Page 1

Volume 9. Issue 1. Jan/Feb 2016


Colour rendering: does TM-30 measure up to CRI?

n Outside

edge: the new LG6 on exterior lighting 1


Secretary Brendan Keely MSLL SLL Coordinator Juliet Rennie Tel: 020 8675 5211 Editor Jill Entwistle Communications committee: Iain Carlile (chairman) MSLL Rob Anderson Jill Entwistle Chris Fordham MSLL Wiebke Friedewald Mark Ingram MSLL Stewart Langdown MSLL Gethyn Williams Linda Salamoun Bruce Weil All contributions are the responsibility of the author, and do not necessarily reflect the views of the society. All contributions are personal, except where attributed to an organisation represented by the author.

Copy date for NL2 2016 is 22 January Published by The Society of Light and Lighting 222 Balham High Road London SW12 9BS ISSN 1461-524X © 2016 The Society of Light and Lighting The Society of Light and Lighting is part of the Chartered Institution of Building Services Engineers, 222 Balham High Road, London SW12 9BS. Charity registration no 278104

Produced by


Printed in UK


The fact that, despite deletions, the forthcoming updated LG6 on exterior lighting is a fifth bigger than the last one to be published says much about the pace of change in the past 24 years, not only in lighting techniques and technology, but in the evolving shape of the actual urban outdoor environment itself and our attitudes towards it. We have made town centres, for instance, more people-centric with an emphasis on pedestrianisation and cafe culture. We have recognised that there is money to be earned in a nighttime economy. That requires more atmospheric and three-dimensional lighting, including well-lit building facades. In the past we have largely viewed exterior lighting in rather more utilitarian terms, shying away from a chiaroscuro approach in favour of a more functional uniformity. The only video facades you would find in 1992 would be in reruns of Blade Runner; coloured lighting would be pretty scarce and the idea of dappled leaf effects on a piazza were a mere twinkle in some prescient lighting designer’s eye. LEDs aren’t even mentioned in the 1992 version for goodness’ sake. But while everything has got a lot

more whizzy and there are considerably more creative opportunities, there is a greater need than ever to adhere to good lighting design principles. Another key change, as with other SLL guidance, is that the onus is less on prescription and more on the professional judgement of the lighting designer. That’s progress. Jill Entwistle

Current SLL lighting guides SLL Lighting Guide 1: The Industrial Environment (2012) SLL Lighting Guide 2: Hospitals and Health Care Buildings (2008) SLL Lighting Guide 4: Sports (2006) SLL Lighting Guide 5: Lighting for Education (2011) SLL Lighting Guide 6: The Outdoor Environment (scheduled early 2016) SLL Lighting Guide 7: Office Lighting (2015) SLL Lighting Guide 8: Lighting for Museums and Galleries (2015) SLL Lighting Guide 9: Lighting for Communal Residential Buildings (2013) SLL Lighting Guide 10: Daylighting – a guide for designers (2014) SLL Lighting Guide 11: Surface Reflectance and Colour (2001) SLL Lighting Guide 12: Emergency Lighting Design Guide (2015) SLL Lighting Guide 13: Places of Worship (2014) New SLL Lighting Guide: Transportation Buildings (scheduled 2016) Guide to Limiting Obtrusive Light (2012) Guide to the Lighting of Licensed Premises (2011)

COVER: Winner of the Office Lighting category of the Lux Awards, Cundall Light4’s scheme for Sainsbury’s Digital Lab in Holborn, London, references a scene in the film 2001: A Space Odyssey, where an airlock features a series of octagonal hoop lights. Translated to a deconstructed hexagon, the chevron fittings are complemented by unorthodox spotlights providing illumination to some of the working hubs, and LED strip uplighting to counter the oppressive concrete coffers. ‘There’s not an office fitting in sight,’ says Andrew Bissell, director of Cundall Light4 ( /Services/Light4.aspx)

Secretary’s column

Happy New Year to all the 3000-plus members of the society. We hope you all had a great break over the festive season and, yes, the SLL’s membership reached more than 3000 towards the end of 2015. We thank all existing and new members for their support and we look forward to a great 2016. I mentioned in the Nov/Dec Newsletter that we were attending the Professional Lighting Design Conference (PLD-C) in Rome as the Official Knowledge Partner, and also as coach of Pernille Krieger and Eik Lykke Nielsen from Aarhus University in Denmark. Pernille and Eik were in the finals of The Challenge student speaker competition and I’m very pleased to confirm that they won. For a full review of the competition and PLD-C take a look at the News section of the website. Thanks go to all the volunteers who helped with stand duty at LuxLive in November, the Young Lighter of the Year (congratulations to Youmna Abdallah, see News, p4), the Jean Heap Bursary update, the presentation by Public Health England (see p10) and, of course, the mini-Masterclasses. It was a busy couple of days at ExCel. My personal congratulations go to Liz Peck, recipient of the Lux Person of the Year Award. I’m sure you will all agree a very worthy winner. Still on the theme of LuxLive, we will be exhibiting at LuxLive Middle East on 13-14 April 2016 with a small stand. So if you are in the Abu Dhabi area, please do register to attend and come along and get all the society’s updates. Prior to that we will be attending the closing ceremony of the Unesco International Year of Light in Mexico, where we will be presenting the Night of Heritage Light to the gathering of international delegates, as well as taking part in a panel discussion to debate the issues of lighting cultural and heritage buildings and sites. We will be reporting on the proceedings of the event throughout 2016. We will also be going to Light and Building in Frankfurt in March 2016. The main purpose for us attending is to keep up to date on technologies and visit as many of our supporters as possible. It’s always a busy few days for us but very worthwhile. As soon as we’re back from Frankfurt we’ll be working with Rose Bruford College for Junior Ready Steady Light on 19 March. We attended the junior event last year and it was a great day. If any of you have contacts at schools, please do encourage them to take part (contact me for more details). The main Ready




Secretary’s column




The white heat of revolution 5 Dorian Kelly looks at a dramatic turning point in theatrical history Outside edge 8 Alan Tulla outlines the major updates to the new SLL guide to lighting the exterior environment

