SLL May/June 18

Newsletter Volume 11. Issue 3. May/June 2018

The Society of Light and Lighting

Part of the Chartered Institution of Building Services Engineers

SHADES OF HISTORY

Munsell: the man who defined colour

CLOCK WATCHING

Mariana Figueiro on the non-visual effects of light @sll100

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Editorial

Secretary Brendan Keely FSLL bkeely@cibse.org SLL Coordinator Juliet Rennie Tel: 020 8675 5211 jrennie@cibse.org Editor Jill Entwistle jillentwistle@yahoo.com 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 4 2018 is 21 May 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

Produced by Unit C, Northfield Point, Cunliffe Drive, Kettering, Northants NN16 9QJ Tel:01536 527297

Printed in UK

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In June, it is the centenary of the death of Albert Munsell, developer of the famous and eponymous colour definition system.

While Munsell seems to have nailed it in terms of some sort of permanent legacy – the system is still in use today, albeit with some modifications – he devised it as a culmination of thinking that dated back centuries. In other words, he was standing on the shoulders of giants, as Sir Isaac Newton would have it, aptly enough in this context as he was, of course, instrumental in developing colour/light theory in the 17th century. As Peter Phillipson points out in his article on Munsell (see p10), Newton’s ordering of the colours of the spectrum has been,

and will continue to be, the cornerstone of electromagnetic theory.

Breakthroughs rarely, if ever, spring out of nowhere. That process is effected both vertically, through history, and laterally, through collaboration.

It is why events such as the LR&T Symposium and the International Day of Light, both on 16 May, are such valuable exercises as they bring together researchers and scientists from different fields to share ideas, and disseminate the latest research and visions for the future.

In his outline of the aims of the IDL (see p13), John Dudley explains that the choice of date is because 16 May 1960 is when laser operation was first observed.

‘The laser is especially appropriate for a recognition of this kind because it is a prime example of how a discovery and invention in science and technology can yield revolutionary benefits,’ he says.

Significantly, the research underpinning the laser began in studies that had no targeted applications in mind. ‘And yet without this very basic research, we would have no lasers, no internet communications, no LEDs, no laser surgery, and our society would look very different indeed.’ It’s amazing what one thing can lead to.

Jill Entwistle jillentwistle@yahoo.com

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 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) LATEST SLL Lighting Guide 0: Introduction to Light and Lighting (2017) 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) Commissioning Code L (2018)

Secretary’s column

‘Each symposium speaker will focus on the future of his or her specialist research field’

Editorial 2 Secretary’s column

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News 4 Kit of many colours RGB reaches saturation point at this year’s hotly contested Ready Steady Light event

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Lighting research around the clock 7 Previewing her presentation for the LR&T Symposium, Mariana Figueiro outlines the latest findings on the non-visual effects of light Colourful character 10 Marking the centenary of Albert Munsell in June, Peter Phillipson considers his famous colour definition system and its origins The dawn of a new day 13 John Dudley explains the aims of the International Day of Light which takes place this month Body of evidence 15 Dummies can play a helpful role in field research, discovers Iain Carlile in his digest of the latest online LR&T papers Events 16 Cover: No future is possible without a past by Olafur Eliasson at the Bloomberg European HQ in London. The lighting scheme for Bloomberg by Tillotson Design Associates is shortlisted in the Lighting Design Awards 2018

James Newton

Ready Steady Light back in March was a great success. All of the teams created brilliant installations with their allotted luminaires and sites, working as usual against the clock (see p5).

Well done to the students of Rose Bruford College, who won both the Technical and Artistic Awards (the latter supported by the IALD and presented by its past president Kevin Theobald), and DPA for winning the Peer Prize. We have a brilliant video of the event, hosted on the CIBSE YouTube channel, so please take a look. Many thanks to Rose Bruford College for collaborating with us again, and the supporters: Erco, Lee Filters, Philips, SGM and White Light.

This year’s Light+Building at Messe Frankfurt was again an amazing event.

We managed to meet with many of the society’s Sustaining Members during the few days that we were there, encouraging them to maximise the benefits of the programme and, of course, thanking them for their ongoing support. The latest members to the programme are Soraa and XAL, who we are pleased to welcome to the society. If anyone would like to know more about becoming a Sustaining Member please do let me know.

