Newsletter Volume 11. Issue 5. Sept/Oct 2018
The Society of Light and Lighting
Part of the Chartered Institution of Building Services Engineers
LETTING IN DAYLIGHT
A model pioneer
A WELL-CONSIDERED MEASURE Metrics for circadian lighting
Secretary Brendan Keely FSLL firstname.lastname@example.org SLL Coordinator Juliet Rennie Tel: 020 772 3685 email@example.com Editor Jill Entwistle firstname.lastname@example.org Communications committee: Gethyn Williams (chairman) Rob Anderson Iain Carlile MSLL Jill Entwistle Chris Fordham MSLL Rebecca Hodge Eliot Horsman MSLL Stewart Langdown MSLL Linda Salamoun MSLL 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 NL 6 2018 is 14 September Published by The Society of Light and Lighting 222 Balham High Road London SW12 9BS www.sll.org.uk ISSN 1461-524X © 2018 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
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There are probably a few unsung heroes of lighting. Until now, Greg Ward has numbered among them. One of two laureates for this year’s Daylight Award, he is the creator of Radiance, the daylight simulation programme that has transformed the field of daylighting research and design (see p5). Aside from his extraordinary technical
contribution to the understanding and promotion of daylight in buildings, what is striking about Ward is the generosity he has shown in terms of both intellectual property and the time he devotes to improving the concept through sharing. As well as his continuous working relationships with researchers, students and practitioners, Ward helps co-sponsor an annual Radiance workshop which enables discussion and dissemination of some of the more interesting research and applications that his now 30-year-old development has led to. In the current climate of protectionism and legal scrapping over patents, he is, well, a ray of light. ‘What never fails to amaze me is just how hands-on Greg still is with helping everyone and anyone understand the suite of programmes that make up Radiance,’ says Cundall Light4’s Andrew Bissell. ‘They should make a film about him.’ Jill Entwistle email@example.com
Current SLL lighting guides SLL Lighting Guide 0: Introduction to Light and Lighting (2017) 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 Exterior Environment (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) SLL Lighting Guide 14: Control of Electric Lighting (2016) SLL Lighting Guide 15: Transport Buildings (2017) SLL Lighting Guide 16: Lighting for Stairs (2017) Guide to Limiting Obtrusive Light (2012) Guide to the Lighting of Licensed Premises (2011) LATEST Commissioning Code L (2018) DUE THIS YEAR SLL Lighting Guide 2: Hospital Lighting SLL Lighting Guide 17: Retail Lighting SLL Lighting Handbook
How to specify a luminaire: light sources, colour temperature, rendering, optics, photometry, manufacturing tolerances, longevity, lamp and luminaire efficacies, flux and form factor, quality of materials, IP/IK ratings, lifetime and reliability, earthing and stray voltages, samples, electronics and control, as well as cost. Retrofit and upgrade: design solutions for a space, compliance, CE marking, obligations of the retrofitter, performance and warranties, LED tube light distribution/issues/compatibility, heritage buildings and conservation, wireless versus hard-wired solutions, energy, monitoring, restraints and access, controls and compatibility, system lifespan, maintenance, testing and commissioning.
‘The updated LG2: Hospital Lighting and the new LG17: Retail Lighting are both due out soon’
We are attending darc room (part of London Design Festival) on 19 September and hope to see many of you there. Myself and SLL coordinator Juliet Rennie, are also being broadcast live that afternoon by the Light Collective at 16:20pm, so if you can’t make the event hopefully you can take a few minutes for a catch-up with the society. The event runs from 19-20 September and registration is free of charge. Both I and Juliet Rennie will be exhibiting at Light Middle East from 23-25 September and we’re looking forward to meeting the region’s existing members and new members. We will also host the third Ready Steady Light ME, judged by the Light Collective. The celebration of 100 years of Munsell event will take place in London on 4 October and more details are on the website. On 14-15 November we will be exhibiting in a pod (really) for the first time at LuxLive, ExCeL London, and hope to see many of you there. We have the final of Young Lighter of the Year on 15 November and, of course, the Lux Awards the same evening. The updated LG2: Hospital Lighting will be published soon and the new LG17: Retail Lighting Guide is also imminent. Both will be available for download from the CIBSE Knowledge Portal by all members. We also look forward to the publication of the new Lighting Handbook in the coming weeks.
Editorial2 Secretary’s column
News4 The man who shed light on simulation The legendary Greg Ward, creator of the Radiance programme, and one of this year’s two Daylight Award laureates Clear vision: design for the older eye An extract from the recent book Enlighten on lighting for the elderly, especially dementia sufferers Made to measure? Dr Gordon Lowry considers metrics for circadian lighting
Global exchange 13 Stuart Mucklejohn and John Stocks report on some of the key areas of discussion at LS16 On the level 15 Iain Carlile looks at three LR&T papers, which in different ways consider degrees of illuminance Events16 Cover: Inujima Seirensho Art Museum, Okayama, by Japanese architect Hiroshi Sambuichi, one of two laureates of this year’s Daylight Award presented in Lausanne, Switzerland, in September
The new LightBytes series will start on 18 October in Birmingham (see News p4 and Events p16).This year’s presenters will be Les Thomas (Fagerhult), SLL immediate past president Richard Caple (Thorlux), Roger Sexton (Xicato) and Graeme Shaw (Zumtobel). The new series, in association with the CIBSE Facilities Management Group, will be split into four topic sessions with the speakers delivering their views in each session:
Internet of Things: what IoT means, automatic optimisation of the environment, intelligent sensors, interconnected protocols, domestic and commercial applications, monitoring, adaptive environments, smart cities, data management/analytics, predictive and proactive systems, planned maintenance, what data can be collected and what it can be used for. Emergency lighting: responsibility, competency and legal obligations, the Regulatory Reform (Fire Safety) Order 2005, standards and codes of practice, risk assessments, consultation, external emergency lighting to a place of safety in both the private and public realm, technology advances, inspection and testing, advisory and statutory requirements, and maintenance.
