Energy Saving with theGreenSpider

The Theory

The US government organisation, The Department of Energy, provided the table below. It shows the 16 basic Windows' colours and the amount of electricity each uses when displayed as a solid colour on a screen.

The leading search engines, such as Google and Yahoo!, use a white background. A CRT monitor displaying a white background consumes 74 Watts of electricty, a massive 15 Watts or 20% more than a monitor displaying a black background.

This small saving might not have much of an impact on your electricity bill, but if everyone using a monitor made the effort, then together we could save energy when we searched the Internet by as much as 20%.

theGreenspider Colours

theGreenspider currently has the following 7 background colour options. The table shows the estimated power usage of a monitor using each colour option and the estimated power saving as compared with a monitor using a white background:

LCD (save up to 7% energy by using theGreenSpider compared to Google)

A liquid crystal display (commonly abbreviated LCD) is a thin, flat display device. LCD monitor are suitable for many types of devices, including computer monitors and battery-powered electronic devices. Unlike CRT monitors, LCDs rely on a constant source of illumination, commonly known as a backlight. Backlights produce light in a manner similar to a CRT display, with the difference that the backlight is always on. Backlights can be any colour; monochrome LCDs usually have yellow, green, blue or white backlights, while colour displays use white backlights that cover most of the colour.

A pixel in an LCD display typically consists of a layer of molecules aligned between two transparent electrodes. When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field. This reduces the light shining through from the backlight, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules are completely untwisted; the result is that the backlight will then be completely blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts, correspondingly illuminating the pixel. As such, LCD display technology is different from CRT technology, and therefore colours that are energy efficient to display on a CRT monitor (e.g. black) are not as energy efficient to display on an LCD monitor.

The Roberson study found that LCD monitors saved up to 3W (7%) by switching from a white to a black screen, and in no case did any of the LCD monitors use more energy displaying black than white. Recently, several informal studies have been done, with results ranging from a 2W reduction when using a black screen vs. Google, up to a 1W increase.

PLASMA (even bigger energy savings than CRT)

A plasma display panel (PDP) is a type of flat panel display commonly used for large TV displays, typically above 37". Many tiny cells located between two panels of glass hold an inert mixture of noble gases (neon, which are contained in hundreds of thousands of tiny cells positioned between two plates of glass. electrodes are sandwiched between the glass plates, in front of and behind the cells. Control circuitry charges the electrodes that cross paths at a cell, creating a voltage difference between front and back and causing the gas to ionize and form a plasma; as the gas ions rush to the electrodes and collide, photons are emitted. To erase a cell, all voltage is removed from a pair of electrodes. Every pixel is made up of three separate sub pixel cells, each with different coloured phosphors. One sub pixel has a red light phosphor, one sub pixel has a green light phosphor and one sub pixel has a blue light phosphor. These colours blend together to create the overall colour of the pixel.

Plasma displays use the same phosphors as CRTs, and are bright, 1000 lux or higher being the norm. Plasma displays use as much power per square meter as a CRT, and consumption varies greatly depending on what is watched on it. Bright scenes will draw significantly more power than darker scenes. Nominal measurements indicate 400 watts for a 50" screen. Currently, plasma displays are not popular for computer monitors. However, since they operate similarly to CRT technology, the energy differentials are similar.

A study conducted by G4TechTV using a Samsung 42" plasma display found a 191W differential for a white vs. black screen in normal mode, and a 138W differential in super energy savings mode. Plasma displays are particularly well suited for the large displays, outpacing other types of display technologies. However, recent improvements in LCD technology have contributed to falling prices, higher resolutions, and often lower electrical power consumption, making them very competitive against plasma displays.

OLED (the future of computer screens)

An organic light-emitting diode (OLED) is any light-emitting diode (LED) whose emissive electroluminescent layer comprises a film of organic compounds. The layer usually contains a polymerpixel that can emit light of different colours, allowing suitable organic compounds to be deposited. They are deposited in rows and columns onto a flat carrier by a simple "printing" process. The resulting matrix of OLEDs are used in television screens and computer displays; a great benefit of OLED displays over traditional LCDs is that OLEDs do not require a backlight to function. Thus they draw far less power and, when powered from a battery, can operate longer on the same charge.

No comprehensive studies have been conducted of a comparison between white vs. black screens, but due to the nature of their construction, it is probable that displaying white will consume more energy than black on an OLED device