This year’s Lighting Knowledge Series: LightBytes continues with only two more

events to go in this season’s calendar: 10 May in Glasgow at Fifteen Ninety Nine, and 7 June in London at the Barbican. The speakers from Fagerhult, Trilux, Xicato and Zumtobel have delivered excellent presentations under the headings of Design, Specify, Build and Future. The feedback from the series has been excellent, so if you are in the area and available please do book in for a fun and educational day.

We look forward to 16 May when we will celebrate the 50th Volume of Lighting Research and Technology with a special symposium. With a line-up including Mark Rea and Mariana Figueiro from Rensselaer Polytechnic Institute, Peter Boyce, Arnold Wilkins from University of Essex, and many more, it promises to be a brilliant day as each speaker focuses on the future of his or her specialist lighting research field. We encourage all to attend what will be a one-of-a-kind event at UCL. Bookings can be made through the website.

On the evening of 16 May we will be celebrating the Inaugural International Day of Light (see p13), again at UCL. This is a free-to-attend event and we hope to see many of you there. Again, bookings for the evening event can be made via the website.

We also look forward to the 2018 Annual General Meeting on 24 May at the Haberdasher’s Hall where new SLL president Iain Carlile will deliver his presidential address. We’ll also, of course, be saying a big thank you to Richard Caple for his amazing year as president. As well as the AGM we will be celebrating the best of the society with the Regional Award, Lighting Award and Honorary Fellowships. We’d love you to join us for the evening so please go to the website to make a booking.

Just a note on SLL past president Stephen Lisk: Stephen will become president of CIBSE on 8 May at The Royal Society. We wish Stephen well in his year and look forward to working with him.

Finally, we are coming towards the end of the lapsing period for those who have not renewed their subscriptions.

We encourage everyone to renew and enjoy the benefits of membership, as well as upgrade their membership. If there is anything that Juliet or I can do please do get in touch with us.

Contents

Brendan Keely bkeely@cibse.org For up-to-date information follow us on Twitter @sll100

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NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...NEWS...

Group launches joint study on dynamic work lighting A group of leading lighting companies, including three SLL sponsors, are teaming up with Aalborg University in Copenhagen for a new study looking at dynamic lighting in the work environment.

The move has been described by the group, which involves Fagerhult, iGuzzini, Tridonic and Zumtobel, as a ‘unique cooperation’.

The study will explore how the interplay of dynamic daylight and dynamic electrical lighting can support individual needs and different work situations.

‘This important joint project has set the goal of developing a new paradigm for how the user can improve the work environment through dynamic lighting,’ according to a joint statement.

Named Double Dynamic Lighting, the study will be carried out by PhD fellow

On the lighter side...

Those of us in the lighting business probably don’t need much of a prompt when it comes to awareness of the cost of energy. However, a lamp on show at the recent Milan Design Week pushes the message home rather literally. Designed by the Colombian MOAK studio, dina actually requires money to operate.

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Sofie Linnebjerg under the direction of Prof Dr Ellen Kathrine Hansen of Aalborg University (pictured left). It will investigate the spatial properties of a dynamic lighting environment and the influence on the wellbeing of users.

It will involve a series of studies conducted in existing dynamic lighting work environments, in Light Lab facilities at the university and in fully interactive, three-dimensional computerised models.

‘The aim of the study is to create a holistic approach to lighting,’ says Dr Hansen, programme director for lighting design in the Department of Architecture, Design and Media Technology. ‘The combination of biological, aesthetic and functional aspects should define the foundation for the design process.

‘At the end of the study, the new research findings will be used in architecture through the lighting designers’ specifications so as to help people in everyday life.’

The insertion of a coin activates the electrical circuit and the lamp lights up. Pulling the wooden sphere switches the lamp off and saves the coin. Cheapskates have also been factored in. To underline the concept of the value of light, it only works with large and mediumsize coins, usually the highest denomination in most currencies.

Thorn celebrates 90th anniversary Thorn Lighting, a long-time sponsor of the SLL, celebrated its 90th anniversary in March. Now part of the Zumtobel Group, what was then the Electric Lamp Service Company was founded by Austrian Jules Thorn (below) in 1928.

His aim was to make ‘great lighting easy’.

The new company quickly went from servicing lamps to manufacturing them, later diversifying into luminaires, domestic appliances, TVs and radios.