Brendan Keely firstname.lastname@example.org For up-to-date information follow us on Twitter @sll100
Rose Bruford College to set up architectural lighting degree
An undergraduate architectural lighting design course is to be established next year at Rose Bruford College of Theatre and Performance in Sidcup, Kent. The Lighting Education Trust (LET) has signed a memorandum of understanding with Rose Bruford to support and collaborate in the production of an undergraduate BA (Hons) Lighting Design (Space and Architecture) course. The LET will give both financial and specialist support to the course, and will act as a facilitator between UCL and Rose Bruford, said LET chair Bob
On the lighter side...
Lighting and ice cream don’t often crop up in the same sentence but Scoop, an exhibition running this summer at the British Museum of Food in London’s King’s Cross, firmly links the two. Visitors can walk through a futuristic luminescent cave with glow-in-the-dark ice cream, and thanks to ice cream company Ben & Jerry’s, they can see what happens inside their heads when they eat ice cream. Brain waves are monitored with a special
Venning, who added that the first intake of students should take place in 2019. The LET was set up in 1995 with the aim of supporting UCL’s MSc course in light and lighting, and to support any other lighting education initiatives deemed appropriate by the trust. Discussions have been maintained with a number of universities, as well as Rose Bruford, over many years. Trustee Mike Simpson has been lecturing at the college for many years, and the SLL’s annual Ready Steady Light event has helped keep architectural lighting on the college agenda. The LET now runs its own distancelearning diploma course in lighting design, in association with London South Bank University. ‘The advent of the Rose Bruford undergraduate course will sit nicely between the LET’s diploma course and the master’s course, completing the first comprehensive study route for those wishing to make architectural lighting design a career,’ said Venning.
headset linked to a laser display unit. All to do with dopamine and pleasure centres which taking a lick will activate. There is also more serious stuff as visitors walk through three centuries of European and British ice-cream history. They can experience rare and unusual flavours, dating back to 1750 when daffodilflavoured ice was apparently invented. The installation runs until 31 September 2018 at Gasholders London, King’s Cross (www.bmof.org).
IN BRIEF The first of the new SLL LightBytes series will be at the MAC Birmingham on 18 October. This will be followed by Belfast on 29 November. The first event of 2019 will be on 24 January in Liverpool, followed by York on 28 February, Bristol on 28 March, Edinburgh on 25 April and the final event of the series on 9 May in London. This year’s topics examine how to specify luminaires; the issues involved in retrofit and upgrade schemes; the Internet of Things, and emergency lighting For the latest details, please go to: www.sll.org.uk CIBSE has announced its CPDaccredited programme for the 2018 Build2Perform Live event in November. Among the topics aimed at lighting professionals are daylighting considerations for integrated design, and lighting and facilities management. Building performance in schools, energy benchmarking, digital future horizons and environmental policies for resilient cities are other subjects that will feature. Build2Perform Live takes place from 27-28 November at the Olympia exhibition centre in Kensington, London. For more details go to: www.build2perform.co.uk Former SLL president Peter Raynham, who edits the SLL’s Code for Lighting among many other society activities, has been appointed professor of the lit environment at the Bartlett School of Environment, Energy and Resources, UCL. The deadline for CIBSE’s 2019 Building Performance Awards is 14 September. The shortlist will be revealed in November and winners announced at the Grosvenor House Hotel in London next February. More details at: www.cibse.org/BPA CIBSE is calling for abstracts for its ninth Technical Symposium, Transforming Built Environments, by 17 September. Go to www.cibse.org/symposium
The man who shed light on simulation
One of two Daylight Award 2018 laureates is the legendary Greg Ward, creator of the revolutionary Radiance daylight modelling programme
On 27 September, a pioneering US researcher will step up to receive The Daylight Award 2018 in Lausanne, Switzerland. Along with his co-recipient, Japanese architect Hiroshi Sambuichi, Greg Ward follows in the footsteps of architects Jørn Utzon, Peter Zumthor and Steven Holl among others. While those names will have a wide resonance, Ward will perhaps only be known to a smaller, specialist circle of people, predominantly those involved in lighting design, architecture and daylight research. In fact it is probably not an overstatement to say that Ward is something of a legend in this circle. He is the creator of the revolutionary daylight simulation programme Radiance, which for the past three decades has underpinned the field of daylighting research and practice,
allowing researchers and designers to accurately assess the effects of daylight on a space. Radiance is widely applied in architecture, product design, horticulture, the film industry, healthcare and medical research. It has also been used in unique situations such as assisting astronauts in training to work under the harsh lighting conditions in space. ‘His contribution in the form of a powerful extendable software suite has enabled unprecedented advances in adjacent fields that require light modelling,’ says the awards statement. ‘He creates and captures a physically accurate representation of the luminous environment and of the human response to intensity, colour, contrast, glare and views in his @sll100
Previous page: daylight simulation (1992) created by John Mardaljevic for an atrium designed by Foggo Associates Above left: early daylit art gallery scene (1991) designed/simulated by John Mardaljevic, overlaid with a Falsecolour illuminance map Above right: air traffic control tower simulation by Greg Ward and Charles Ehrlich
computer software,’ the statement continues. ‘His passion for iterating and improving the software has led to a strong community of Radiance users who further impact the fields of daylight research and daylight in architecture.’ Ward has investigated the interaction of light and matter across a wide range of physical scales, from unique building materials with specialised optical properties, to the spatial definition of complex building interiors and facades, as well as urban and natural environments. ‘The programme, which has been in use now for over 30 years, captures all of the subtle interactions that light has with the environment – from how it transfers through glass to how it bounces off surfaces inside a room to how people actually experience it in an indoor or outdoor space,’ says Stephen Selkowitz, member of the Daylight Award jury. Ward has initiated numerous daylight seminars and taken a personal interest in helping young researchers and PhD students as well as professionals. ‘Each year he helps cosponsor a Radiance workshop which brings together some of the more interesting research and applications with the software as well as engaging the people who use it,’ adds Selkowitz. ‘My emphasis has always been on working, practical systems, as opposed to purely academic pursuits,’ says Ward. Ward graduated in physics from the University of California at Berkeley, and earned his Master’s in computer science from San Francisco State University in 1985. He became a staff scientist at Lawrence Berkeley National Laboratory in California, where he started developing Radiance in 1985, and later set up the independent consulting firm Anyhere Software in 2002. Over the past three decades, he has published numerous papers on computer graphics and illumination engineering. He is also the inventor of an imaging gonioreflectometer for the measurement of reflectance of architectural materials, and the developer of the Materials and Geometry Format for lighting information exchange. He has established an annual international symposium and is invited as visiting scholar at daylighting research centres globally. ‘Greg Ward sustains a community of daylighting researchers