The SLL’s membership reached more than 3000 towards the end of 2015. We look forward to a great 2016 Steady Light event will take place on 22 March and, with only 14 team places available, we’re expecting this to book up quickly so please don’t delay in securing your team place. We expect the work of Public Health England on LEDs to be released for download during January, while the new LG6: The Outdoor Environment (see p8) should be ready for download in January/February. We are also currently planning to create a new guide with an old number: LG3. Yes, it’s been a while, but it’s now in the process of being written and will be dedicated to lighting for control room environments. If anyone has contacts working or specialising in control room design, or has images or first-hand accounts, we would be interested to hear from you. Site visits would also be welcome. If you are happy to get involved please contact me by 29 January. Finally, we confirm that the 2016 Young Lighter of the Year and Jean Heap Bursary competitions are open for entry. The competitions are open to all involved in light and light-related topics, including design, engineering, product design, research, photography, theatre and the science of light. If you would like to enter, please go to the website and register your interest (

Source of contention? John O’Hagan reports on the PHE research into the effect of LEDs on humans


True colours 11 Is TM-30 a viable replacement for the colour rendering index? Peter Raynham offers an analysis Out of darkness 13 Gerardo Olvera looks back at the impact winning the YLOTY award had on his carreer Shades of distinction 14 Iain Carlile finds that colour rendering is high on the agenda in the latest LR&T Obituary Dr Arthur Tarrant 1929-2015


Cover Sainsbury’s Digital Lab


16 For up-to-date information follow us on Twitter @sll100



YLOTY winner focuses on light poverty

Youmna Abdallah of MBLD (pictured second from right) is the 2015 winner of the SLL’s Young Lighter of the Year award. Her presentation, Light Poverty in Precarious Environments within Developing Countries, also picked up the Best Written Paper award.

SLL president wins top Lux accolade Also honoured at the Lux Awards was SLL president Liz Peck, who was named Lux Person of the Year. The judges cited her ‘enormous contribution to the lighting family and the wider community’.

In an all-female final at LuxLive at London ExCel, Inessa Demidova of GIA Equation won the Best Presentation Award for her paper, Practical Implementation of Circadian Lighting in Office Environments. Both these last categories were ‘I’m overwhelmed to be named the Lux Person of the Year,’ she said afterwards. ‘I give my time freely simply because I love what I do. In the International Year of Light, this award is a huge honour.’

CIBSE award shortlist announced CIBSE has announced the shortlist for the 13 categories of the 2016 Building Performance Awards. Contenders for the Lighting for Building Performance Award are: National Theatre – NT Future, London (Atelier Ten) WWF, Living Planet Centre, Woking (Atelier Ten) New emergency department and 24-bed

ward, Antrim Hospital, Northern Ireland (Beattie Flanigan Consulting Engineers) The winners in all categories, as well as the recipient of the overall Building Performance Champion, will be announced at the Building Performance Awards event to be held on 24 February 2016 in London. More details at

On the lighter side... A light fitting designed by architect Zaha Hadid and Patrick Schumacher has just sold for a record price at a Sotheby’s London auction. The VorteXX pendant went for £106,250, the largest-ever amount for a lighting product. The sculptural light was made by Zumtobel in collaboration with Sawaya and Moroni. London is apparently capitalising on its reputation as an international design hub by turning into the global


centre for the collectable design market. Definitely worth dusting off that old Arco or Artichoke.

judged by the Lighting Education Trust (LET), which provided the cash prizes. Also taking part in the final were Christina Hébert of Nulty+ with her paper, A Symbol of Urban Identity, and Zeynep Keskin whose topic was Daylight and Seating Preference in Open-Plan Spaces. Abdallah was presented with her award at the Lux Awards at The Troxy in east London on 19 November, the evening of the final. The 2016 competition, now in its 22nd year, has just opened for entries. All four finalists’ video presentations can be viewed on the SLL website:

Historic breakthrough

Loughborough University has carried out new research on behalf of the National Trust into the distribution of natural light and its level of exposure in historic buildings. The study was led by John Mardaljevic, professor of Building Daylight Modelling in the School of Civil and Building Engineering, and conducted in partnership with CannonBrookes Lighting and Design. It focused on Ickworth House near Bury St Edmunds, Suffolk. It involved using high dynamic range (HDR) imaging to measure where the natural light falls at different points throughout the day and over several months in the house’s Smoking Room. ‘This is the first time we have used HDR in a heritage setting to create a cumulative luminance image, from which a physical measure of illumination exposure across the camera’s wide-angle perspective is derived,’ said Mardaljevic. ‘Used together with climate-based daylight modelling, this is a great way of better understanding natural light, especially at a time when historic houses are being encouraged to extend access.’ As a result of the research, the National Trust is looking into the feasibility of revising the daylight management guide for its historic houses. John Mardaljevich will give a detailed outline of the study in the March/April issue of the Newsletter

Events: Masterclass 2013/14 Events

The white heat of revolution The Savoy Theatre in London’s Strand was the first in the world to be lit with incandescent lamps. Dorian Kelly looks at a dramatic turning point in theatrical history

The Savoy Theatre

D’Oyly Carte wanted the new theatre to be the best it could be

whatever venues he could get hold of, so when his lease of the Opera Comique came to an end, and he was presented with an unaffordable rent rise, enough was enough. The result was independence and the Savoy Theatre. This would be the best theatre he could make it. Never again would he attempt to cram ‘twenty love-sick maidens’ on to a stage ideally suited to 10. The orchestra pit was large enough for the extra musicians for which Sullivan was always agitating. And spurred by Gilbert, he intended to make the technical facilities second to none. It would have the best of taste in decoration, the finest ventilation systems – and would be the first theatre in the world to be lighted throughout with the incandescent filament lamp. The phenomenon of light produced by electricity had been known since around 1800, when Sir Humphrey Davey (he of safety lamp fame), discovered that the voltaic battery could be used to heat strips of platinum to incandescence. He also showed a brilliantly blinding light could be produced between the tips of two carbon rods if they were briefly touched together, and that this light could be maintained for as long as they, and the power, lasted. This led to many devices for floodlighting and public street lighting, but it was not until 45 years later that it was used in the theatre. At the Princess’s, Charles Kean used an arc lamp as a wide-angle floodlight in a pantomime entitled Harlequin and the Enchanted Arrow. Fundamentally the arc was not really suitable for large-scale, wide-angle lighting. It flickered and it wasn’t that bright when spread out over a stage. Another answer had to be found. The first patented incandescent lamp was in 1841. This consisted of a glass globe filled with powdered charcoal. It worked for a while, but envelope blackening and its tendency to catch fire at an alarming rate rendered it impractical so experiments continued.


