black' proxy sites are only usable on LCD screens, and this would negate the energy savings.
• Proxy sites cannot handle the heavy load that high volume sites are accustomed to. For example, on August 1st, 2007 and several prior occasions, the Blackle web server was producing intermittent error messages for extended periods of time.

So, already back in 2007, most people were questioning the usefulness for the black background web pages for saving energy.

If we were all still using CRT monitors then yes you could save a lot of energy by using the black backgrounds. But, this is 2011 and the few CRT monitors left in existence are sitting in the corner of our basements unplugged and waiting to be taken to the electronics recycling graveyard.