Radiance includes a renderer as well as many other tools for measuring simulated light levels. It uses ray tracing to perform all lighting calculations, accelerated by the use of an octree data structure. It pioneered the concept of high dynamic range imaging, and implements global illumination using the Monte Carlo method to sample light falling on a point and practitioners who share and support the tool, and over time have added a whole new genre of user interfaces to Radiance,’ says the jury’s statement. ‘Its ability to model how light interacts with complex architectural designs and new materials is pivotal in the development of design workflows enabling designers to innovate daylighting solutions. ‘He has complemented this work with the development of new data protocols to capture image data, new visual display technology and novel instruments to measure optical properties of architectural glazing and materials,’ the statement continues. ‘The breadth of Greg Ward’s work has transformed the field of daylight modelling. It has empowered generations of researchers and practitioners to understand, anticipate and effectively integrate daylight in the built environment.’ Established in 1980, The Daylight Award recognises prominent practitioners in the fields of daylight in architecture and daylight research for the benefit of human health, wellbeing and the environment. It is presented by the philanthropic foundations Villum Fonden, Velux Fonden and Velux Stiftung, established by Villum Kann Rasmussen, inventor of the Velux roof window. The 17th International Radiance Workshop will be hosted by Eleonora Brembilla and John Mardaljevic at Loughborough University from September 3-5, 2018. For more information go to: http://climate-baseddaylighting.com/doku.php?id=radiance2018
‘I was probably one of the first people in the UK to get to grips with Radiance – around 1990, shortly after the first public release. Or rather, tried to – Radiance quickly earned a reputation for being fiendishly difficult to use. However, the originator, that is Greg Ward, did not deliberately make Radiance seemingly impenetrable. Rather, the perceived baffling nature of the Radiance system – a large collection of individual programmes instead of a “user friendly” graphical interface – was part-and-parcel of its power: Radiance was founded on the UNIX toolbox model. Once the user had attained some skill in writing UNIX scripts, the individual Radiance “tools” could be configured to solve almost any lighting problem, including many that the originator hadn’t thought of. That is why a number of us stuck with Radiance, with its almost limitless power and flexibility. Much of the hard-won knowledge of the early adopters appeared in the Radiance book in 1998, for which I contributed the chapter on daylight simulation.’ – John Mardaljevic, Professor of Building Daylight Modelling, School of Architecture, Building and Civil Engineering, Loughborough University ‘Greg Ward was very much the right man at the right time who did the right thing. Developing ray tracing software before the late 1980s was difficult due to the high cost and limited performance of computers that made detailed analysis using the ray tracing technique impossible. Up to that point, ray tracing was very much restricted to the luminaire design community and they tended to use gross simplifications to get some form of results in a finite time. Radiance itself was developed in a very open
way that made access to code available and, more importantly, all of the parameters used to control the calculation processes are also exposed to the user. The ray tracing process is a very good way to perform lighting calculations and in the early 1990s it became clear that Radiance was the best software for creating photometrically correct images, easily beating a number of radiositybased packages that were out at the time. Due to the openness of Radiance it has been used in a number of academic studies and it is probably the most validated bit of lighting software. Now as we are coming up to the 30th anniversary of the original paper in Computer Graphics* it is only right that we recognise Greg’s achievement.’ – Peter Raynham, Professor of the Lit Environment, Bartlett School of Environment, Energy and Resources, UCL * Ward G, Rubinstien F and Clear R. A Ray Tracing Solution for Diffuse Interreflection Computer Graphics, 22, 4 August 1988
‘There cannot be many pieces of software developed in the late 1980s which are still in use now and which are still the industry leader in their field as Radiance is. I first used the suite of software in 1998, albeit with a lot of head scratching and furious thumbing back and forth in my copy of Rendering with Radiance. It is testament to Greg Ward that we can all still use the software now to help us design our daylight solutions for buildings. What also never fails to amaze me is just how hands-on Greg still is with helping everyone and anyone understand the suite of programmes that make up Radiance. They should make a film about him.’ – Andrew Bissell, Director, Light4 Cundall
Different daylight scenarios for Amherst College New Science Center, Massachusetts, by Integral Light Studio
Lighting for the elderly
Clear vision: design for the older eye Enlighten, a recently published book by David McNair and Richard Pollock, looks at the issues of lighting for elderly people, particularly those with dementia. The following is an edited extract For an older person with dementia, it’s challenging to remain independent and dignified. Adjusting the living environment through both natural and artificial forms of lighting can help compensate for a number of impairments caused by dementia – particularly those that are visual and sensory. The visual sense can act as a critical tool, allowing the person with dementia to better understand their environment and maximise their remaining abilities. As a result, they can experience more independence, choice and dignity. In the same way, if environments are not designed to account for the typical impairments associated with ageing and dementia, people with the condition will be hindered rather than assisted by what is around them. Not only does lighting help ensure the environment for a person with dementia is suitable, functional and enabling, the right amount of sun or light exposure can stabilise sleep patterns, improve mood, increase muscle strength and provide the means for a more enabling and dignified living. In this sense, light can also be considered as a drug, able to promote various mechanisms in the body. Shortage of adequate exposure can adversely impact sleep and health, contribute to a high accident rate and increase anxiety. On the other hand, excessive exposure to direct sunlight can cause skin cancer. So there are a series of balances to be considered.