Let me take you back, 135 years, to 1881 to tell you about a technology that changed everything. Not just lighting techniques, but scene painting, make-up, costume, acting styles, and playwriting itself. In October 1881, for Richard D’Oyly Carte, the idea of a new theatre was a dream. Carte’s real ambition was to develop an English form of light opera that would displace the bawdy burlesques and badly translated French operettas then dominating the London stage. He formed the Comedy Opera Company and then commissioned Gilbert and Sullivan to write a comic opera that would serve as the centrepiece for an evening’s entertainment. In his capacity as managing director he somehow held the company together for nearly five years. But he was fed up with getting theatre performance slots only wherever he could in




The Savoy interior: ‘electric light in some form is the light of the future in theatres,’ said D’Oyly Carte

Until, that is, Thomas Edison in New Jersey and Joseph Swan in Newcastle-on-Tyne, independently set about passing currents through filaments made from a variety of materials. While Edison wowed the crowds across the Atlantic with his original public demonstrations, by 1880 Swan had lit his workshop and indeed the whole of the street with electricity. Both men had succeeded in their principal aim: to produce an electric lamp that was within reach of all. Initially, the two companies were very successful but later there were arguments and patent suits as to who was the true inventor. The truth was both men simultaneously responded

Typical electric footlight trough adapted for electricity 1881


to the needs of the time, taking what was obviously the next logical step. They soon realised cooperation was better and eventually amalgamated into the Edison and Swan United Electric Company. It was to the Swan Company that Richard D’Oyly Carte turned when the concept of electrifying the Savoy was mooted. Having first seen ‘electric light in lamps’ exhibited outside the Paris Opera House some years previously, he had been convinced that ‘electric light in some form is the light of the future in theatres’. At the Savoy, electric power was produced in a shed that had been erected on a piece of wasteland outside. A collection of steam engines were arranged to drive six large Siemens alternators. The field coil excitation voltage for these was simultaneously generated by six small dynamos. The theatre itself was wired in six main circuits, corresponding to the number of generators, various areas being protected by sub-fuses. Each area was initially provided with a switch. Main switches for each group were also provided, and it is reported that when they were operated, the flash that resulted could be seen in the auditorium if the scene was dark. Altogether there were 1158 Swan lamps in the theatre: 114 in the auditorium, 221 in the dressing rooms, and 824 on the stage, giving in total a stage light output equivalent to around 3000 modern halogen watts. Of those, 718 were above the actors’ heads, 50 were floats and portable units, and the remainder were fixed to the side wings in the traditional manner. The 114 lamps that comprised the houselighting were mainly in three-branched brackets around the auditorium circle fronts. One of the more impressive features of the incandescent lamps was the fact that, as the applied power was decreased, the output light also decreased, more or less in proportion. Siemens Bros and Co manufactured a series of open spirals


Faraday three-light electric bracket used in the auditorium

of iron wire in a frame, and connected them between the generators so that each group of stage lamps switched in and out of the circuit as required. They acted as the first-ever resistance dimmers. There was something of a carnival air in the auditorium the night the theatre opened, especially when D’Oyly Carte stepped forward to address the audience. After a brief introduction, he announced that although the stage lighting was not ready, the auditorium would be lit by electricity. He

went on to warn the audience that the system might fail due to the experimental nature of the installation, in which event, the gas system, a small part of which would remain alight at all times, would instantly be brought into full use. Then, at his signal, the gas was turned down and, as the Telegraph wrote, ‘there was a hum of expectation and anxiety throughout the house. The effect was instantaneous. A start, a pause, a tremor, and suddenly the auditorium was literally brilliant with the novel light’. The system behaved itself admirably throughout the performance of Gilbert and Sullivan’s Patience that evening, and at the end the public expressed a verdict of success not only of the lighting, but also of the production. It took another 11 weeks of hard work before it was considered ready to announce the lighting of the stage by electricity. The eventual solution of the problem was quite elegant in its simplicity. The iron resistors were removed and replaced by a much smaller six-way regulator. This consisted of half a dozen

This was a real technological and artistic revolution, not only of theatre technology but also the development of world theatre itself six-position switches connected to tappings on coils of German silver wire. These were mounted in a wooden frame positioned on the fly floor and were electrically connected, not to the output of the alternators, but between the dynamos and the field coils of the alternators. The operation of these resistances reduced the magnetic flux in the alternator and therefore the output voltage. It had the added bonus that it also reduced the magnetic drag in the system, thereby effecting a saving in prime-mover power. By the afternoon of 28 December 1881, the installation was judged to be completed, and the public and press gathered to see the latest wonder of the age. While the introduction of electric light to the art of theatre was a blow to everything the Irvings, Terrys, Trees and Harkers of the era stood for, others seized on the new medium with ferocious delight. Already, by the time the Savoy had settled, the Alhambra Theatre had installed auditorium lighting to a limited extent and elsewhere in Britain all the new theatres nearing completion or in planning were converted to the electric power as a matter of course.For a while the invention of the incandescent gas-mantle threatened to slow down the introduction of electricity but by the mid-1880s, the improvement to the accumulator allowed the electric light to be completely steady, flicker free and more or less secure against loss of power. This eventually cleared the way for theatres to take the step of abolishing gas and oil as the primary sources of light in their buildings altogether. n

Ellen Terry: electric lighting was a blow to everything she and fellow actors of the period stood for

This short feature is based on a presentation, White Heat of Revolution: an examination of the effects of the coming of the incandescent lamp to the theatre, given by Dorian Kelly at the Savoy Theatre last November. Part of the International Year of Light 2015 celebrations, the event was organised jointly by the SLL, the Association of Theatre Technicians and the Association of Lighting Designers. Director of Illuminati Creative Services, Dorian Kelly is a lighting designer, and theatre and festivals director.


