For the past couple of years electronics companies researching Oled (organic light emitting diode) displays have been making technology promises that are almost as bright as the displays themselves, but commercial products have been slow to follow.

The first commercial Oled began shipping in March. However, both it and the latest batch of prototypes suggest that the power-reduction promises made about the technology may have been optimistic, at least for the first generation of products.

Oleds are a fundamentally different technology to LCDs (liquid crystal displays). They are made by sandwiching a layer of organic material between two electric connectors. When a charge is applied to one connector it flows through the organic material, causing it to glow.

This means that, unlike an LCD, no backlight is needed and so the entire display panel can be made thinner, lighter and will require less power than an equivalent LCD. At least, that's what was promised. Current prototypes, on display yesterday in Tokyo at Edex (the Electronic Display expo), consume around the same power as an LCD and in some cases more.

A prototype 2.1in panel from Seiko Epson consumes around 150mw (milliwatts) when displaying a moving image. A TFT (thin-film transistor) LCD of a similar size consumes just over 150mw with its backlight switched on, making the Oled power saving negligible.

"The technology is still young," said Tsutomu Takenouchi of Seiko Epson's Oled technology division. "We hope to improve the power saving with future generations."

Prototype versions of 2.2in and 3.5in panels were also displayed by Toshiba. Commercial production is scheduled to begin sometime in 2004, said Jun Hanari of the company's research and development centre. Power consumption, according to Hanari, could in some cases, such as a still screen of black text on a white background, be as much as double that of a modern LCD.

However, to write off Oled technology just because it doesn't live up to promises about power consumption would be to ignore its other features, and to dismiss a market that DisplaySearch estimates will reach $8bn in 2007.

In addition to being physically smaller, the prototype displays on show in Tokyo were brighter, showed more vibrant colours and were much better at displaying moving images than similar LCDs.

One of the biggest hurdles to commercialisation for many companies is the length of time the display can be used before its organic structure breaks down, said David Hsieh, an analyst at DisplaySearch in Taiwan. The problem is that the organic layer slowly succumbs to a chemical reaction that eventually renders it useless, he said.

"The stability of the organic materials is not easy to control," said Hsieh, "but if the layers can be well controlled, Oled stability is will be achievable and then commercialisation will follow."

For applications such as mobile phones and camcorders, the industry is aiming for a lifetime of over 10,000 hours. Most of the prototypes developed so far, Hsieh estimates, have a lifetime of between 6,000 and 8,000 hours.

Many of the Oled displays on show were small in size and offered a relatively low resolution. They are being targeted at the handheld and mobile phone markets.

But it's not just in the area of small-size displays that work is taking place. Because of their bright and high-contrast images and suitability for moving images, some companies are looking at using the technology in future flat-screen televisions. For larger displays there is more work to be done, said Hsieh.

"I think 10,000 hours is easy to achieve but once you get up to above 15,000 hours, the organic layer will have lifetime issues," he said. While a lifetime of 15,000 hours and above is not essential for portable electronics, it is a requirement for displays that will be used as televisions or computer displays.

The Sanyo booth featured a prototype 15in Oled, the largest on display at the Tokyo show.