Primary features explained Provide lighting at twice ‘normal’ levels Lighting design standards are determined by firstly assessing
People with dementia need: Easy to understand environments Direct sightlines to key areas Good tonal contrast where adjacent surfaces have to be distinguished (and none where they are not to be) An absence of confusing patterns Diffuse rather than specular (shiny) finishes. For this latter age range enhanced lighting levels at a factor of two are recommended
the complexity of the visual task at hand and then deciding how much light is needed to facilitate effective viewing of it. Saturation occurs when additional illumination does not improve visual performance but increases energy use. Consider, however, that the human visual system reaches optimum capability at a very early age and that light transmission through the eye deteriorates continually with life. Some writers cite the well-known work of Weale1: 60-year-olds require three times as much light as 20-yearolds. As authors, we entirely agree with this. However, lighting design standards are generally specified for people in the age range of 45 to 50 years2 and most people with dementia are older than 75. Taking these age groups together it can be determined that a 75-year old requires twice as much light as a 45-year- old for equivalent visual performance.3 This recommendation is based on age alone without allowance for the additional challenges presented to people living with dementia. The use of local lighting at key task areas can make a significant contribution to achieving the necessary lighting levels. Expose people to the 24-hour cycle of light and dark As mentioned, when people are exposed to bright light in the morning there is an excellent chance that their circadian rhythms will remain synchronised and the minimum benefit will be improved sleep. An easy way to achieve sufficient exposure is to go outdoors, as light levels there are very much higher than indoors. An additional benefit is that increased physical activity levels do even more to improve sleep efficiency.4 These high levels experienced outdoors can reduce the risk of seasonal affective disorder and can also increase vitamin D levels in the body via skin exposure to direct sunlight. In bedrooms overnight it is best to avoid stray light from corridors, street lights, gardens and electronic indicators as, at best, it can delay and/or disturb sleep and, at worst, suppress melatonin production. Consider surfaces: reflection, contrast and perception Reflection and contrast are the keys to vision – the light reflected from objects to the eye allows them to be perceived, but they will only be perceived if there is sufficient contrast to distinguish them from their surroundings. Older people have
Lighting for the elderly xxx
A recreation of the effect of various vision impairments. Clockwise from far left: cataracts, glaucoma, macular degeneration, diabetes
reduced contrast sensitivity compared to those who are younger, and people living with dementia need even more contrast in order to give their brains a chance of interpreting the visual scene. Providing good contrast to selected surfaces can aid vision – for example, a dark seat on a light toilet or a dark frame around a white light switch. A light reflectance value (LRV) of 30 points is recommended for the detection of adjacent surfaces. On the other hand, inappropriate contrast can cause confusion – for example, a dark drain cover on a light path might be perceived as a hole to be avoided, or the changes in tone on level surfaces might contribute to falls if people think that there is a change in level. That is a circumstance very important to avoid. Patterns on surfaces can easily be misperceived, with people having dementia trying to avoid sections of carpet, or perpetually attempting to clean crumbs from speckled worktops.
The primary features of dementia-inclusive lighting are: Lighting at twice ‘normal’ levels Exposing people to the 24-hour cycle of light and dark Considering surfaces: reflection, contrast and perception Using daylight wherever possible Sufficient ‘domestic style’ fittings to help promote a recognition of place Alongside these, other lighting design considerations include: Ensuring there is good uniformity and satisfactory light levels shed on walls and ceilings Avoiding sudden changes in light level Ensuring good colour rendition Designing for low glare
References 1 RA Weale, Retinal illumination and age, Trans Illum Eng Soc, Vol 26, no 2, 1961 2 CIBSE, Code for Interior Lighting, CIBSE, London, 1994.
This extract is taken from Enlighten: Lighting for Older People and People with Dementia by David McNair and Richard Pollock with Colm Cunningham, and is published by HammondCare Media: www.hammond.com.au/news/enlightenlighting-for-older-people-and-people-with-dementia
3 PL Turner and MA Mainster, Circadian photoreception: ageing and the eye’s important role in systemic health, British Journal of Ophthalmology, Vol 92, 2008, pp1439-1444 4 A Nioi, Evaluation of blue light exposure, illuminance level and the associations with sleep/wake patterns in two populations living with sensory impairment, HeriotWatt University, 2016, pp145
Made to measure? Shutterstock
Summarising his paper at the 2018 CIBSE Technical Symposium, Dr Gordon Lowry considers the issue of metrics for circadian lighting and the criterion adopted by the WELL Building Standard In the lighting community much has been written on the function of the intrinsically photosensitive retinal ganglion cells (ipRGC) in the eye. The signals from ipRGC inform the brain’s regulation of the body’s circadian pattern, and this has significance for our health and wellbeing. The level of stimulation of ipRGC depends on the irradiance at the eye, but ipRGC sensitivity varies with wavelength. This has led to a number of attempts to refine an ‘action spectrum’ to account for the variation in a way that is analogous to the photopic vision spectrum used to quantify visual effects, one of which has been adopted in the WELL Building Standard.1 So, does it matter which metric is used?
