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LED technology comes of age

Jun 06, 2006
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Peter Cook looks at the benefits offered by LED technology and outlines the key areas where LEDs are beginning to edge out fluorescent lamps as the light source of choice.

LED technology has frequently been billed as the light source of the future, but despite all the recent hype it is still not really a practical solution for mainstream commercial lighting schemes. However, LEDs are now beginning to supplant fluorescent lamps as the preferred light source in a number of specific applications – the main one being emergency lighting.

Exit signs

The first type of emergency lighting product to take advantage of LED technology was the exit sign. Before LEDs of sufficiently high light output became available, most exit signs used 8W fluorescent lamps, which have a life of around 6000 hours. Because exit signs are usually operated in maintained mode, i.e. they are permanently illuminated, failed lamps needed replacing roughly every 8 months. This had two major disadvantages.

First, it meant that the building operator incurred significant maintenance costs throughout the life of the exit sign. Secondly, there was the environmental impact of frequent lamp changes. Each fluorescent exit sign typically requires 15 replacement lamps over a lifetime of say 10 years. The fluorescent lamps contain mercury and therefore at the end of their life they need to be treated as hazardous waste and disposed of appropriately. Furthermore, each replacement lamp requires significant amounts of energy for its manufacture, has associated packaging that creates additional waste, and will consume more energy when transported around the world from the point of manufacture to the point of use and ultimately to the point of disposal.

While ever there was no realistic alternative to 8W fluorescent lamps, these consequences were simply accepted by the industry as the inevitable price to be paid for ensuring adequate provision of emergency lighting.

LED development

In the mean time, LED technology was progressing apace. Early LEDs were low-output, inefficient devices, available only in red, green and amber. With power levels in the milliwatt range, they had to be used in clusters to produce any appreciable light output. Eventually white LEDs appeared, and these have now been developed to the point where single devices are available with power ratings of several watts, making them an attractive alternative to traditional fluorescent light sources for the relatively low illumination levels required for emergency lighting.

Benefits of LEDs

So, what is it about LED technology that makes it so attractive? Probably the key selling point of the technology is that it offers a working life of typically more than 50,000 hours, which is up to ten times longer than conventional fluorescent lamps. This long life translates into major benefits with regard to maintenance and environmental impact.

Whereas the fluorescent lamps in maintained emergency lights need replacing every 8 months, plus battery replacement every 4-5 years, the only maintenance requirement for a maintained LED-based luminaire is a single replacement of the battery and light source every 4-5 years. As well as dramatically reducing the disruption caused by lamp changes, this minimal maintenance means that an LED-based luminaire can end up costing the building operator significantly less than a fluorescent equivalent over the lifetime of the product.

In terms of environmental benefits, the LED-based luminaire contains no mercury, it eliminates the waste and energy consumption associated with frequent lamp changes, and it provides ongoing energy savings: a maintained LED exit sign typically uses 20% less energy than a maintained fluorescent exit sign.

LED technology has also had a significant impact on luminaire aesthetics. Whereas the design of traditional exit signs was constrained by the size and shape of the 8W fluorescent lamp, LEDs are such compact devices that the light source no longer determines the dimensions of the luminaire. Instead, the exit sign can be designed around the pictogram, with the light source unobtrusively concealed. This has enabled new design possibilities to be opened up: small compact signs for ceiling mounting on escape routes are now readily available, while large signs with extended viewing distances can easily be produced using multiple LEDs.

Being a low-voltage source, the LED-based luminaire does not need to incorporate protection from the high voltages required for fluorescent types. The control gear can be safely tucked away, and only minimal wiring is needed for the sign itself.

Finally, the wide operating temperature range of LED devices has created new possible uses. For example, whereas striking of fluorescent lamps is difficult below 0 degC, LEDs can operate quite happily at sub-zero temperatures, so this has paved the way for applications in extreme environments like cold stores.

Emergency luminaires

Although mass-market LEDs do not provide a high enough light output to deliver the 400-450 Lux required for normal mains lighting in a typical office environment, they are easily able to achieve 0.5 or 1 Lux, which is all that is needed for emergency lighting applications. Following the successful implementation of LEDs in exit signs, the technology is now being used to produce very compact and unobtrusive emergency luminaires.

With luminaire design no longer constrained by the lamp shape, these low-profile products are available in a variety of aesthetically pleasing styles. Allowing accurate directional control of the light source so that there is very little ‘wasted’ light, some of the latest generation of LED-based products have been optically engineered to provide maximum performance when mounted axially, thus complementing the typical mains lighting layout.

One such product, the innovative Briteway luminaire, uses purpose-designed optical lenses and dual LEDs to achieve a distribution that is optimised for escape route illumination, with maximised spacings between luminaires (typically 8m). When used in maintained mode, products like Briteway are ideal for nightlighting or background illumination applications in, for example, hospitals, student accommodation and places of entertainment.

Other innovative designs concentrate on delivering unobtrusive and aesthetically pleasing emergency lighting using tiny circular low-profile luminaires with diameters of just a few centimetres, thereby avoiding the need for bulkhead luminaires on a ceiling. Such luminaires provide a versatile solution that can combine the role of emergency lighting with mood lighting in say hotels, pubs, nightclubs, reception areas and retail interiors.

Conclusion

Although LED technology does not provide high enough light output or efficiency for use in mainstream commercial lighting applications, it will become more and more popular as a light source for emergency lighting, providing major benefits in terms of maintenance, environmental impact and luminaire design.

Biography

Peter Cook is product marketing manager at Cooper Lighting and Security, with responsibility for product development and marketing of the company’s Menvier and JSB ranges of central battery systems, emergency lighting and fire detection systems. He has over 20 years’ experience with the company.