19.10.2005 Overview

Energy savings for laptops

Osram Opto Semiconductors equips a demo system with LED backlighting

LEDs such as µSideLEDs are the ideal alternative to cold-cathode fluorescence lamps for display backlighting. They do not need any time to warm up, contain no lead or mercury and provide at least the same bright light but with a lower energy consumption.

Source: OSRAM

Osram Opto Semiconductors will be showing how power can be saved in laptops with a demo system featuring LED backlighting at the Flat Panel Display Fair from October 19 to 21 in Yokohama. With a power draw of just 5.5 W the demo system achieves a luminance of 220 cd/m², even outperforming conventional units that need 8 to 10 W to produce an average luminance of 200 cd/m².

Small mobile computers such as laptops and notebooks are popular and powerful but they have one major drawback – they consume too much power. This has an impact on battery life and places serious restrictions on mobility. An "Enhanced Battery Life" working group has been set up to identify potential energy savings and prolong battery lifetimes. Osram Opto Semiconductors has been involved in this project by providing appropriate light sources.

A full 33 percent of the power needed by a laptop computer is consumed by the LCD display, with the backlight taking up the majority of this (source: Intel). With cold-cathode fluorescence lamps, the power required is presently between 8 and 10 W.

Consumption is much less if light emitting diodes are used instead of conventional lamps. The 15“ demo laptop is equipped with 69 white µSideLEDs. As their name suggests, these LEDs emit light from their sides. They are used in the outer frame of the display, injecting their light into an lightguide that distributes the light uniformly over the entire display. In normal bright surroundings they need just 5.5 W but achieve at least the same luminance as the cold-cathode fluorescence lamps that are traditionally used.

There is additional potential savings in linking the display backlighting to the amount of ambient daylight available. The brightness of the display can be adjusted by an ambient light sensor or by users themselves. In darker rooms, for example, power consumption would be reduced and visual comfort improved as a lower luminance in dark rooms is easier on the eye and does not lead as quickly to fatigue. A luminance of 60 cd/m², for example, can be achieved with LED backlighting from an input power of only 1.2 W.

µSideLEDs combine high luminance and low energy consumption with other significant benefits such as small dimensions, long lifetime, dimmability and shock resistance. Their side beam characteristics, coupled with expected increases in brightness from the same power consumption, make them ideal for display backlighting.