Most measures of circadian effects use nocturnal melatonin suppression as a marker. Measurements based on narrowband sources showed that melatonin suppression was wavelength dependent.2,3 In order to account for the total effect of a broadband mixture of wavelengths, various additive models have been proposed. These models are based on the relative sensitivity of the circadian response to different wavelengths, λ, which would be formulated as a function of wavelength, for example, C(λ). Then the circadian potential is calculated for a power spectrum, P(λ) thus:
If a criterion for the circadian stimulus is agreed, then the corresponding amount of radiation required from a given source can be determined. As the spatial distribution of light radiation is already quantified using luminous flux, it is useful to relate the quantity of circadian stimulus to the luminous flux generated from the same source. Thus the values are commonly normalised for use with conventional photometric calculations of luminous flux and illuminance. For a given spectral power distribution P(λ), a conversion factor can be calculated from the source spectrum thus:
where the choice of scaling constant k depends on the way that the function C was originally scaled. It should be noted that circadian effects are not simply proportional to these metrics. At best, they provide measurements on ordinal scales, but they can be used to rank sources by their circadian stimulus potential. We can then see whether it matters which metric is used by comparing how lamps are ranked: Circadian action factor Gall and Bieske4 developed an action spectrum that was fitted to earlier measurements2,3 and a circadian action factor, acv, was calculated as the ratio of circadian action to photopic action for the same spectrum. It was noted that the action spectrum resembled the colour-matching function, .5 Since the photopic flux is proportional to the chromaticity coordinate, y, acv might be estimated directly from the ratio of source chromaticity coordinates z/y.
‘Evidently the choice of metric matters. The melanopic based metrics clearly differ significantly from circadian light’ Melanopic sensitivity The photosensitivity of the ipRGC is understood to result from the properties of the protein melanopsin. Study of this has led to a melanopic sensitivity function Vz(λ).6 This can be used rather like the photopic function V(λ)5 to determine ‘melanopic illuminance’. This approach has been adopted in the WELL Building Standard. Melatonin suppression index Aubé et al introduced their melatonin suppression index, MSI,7 which is evaluated using a melatonin suppression action spectrum derived by curve fitting to the 2001 data.2,3
CL per lux
Table A: calculated circadian measures for typical lamps key: WELL MSI z/y acv CL
WELL Building Standard conversion factor melatonin suppression index ratio of chromaticity coordinates circadian action factor ratio of circadian light to photopic light per lux
Circadian light There are problems with the action spectrum approach as effects from a mix of wavelengths are not simply additive, and allowances might need to be made for the way that signals from the rods and cones may ‘interfere’ with the ipRGC response. Consequently an alternative non-linear model of ‘circadian light’ has been formulated.8 It has been proposed that the influence of rods and cones might be accounted for if a model can include spectral opponent input from the blue-yellow channel.9,10,11 The subsequent relationship between circadian light and the level of circadian stimulus has been modelled by Rea et al.11 Correlated colour temperature Finally, it has been suggested that CCT might be used as an indicator of relative circadian effect.4 If so, this is important because CCT values are more readily available than details of spectrum.
Example lamp results
Evaluation of lamp metrics requires the lamp spectrum: here (Table A), I have used the spectra for typical white lamps published by Aubé and Roby.12 Calculation tools offered by advocates of different measures (see appendix in original paper) were used to calculate values for typical lamps. They have been calculated relative to
related photometric quantity, flux or illuminance using the second equation above. If the different metrics were not significantly different from each other, there would be agreement in how they ranked lamps for circadian stimulus potential. The level of agreement can be assessed through the Spearmann rank correlation coefficient (Table B). There is poor agreement between circadian light and the other measures. WELL, MSI and acv are in close agreement. The much simpler CCT and z/y measures, derived purely from chromaticity information, do not perform as well but remain attractive for their ease of derivation. Evidently the choice of metric matters. The melanopic-based metrics clearly differ significantly from circadian light.
WELL Building Standard criteria
The WELL Building Standard has adopted the minimum ‘equivalent melanopic lux’ (EML) criterion. As noted previously, photopic illuminance can be calculated conventionally and then a conversion factor applied in order to determine the melanopic quantity. This calculation implicitly assumes that the spectrum remains constant for direct and indirect illuminance. Potentially, indirect illuminance will have a spectrum altered from that of the source depending on the reflective properties, in other words the colour, of room surfaces.13,14 Either of these criteria will satisfy the standard: •
200 EML every day on the vertical plane perpendicular to direction of view 1.2m AFFL at 75 per cent of workstations from artificial lighting and daylight from 9am to 1pm 150 EML from artificial lighting alone at 100 per cent of workstations
Vertical face illuminance is conventionally addressed with design criteria for cylindrical illuminance at headheight, for reasons to do with the appearance of people engaged in face-to-face communication. A mean value
Table B: Spearmann rank correlation CCT
acv CL per lux
CL per lux
of 150 lux is specified in BS EN 12464.15 However, the spatial uniformity criterion is only 0.1, so the 150 lux would not be assured over all workstations. And, cylindrical illuminance is not direction specific, but averaged over 360 degrees of orientation, so it does not assure a value in the particular direction of view. At most workstations, workers will be spending many hours viewing computer screens. The circadian effect of screen use has been noted for some time, and is a concern when this occurs late in the day.16 During the day, however, the screen output may aid in delivering EML. For example, a typical 300 cd/sqm luminance from a 0.1sqm screen spaced 0.75m away from the face could provide approximately 50 lux. Finally there may be a useful contribution from Cuttle’s perceived brightness criteria.17,18 He argues that the perceived brightness for a space is determined by the mean room surface exitance (MRSE), in other words the average output of reflected flux from the room surfaces. Cuttle suggests that MRSE of 100lm/sqm is the minimum acceptable for a space not to appear dim, which we should normally expect to be exceeded in conventional work spaces. The MRSE equates to the average indirect illuminance in the space in lux. A bright appearance would have 300lm/sqm, at which point the cylindrical illuminance will average at least this as there would be direct illuminance to add. Possibly, then, adoption of Cuttle’s approximate guide would help secure facial illuminance approaching levels needed to deliver the required EML value. So currently, 200 lux is a reasonable expectation at eye level before considering daylight. The conversion to an EML value will depend not only on the lamps, but any spectral shift resulting from the reflection from room surfaces, and the nature of the screen lighting. Daylight may be included in satisfying the first WELL criteria, but is likely to be indirect because the viewing direction would be oriented to avoid sunlight glare, and again the effect of surface colour might need attention.