In 1936, under the new name Thorn Electrical Industries, the company floated on the London Stock Exchange.

By 1959 it had become the 10th largest company in the UK, and its new purposebuilt head office at Thorn House (today’s Orion House) was one of the tallest buildings on the London skyline.

In the 1980s the company acquired a number of lighting manufacturers in Europe and Australia. By the time a management buy-out separated the lighting business from the rest of the group in 1994, Thorn was a major global player in the lighting industry.

‘Everybody thought Jules was mad when he decided to build a 30-million-ayear capacity lamp factory,’ recalls Lou Bedocs, lighting applications advisor at Thorn, and one of the company’s longest-serving employees.

‘But he went ahead and built more than 70 factories around the world not just for lamps but also for luminaires, control gear and lighting accessories. Now 90 years later we can look back on a true pioneer who left his mark on the world of industry.’

Kit of many colours

The 2018 Ready Steady Light proved a hotly fought contest with a polychromatic theme

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Photography by RAID Photographic

Events

Previous page: the Peer Prize winner by the dpa lighting team. Clockwise from top left: the scheme by the Rose Bruford team which won both the Technical and Artistic Awards; UCL Team A’s installation; the doubly highly commended scheme from Arup; Kevin Theobald (left) with Rose Bruford; Nick Hunt of Rose Bruford (left) with the dpa lighting team

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The team from Rose Bruford College shone at this year’s Ready Steady Light, scooping both the Technical and Artistic Prizes, though the awards were hotly contested with Team Arup getting highly commended for both categories. The Peer Prize went to dpa lighting consultants.

Numbers were a little depleted this year because of Light + Building the following week, which meant that some practices were unable to free up designers for the event. However, there were still nine strong teams, including three teams from UCL. ‘The quality of the installations was still very high and it was good to see students from UCL and host Rose Bruford taking part alongside the professional teams,’ said Kevin Theobald, representing the IALD which sponsors the Artistic Prize.

‘Over the years the influence of LED luminaires has progressed and this year there were only a very small number of “old technology” sources used,’ he continued. ‘As the LED fixtures are mostly capable of colour change it is unsurprising that a lot of saturated colour was used. A limited amount of control was available and was put to good use in dynamic lighting and for balancing light levels.’

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Danish entertainment and architectural lighting company SGM was a new supporter for this year’s competition (joining Erco, Lee Filters, Philips and White Light) adding colour-change LED kit to the selection that the teams had to choose from.

The winning installation by the team from Rose Bruford was nevertheless mainly monotone, albeit that the tone was blue, though the Peer Prize winners from dpa lighting exploited the use of dynamic lighting scenes.

Judges for the Technical Award were SLL president Richard Caple, president-elect Iain Carlile, vice president Ruth Kelly Waskett and past president John Aston. The judges for the Artistic Award were Kevin Theobald, Chris Sutherland, design director at StudioFractal, and lighting designer Andrew Ellis.

The awards were presented by Rose Bruford’s Nick Hunt (Peer Prize) SLL president Richard Caple (Technical Prize) and Kevin Theobald (IALD Artistic Prize).

Junior Ready Steady Light took place the day before, with six teams competing, all from the Bexley area. Taking the first prize was a team from Trinity School, who went on to light the roof of the National Theatre for a week from 28 April 2018.

LR&T Symposium

Lighting research around the clock In recent years, research has shown that light can have a profound effect on human health and wellbeing, far beyond the visual aspects that are familiar to most lighting designers and specifiers. Light incident on the retina sets the timing of our biological clocks and entrains us to the local time on Earth. In addition to stimulating the visual system, light stimulates various biological functions, most notably the human circadian rhythms that control everything from sleepwake patterns to hormone production. These are referred to as the non-visual effects of light.

My colleagues and I recently conducted a review of the research to date that explores these non-visual effects,1 including the lighting characteristics that affect the circadian system, the devices and techniques available for measuring light’s non-visual effects, and also recent applied and field research on various populations who could benefit from a tailored lighting scheme.

The circadian system: lighting characteristics, resulting outputs, and their measurement Nearly all creatures are exposed to a 24-hour light-dark cycle to which they have adapted by developing circadian rhythms.

