Energy-saving bulbs may have some competition in the shape of an ageing technology. Scientists have developed a new kind of incandescent light bulb that uses modern science to ramp up its efficiency, almost matching that of commercial LED bulbs. Incandescent light bulbs are intrinsically inefficient. They work by pumping electricity through a thin tungsten filament, the electrical resistance of which causes its temperature to reach in excess of 2760C. At such high temperatures the filament glows, giving off light — and a lot of heat, in the form of infrared radiation. In fact, a normal incandescent bulb only turns 2 per cent of the electricity it uses into light. For comparison, an LED bulb manages to squeeze out light from between 5 and 15 per cent.
Now, a team of researchers from MIT has developed a new kind of incandescent bulb that uses a kind of nano-scale mirror to make use of the wasted infrared emissions. The team has developed a new kind of what they refer to as photonic crystals: materials that allow light in the visible spectrum to pass straight through, while reflecting infrared back towards the filament. There, energy from the infrared radiation is absorbed and re-emitted once more, but some this time as visible light. That back-and-forth can continue, helping to improve efficiency.
The process wasn't quite as straightforward as that makes it sounds, though. First the team had to make the photonic crystals, specially tuned to allow transmission of visible light and reflection of infrared. Ultimately that required layering 90 nano-scale layers of tantalum oxide and silicon dioxide on top of each other. The team also had to redesign the filament, creating a larger surface area capable of absorbing the reflected radiation. You can see the final design in the image above: a thin, folded ribbon of tungsten.
The good news is that it worked. The new bulb converts 6.6 per cent of the electricity into light. That's three times better than a regular incandescent bulb, and better than the least efficient of LED bulbs that are available. The team reckons that the efficiency can be boosted even further, too, perhaps even to as much as 40 per cent. The research is published in Nature Nanotechnology.
These bulbs are, however, far from being a commercial reality and plenty of research and development will be required before you twist one into a lamp fitting in your home. But even if it takes a while, Thomas Edison's ageing technology may yet get a new lease of life.
Image by O. ILIC ET AL./MIT