Authors: Dr Kevin Kelly is head of electrical services engineering, Dublin Institute of Technology and James Thomas Duff, Arup and PhD student, Dublin Institute of Technology In the first article in this two-part series, we looked at how increased demands for more daylight, linked to improved lighting control, are increasingly leading to more holistic design. As a result, architects, engineers and facilities managers must work more closely to provide a holistic solution. For people reading commercial lighting publications or attending trade shows, it would seem that there is a single solution for all lighting problems – which is light-emitting diodes (LEDs). It is suggested [1] that the growth of LEDs has happened for three reasons. The first is the immense quantity of money invested in LED by organisations and the consequent rapid development in their capabilities. The second has been the enthusiasm of regulators who see LEDs as the ultimate replacement for incandescents. The third is fashion. At present, opting for LEDs is considered progressive and enlightened. [login type="readmore"] The outcome of these factors has been explosive growth in the LED market and, similar to all such markets, it has attracted many suppliers. Some of these have a reputation to uphold, but many do not. As a result, the market is now saturated with LED products of unknown pedigree. This raises an issue for designers, specifiers and purchasers. How can they distinguish good equipment from bad? Surely lighting research can provide this answer? Sadly, it cannot. As a result, very little guidance is available for the purchaser when selecting LED equipment [2]. Boyce has suggested [1] that a valuable contribution to the lighting community would be a set of standard, simple questions to ask the LED supplier. Any supplier that is unwilling, or unable, to answer these questions should be treated with caution. These questions would address some of the major issues associated with LED products. Traditionally, not many standards have been in place to regulate the construction, manufacture, performance and operation of LEDs, but in recent years, this has improved somewhat with the introduction of IESNA LM-79-08 (IES Approved Method for the Electrical and Photometric Measurement of Solid-State Lighting Products) [3] and IESNA LM-80-08 (IES Approved Method: Measuring Lumen Maintenance of LED Light Sources) [4]. Both of these test methods allow manufacturers to have their products tested in an independent laboratory, to a standard set of testing procedures. This offers designers, purchasers and specifiers a fair comparison between products. Now that this standard set of test procedures is available, the International Electrotechnical Commission (IEC) has gone one step further and published a Publically Available Standard (PAS) IEC/PAS 62722 Performance requirements – LED luminaires for general lighting [5]. This document suggests the quality criteria that should be used when comparing LED products and also suggests that this information should be published on product datasheets. The criteria listed include:

• Input power,
• Luminaire luminous flux,
• Luminaire efficacy,
• Luminous intensity distribution,
• Photometric code,
• Correlated colour temperature (CCT),
• Colour rendering index (CRI),
• Rated chromaticity co-ordinate values, both initial and maintained,
• Lumen maintenance code,
• Rated life in hours of the LED module and the associated lumen maintenance (Lx),
• Failure fraction (Fx), corresponding to the rated life of the LED module in the luminaire,
• Ambient temperature (Tq) for a luminaire.

CHROMATICITY ISSUES Of these, newest and most important to designers and specifiers are chromaticity issues and how the life of an LED product is stated. LEDs have the potential to exhibit extremely long lifetimes and for that reason, LM-80-08 tests luminaires only until 6,000 hours of operation [4]. Once the fitting has been tested for 6,000 hours, IESNA TM-21-11 (IES Approved Method: Making Useful LED Lifetime Projections) is used to extrapolate these measurements and estimate useful life of the LED product [6]. LED lifetime is then specified in terms of parametric and catastrophic failure, to a chosen time. An example would be 50,000 hours to L70F10. This would mean that after 50,000 hours of operation, this luminaire will emit 70 per cent of its initial light output and 10 per cent of the individual LEDs within will have failed, thus meaning that the luminaire is at the end of its useful life. Again, this offers designers and specifiers the opportunity to compare LED product lifetimes on a fair basis. Chromaticity co-ordinates are recorded initially and every 1,000 hours until completion of testing. These results will give designers and specifiers realistic information about how the colour appearance of the tested LED products will vary initially and also how it will vary during the life of the product. Insisting that these test results are produced and spending time to fully understand what the results are portraying will go a long way to ensuring better-quality LED products are specified and installed [7], which should dispel some of the tales and scepticism that surrounds poor-quality LED installations that have undoubtedly have taken place over the number of years. If we now have an idea how to differentiate good-quality LED products from bad-quality LED products, where are they applicable? Solid-state technology is developing at an amazing pace and recent developments have seen LED efficacies equal that of fluorescent T5 lamps. Add to this, that once light-loss factors such as diffusers and louvers are considered, LED can be almost 20 per cent more efficient. But good-quality LED products are expensive, approximately two-and-a-half to three times the equivalent T5 fluorescent fitting, giving an eight- to 12-year payback period in most cases. This, amongst other factors, leaves linear fluorescent lighting the prime choice for general lighting solutions the near future. Areas within general lighting where LED is financially viable at present include: architectural lighting, replacements for halogen lamps, replacements for compact fluorescent downlights and replacements for external metal halide fittings, particularly the lower wattage (>70W) fittings. LIGHTING CONTROLS EN 15193, the Energy Performance of Buildings Directive, details a method of estimating lighting energy consumption that