References 1 WELL Building Standard® v1, Q4 2017 version, International WELL Building Institute. 2 Brainard GC, Action Spectrum for Melatonin Regulation in Humans: Evidence for a Novel Circadian Photoreceptor. Journal of Neuroscience 2001, 21: 6405-6412 3 Thapan K, An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans, Journal of Physiology, 2001, 535: 261-267 4 Gall D, Bieske K, Definition and measurement of circadian radiometric quantities, Light and health – non-visual effects: proceedings of the CIE symposium 2004, Vienna, Austria, 30 Sept-2 Oct 2004 5 British Standards Institution, BS EN ISO 11664-1:2011 Colorimetry. Part 1: CIE standard colorimetric observers, London: BSI, 2011 6 Enezi J, Revell V, Brown T, Wynne J, Schlangen L and Lucas R, A ‘Melanopic’ Spectral Efficiency Function Predicts the Sensitivity of Melanopsin Photoreceptors to Polychromatic Lights, Journal of Biological Rhythms, 2011, 26(4): 314-323 doi: 10.1177/0748730411409719
From the small sample of lamps examined here, it is evident that the assessment by ranking of the relative circadian potential of lamps depends on the model used. In particular, it needs to be established how and whether the additional effects of rod and cones on the ipRGC stimulus can be effectively accounted for in a single metric, such as in Circadian Light. If melanopic response is used for assessing circadian effects, then for the sample of lamps used here the alternative metrics – circadian action factor, MSI and the WELL factors – are similar. But since full spectral data may not be easily available, there may be some utility in approximate metrics, such as CCT or z/y that do not require full spectral data until lamp manufacturers start to calculate and publish metrics on a standard basis. Finally, there is a convergence possible between the various lighting criteria affecting the vertical illuminance experienced at eye level. It might be timely to concentrate our design on vertical face illuminance, thus ensuring: • adequate circadian stimulus, though this might need to be moderated later in the afternoon • facial illuminance to facilitate comfortable face-to- face communication • the visual environment has a bright appearance In each of these outputs, indirect illuminance will be especially important as the direct facial illuminance would be limited by the need to control glare. Therefore the specification of surface colours needs to be carefully considered. Dr Gordon Lowry is associate professor at the School of the Built Environment and Architecture, LSBU. Full acknowledgements and appendix appear in the original paper, available on request
of Circadian Rhythms 2010, 8:2 doi:10.1186/1740-3391-8-2 10 Rea MS and Figueiro MG, A Working Threshold for Acute Nocturnal Melatonin Suppression from ‘White’ Light Sources used in Architectural Applications, Journal of Carcinogene Mutagene, 2013, 4: 150 doi: 10.4172/2157-2518.1000150 11 Rea MS, Figueiro MG, Bullough JD and Bierman A, A model of phototransduction by the human circadian system, Brain research Reviews, 2005, 50: 213-228 doi:10.1016/j.brainresrev.2005.07.002 12 Lamp Spectral Power Distribution Database, last accessed 18 August 2017, http://galileo.graphycs.cegepsherbrooke.qc.ca/app/en/lamps 13 Geisler-Moroder D, Dür A, Estimating Melatonin Suppression and Photosynthesis Activity in Real-World Scenes from Computer Generated Images, Conference on Colour in Graphics, Imaging, and Vision, Joensuu, Finland, Society for Imaging Science and Technology, 2010 14 Bellia L, Pedace A and Barbato G, Indoor artificial lighting: Prediction of the circadian effects of different spectral power distributions, LR&T 2014, 46: 650–660 doi: 10.1177/1477153513495867 15 British Standards Institution. BS EN 12464-1:2011 Light and lighting – Lighting of work places. Part 1: Indoor work places, London: BSI, 2011
7 Aubé M, Roby J, Kocifaj M, Evaluating Potential Spectral Impacts of Various Artificial Lights on Melatonin Suppression, Photosynthesis, and Star Visibility, Public Library of Science One, 2013 8(7): e67798 doi:10.1371/ journal.pone.0067798
16 Cajochen C, et al. Evening exposure to a light-emitting diodes (LED)backlit computer screen affects circadian physiology and cognitive performance, Journal of Applied Physiology, 2011, 110: 1432–1438 doi:10.1152/japplphysiol.00165.2011
8 Rea MS, Figueiro MG, Bierman A and Hamner R, Modelling the spectral sensitivity of the human circadian system, Lighting Research and Technology, 2012, 44: 386-396 doi: 10.1177/1477153511430474
17 Dai Q, Cai W, Shi W, Hao, L, Wei M, A proposed lighting-design space: circadian effect versus visual illuminance, Building and Environment, 2017, 122: 287-293
9 Rea MS, Figueiro MG, Bierman A and Bullough JD, Circadian light, Journal
18 Cuttle C, Lighting Design: A Perception-based Approach, Routledge, 2015
Stuart Mucklejohn and John Stocks report on some of the key areas of discussion at the16th International Symposium on the Science and Technology of Lighting (LS16)
The International Symposium on the Science and Technology of Lighting has a 40-year history of providing a forum for scientists and engineers worldwide, in academia, national laboratories and industry, allowing them to share and exchange the latest progress on the science and technology of lighting. At the opening of the symposium, after brief introductions from the chairs of the local and international organising committees, the stage was given over to Rachel Shaw, winner of the Worshipful Company of Lightmongers’ award for the best student graduating in 2017 from UCL’s MSc in Light and Lighting. Rachel highlighted the beneficial role played by the professional and industry bodies in supporting people in their careers, providing not only support and guidance but also giving members of the profession a strong sense of purpose and community. The week started with a fascinating talk by Robert Karlicek from Rensselaer Polytechnic Institute who looked to the future, seeing a world where lighting systems are attuned to the occupants’ activities, adjusting to suit the task or atmosphere. The lighting, being linked to the Internet of Things, enables