These rhythms are regulated by the body’s biological clock, located in the suprachiasmatic nuclei (SCN) of the brain’s hypothalamus region. In the absence of any external cues, the biological clock runs on a period slightly longer than 24 hours,

but daily exposure to light-dark patterns entrains the biological clock’s timing to match that of the local 24-hour clock. Light is known to affect the biological clock’s outputs, such as hormone production (for example, melatonin and cortisol), core body temperature, and measures of performance and alertness.

When a person’s activity-rest patterns become asynchronous with the local time, such as when travelling across multiple time zones or working the night shift, circadian disruption can occur. Disruptions can lead to poor sleep and performance in the short term, and potentially more serious diseases such as diabetes and cancer in the long term.

The lighting characteristics that affect the circadian system, as measured by acute suppression of the hormone melatonin and shifts in the timing (or phase) of its production, are different from those that affect visibility. (Melatonin is a hormone we produce at night and in darkness that tells our body that it is night and time for sleep.) Even low levels of light can affect the body’s melatonin production, but those levels are still higher than the light levels that are required to affect vision.2, 3 Humans are ‘blue sky detectors’ because the peak sensitivity for acutely suppressing and shifting the phase of human melatonin production is close to 460 nanometers (nm).3-5 The timing of light exposure affects the circadian system differently at different times of the day. Morning light, experienced after the trough of core body temperature (one of our circadian rhythms) that typically occurs in the second

An LRC study in five office buildings showed workers who received high circadian stimulus through the entire workday experienced better sleep quality (left and centre) and reduced depression scores compared to colleagues who received low levels of CS in the morning

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Based on her presentation at the LR&T symposium, Mariana Figueiro outlines the latest findings on the non-visual effects of light

LR&T Symposium

Author Mariana Figueiro with the specially designed LED light table that delivered very high circadian stimulus to older adults with Alzheimer’s disease and related dementias residing in a nursing home

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half of the night, will advance the timing of sleep in the following cycle. On the other hand, evening light experienced prior to the trough of core body temperature will delay the timing of sleep.6 Closely connected with the timing of exposure is one’s cumulative history of light exposures over the 24-hour day.

Research has shown that measuring this history is far more informative than simply taking a ‘snapshot’ measurement of light exposure at one certain place and time.7, 8 As the circadian system appears to closely monitor light exposure, knowing the unique patterns of light and dark experienced over the past 24 hours can help determine the best lighting prescription for the next 24 hours.9 Therefore, while the spectrum and timing of light exposures are very important factors, lighting that aims to promote circadian synchronisation (or entrainment) should also keep track of time and control the total circadian light exposure during waking hours.

Through the course of research, scientists have also agreed that commercially available light meters using V(λ) are inappropriate for specifying and measuring circadianeffective light because the circadian system is maximally sensitive to short-wavelength light, whereas V(λ) peaks in the mid-wavelength range. The Daysimeter was first developed at the Lighting Research Center to fill a known gap in the ability to accurately obtain human circadian light exposure data.10 The original Daysimeter was designed to be worn at eye level to continuously measure light reaching the retina, but newer iterations can be worn at various locations on the body, such as a lapel pin or pendant (see image opposite), to maximise the comfort of experimental subjects.

The Daysimeter is used in conjunction with a quantitative method called phasor analysis, which examines the relationship between the 24-hour (circadian) light-dark exposure pattern, the stimulus and the activity-rest pattern.7 Phasor analysis provides a method for quantifying circadian disruption in field and laboratory settings, as well as a bridge between ecological measurements of circadian entrainment in humans and parametric studies of circadian disruption in animal models.11, 12

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Promoting circadian entrainment/alertness with light Most of the published laboratory and field research to date has examined lighting for office workers, older adults with Alzheimer’s disease and related dementias (ADRD), and adolescents. A number of studies have attempted to demonstrate the benefits of lighting that provides higher circadian stimulation (CS) in the built environment during the daytime, with some studies also employing a reduction in circadian stimulation during evening hours.

Researchers generally agree that lighting schemes for daytime workers should be designed to promote circadian entrainment, which in turn should result in better sleep, mood, health, and perhaps performance. Additional research has also examined how light can be used to increase alertness, without regard to its impact on circadian phase. This is particularly relevant for night-shift workers, who need to be alert at work but also should avoid disrupting their melatonin cycle.