Lighting guides

Outside edge The last SLL guide to lighting the exterior environment was published 24 years ago. Alan Tulla outlines the subsequent changes in technology and technique, and summarises the revisions in the new edition A quarter of a century on, the new LG6 reflects the massive changes in lighting since 1992. Even with topics deleted, it is 20 per cent larger. I certainly couldn’t have revised it without a great deal of help from the other members of the task group. Which leads me to another big difference, namely that the current edition was mainly written by practising lighting designers/engineers. The previous guidance was predominantly written by manufacturers. Mind you, at that time, most lighting design was done by the illuminating engineering department of the major luminaire manufacturers – the profession of independent lighting designer hardly existed. The new guide is also much less prescriptive than the previous one. Rather than recommend a particular lux level, for example, it explains to the reader what design criteria need to be considered. It then gives practical advice on how to achieve the result you want. One reason for this change is that there is a lot more legislation related to lighting nowadays. This is constantly being updated and so LG6 tells you what standards (or other SLL Lighting Guides) may apply and it is up to readers to get the latest information. In essence, the reader is expected to use his or her own professional judgement rather than tick a box. LG6 is there to help you make the right decision. n The key changes Early in the guide, we have a large section on masterplans and nightscape strategies. You can design lighting for years without ever being asked to produce one so this section tells you the general approach to take and what to consider. Aspects such as views, vistas and the visual impact of artificial light are among the areas included. We are much more aware nowadays of the possible effect of artificial light on the environment. A constant theme throughout the guide is whether lighting is necessary. ‘A lighting scheme that does not benefit society, in some way, should not be installed in the first place,’ we state in the introduction. The effect of ALAN (Artificial Light At Night) on wildlife such as birds, mammals, reptiles, invertebrates, plants and so on can be found in the Appendix. You can even discover the effect of ALAN on fireflies and frog hormones. While on the topic of the environment, there is a section on photovoltaics (PV) and off-grid lighting. It describes in simple terms what factors need to be considered. For example, allnight lighting requires vastly more battery back-up than lighting that is triggered by PIR. There are pros and cons for both. The tilt angle of the PV array is considered, as is the type of driver/ control gear to use. One area that is definitely new is computer visualisations. This is included in the section on how to present your ideas visually to a non-specialist, for instance, a planning authority. The methods range from yellow crayon sketches on black paper to pseudo-colours to 3D renderings. We also highlight the importance of the original photometry. Intensity values


‘In essence, the reader is expected to use his or her professional judgement rather than tick a box. LG6 is there to help you make the right decision’ measured at five-degree intervals are pretty much useless in most applications. There is a brief description of the software packages available. There is a huge section devoted to the lighting of building facades. As well as supplying light to the interior, windows play a large part in the night-time appearance of a building. Various techniques are described and, as in the previous edition, there is a section on lighting stained glass windows both from the inside and outside. Fixing the luminaires to the building is of special concern for heritage and ancient monuments, and there is guidance on how to tackle this sometimes knotty problem. Another totally new section concerns video and digital facades. Most of us wouldn’t have the first idea of how to approach such a project. As such, this is quite a long chapter because it takes us from first principles such as pixel size, viewing distance and luminance all the way to video protocols and frame refresh rates.

Windows play a large part in the night-time appearance of a building: Tudor Square, Sheffield (DPA Lighting)

Lighting guides

However, before you get to the glamour of video, we do describe the basic techniques of security lighting, car parks, road lighting, cycleways and paths. It’s in this section that you will find a discussion of photopic, mesopic and scotopic vision. Mesopic levels are especially relevant to road lighting and BS 5489, but they should also be a consideration for any outdoor lighting falling within this luminance range. You will be pleased to know that we do list the upper and lower luminance limits but may be less pleased to discover that there is not common agreement on what they are. We couldn’t find much guidance on emergency lighting once you had left the building, for example, the route from the exit door to a muster point or place of safety. We have suggested illuminance levels taking into consideration the recommendations of BS 5266. Since many of us work on projects outside the UK and the SLL has many members overseas, there is a section on luminaires used in extreme environments. The high ambient temperatures and dusty environments of the Middle East are an obvious example. Where salinity is concerned, marine and coastal regions are another area of common concern, and we also include extreme cold and wet environments. Light sources are covered in great depth in the 1992 edition but there is no mention of LEDs. Since they are now becoming the de facto light source for exterior applications, we did discuss totally omitting conventional light sources. However, these are included because they will be around for a long time – I know of one street lighting authority which still has MBF/U lamps on its roads. Readers may be surprised that we still include point source calculations. The first reason is that you can’t really do lighting design without an understanding of how a beam of light works. The other is the same reason for using a sketch in preference to an ACAD drawing – the idea comes before the detail.

In the right context, water features are an opportunity for more playful, colourful lighting: Marine Parade Plaza, City Beach, Southend (Ustigate)

n What did we omit? Sad to say, the specific sections on the lighting of bandstands, clock towers and sundials are no longer there. Neither are festoon lighting and festival decorations, but this is mainly because you can find excellent guidance elsewhere. Also, many areas that were treated individually in the 1992 guide have been rolled into one. n Summary This is the first revision, more like a complete rewrite, in a long time. Even now, I think of topics to add and sections to change. But we had to stop somewhere otherwise it would never have been produced. LG6 could easily have been twice as long again, but then it would have been a textbook rather than a guide. Perhaps the biggest change is that it guides you to a solution rather than telling you. n Lighting Guide 6 (LG6): The Outdoor Environment is scheduled for publication in early 2016. Lighting Guide 6 task group: Alan Tulla (chair) Lorraine Calcott

David Mooney Chris Wilkes Theo Paradise-Hirst

The task group wishes to acknowledge the individual contributions to the guide provided by: Francesco Anselmo, Iain Carlile, Pat Holley and Ray Pang

Precise modelling of sculptures and statues creates important focal points: statue of King Alfred, Wantage (Alan Tulla)