the building to learn to adapt to its ever-changing uses. In contrast, Ian Tutt, formerly of Trinity House, provided a beautifully illustrated history of light sources for lighthouses. This story is not only about sources but ensuring the lighthouse has sufficient energy available to power them, an essential consideration before the days of widespread electrical power distribution networks. Ling Wu, secretary general of the Chinese Solid State Lighting Alliance, highlighted the rapid improvement in the efficacy of white light LED chips, which has risen from 20lm/W in 2003 to a reported 180lm/W in 2017. The alliance is now extending its interests to smart lighting systems, visual light communication and more specialist applications such as horticulture, animal breeding, aquaculture and water sterilisation. The symposium had several papers on the developing area of nitride semiconductors based on InGaN and AlGaN. Sir Colin Humphreys (Cambridge Centre for Gallium Nitride) illustrated why GaN LEDs, though highly efficient, were expensive to produce. These costs can be substantially reduced if the chips are grown on silicon rather than sapphire but this has numerous challenges in avoiding dislocations and cracks. However, Plessey, in its Plymouth facility, has already successfully commercialised this. An afternoon session was devoted to horticultural lighting, an area that while continuing to expand has confirmed the limits of both the lighting and plant-growing communities’ understanding of what is really needed. In the natural world plants evolved under many varying light conditions and cycles, so the ‘one-spectrum does all’ approach will not provide the optimum lighting condition for all plants or for individual plants throughout the full growth cycle. As well as the commonly used red and blue spectra, it was pointed out that green, far red, UV-A and UV-B all made contributions to the development of certain aspects of plants, from germination, biomass development, flowering, and seed and fruit development to colouration and nutritional content. The creation of artificial light has enabled humans to carry out activities when the sun goes down but our bodies have evolved to take environmental signals from the light @sll100
Future developments in lighting were on the agenda, from lighting systems attuned to peoples’ activities to the refinements still needed for horticultural applications of LEDs
conditions to activate the rest/sleep periods essential to our health. Mariana Figuero (Rensselaer Polytechnic Institute) presented research showing how important it is to tailor lighting installations to ensure our day/night cycles are maintained. The work shows how this is possible and how carefully designed lighting systems can stimulate circadian entrainment, alertness, positive mood and healthy sleep, and contribute to general health and wellbeing. These themes were also raised in the special session of the Colour Group. Annette Allen (University of Manchester) described how recently identified photoreceptors in the eye, ipRGC (intrinsically photosensitive retinal ganglion cells), act to entrain the circadian clock, control pupil restriction and impact our daily rhythm of rest/activity. The increasing nightly use of screens, including televisions, mobile phones and tablets, can disrupt the generation of melanopsin, which in turn leads to a suppression in melatonin levels, delaying the onset of sleepiness. It is possible to design screens which do not suppress melatonin levels but do maintain a pleasant visual appearance for the user. Xavier Denis, from Nichia, demonstrated the progress made recently in developing phosphors to close the efficiency gap for high CRI LEDs. Although CRI >80 can be achieved for LEDs at 5000K, 4000K and 3000K, there has been a significant reduction in efficacy at the lower colour temperatures. This fall off has now been addressed and ultrahigh colour rendering LED chips can be made with Ri >90 for all 15 indices in the CRI scale. Measurement and standardisation challenges are high on the agenda for the whole of the lighting industry. Gareth John, from the LIA, showed how light measurement equipment in the new era of solid state lighting, with its high emission levels in the blue and UV regions, can provide misleading results. It was pointed out that the spectral sensitivity characteristics of a
detector should be carefully compared to the spectral luminous efficiency function of the human eye, in other words the V(λ) curve, particularly in the blue region where many white LEDs have a significant peak. The design of outdoor lighting systems with a focus on energy saving and minimising environmental disturbance was discussed by Allan Howard of WSP. He presented some fascinating Scandinavian trials of street and road lighting that keeps the pedestrian or vehicle in a ‘light bubble’ during passage along it. Light is only present when and where required. Steve Fotios, from Sheffield University, gave an in-depth analysis of the importance of precise experimental design in lighting research. For example, careful attention has to be paid to experimental conditions to avoid unintentional range bias in subjective assessments. He cited the infamous Kruithof Curve, describing the range of illuminance and colour temperatures that are considered to be comfortable to an observer, which has been shown to be based on unreliable research methods. We have only provided a brief overview of what was presented as a sample of the many excellent talks and posters presented. The LS16 proceedings volume will be available later this year from FAST-LS. The SLL was one of the supporting organisations for the 16th International Symposium on the Science and Technology of Lighting (LS16) held from 17-22 June at the University of Sheffield. It was organised by the Foundation for the Advancement of the Science and Technology of Light Sources (FAST-LS) with The Centre for GaN Materials and Devices at the University of Sheffield. The CIE was technical co-sponsor and main sponsor was Nichia. The Optical Society (OSA) Color Technical Group and the Colour Group (GB) put together a special joint session on Colour Science and Technology.