A recent Lighting Research Center study in five office buildings showed that office workers who received high amounts of CS in the morning fell asleep faster at night, had better circadian entrainment, and experienced better sleep quality compared to their colleagues who received low levels of CS in the morning. The study also found that workers receiving high CS throughout the entire day reported reduced symptoms of depression.13 While the importance of reducing evening light exposures to maintain a regular sleep-wake cycle is already widely known, this study also demonstrated the benefit of providing good circadian stimulation throughout the entire workday.

Field research focused on older adults with ADRD has shown that a lighting intervention providing high circadian stimulation during the day and low stimulation at night reduced depressive symptoms among those living at home.14 In nursing homes, where light exposures are more easily controlled, the same intervention resulted in improvements to sleep, depression and agitation.15 In another study conducted in a nursing home, we delivered a lighting intervention with

LR&T Symposium

very high circadian stimulation to residents using a specially designed LED light table.16 Residents who sat around the table, as residents conventionally do in nursing home common areas, showed significantly increased sleep duration and reduced agitation and depression scores.

The transition from childhood to adolescence often involves a shift toward later sleep and wake times. Consequently, adolescents can be chronically sleep deprived because they are unable to fall asleep early and face fixed wake-up times on school days, which has been linked to depression, behavioural problems, poor performance at school and car accidents.

This problem can be compounded by adolescents spending most of their day indoors in dimly lit classrooms, which inhibits the synchronisation of their circadian systems with the solar day, and by the use of self-luminous electronic devices in the evening, which can even further delay their circadian phase.

These studies point to the importance of controlling the entirety of 24-hour light-dark patterns to effectively promote circadian entrainment and reduce sleep restriction in adolescents.17 The future of light and health research It is well established that a regular 24-hour light-dark pattern minimises circadian disruption and promotes entrainment, which in turn supports positive health and performance.

To date, most of the work investigating the impact of light on health outcomes and wellbeing has been performed in laboratory settings. The number of field studies has been growing, and it is important that we continue to investigate the robustness of light’s impacts on health and wellbeing outside laboratory conditions.

One major challenge facing lighting for healthy outcomes is that researchers have been tied to thinking about the lighting of a particular space or building, ignoring the fact that the circadian effect of light is cumulative, not instantaneous.

Because people today have luminous displays and active lives

References 1 Nagare R, Plitnick B and Figueiro MG. Effect of exposure duration and light spectra on night-time melatonin suppression in adolescents and adults.

LR&T 2018: In press.

2 Rea MS, Figueiro MG, Bullough JD and Bierman A. A model of phototransduction by the human circadian system. Brain Res Rev. 2005; 50: 213-28.

3 Rea MS, Figueiro MG, Bierman A and Hamner R. Modelling the spectral sensitivity of the human circadian system. LR&T 2012; 44: 386-96.

4 Brainard GC, Hanifin JP, Greeson JM, et al. Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor.

J Neurosci. 2001; 21: 6405-12.

5 Thapan K, Arendt J and Skene DJ. An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans. J Physiol. 2001; 535: 261-7.

6 Khalsa SB, Jewett ME, Cajochen C and Czeisler CA. A phase response curve to single bright light pulses in human subjects. J Physiol. 2003; 549: 945-52.

7 Rea MS, Bierman A, Figueiro MG and Bullough JD. A new approach to understanding the impact of circadian disruption on human health.

J Circadian Rhythms. 2008; 6: 7.

8 Figueiro MG, Hamner R, Bierman A and Rea MS. Comparisons of three practical field devices used to measure personal light exposures and activity levels. LR&T 2013; 45: 421-34.

9 Figueiro M, Nonaka S and Rea M. Daylight exposure has a positive

A system for delivering a custom lighting prescription using a smartphone application. Clockwise from the lower left, the user’s wrist-worn actigraph and lapel-worn Daysimeter transmit activity and light exposure data to the phone, where an algorithm then generates the prescription

that influence their 24-hour pattern of light and dark, they no longer have a single lighting entity that is responsible for total 24-hour light exposure patterns.

Perhaps a new lighting profession needs to emerge, one that provides individualised light exposure coaching, or new software applications can be designed to track light-dark exposure and provide recipes for maintaining circadian entrainment. Future research should continue to look for ways to use lighting to minimise circadian disruption and thereby improve health and wellbeing.

