Look up at the ceiling above you, and chances are there is a centuries-old piece of kit swinging from a cord. The light bulb has been hanging around for more than 150 years. Yet between its invention and the present day, its design has hardly changed.
But now the days of the traditional incandescent bulb look numbered. These electricity-sapping glass orbs have fallen out of favour with environmentally-conscious governments and consumers. And waiting in the wings is a new breed of hi-tech light based on the humble LED (light-emitting diode), the small lights found in everything from TV remote controls to bike lights. Not only do they promise to solve the bulb’s environmental woes, their backers say they will also respond intelligently to your surroundings and even influence the way we behave.
“LEDs are about to change the way we see things forever,” says Tim Holt, chief executive of Strathclyde University's Institute of Photonics in Scotland. “We are only just at the start of the LED lighting revolution.”
Already, the efficiency and long life of LEDs is making them a popular – if costly – option in places where changing bulbs is inconvenient or expensive, such as in motorway lights, traffic signals, airport runways or on large buildings and bridges. For example, the Louvre museum in Paris is currently replacing 4,500 bulbs with LED equivalents, a change that is expected to result in a 73% reduction in energy consumption. Plans are also in place to replace the 25-year-old lighting system that illuminates Tower Bridge in London with LED lighting in time for the 2012 Olympic Games
But the real hope of the LED industry is that arrays of these tiny twinklers packed into something that resembles a bulb will become the light of choice in your bedroom, bathroom or study, allowing them to grab a slice of a global lighting market that was worth an estimated €52bn in 2010. Their cause is helped by the numerous governments around the world which have chosen to phase out the sale of incandescent bulbs. An EU-wide phase-out is already underway, and in November 2011 the Chinese government announced that the import and sale of incandescent bulbs would start to be banned from October 2012. Over 1 billion incandescent bulbs were sold in China during 2011, meaning the announcement was enough to drive investors into a frenzy: the share price of Cree, a United States-based LED manufacturer, increased by almost 10%.
Of course, the death warrant for the incandescent bulb has been signed before. Compact fluorescent lamps (CFLs) – or energy efficient bulbs, as they are more commonly known – were supposed to spell the end of the light bulb in the 1970s. But despite rising to prominence in the 90s and constantly improving, they have failed to deliver on their promise. In part this is down to them costing more than regular bulbs, taking an age to warm up and often producing low quality light. And that is without even mentioning the environmental concerns over bulbs that contain mercury.
LEDs, it is claimed, will help overcome these problems. These tiny lights were invented by GE in the early 1960s and were initially only available in red, a property that defined the look of early pocket calculators and digital watches. Over the years, however, more colours have appeared.
These are all made in the same way: from wafers of semiconductor, the material used to make computer chips. As their name suggests, LEDs consist of a simple diode. In traditional electronics these are two metal posts – an anode and a cathode – placed very close to one another, through which power can only flow in one direction. In LEDs, the anode and cathode are formed by depositing two areas of semiconductor that have been “doped” – impregnated with impurities – next to one another. As power flows through the junction between these two patches, some of it is unable to make it through and is instead emitted as photons of light. The colour of the light is dictated by the properties and structure of the semiconductor used to make the LED. For example, the bluish light seen in many pocket LED torches is created using materials such as zinc selenide and indium gallium nitride.
