An environmentally friendly bulb that may never need changing

DESPITE its use to symbolise a bright idea, the traditional incandescent lightbulb is a dud. It wastes electricity, radiating 95% of the energy it consumes as heat rather than light. Its life is also relatively short, culminating in a dull pop as its filament fractures. Now a team of researchers has devised a lightbulb that is not only much more energy efficient. It also lasts, in effect, forever—that is, it is expected to last longer than the devices into which it is inserted. Moreover the lamp could be used for rear-projection televisions as well as general illumination.

The trick to a longer life, for lightbulbs at least, is to ensure that the lamp has no electrodes. Although electrodes are undeniably convenient for plugging bulbs directly into the lighting system, they are also the main reason why lamps fail. The electrodes wear out. They can react chemically with the gas inside the lightbulb, making it grow dimmer. They are also difficult to seal into the structure of the bulb, making the rupture of these seals another potential source of failure.

Scientists working for Ceravision, a company based in Milton Keynes, in Britain, have designed a lamp that eliminates the need for electrodes. Their device uses microwaves to transform electricity into light. It consists of a relatively small lump of aluminium oxide into which a hole has been bored. When the aluminium oxide is bombarded with microwaves generated from the same sort of device that powers a microwave oven, it generates a concentrated electric field in the void.

If a cylindrical capsule containing a suitable gas is inserted into the hole, the atoms of the gas become ionised. As electrons accelerate in the electric field, they gain energy that they pass on to the atoms and molecules of the gas as they collide with them, creating a glowing plasma. The light is bright, and the process is energy efficient. Indeed, while traditional lightbulbs emit just 5% of their power as light, and fluorescent tubes about 15%, the Ceravision lamp has an efficiency greater than 50%.

Because the lamp has no filament, the scientists who developed it think it will last for thousands of hours of use—in other words, decades. Moreover the light it generates comes from what is almost a single point, which means that the bulbs can be used in projectors and televisions. Because of this, the light is much more directional and the lamp could thus prove more efficient than bulbs that scatter light in all directions. Its long life would make the new light ideal for places where the architecture makes changing lightbulbs a complicated and expensive job. Its small size makes it comparable to light-emitting diodes but the new lamp generates much brighter light than do those semiconductor devices.

Another environmental advantage of the system is that it does not have to use mercury. The metal is highly toxic and is found in most of the bulbs used today, including the energy-saving bulb, fluorescent tubes and the high-pressure bulbs used in projectors. Its developers reckon it should be cheap to make.

With lighting accounting for some 20% of electricity use worldwide, switching to a more efficient system could save not only energy but also on emissions of carbon. Now that would be a bright idea.

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