Source of contention? John O’Hagan reports on research into the effect of LEDs on humans, specially commissioned by the SLL Public Health England (PHE) was commissioned by the SLL and CIBSE to review the impact of LED lighting on humans. PHE is responsible for providing advice to government, professional bodies and the public on optical radiation safety. Questions may come from MPs as a result of enquiries or the concerns of their constituents. They may also come from local authorities, which may be dealing with issues raised by campaigners. This study involved a review of the emissions from domestic LED lighting, office LED lighting and LED street lights. Domestic lighting was purchased directly from the major retailers likely to be used by the public. Some of the office lighting was bought from building suppliers and some supplied direct by manufacturers or their agents. All of the street lights were supplied direct by UK manufacturers or their agents. The work consisted of three packages: colour, flicker and spectrum. Measurements of the emissions were made in a controlled laboratory environment at 300mm for the domestic and small panel office lighting, and at 2m for the street lights and large panel office lighting. This last distance was considered a reasonable worse-case situation for most people. Comparison was also made with non-LED luminaires where the domestic sources were concerned. A number of press reports have claimed that LED sources are potentially harmful, but scrutiny of the claims usually shows that the exposures are under highly unrealistic exposure situations. These have included exposure to the blue LED chip following failure of the phosphor covering, or staring at the source for many hours with the LED very close to the eye. The spectral irradiance for the domestic and office lighting was weighted with the blue light hazard function and compared with the exposure limits published by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). None of the sources exceeded the exposure limits. When interpreting this result, it is important to recognise that someone could be exposed at a closer distance for a short period of time, but this would be balanced against most of the time where the exposure distance was greater than 2m. This is the so-called time-weighted average exposure. The UV and retinal thermal hazards were considered, but none of the sources assessed were capable of exceeding the retinal thermal exposure limit. The domestic sources were mainly fitted with some form of diffusing optical arrangement or the LED chips/phosphors were in linear arrays with lower luminance than many of the earlier chip arrangements. This development made the sources more aesthetically pleasing. The office lighting panels considered were also low luminance sources which were comfortable in the environment.


Some of the domestic and office LED luminaires and lamps used in the PHE study

However, most of the street lights were still arrays of single LED chips. Some arrangements produced extremely uncomfortable luminance levels and could present a glare source. Given the lack of ultraviolet radiation from these sources, it would be reasonable to use etched glass or simple plastic optics, such as microlens arrays, to reduce this problem. The spectral emission of the LEDs was also considered in terms of non-visual effects, such as impact on circadian rhythm and alertness. For the domestic and some of the office lighting, the LED sources were found to be similar to incandescent lighting. However, the street lights and around half of the office lighting emitted higher proportions of blue light. Colour was also assessed from the spectral data. It was noticeable that the blue peak emission had greatly reduced compared with domestic and office lighting previously assessed. This resulted in colour temperatures generally around 2700K for domestic lighting. However, the street lights and several of the office lights were all greater than 3600K and two samples were around 6500K. It is understood that such high colour temperatures are driven by energy efficiency. However, consideration needs to be given to lighting quality. All of the sources studied were also assessed for flicker. None of the street lights flickered significantly, but some of the domestic LED sources flickered with 100 per cent modulation at 100Hz. Some of the office panels also flickered. The concern is that some people suffer a range of adverse health effects when exposed to flickering light, especially when in their peripheral vision. There is also the real risk of strobing effects, which make moving objects appear to stand still. Although this has traditionally been a concern in industry, the use of domestic LED lighting that makes moving food mixer blades or a sewing machine needle appear to be stationary is a real worry. The impact of rheostatic dimming controls on domestic and office LED lighting was also assessed. The method of dimming was clearly important, and rheostatic dimmers are widely used. Flicker was increased for some of the domestic and office LEDs that were marked dimmable, so that a light that was acceptable undimmed may be a concern when dimmed. n The full report is available by emailing technical@cibse. org. John O’Hagan heads the Laser and Optical Radiation Dosimetry Group at PHE’s Centre for Radiation, Chemical and Environmental Hazards. The report was produced with the assistance of Luke Price and Marina Khazova


Is TM-30 a viable replacement for the colour rendering index? Peter Raynham explains how it works and offers an initial analysis As reported in the last issue of the Newsletter (Nov/Dec 2015), the US Illuminating Engineering Society (IES) has published a Technical Memorandum proposing a new approach to evaluating colour rendering. TM-30 Method for Evaluating Light Source Color Rendition has been backed by the US government, although it has yet to be sanctioned by the CIE. The proposal has prompted much discussion – will it catch on or will it suffer the same fate as the failed CQS (colour quality scale) metric? To answer this question fully perhaps we are going to have to wait a few years. The purpose of this article is to describe the various elements of TM-30 so that the nature of its provisions can be understood, and at least to provide an initial analysis of its likely effectiveness. TM-30 sets out two basic metrics of colour quality for light sources. One is a potential replacement for the existing CRI metric and the other gives an indication of the change in colour gamut associated with a particular light source. These two metrics are called Rf and Rg: the f stands for colour fidelity and the g is for colour gamut. The calculations involved are in many ways similar to those used for the existing colour rendering index system, and in general the main changes increase the complexity. The basic principle is to evaluate the colour of a series of colour samples when illuminated by a test source and then when illuminated by a reference source, assess the colour differences and use the values to evaluate a quality metric.

‘The whole point of a document such as TM-30 is that it has to be definitive if it is going to provide a means of comparing light sources across the industry’

The basic calculation of the CCT of a light source has not changed. However, the way the reference source is calculated for a given test source is a bit more complex in TM-30 than with the existing CRI method. There is no longer a sharp barrier at 5000K where the black body spectrum is swapped for a daylight illuminant, but a gradual transition between 4500K and 5500K. The idea behind this change is to prevent two very similar sources being evaluated in quite different ways due to a

A plot of the Rf values for the 12 CIE reference sources

Colour Management Systems. The colour difference is then averaged, scaled and subtracted from 100 to give Rf, which is a number between 0 and 100 that represents the colour fidelity of the source, just like the existing Ra value. The Rf values calculated by this process are very similar to those calculated using the same formulae but using the twodegree colour match functions. As an example, the chart above is a plot of the Rf values for the 12 CIE reference sources, calculated using the two-degree functions against the same values based on the 10-degree functions. The fit line shows that values have a strong linear relationship and that the Rf based on the two-degree is slightly less than the values based on the 10-degree functions specified by TM-30. The Rg metric is calculated by evaluating the gamut area of the test colours under the reference source then comparing the result to the area of the colours under the test source. This process would normally involve the calculation of the area of a 99-sided polygon. So for a slight ‘simplification’ colour samples are grouped into 16 clusters according to their hue angle, and then averaged so it is only necessary to calculate the area of a 16-sided polygon. This process is made more complex as the colour of each of the 99 samples depends to some extent on the spectrum of the reference illuminant and so may change which of the 16 clusters that it belongs to. A comparison of the Rg values calculated based on the 10-degree colour match functions with those calculated using two-degree functions demonstrates that the change of functions makes very little difference.