Mariana Figueiro, PhD, FIES, is professor and director of the Lighting Research Center, Rensselaer Polytechnic Institute in Troy, NY. Her paper, entitled Understanding the Non-visual Effects of Light, will be presented at the LR&T Symposium on 16 May at the Darwin Building, UCL

carryover effect on night-time performance and subjective sleepiness. LR&T 2014; 46: 506-19.

10 Bierman A, Klein TR and Rea MS. The Daysimeter: A device for measuring optical radiation as a stimulus for the human circadian system.

Meas Sci Technol. 2005; 16: 2292-9.

11 Radetsky LC, Rea MS, Bierman A and Figueiro MG. Circadian Disruption: Comparing humans with mice. Chronobiol Int. 2013; 30: 1066-71.

12 Figueiro MG, Radetsky L, Plitnick B and Rea MS. Glucose tolerance in mice exposed to light-dark stimulus patterns mirroring dayshift and rotating shift schedules. Sci Rep. 2017; 7: 40661.

13 Figueiro MG, Steverson B, Heerwagen J, et al. The impact of daytime light exposures on sleep and mood in office workers. Sleep Health. 2017; 3: 204-15.

14 Figueiro MG, Hunter CM, Higgins PA, et al. Tailored lighting intervention for persons with dementia and caregivers living at home. Sleep Health. 2015; 1: 322-30.

15 Figueiro MG, Plitnick BA, Lok A et al. Tailored lighting intervention improves measures of sleep, depression, and agitation in persons with Alzheimer’s disease and related dementia living in long-term care facilities.

Clin Interv Aging. 2014; 9: 1527-37.

16 Figueiro M, Plitnick B and Rea M. Research Note: A self-luminous light table for persons with Alzheimer’s disease. LR&T 2016; 48: 253-9.

17 Figueiro MG and Rea MS. Short-wavelength light enhances cortisol awakening response in sleep-restricted adolescents. Int J Endocrinol. 2012; 2012: 301935.

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Events

Colourful character Next month is the centenary of the death of colour notation pioneer Albert Munsell. The SLL will mark the occasion with a special event, and here Peter Phillipson considers the famous system and its origins

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He had been inspired by the work of physicist James Forbes who studied colour wheels in depth. The purpose of his experiments was to measure the proportions of the primary colours on the outside of the colour wheel that constituted

A 3D representation of the 1943 Munsell renotations. Munsell determined colour spacing by taking measurements of human visual responses. In each dimension, Munsell colours are as close to perceptually uniform as he could make them, which makes the resulting shape quite irregular

SharkD/Wikimedia

When Newton was sent home to quiet Woolsthorp in Lincolnshire from Cambridge University, in order to avoid the plague in 1665, he did some experiments with prisms in his darkened bedroom. He covered the windows, allowing a very narrow pinhole of daylight to enter. Placing a prism in its path, he saw vividly the dispersion of the midday sun as it refracted through the glass.

It is a matter of debate whether he was partially or totally colour blind. But he did ask a friend to draw lines on the wall to delineate between the patches of colour. Initially he wrote down that there were seven colours: red, orange, yellow, green, blue, indigo and violet. Some think that seven colours were chosen as the figure seven was a significant number: seven days of the week, seven deadly sins, and the fact that only seven metals were known at the time and, being interested in alchemy, the number seven was therefore meaningful for him in that respect.

He devised a colour wheel, in which the colours are arranged clockwise in the order they appear in the rainbow. Each spoke also features a letter, as he was also convinced that there might be a correlation to the number of notes in music: do, ray, me, fa, so, la, tee (disproved). Of course there are an infinite set of colours, but it is hard to see more than five, six or seven. Crucially, however, he wrote down the order in which the colours were dispersed and this order has been the cornerstone of electromagnetic theory and always will be.

After the work of polymath and physician Thomas Young (1773-1829), who had suggested that the eye had three types of colour receptors that responded to red, yellow and blue, the Victorian mathematical physicist James Clark Maxwell also studied colour wheels. He used red, green and blue as primary colours as the distinction between the mixing of light and of pigments had been established by him.

Jacob Rus/Wikimedia

Events

Left: Newton’s colour wheel which includes subsequently redundant letters on the spokes for musical notes. Right: the Munsell colour system showing a circle of hues at value 5 chroma 6; the neutral values from 0 to 10; and the chromas of purple-blue (5PB) at value 5

1 Hue (H): the colour such as orange, yellow, green and so on 2 Value (V): the lightness of the colour 3 Chroma (C): the saturation of the colour They can transcend uniformly to show a progression of change, but more often these three numbers can be depicted, in steps, on a Munsell Colour Tree and give an instantly understandable relationship to how each colour can relate to another.

