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LED lighting: not just a pretty place

Jul 20, 2007
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LED technology offers major advantages as a light source and has massive potential for the future, but there are some pitfalls to avoid. Leighton James takes a look at the state of the technology today.

Although LED technology has been the subject of a great deal of hype in recent years, there is no doubt that it has much to offer and will inevitably find its way into more and more lighting schemes as time goes on. Having already become the light source of choice for exit signs and other types of emergency luminaire, it is now beginning to provide a realistic alternative to traditional sources such as 35W tungsten-halogen and 70W metal-halide lamps, as well as featuring increasingly in decorative and display lighting applications (see Fig. 1).

However, as happens with any rapidly evolving technology, there are some inferior fittings on the market, and contractors need to be aware that such products may not actually deliver all the benefits they promise.

Today’s LEDs

A fundamental point to understand is that there are two types of LED used in light fittings: 5mm LEDs and high-output chip-on-board LEDs (see Figs. 2a and 2b). While the 5mm types were used by some manufacturers in early commercial fittings, these are now being replaced by high-output (HO) LEDs, for the simple reason that the HO LEDs offer far superior lumen maintenance. After 6000 hours, the output of a 5mm LED drops to 50% of its original value, whereas the HO LEDs drop by only 5%. In other words, the HO LEDs will last for 10 years or more, but the cheaper 5mm LEDs will grow dim after just 2 years. Consequently, the 5mm LEDs are now predominantly used in fittings for the domestic market.

The HO LEDs offer the additional advantage that they can be integrated with different optical components, allowing a variety of beam angles and other effects to be produced.

In terms of efficacy, the headline figure of 160 lm/W is often attributed to the latest HO LEDs, but this level of performance requires a drive current of some 700mA – double the 350mA norm – which impacts on the life of the LED. In terms of commercially viable use, the best LEDs today deliver 100 lumens, which equates to around 85 lm/W in a practical application.

Despite its rapid progress and development, LED technology has not yet reached the point where it can be used as a widespread substitute for fluorescent lamps in mainstream commercial lighting applications. However, in applications where it is suitable for use, LED technology does offer some very compelling benefits, including long service life, high reliability, energy efficiency, coloured lighting and discreet integration into building fixtures.

Long life

High-output LEDs will maintain over 70% of their initial light output for at least 50,000 hours (typically 10 years’ commercial use), compared with around 12,000 hours for traditional fluorescent sources and 5000 hours for halogen lamps. However, maximising this operational life is dependent on effective thermal management and accurate drive-current control.

LEDs do not generate heat from the front, but from the rear, and heatsinking is required to keep the junction temperature down. For this reason, light fittings must be specifically designed to accommodate LED components. If LEDs are merely clustered together into an existing fitting that was originally designed for a traditional light source, they will simply overheat and deteriorate within a couple of years. But this is exactly the approach that has been taken by some manufacturers at the lower end of the market, so contractors should be very wary of just using the cheapest LED fittings available.

Reliability

LED technology already has a proven track record of high reliability as it has been used successfully for a number of years in emergency-lighting applications. Essentially, this reliability stems from the fact that LEDs are solid-state devices, which have no moving parts and are not subject to component ruptures, breaks or leaks. As long as LED fittings use quality components from a reputable source and are designed and manufactured correctly, they will provide completely reliable service for many years without requiring any maintenance at all.

And when the LEDs do eventually near the end of their life, they will not suddenly fail like conventional light sources, but just get gradually dimmer, thereby providing a safer lit environment.

Since they are maintenance-free, LED fittings are ideal for applications where lamp replacement has traditionally been problematic - for example, wherever access is difficult because fittings are submerged or installed at high level. The traditional in-ground luminaire is also a good example: although access is straightforward, if the IP seals on these luminaires are not re-seated correctly after a lamp has been replaced, the result is condensation on the inside of the glass and possible failure of the fitting itself. LED versions (see Fig. 3) overcome these problems because they completely eliminate the need for lamp replacements.

Energy saving

Another major benefit of LED technology is its energy efficiency. Climate change is firmly at the top of the political agenda, and as lighting accounts for a major proportion of the electricity consumption in a typical building, any improvement in the efficiency of the light sources used will have a significant impact on efforts to save energy.

For example, a 3 x 1W LED can be used instead of a 35W tungsten-halogen lamp, but care must be taken when replacing traditional light sources, as the lighting effect with LEDs may be slightly different. In this case, a tungsten-halogen dichroic lamp produces a soft cone of light, whereas an equivalent LED fitting will produce a much sharper cone.

Coloured light

Perhaps the one application most generally associated with LED technology is coloured lighting. Light from different coloured LEDs (see Fig. 4) can be combined to generate any colour in the spectrum for either fixed or dynamically changing illumination (see Figs 5a, 5b and 5c), and as the colour is generated at source, there is no need for filters which absorb the light.

Although LED technology is capable of producing exciting coloured lighting effects for discos or trendy bars, these will probably not be appropriate in most commercial applications. However, in many workplaces, there is scope for smooth, slow colour changes, which can help to create a comfortable, pleasing environment. Furthermore, LED technology can be used to vary the shades of white light within a building. For example, in a hotel in winter, a warm white would create a cosy and inviting ambience, whereas in the summer a cooler shade might be more welcome.

An important consideration when sourcing LED fittings is colour consistency. When a batch of LEDs is manufactured, it is allocated a particular colour temperature band or bin number, depending on the exact shade it produces. While reputable lighting manufacturers will only use LEDs from the same bin, cheap fittings often include a mixture of LEDs from different bins, with the result that the final lighting effect may be inconsistent and disappointing.

Integration

Due to their compact design, LEDs can be discreetly integrated into building fixtures or furniture (see Fig. 6) to create new architectural and display lighting applications, sometimes with the light source hidden from view (see Fig. 7). Popular examples include LEDs integrated into architrave, coving and counter trims.

Conclusion

Although LED technology is widely associated with dynamic coloured lighting in discos and bars, it also offers several major benefits in a variety of less glamorous commercial lighting applications. The demand for LED-based lighting looks set for rapid growth as LED efficacy levels steadily rise and as building operators become increasingly aware of the potential savings in time, money and energy.

Biography

Leighton James is product marketing manager for the recently launched Axent brand of architectural lighting at Cooper Lighting and Security. He has over 18 years’ experience with the company, having originally joined as an engineering apprentice. After completing his apprenticeship, he was appointed to the position of production engineer and then spent four years as a product designer, specialising in the mechanical and optical design of luminaires. In 2001 he was appointed product marketing manager for mains lighting and is now responsible for the development and marketing of the Axent range of products.