I’ve found this slightly ridiculous site and think it’s important to point out the significance of the error the creators made.

Blackle is, in short, a black version of With the amount of traffic Google receives, the amount of energy used displaying its search results is phenomenal and according to research done by the creators of Blackle, by displaying a black instead of a white background on Google, the world could save 750 MWh/year (=86KW). So, let’s take a closer look at this idea.

The underlying assumption is that black screens use less energy than white ones. I agree fully that this may have been true in the retro days of CRT screens: fewer electrons will need to be fired at the front of the screen so less electricity will be required. Unfortunately CRTs are somewhat backward and our world is very much a flat panel place nowadays. There are two types of flat panel: LCD and plasma displays. LCD stands for Liquid Crystal Display and the principle is actually really quite beautiful.

A liquid crystal can be seen as a polarising tube: when light is shone down one end it gets polarised. However this tube is composed of several layers like a lot of very flat cylinders concatenated end-to-end, each with a polarising slit. In its natural state the crystal (tube) is twisted so that each layer is slightly out of line with the adjacent ones. Imagine looking at a slinky end-on then twisting it. When light is shone on one end of this twisted liquid crystal, the first layer polarises it. The second layer then blocks some of this light because it is polarised in a slightly different orientation and allows some through, re-polarising it. This is repeated for all the layers of the crystal and eventually some light gets through. The last layer’s polarisation is orthogonal to that of the first layer.

When electricity is passed through this crystal however, it straightens out and becomes an untwisted polarising cylinder which just polarises light like a normal polarising sheet.

To construct an LCD screen, a sheet containing an array of cells made of these crystals is placed in front of a sheet of normal polarising material. A backlight is placed behind both these sheets. An electronic grid allows electricity to be passed through any cell independently of all the others. In the un-electrified state, all the liquid crystals are arranged so that the polarisation of the back face (next to the polarising sheet) is in line with that of the polarising sheet (say, vertically) and of course the crystal is twisted 90 degrees so the front is polarised horizontally. This way, light from the backlight can get through both sheets since the back of the crystal is aligned with the sheet and light can get from the back to the front of the crystal. However the front of the crystal is fixed in orientation so when the sheet is electrified and all the crystals untwist, the back of the crystals end up horizontal. Now the crystal acts like a second polarising sheet but in an orthogonal direction to the first sheet. No light gets through and the screen is black.

So, what does that mean? No electricity needs to pass through the crystal to display a white screen but every single cell (pixel) needs current passing through it to display a black screen. The assumption was false for LCD monitors, which in 2006 accounted for 80% of all computer monitors.

The other flatscreen technology is plasma displays which physically illuminate each pixel with a separate light source (some sort of LED I’d imagine). These I think do conserve energy when displaying a black screen.

So the website, at the user end of things, actually does the opposite of the stated intention for 80% of computer monitors. To make things worse, the functionality of this site is much lower than Google. Since it’s a Google custom search, the site only has the Google features available to Google affiliates and lacks things like Google cache, translator, webapps etc.

Enough about the frontend – now for the backend. The site must receive tens of thousands of hits every day, and must therefore need some quite meaty servers to deal with the traffic. Let’s say it requires a server that draws 500W (including cooling), an average power consumption for a server. According to the internet archives, Blackle has been around since the beginning of 2007. Over 2 years this server would have burnt through 8.8MWh. The site advertises it has saved a total of about 1MWh. Blackle has in fact caused the world to use an extra US household’s year’s supply of energy. Oops. In fact, even if the server drew 60W (ridiculously low), it would still have used 1.05MWh to date, and the creators would have actually increased world energy consumption by 50KWh.

So yet again someone with good intentions has done the wrong thing. Far from solving the world’s energy crisis, the creators of Blackle have created something which is inconvenient to use and actually does the opposite of what it was originally supposed to do. It is, I wholeheartedly agree, a brilliant and novel idea, but sadly one which doesn’t work at all.


3 Responses to Blackle

  1. egbertonline says:

    I don’t follow your point about the power consumption on the servers. Surely people use Blackle instead of Google or a similar search engine, as opposed to not using one at all and therefore any energy used by Blackle is not used elsewhere?

  2. Bryant Tan says:

    Apologies, I should probably have made that more clear.

    First of all, Blackle uses Google custom search and is thus itself not a search engine. All it does is display a page with a search box. The search is submitted to the Google server hardware to crunch. Results are returned to Blackle where it is packaged into a black page and displayed.

    Examining the per-page energy consumption: sure, Google don’t have to turn the XML results (or whatever format the results are delivered in) into an HTML page, but the amount of energy saved there is truly negligible – the energy used per page generated is tiny. Besides I’d be willing to bet Google use less electricity per calculation than Blackle owing to superior efficiency servers so actually Blackle are shifting the load onto less energy efficient servers. The Google servers are therefore actually working just about as hard as with a normal Google search so no (or negative) energy is conserved there.

    However on top of this per-page decrease of efficiency, Blackle are using electricity for their own servers to be kept on and cooled so there is a net increase in energy consumption server-side.

    Does that answer your question?


  3. kirk says:


    bryant, this is a phenomenal response.

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