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Low-Energy LED Lighting Is “Streets Ahead”
BER ways to exploit the advantages of LED (light-emitting diode) technology in street lighting aTTEre expected to emerge from collaboration between university researchers and an LED lighting specialist company, both in the UK.LEDs first appeared in digital watches and calculators in the 1970s. Today, the technology has progressed to the point where it can be used to create durable and community-friendly, low-energy street lighting. The benefits include long-life expectancy (up to 100,000 hours) together with increasingly high-light output in relation to their size and energy consumption, making LEDs a realistic alternative to conventional sodium vapour units for general and directional lighting. And because LEDs are so small, the possibilities for manufacturers to create sleeker, smaller, lightweight luminaries are greatly extended.Importantly, LEDs are also environmentally friendly and safe. They contain no glass, filaments or mercury and so can experience none of the exploding failures associated with halogen and HID (high intensity discharge) lamps. And they are free from the cost and restrictions of mercury disposal that is involved with sodium vapour units. Operating at low-voltage direct current ensures complete consumer safety. Coloured LED modules are very vivid and even more energy-efficient than white light units.
In the latest joint project between the University of Manchester, northern England, and LED lighting specialist Dialight Lumidrives - a company founded by a successful former student of the university - researchers in the School of Electrical & Electronic Engineering are using their expertise to investigate how tightly packed groups of LEDs can be made to work safely and reliably.Lighting solutions that use LEDs in this way have the potential to reduce energy consumption by 25-50 per cent, depending on the application. But thermal and electrical issues at lighting levels of 12,000 lumens and above (a typical 60whousehold light bulb produces 800 lumens) are barriers to the wider adoption of LED technology.The university engineers will be working with the York-based Dialight Lumidrives to tackle tough issues such as the amount of heat generated by LEDs packed closely together. Because the LED modules will be used outside, they will need to consider practical environmental factors, such as the possibility of birds nesting over a vital heatsink.
Another hurdle is presented by the regulations that govern aspects such as glare and light pollution; directing the LED light sources specifically on to the required area will form a serious challenge.The one-year project has been funded by a grant of 175,000 pounds from the UK government, matched by a similar amount contributed by Dialight. A key aim of the project is to develop a solution that is very reliable but not prohibitively expensive.Dr Roger Shuttleworth, from the Power Conversion Group at Manchester University, said: “LED technology first came to prominence in instrument displays in the 1970s, but we are increasingly seeing it used in things like traffic signals and car lights. “Towards the end of the 20th century, the old-fashioned sodium street lights that made everything look orange were gradually replaced by high-pressure sodium lamps. While these are brighter and more aesthetically pleasing, and can help tackle street crime and anti-social behaviour, they are also less energy efficient.“With the environment at the top of the public and political agenda, energy saving has become a very important issue. When you consider how many street lights there are in the UK alone, it is clear there are some big opportunities for energy and cost savings,” he added.
Dialight Lumidrives’ managing director Gordon Routledge studied electrical and electronic engineering at the University of Manchester Institute of Science & Technology (UMIST), graduating in 1996. He explained: “LEDs are on track to become a major source of lighting over the next decade. Although significant investment is on-going in the core development of the LEDs, the surrounding technology development is being left to manufacturers who have little knowledge of electronics or LEDs.“We are proud to be working with the University of Manchester to develop technology which will drive the adoption of this revolutionary lighting source in everyday applications,” he added.Although high-pressure sodium vapour street lighting - common across much of Europe - gives an efficiency of about 85 lumens per watt, he claimed that LED technology was already on track to exceed 150 lumens per watt and predicted this figure would rise further as new semiconductor developments occur. As well as cutting energy consumption and overall running costs, researchers say that LED street lighting helps reduce light pollution; the sky glow that radiates from big cities could become a thing of the past. It is also proposed that LED street lighting could be controlled and dimmed when necessary.Their longer lifespan means that LED street lights need to be replaced less often, reducing potential traffic disruption and council repair bills. The lifetime of the LED module that the collaborators are working on is in excess of 10 years in a road lighting application, some four times longer than a conventional street light. Although LEDs do experience a gradual and permanent reduction in light output during their normal operating life - caused either by a reduction in the light-generating efficiency of the LED die, or a reduction of the optical path within the LED package - the Dialight street LEDs are expected to provide about 70 per cent of their original light output after 50,000 hours or 10 years, provided that they are not overdriven. This is not as significant as it sounds because the human eye is relatively insensitive to changes in light output, and a reduction to about 50 per cent is necessary to create a noticeable change.
It is, says the company, easy to convert existing street lighting to an LED source because no electronics skills are required. It has been developing and exploiting LED technology for lighting applications for almost five years, with a successful produce range supplied to many of the world’s leading equipment manufacturers.