As well-informed people know, today's version of low-energy lighting, using compact fluorescent lights (CFLs), is the wrong technology. The products are relatively cheap to buy, but they have a number of practical disadvantages, as well as significant ecological problems in their production and disposal. Although they are evidently the wrong solution, up to now the right way to go has been too expensive for domestic use.
Brighter future
The brighter future is the light-emitting diode or LED. Based on a far more efficient light source and producing a purer white light, the affordable LED lamp bulb is seemingly within our reach at last. According to Prof Colin Humphreys of Cambridge University's Centre for Gallium Nitride, the new breed of LED lamp bulbs will last 60 years and could slash the proportion of electricity used for lighting from 20 to just five percent.
In Britain, this could eliminate the need for eight power stations. Even better, the new bulbs do not contain mercury and they are dimmable.
Humphreys says, “We are very close to achieving highly efficient, low-cost white LEDs that can take the place of both traditional and currently available low-energy light bulbs. This could well be the holy grail in terms of providing our lighting needs for the future. That won't just be good news for the environment; it will also benefit consumers by cutting their electricity bills”.
New recipe
LED lamps are not new by any means and they are already used widely in torch bulbs, camera flash units, vehicle lights and display lighting in shops, to mention just a few applications. But for ‘general lighting service' (that's ordinary lamp bulbs to you and me), the production costs are too expensive for widespread use in homes and offices.
Colin Humphreys' breakthrough at Cambridge University has been to make the new LEDs from Gallium Nitride (GaN), a man-made semiconductor that emits a brilliant bright light but uses very little electricity. His team has developed a new way of making GaN that could produce LEDs for a tenth of current prices.
The new technique grows GaN on silicon wafers, which achieves a 50 per cent improvement in cost and efficiency on previous approaches employing expensive wafers of sapphire, used since the 1990s. The idea is that commercially-produced versions of Humphreys' LED will be in use around homes and offices within five years.
Fine tuning
Demonstrating a concept in the lab is one thing, but refining it for mass production is another. The light produced by most ‘white' LEDs tends to have a blue-ish cast, which is not suitable for domestic lighting. The ‘golden yellow' LEDs are not ideal either. Humphreys says that by applying a phosphor to the LED, it can produce a more agreeable white light.
Another stumbling block to overcome is turning point sources of light into a bulb or globe that radiates in all directions. LEDs used in torches, spotlights and vehicle head and tail lights tend to be focused in a single direction. This glare is unwelcome in homes and offices, where people prefer a more omnidirectional and diffuse light source.
The team at Cambridge is also carrying out research into more specialist but equally vital applications for GaN light. They want to see how these could mimic sunlight to help three million people in the UK with Seasonal Affective Disorder (SAD). Ultraviolet rays produced from GaN lighting could also aid water purification and disease control in developing countries, identify the spread of cancer tumours and help fight hospital ‘super bugs'.
On the right lines
One field where existing LED technology is making rapid inroads is aboard trains, even though you might not have noticed. Here, ruggedness, low maintenance and reduced power consumption outweigh the initial installation cost of retro-fit LED lighting. The figures work out well, as this example from British firm Dialight proves.
A typical fluorescent-tube lighting installation on a commuter train requires 2kW of electricity to achieve adequate brightness for reading. LED fixtures can achieve the same lighting level from 500W, reducing the number of voltage converters from 52 to just four. Reflectors control the direction of light across the carriage ceiling via a range of optical beam patterns, rather than bouncing it straight down to the floor. With lights left on in trains for 16 hours a day, it's obvious that significant energy savings are possible.
Another British firm actively involved in exploiting the market for ‘lighting class' LEDsis Zetex, which employs more than 750 people worldwide. If the name doesn't ring a bell, let me just mention that Zetex is the semiconductor division of the Ferranti company of lengthy heritage. Its ZXLD1362 switching LED driver operates from input voltages of 6V to 60V at up to 95 per cent efficiency. The smallest of its kind at this current rating, it can drive up to 16 high-power LEDs with an adjustable output current of up to 1A.
The race is on
With the world's nations determined to develop their way out of the recession and also reduce energy consumption, the race is on to develop more efficient methods of solid-state lighting. Cambridge University's breakthrough in white LEDs could lead to mass manufacture in the UK. Prof Humphreys is well aware of the technical difficulties of growing LEDs on a silicon substrate, but is optimistic nevertheless.
He told trade paper Electronics Weekly: “We have only been working for a year or so and we are still on a steeply rising curve. [Nevertheless] our way is so much cheaper, I think it is probably commercially viable even now”. His team is working with QinetiQ, formerly known as the Defence Evaluation & Research Agency, and the German manufacturer Aixtron to turn its science into a commercial production process.
The US government is also backing the LED lighting revolution, with an $18.5 million five-year award to the Smart Lighting Engineering Research Center at Rensselaer Polytechnic Institute in Troy, New York. A recent study authored by RPI professors Fred Schubert and Jong Kyu Kim issued ‘a call to arms for scientists and engineers', stating that over the next 10 years savings of more than $1.8 trillion will eliminate the need to burn almost a billion barrels of oil in power plants that would otherwise produce 10 gigatons in carbon dioxide emissions.
“Such enormous savings will result from replacing 80 per cent of traditional lighting with LEDs over the next 10 years. And besides replacement, there are also new capabilities possible in this lighting revolution”, declared Prof Jong Kyu Kim.
One of the most interesting applications under development at RPI is spectrum control, which they say will enable the colour of lighting to be altered during the day to influence the mood of workers positively, as well as curing certain medical problems that are caused today by poor lighting conditions.