Newton et al had identified a natural order to the colours and Munsell drew them in a circle. He called red, yellow, green, blue and purple the principal hues, and in between these were five intermediate hues: yellow-red, green-yellow, blue-green, purple-blue and red-purple, which he abbreviated accordingly: R, YR, Y, GY, G, BG, B, PB, P and RP. It is possible to mix paints adjacent to each other to form a continuum. Therefore mixing red and yellow in differing proportions can create all the colours between them: red through to yellow red (orange) through to yellow. The same can be achieved with mixing any

‘The real triumph of Munsell’s notation system is that it allowed an engineering approach to defining colour’ adjacent pairs of colours around the circle. Colours with a hue are called chromatic colours.

The value is a measure of the lightness of the colour. The value 0 is pure black and 10 is pure white. The values in between are neutral colours and are shades of grey. If one covers a coloured object with a neutral density film it will attenuate all of the visible wavelengths by the same amount making the colour the same but appearing darker. These films can be used to stop down a camera, for example, or to reduce the amount of daylight passing through windows in a museum without tinting the daylight. So the use of the value for a particular hue creates colours of one hue but of differing lightnesses.

The chroma is a measure of how far a chromatic colour differs from a neutral colour of the same value. So a chroma of 0 would be a neutral colour, then as it increases it becomes more saturated. Initially chroma had a range of 0 to 20 for most colours but there is no upper limit. Some pigments, for example, can have chroma of 30.

Munsell first describes his system in his 1905 publication, A Color Notation, but it is the 1915 Atlas of the Munsell Color System that was the first to show the system in colour.

They are used to define the colours of materials used in construction and paint finishes, and even determine the @sll100

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a test sample colour in the middle. By adding amounts of black to the centre, the difference in the brightness between the outer and inner colours could be reduced. By spinning the disc, a colour match between the outer and inner coloured annuli could be observed providing the proportions of the primaries were correct.

Despite US board game pioneer Milton Bradley’s patent on colour wheels and his invention of a colour system, it was the system of colour definition devised by fellow American Albert H Munsell (1858 – 1918) that became the established way of defining colour. Munsell was an artist and educator and an advocate of teaching an appreciation of colour mixing to young people.

In the Munsell Colour System, each colour is defined by three parameters:

Events

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colour of soils when describing the use of fertiliser in agriculture.

It must be stressed that in order to view a colour chart, other than being out in daylight itself, a D65 artificial daylight source should be used. If other coloured sources with a different spectral emittance are used, then a metamorism will occur whereby the surface reflectance will look different in colour compared to when lit by the D65 source. Additionally, the background to a colour chart is nearly always white or another neutral colour. If the background colour is itself chromatic, then the brain will interpret the colour of the sample differently and therefore moodboards showing sample juxtapositions with their intended backgrounds are essential and should be as large as possible.

The paint charts that are familiar to architects and engineers, and are so common in hardware shops that sell paint, are a direct manifestation of this idea.

All systems of colour definition have their flaws. Even the Munsell system has had the number of hues increased from 10 to 20, and the value of around 20 for most colours has intervals that are not quite linear. But these ideas form the basis of standards such as BS 4800/5252, DIN 6164 and various RAL Standards and Pantone colours.

It might be argued that with the availability of spectrophotometers, the need for the Munsell system has been surpassed, but the large array of data produced by these devices still needs to be represented in some tangible analogue form for it to be useful. The Munsell system provides an intuitive and instantly understandable description of what others might want as a colour and this can always be augmented by the use of more modern techniques.

The real triumph of Munsell’s system is that it allowed an engineering approach to defining colour. Not everyone has the time or inclination to study the academic theories of colour, but Munsell’s almost layman-friendly approach led the way for the standards so that an engineer, for example, who wants to define a paint finish for a product can easily specify it.

There will be an SLL event in early July on colour and colour measurement to mark Munsell’s centenary.

Among the speakers will be Malcolm Longair from the Cambridge Cavendish Laboratory, who will talk about James Clark Maxwell, and feature some of Maxwell’s original artefacts. Peter Phillipson will also have a demonstration of modern colour measurements.