delves beyond maximum installed loads. The method is called LENI, the Lighting Energy Numeric Indicator [5]. LENI is a measure of the total lighting energy consumption for a given space for an entire year, divided by the area of that space. It is recorded in kWh/m^­2 per annum and gives a much more realistic indication of energy consumed by a lighting installation [5]. Over the past decade, automated lighting controls have become commonplace in building engineering. However, they are not without problems. Ensuring user satisfaction throughout the working day requires integration of the lighting control system in an acceptable way to ensure lights are on when needed and off or dimmed when appropriate. Gradual dimming is often preferred by users, as opposed to sudden switching off [8], which can be distracting for people using the space. Dimming without override facilities often results in user dissatisfaction [8]. Various studies have shown that there can be much user dissatisfaction with poorly operated control systems. For the future, however, it may become normal for individuals to have control of their own lighting. Technology is already moving in this direction. LED luminaires are already easily dimmed and can change spectrum and light distribution on demand. Developments in wireless communication and computing power are making it possible for a regular array of luminaires to be adjusted to provide occupants with their preferred illuminances at minimum electricity consumption, and doing this without moving luminaires when workstations are moved [7]. Boyce suggests that with these developments, the concept of ‘plug and play’ lighting cannot be far away. But will this cause chaos, or will it be an improved solution comparable to automated controls? There is already evidence to suggest that giving individuals control improves occupant satisfaction. People prefer varying illuminances for the same task [9-12]. This means that for any chosen, automatically fixed illuminance, only a minority of occupants will experience their preferred condition. When users have their desired lighting conditions, this results in improved mood and improved judgments of environmental satisfaction [10, 13]. Additionally, the improvements in mood, lighting satisfaction and discomfort that are achieved by giving people individual control of their lighting are proportional to the difference between the fixed illuminance and the preferred illuminance [14]. An extensive field study [15] has also shown that direct/indirect lighting suspended over each workstation and providing individual control is considered better than uniform lighting with simple switching – and it saves energy. CONCLUSION To sum up, this is an exciting and challenging time for the lighting industry. We are challenged to provide robust solutions that maximise the benefits of new technologies, whilst protecting our clients from poor-quality products and installations. We must maximise light quality and minimise energy use by integrating daylight with appropriate artificial light in a way that lifts the spirit of those using the space and enable them to operate and override automatic lighting controls when required. We also have to ensure the reliability of products we specify and this is particularly challenging when technology is evolving so quickly. Dr Kevin Kelly is head of electrical services engineering in the Dublin Institute of Technology. He is also the president of the Society of Light & Lighting for 2013/14. James Thomas Duff works for Arup, Dublin and is a PhD student in Dublin Institute of Technology. References:  [1] PR Boyce. Editorial: 'LEDs are the answer, now what’s the question?' Lighting Research and Technology, June 2013 45: 265. [2] Lighting Industry Liaison Group, 'A Guide to the Specification of LED Lighting Products'. London 2012. [3] The Illuminating Society of North America. LM-79-08, IES Approved Method for the Electrical and Photometric Measurement of Solid-State Lighting Products. ISBN: 978-0-87995-226-6. [4] The Illuminating Society of North America. LM-80-08, IES approved Method: Measuring Lumen Maintenance of Light Emitting Diode Light Sources. ISBN: 978-0-87995-227-3. [5] International Electrotechnical Commission. Publically Available Standard 62722 Performance requirements – LED luminaires for general lighting. ISBN 978-2-88912-567-8. [6] The Illuminating Society of North America. TM-21-11, IES Approved Method: Making Useful LED Lifetime Projections. ISBN: 978-0-87995-227-3. [7] CELMA. 'Why standardisation of performance criteria for LED luminaires is important.' Federation of National Manufacturers Associations for Luminaires and Electrotechnical Components for Luminaires in the European Union. 2011. [8] GR Newsham, MBC Aries, S Mancini and G Faye. Individual control of electric lighting in a daylit space. Lighting Research and Technology, March 2008; vol. 40, 1: pp. 25-41. [9] D Maniccia, B Rutledge, MS Rea and W Morrow. 'Occupant use of manual lighting controls in private offices.'  Journal of the Illuminating Engineering Society 1999, Vol 28, pp42-56. [10] G Newsham, J Veitch. 'Lighting quality recommendations for VDT offices: A new method of derivation.' Lighting Research and Technology, 2001, Vol 33, pp97-116. T Moore, DJ Carter, AI Slater. 'Long-term patterns of use of occupant controlled office lighting', Lighting Research and Technology 2003, Vol 34, pp207-219. [11] PR Boyce, JA Veitch, GR Newsham, CC Jones, J Heerwagen, M Myer, CM Hunter. 'Occupant use of switching and dimming controls in offices.' Lighting Research and Technology 2006, Vol 38, pp358-378. [12] PR Boyce, JA Veitch, GR Newsham, CC Jones, J Heerwagen, M Myer, CM Hunter. 'Lighting quality and office work: two field simulation experiments.' Lighting Research and Technology 2006, Vol 38, pp191-223. [13] GR Newsham, JA Veitch, C Arsenault, C Duval. 'Effect of dimming control on office worker satisfaction and performance.' Proceedings of the IESNA Annual Conference, Tampa, FL. New York: IESNA, 2004. [14] AD Galasiu, GR Newsham, C Suvagau, DM Sander. 'Energy saving lighting control systems for open-plan offices: a field study.' Leukos, 2007, Vol 4, pp7-29. [15] JA Veitch, CL Donnelly, AD Galasiu, GR Newsham, DM Sander, CD Arsenault. 'IRC Research Report 299 Office Occupants’ Evaluations of an Individually-Controllable Lighting System.' Ottowa: National Research Council Canada, Institute for Research in Construction, 2010.