Light-emitting diodes are rapidly replacing conventional incandescent and fluorescent bulbs in everything from traffic lights to flashlights, but there's one thing they haven't been able to do: Produce an even spread of illumination.

Now, Omron of Kyoto, Japan, has announced that its research labs have prototypes of what they dub a "flat light source," an LED-powered lamp that produces an even glow over a wide surface.

Such a device could potentially have applications in general room lighting, said a spokesman. What's more, because the new light source produces white light by mixing blue, green and red, the source can emit any colour in the spectrum by varying the mix.

LEDs are a hot area of research because they last much longer than incandescent or fluorescent bulbs and consume far less energy. However, LEDs are several times more expensive than standard bulbs. In countries such as Singapore, authorities are replacing conventional streetlights and traffic lights with LED-powered lamps--some of them powered by batteries charged from solar cells atop the light poles.

However, each LED bulb is small, and so needs to be placed in a bunch in order to spread the illumination over the same area as a standard bulb. Grouping increases the bulkiness and price of each lamp, as well as decreasing the uniformity of the light spread, says Omron, a maker of consumer and industrial electronics.

The company's prototype incorporates red, green and blue LEDs in an optical capsule. This mirrored and lensed shell flattens the point beams out into a square 3 centimeters by 3 centimeters, with a thickness of just 6 millimeters.

With this, Omron's scientists have achieved 50 times the illuminated surface area of a single LED of the same thickness as the capsule, the company said.

Omron predicts that when the lamps go to market months down the road, it could be used in much the same way that standard bulbs are.