True colours

very small difference in CCT. The maths to support this change, however, is quite complex. The next big difference between the two systems is the colour sensitivity functions associated with colorimetric observers. The CRI formula uses the standard two-degree observer that is used to define the standard 1931 chromaticity, whereas TM-30 uses the CIE 10-degree observer. The logic behind this is not clear, and given that the colour difference formulae used were designed for use with values calculated with the two-degree colour sensitivity functions, this seems to be a bit of a nonsense. The next stage compares the appearance of the series of colour samples when illuminated by both the test and reference sources. There are two differences in this part of the process compared to the existing calculation of CRI. First, the system uses 99 colour samples and, second, the colour difference formulae are different and rely on the CIECAM02 colour space as defined by CIE 159: 2004 A Colour Appearance Model for


Metrics YLOTY

It is also possible to show this process of gamut evaluation diagrammatically. The figure below shows the gamut calculation for a high-pressure sodium lamp. The white line joins the average colour points for the samples illuminated with the reference lamp (full radiator with temperature of 1841K). The black line joins the averages of the points illuminated by the HPS lamp, and the arrows indicate the degree of colour shift. In this example the HPS lamp has an Rf value of 27 and an Rg value of 57. This is quite a good score for a lamp that has an Ra of 12.

Gamut calculation for an HPS lamp

It is possible to compare the results of TM-30 colour calculations with standard Ra calculations. The table below gives the results for five lamp types. In general Ra and Rf are quite similar, the exception is that of the SON lamp. Given the closeness of the results it is going to be difficult to demonstrate that Rf is a big improvement over our existing colour rendering metrics. Having a metric for colour gamut is a good idea and it is something that the industry has been talking about for a number of years, but basing it on a rather arbitrary grouping of the 99 colour samples is a bit odd, and it is not clear if Rg is any better than the other metrics that have been proposed. To accompany TM-30 there are two Excel spreadsheets which can be downloaded (from and used to calculate Rf and Rg. However, there seems to be a bit of an oddity in the data in the sheets. The problem is that while the TM-30 document states that you should use the colour-matching functions from CIE S014-1/E: 2006, the values in the spreadsheet are slightly different to the Lamp type










White SON





Cosmo white





TL 84





High spec LED





Comparison of TM-30 with standard Ra colour calculations


published values. Now the differences are small, but the whole point of a document such as TM-30 is that it has to be definitive if it is going to provide a means of comparing light sources across the industry. To sum up, TM-30 is a new approach to colour metrics and while there are some areas where it has made some logical steps towards doing things in a better way there are some outstanding questions that need to be answered. It has defined two new colour metrics and the maths to calculate them, but is it the best way forward? The sliding crossover between full radiator and daylight for the reference source has removed an anomaly in the current system, while the introduction of a colour gamut metric is a good idea and the use of CIECAM02 to calculate colour difference is an improvement. However, CIECAM02 was designed for use with colour functions derived with the two-degree observer functions and not 10-degree functions and therefore there is some uncertainty in the results. It is also not clear what was gained by the use of the 10-degree observer, particularly as doing the same calculations using the the two-degree functions gives very similar results. Secondly, the value of using 99 colour samples has to be questioned. Why 99 and why group them into 16 bins for the gamut calculation? Another question is whether the numbers generated are more meaningful than those from the conventional Ra system? Will the TM-30 approach to colour gain in popularity and be widely adopted? Only time will tell. n

Extract from an editorial by Peter Boyce in the Dec 15 LR&T The arrival of solid state lighting has exposed [the] limitations [of CRI]... In the face of this problem, the CIE has dithered. The first technical committee set up to study the problem was disbanded after nine years without making any recommendation. Two new technical committees were then established, one to investigate what should be done about colour fidelity and the other to look at colour preference. Neither has yet reported although the colour fidelity committee is rumoured to be close to doing so. The other looks to be wading into a swamp. The more research that is done on colour preference, the more it becomes apparent that colour preference depends on what is being lit, who is doing the observing and the context in which the observing is being done... This publication [TM-30] is unusual in that it recognises the needs of different audiences. For those who want to continue with a single-number approach it removes some of the limitations of the Ra by updating the colour space and colour adaptation systems used and by adopting a new sample set. For those who want to use a two-number approach it provides a relative gamut metric as well as a colour fidelity metric. For those who want to delve even deeper it offers vector graphics showing the shifts in hue and saturation. Software is available to enable the necessary calculations to be carried out. This initiative is to be applauded and deserves careful study. How successful it will be will depend on the interplay between specifiers and designers, the lighting industry and the CIE. That there is considerable support for the approach represented by TM-30 is evident from the open letter published in [the Dec 2015] issue [of LR&T] and the status of the signatories. If nothing else, it indicates that research on colour is alive and well and determined to be relevant to the future of lighting.

YLOTY: where are theyYLOTY now?

Out of darkness More than a decade after he won the YLOTY award, Gerardo Olvera looks back at the impact it had on his career

Photography: Starr Restaurant Organisation/David Joseph.