On the level
An experiment was conducted in which 47 subjects viewed 36 different conditions comprising differing glare source luminance (20,000-750,000 cd/sqm), positions (0 degrees, 10 degrees), sizes (10-5, 10-4 sr) and backgrounds of lowluminance (0.03-1 cd/sqm). The results showed that relative pupil size correlated with subjective responses to discomfort glare to some extent. The authors identified that an increase in relative pupil size was strongly related to a decrease in the background luminance. Chronotypes relate to an individual’s circadian phase. These phases reveal the time of day at which an individual’s physical functions, cognitive faculties and sleeping patterns are active. An individual’s preferences for particular sleeping and waking timings are used to identify their chronotype. Yang et al conducted a study to investigate the synchrony effect between chronotype and time of day on task switching and vigilance, and the effect of high illuminance on the performance of two chronotypes at their non-optimal time. An experiment was undertaken where low (200 lux) and high (1200 lux) illuminance was provided at the eye at different times (1.5 hours and 10.5 hours after waking up). The authors identified that the effects of ambient light on task switching depended on the chronotypes Pupil diameter (in mm) during one momentary flash sequence that consisted of three of the people exposed. Evening flashes of the glare source types (ET) had better task-switching Beginning with road lighting, Fotios and Yao’s paper looks performance under high illuminance compared to low at the scotopic/photopic ratio (S/P) parameter used within illuminance, and morning types (MT) typically performed its design. The S/P ratio relates to visual performance. better in low illuminance than ET. The authors also identify Current UK lighting guidance allows a lower photopic that high illuminance could significantly decrease subjective illuminance when a higher S/P ratio is used, which may lead sleepiness regardless of chronotype. to lower energy consumption and associated costs. Higher S/P ratios are typically associated with higher correlated Iain Carlile, MSLL, is an associate of DPA Lighting and colour temperature (CCT) values and cooler appearance, current president of the SLL which has received widespread public criticism where traditional sodium sources have been replaced with high Lighting Research and Technology: OnlineFirst CCT LED light sources. In advance of being published in the print version of Taking 297 light source spectra identified in the IES Lighting Research and Technology (LR&T), all papers Technical Memorandum, IES Method for Evaluating Light accepted for publishing are available online. SLL Source Color Rendition (TM-30-15), the authors compared members can gain access to these papers via the SLL the S/P ratio and CCT of each spectra in order to test the website (www.sll.org.uk) assumption that higher S/P ratios demand higher CCT values. They found that there is a strong relationship The association between correlated colour between the S/P ratio and CCT, therefore for a given temperature and scotopic/photopic ratio CCT only a small variation in the S/P ratio is available. S Fotios and Q Yao The results also suggest that a larger variation in the S/P
Iain Carlile looks at three recently published papers, which in different ways consider degrees of illuminance
ratio is possible if the designer responsible can consider changing lamp type, but this may have an impact on cost, optical control and maintenance considerations. Tyukhova and Waters present a study into discomfort glare, considering small, high-luminance light sources and the human response to them, both subjective and pupil reaction, when viewed against a low luminance background, such as high luminance light sources in an exterior lighting application.
Subjective and pupil responses to discomfort glare from small, high-luminance light sources Y Tyukhova and CE Waters
The effects of ambient light on task switching depend on the chronotype J Yang, T Ru, Q Chen MSca, T Mao, Y Ji and G Zhou
2018 13-14 September Symposium on Promotion and Protection of the Night Sky Location: Capraia Island, Italy http://capraianightsky2018.com 20 September How to be Brilliant (organised by the ILP) Speaker: Rebecca Hutchison, John Cullen Venue: darc room, Nicholls and Clarke Building, Shoreditch, London E1 www.theilp.org.uk/brilliant 23-25 September Light Middle East (including Ready Steady Light ME with the SLL and Light Middle East Awards) Venue: Dubai International Convention and Exhibition Centre www.lightme.net 26 September Lighting for Health and Wellbeing Venue: Cavendish Conference Centre, W1 http://lightingforhealthandwellbeing.com 3 October CIBSE training: Lighting – Legislation and Energy Efficiency Venue: CIBSE, Balham, SW12 email@example.com 4 October CIBSE training: Lighting Design Principles and Application Venue: CIBSE, Balham, SW12 firstname.lastname@example.org 5 October CIBSE training: Emergency Lighting to Comply with Fire Safety Requirements Venue: CIBSE, Balham, SW12 email@example.com 9 October Lightscene (organised by the ILP) Venue: Rotherham United Football Club firstname.lastname@example.org 11 October SLL and CIBSE South West Region Lighting for Emergency Situations (LG12) Venue: Exeter College, Exeter email@example.com
25-27 October: PLDC, Marina Bay Sands, Singapore
25-27 October Professional Lighting Design Conference Venue: Marina Bay Sands, Singapore https://pld-c.com 6-9 November Interlight Moscow Venue: IEC Expo Centre, Moscow https://interlight-moscow. ru.messefrankfurt.com/
Lighting Knowledge Series: LightBytes The Lighting Knowledge Series is kindly sponsored by Fagerhult, Thorlux Lighting, Xicato and Zumtobel. For venues and booking details: www.sll.org.uk
7 November Fundamental Lighting Course Venue: ILP, Regent House, Rugby firstname.lastname@example.org 14-15 November LuxLive (including SLL Young Lighter of the Year) Venue: ExCeL London http://luxlive.co.uk 15 November Lux Awards 2018 Venue: Intercontinental London – The O2 http://luxawards.co.uk/ 29 November SLL Lighting Knowledge Series: LightBytes Venue: MAC, Belfast email@example.com
17 October How to be Brilliant Speaker: Lauren Lever, Light IQ Venue: Body and Soul, London EC1 www.theilp.org.uk/brilliant
24 January SLL Lighting Knowledge Series: LightBytes Venue: The Bluecoat, Liverpool firstname.lastname@example.org
18 October SLL Lighting Knowledge Series: LightBytes Venue: MAC, Birmingham email@example.com
28 February SLL Lighting Knowledge Series: LightBytes Venue: The Hospitium, York firstname.lastname@example.org
LET Diploma: advanced qualification by distance learning. Details from www.lightingeducationtrust.org or email LET@cibse.org CIBSE Training: various courses across the whole spectrum of lighting and at sites across the UK. Full details at www.cibse. org/training-events/cibse-cpd-training LIA courses: details from Sarah Lavell, 01952 290905, or email email@example.com For up-to-date information follow us on Twitter @sll100