After graduating from the MSc Light and Lighting course at the Bartlett, I decided to look for a job in London. Back in 2000 there were only a handful of established lighting designers so applying for a job in the lighting industry really narrowed your options. As luck would have it, Barrie Wilde – one of the greatest lighting designers in this country – and BDP Lighting decided to sponsor my work permit (I was born in Mexico) and take me on board as an assistant lighting designer. It is worth pointing out that back then the Home Office had very little idea of what lighting design was or what it involved. It took a very long letter to the office of David Blunkett (then Secretary of Education and Employment) to challenge the Home Office’s decision to deny me a work permit. Their decision implied that changing light bulbs and carrying out lighting maintenance was not a highly skilled profession. The lesson here is not to give up but to try harder, especially when it comes to red tape. At BDP Lighting the team was very small. Barrie had only two designers – Nicky Burridge and Kate Lownes – to help on the vast array of architectural projects that the studio had to cope with. After two years’ experience in the field of purely architectural lighting, with projects as varied as school buildings, shopping centres, facade lighting and the prestigious Royal Albert Hall, Barrie finally persuaded me to enter the Young Lighter of the Year competition in 2003. Early on, Barrie expressed his interest in my MSc dissertation, which focused on the external lit environment in Nordic cities and its possible relationship with seasonal affective

disorder. I was very intrigued by the notion of lack of sunlight given that I was born and raised in Mexico City where daylight availability throughout the year is fairly constant. Spending one week in Helsinki during the peak of the winter was more than enough to understand the challenges and achievements of artificial exterior lighting in the built environment. I carried out a detailed photographic survey of the most prominent streets and avenues of the city, as well as the key pedestrian areas of confluence and congregation. A photometric analysis of several streets and avenues also helped to understand the perceived brightness of the city after dark. This academic research was the perfect foundation for the topic of the YLOTY presentation. BDP’s myriad large-scale projects taught me the complexities of exterior lighting: the lengthy process of designing, testing, calculating and, most important, pricing. By combining this short experience and the concepts presented and discussed in my dissertation, I was able to present a much clearer picture of why Nordic urban environments required an overlay of architectural lighting (more precisely vertical Illuminance) along the cityscapes in order to compensate for the long periods of darkness. The presentation was a success and I won the YLOTY award, much to Barrie’s satisfaction. It’s been 12 years and three more challenging jobs (Speirs and Major, Isometrix and now Light IQ) since I presented my paper and I still hold that it was one of the greatest experiences of my, now lengthy, career in lighting. It certainly helped me to expand my vision of how amazing and important lighting design is, even on a daily basis. Without a doubt if I were a young person with an interest in lighting today I would push myself to enter the YLOTY award. It is not a competition, it is a career move. n

Buddakan restaurant, New York, winner of Best International Lighting Scheme 2007 (LDA UK) with Isometrix


LR&T essentials

Shades of distinction Iain Carlile finds that colour rendering is high on the agenda in the latest LR&T, as well as exterior lighting and shadows In his editorial (see extract on p12), Peter Boyce applauds the initiative of TM-30. In the face of prolonged inaction, it merits further study, he says. Dangol et al investigated the performance of three different colour fidelity metrics, the CIE colour-rendering index (CRI), colour quality scale (CQS) and CRI2012. From lighting booth experiments with LEDs, they found that all three metrics were highly correlated with visual colour difference. They also found that the CQS provides better prediction for LED sources that highly increase the object chroma. Rea et al present two papers on spectral considerations for external lighting. The first paper compares the psychological benefits of lighting in a car park against using recommended illuminances. Perceived brightness and safety are not affected by illuminance levels and can be different subject to the spectral distribution of lamps. They argue that it would be better to use a perceived scene brightness metric. They present a method of equating brightness for different spectral power distributions. The second paper considers sky glow and the human visual system. They present a general method for assessing sky glow based on atmosphere aerosol content, spectral power distribution and the specific operating characteristics of a detector, human or otherwise. Considering the safe use of roads, Villa et al present a study on the use of LED road studs, investigating their visibility and glare under different environmental conditions. Based on the results of their experiments, they suggest tuning the luminous intensity of LED road studs to suit the illumination and road surface conditions. Also considering the external environment, Ho and Lin consider the CIE sign luminance limits and light trespass, specifically from advertising signs in Taiwan. Using field measurements they found that most signs are lower than the CIE limits, but still cause serious light trespass due to their size, density and poor installation. They recommend urban planning policies to control the problems identified. Considering facial expression recognition, Yang and Fotios performed a repeat experiment to estimate appropriate light levels for outdoor lighting. They found that a luminance of 1.0 cd/sqm allows a 50 per cent correct identification probability at a distance of 15m. Lewis’s paper investigates daylighting in extra-care housing for older people and the barriers to compliance with current UK guidance. Survey findings suggested that these include architects’ reluctance to perform daylight factor calculations, and the need to reduce window size to prevent solar gain, meet planning requirements and minimise construction costs. Aydın-Yağmur and Dokuzer-Öztürk undertook a study to


Examples of the harsh–soft and light–dark attributes for cast and self-shadows (Aydın-Yağmur and Dokuzer-Öztürk)

characterise the harshness-softness and lightness-darkness attributes of shadows. Visual evaluations and calculative methods were compared against, and found to be consistent with, the subjective judgements of shadows in a mock-up room. Ku et al present a tool for assessing the impact of stroboscopic effects caused by different flicker wave shapes. Looking at light pipes with profiled Fresnel collectors to enhance light at low solar altitudes, Nair et al found that the introduction of laser-cut panels of varying depth-to-width ratios helped to redirect low altitude sun rays axially down the pipe, enhancing the light during early morning and late evening hours. The journal finishes with an open letter in support of the IES method of evaluating light source colour rendition (see p11). Iain Carlile, MSLL, is an associate of DPA Lighting Lighting Research and Technology Vol 47, No 8, December 2015 Editorial: Moving forward in colour Peter Boyce Opinion: The dosimetry chain Luke Price Performance of colour fidelity metrics R Dangol, P Bhusal and L Halonen Spectral considerations for outdoor lighting: designing for perceived scene brightness MS Rea, JD Bullough and JA Brons Spectral considerations for outdoor lighting: consequences for sky glow MS Rea and A Bierman Analysis of and control policies for light pollution from advertising signs in Taiwan CY Ho and HT Lin Visibility and discomfort glare of LED road studs C Villa, R Bremond and E Saint Jacques Lighting and recognition of emotion conveyed by facial expressions B Yang and S Fotios Daylighting in older people’s housing: barriers to compliance with current UK guidance A Lewis Determination of the harshness-softness attribute of shadows Ş Aydın-Yağmur and L Dokuzer-Öztürk Predicting the stroboscopic effects of measured and artificial flicker waveforms through simulation S Ku, D Lu and P Chen Daylight enhancement using laser-cut panels integrated with a profiled Fresnel collector MG Nair, AR Ganesan and K Ramamurthy Correspondence: In support of the IES method of evaluating light source colour rendition


Dr Arthur Tarrant 1929-2015 Iain Maclean looks back on the career of Dr Arthur Tarrant, FSLL, FCIBSE, who died last November aged 86

Arthur Tarrant studied physics at Chelsea College, part of the University of London, and first went to work at the Colour Measurement Section of the National Physical Laboratory in Teddington. In 1958 he moved on to the Spectroscopy Section of Battersea College of Technology, later the University of Surrey. His teaching there included optics, instrumentation, spectroscopy, lighting and several other topics. He lectured to students of every faculty within the university. His main research topics had been the spectroscopy of daylight, scattered light in optical instruments, lighting in the home, the names which people give to colours and visual colour measuring instruments. When he retired from full-time employment he continued with much lecturing work, including his Colour is Fun demo and talk. He was also a Visiting Research Fellow at Leeds University. Within the SLL he chaired numerous task groups preparing specialist lighting guides, including LG5 on lecture theatres and conference rooms in 1991, and LG9 on communal and residential buildings in 1997. In 1998, he received the Lighting Division (now SLL) award for his service to the division over the years, particularly for his work on its publications. He was also given the CIBSE Bronze medal for distinguished services to lighting. His final chairmanship role was in 2011 for the guide to the lighting of licensed premises. Arthur gave several lectures to the National Lighting Conferences. Especially memorable was the one where he produced jellies in all the wrong colours to demonstrate how we associate the flavour of foods with colour and how easy it is to be visually fooled. He was also very committed to the London International Youth Science Forum (LIYSF), giving regular lectures, including at least one at the Royal Institution. He had also worked at various times at the Scientific Instrument Research Association and in the professional theatre. For many years he was a governor of the Wimbledon College of Art. He was both a chartered physicist and a chartered engineer. Arthur is survived by his wife Kathleen, three children and one grandson. n

Arthur was a keen railway enthusiast, writes Benedict Cadbury. For many years he was a driver both on the standard gauge Isle of Wight steam railway and the narrow-gauge Wells and Walsingham Light Railway; at least a week of his summer holiday would be spent at each of these railways. His engineering knowledge and skills enabled him to build two fine five-inch gauge steam locomotives using the garage as his workshop. In 1990 he founded the WWLR’s Support Group, serving as its first chairman and newsletter editor for 10 years. His lecturing skills and scholarly approach resulted in fascinating talks about railway history and technology, much in demand at AGMs. He would give a talk about the WWLR to model railway societies up and down the country, which neatly caricatured its rural Norfolk location by including a slide of a road sign that indicated nothing but Village Hall and Great Snoring.

‘I have known Arthur for well over 50 years, first in IES circles when he was at Chelsea University and had taken a keen interest in photocells and colour measurements. He was a great contributor to the TPC activities, and regularly attended our meetings in London and regional conferences. I feel that our society has lost a well-liked, hardworking member’ – Lou Bedocs, FSLL ‘He was always to be seen at the AGM and Presidents Address and often at London sessional meetings. Another of the ‘characters’ of the lighting industry who will be sadly missed’ – Barrie Wilde, FSLL ‘Arthur was always passionate about the society and his dedication to it was total. I had the pleasure of working alongside him in the development of the guide to the lighting of licensed premises and was fortunate to enjoy his very jovial company at that time. He will be greatly missed, especially at London Events where he was such a regular attendee and supporter’ – Liz Peck, SLL president 15


2016 14-17 January Lumiere London light festival Venues: West End, King’s Cross, Main Plaza at Regent’s Place

Aerial net sculpture at Vivid Sydney by Janet Echelman

21 January SLL Masterclass Inside Out: Lighting and Architecture Location: Manchester 8-12 February Exterior Lighting Diploma Module 1 (Organised by the ILP) Venue: Draycote Hotel, Rugby 9-11 February Light School at the Surface Design Show (Supported by the ILP and organised by Light Collective) Venue: Business Design Centre, London N1 light-school 18 February SLL Masterclass Inside Out: Lighting and Architecture Location: York 23 February Fundamental Lighting Course (Organised by the ILP) Venue: Regent House, Rugby 24 February CIBSE Building Performance Awards Venue: Grosvenor House 13-18 March Light and Building Venue: Messe Frankfurt 19 March Junior Ready Steady Light (SLL event) Venue: Rose Bruford College, Sidcup, Kent 22 March Ready Steady Light (SLL event) Venue: Rose Bruford College, Sidcup, Kent 31 March SLL Masterclass Inside Out: Lighting and Architecture Location: Belfast

14-17 January: Lumiere London light festival

11-15 April Exterior Lighting Diploma Module 2 (Organised by the ILP) Venue: Draycote Hotel, Rugby

Lighting Masterclasses: Masterclasses are kindly sponsored by Philips, Thorn, Trilux and Xicato. For venues and booking details :

13 April SLL Masterclass Inside Out: Lighting and Architecture Location: Edinburgh 13-14 April LuxLive Middle East Venue: Abu Dhabi National Exhibition Centre 5 May Lighting Design Awards Venue: London Hilton, Park Lane 26 May SLL Masterclass Inside Out: Lighting and Architecture Location: London 15-16 June Professional Lighting Summit (Organised by the ILP) Venue: TBC 9 November Fundamental Lighting Course (Organised by the ILP) Venue: Regent House, Rugby

LET Diploma: advanced qualification by distance learning. Details from or email Mid Career College: the college runs various courses across the whole spectrum of lighting and at sites across the UK. Full details at LIA courses: details from Sarah Lavell, 01952 290905, or email For up-to-date information follow us on Twitter @sll100

Profile for Matrix Print Consultants Ltd

SLL jan/feb 2016  

SLL jan/feb 2016