Details will be confirmed on the website (sll.org.uk) Left, from top: in the Munsell system, each colour is defined by three parameters – hue, value and chroma

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Images from Munsell Color (http://munsell.com)

‘The Munsell system provides an intuitive and instantly understandable description of what others might want as a colour and can be augmented by more modern techniques’

International Day of Light

IDL: the dawn of a new day

Three years after the IYL, John Dudley explains the primary aims of the first International Day of Light, taking place this month

The IDL sprang from the International Year of Light held in 2015

‘The purpose of this day will be to continue the mission begun in 2015, to highlight the central role that light plays in the lives of the citizens of the world’ the citizens of the world. And from the perspective of Unesco, the breadth of an International Day of Light will allow many different sectors of society to participate in activities to show how science and technology, art and culture can combine to achieve Unesco’s goals – education, equality and peace.

The 16 May was selected for celebration because it was on @sll100

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The year 2015 was a fantastic period of 12 months for the international community interested in and working with light and lighting. The United Nations International Year of Light was a truly remarkable celebration that saw more than 10,000 events take place in over 140 countries worldwide to raise awareness of how important light is to society.

At the end of 2015 it was difficult to imagine that we would be able to top the success of an international year. But through the leadership of the United Nations Educational, Scientific and Cultural Organisation (Unesco) and the continued support of a broad consortium of science and industry partners, we will now benefit from a permanent recognition of the importance of light in the form of an annual International Day of Light that will be celebrated each year on the 16 May. The purpose of this day will be to continue the mission begun in 2015 in giving us a focal point to engage with society at large in order to highlight the central role that light plays in the lives of

International Day of Light

Children in Mexico (left) and Iran in 2015: education was a strong feature of IYL and engaging the community at large remains a key aim

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this day in 1960 that laser operation was first observed. The laser is especially appropriate for a recognition of this kind because it is a prime example of how a discovery and invention in science and technology can yield revolutionary benefits to society in communications, healthcare and many other fields.

Moreover, at a time where R&D investment is under pressure to focus on short-term objectives, the story of the laser is a salient reminder of the need to support long-term investments.

The research underpinning the laser began in studies that had absolutely no targeted applications in mind. And yet without this very basic research, we would have no lasers, no internet communications, no LEDs, no laser surgery, and our society would look very different indeed. An International Day of Light gives us all the opportunity to make this important point. We all benefit from the applications of science, but history teaches us that the most revolutionary and disruptive technologies have had their origins in the most basic and fundamental areas of science.

This said, an International Day of Light is not just about lasers and science. Light is, of course, ubiquitous and the day dedicated to the subject will include aspects of art, culture and entertainment. In an age of blurring boundaries between fact and fiction, an International Day of Light allows us to speak of wider issues extending to philosophy and enlightenment.

What’s more, as we think about light in general terms, a special Day of Light is also an occasion to reflect on how important it is that both the quality and the presence of artificial sources of light are managed responsibly. While the absence of safe artificial light is a real bottleneck to education and development in many remote regions of the world, ironically the majority of developing countries suffer from the contrasting problem of light pollution that precludes appreciation of the natural beauty of the night sky.

The development of smart lighting sources is important from many other points of view – from improving sleep quality to reducing energy usage. There is a great deal of work to be done in these areas, and we can use an annual celebration such as this to ensure that these issues are regularly brought to the attention of both the public and other appropriate audiences.

Unesco will inaugurate the first International Day of Light at its headquarters in Paris on 16 May 2018. In addition to the many events taking place worldwide on this day, the flagship inauguration in the French capital will bring together Nobel

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laureates, other science and industry leaders, diplomats and decision-makers, and many others to listen to lectures, symposia and round-tables covering areas of basic science, architecture and culture, international collaborations, science policy, and more.

This first Day of Light will see presentations on the full diversity of topics related to light, but as it will be an annual celebration, it will be up to us as a community to work with Unesco to see how we wish this event to evolve in the future.

For example, it may well be that future International Days will have a more specific focus on challenges such as education, development or cultural heritage; there are many possibilities, and we have the opportunity now to work with Unesco and other partners to influence themes appropriate for highlighting.

It is really up to us to ensure that the International Day of Light becomes a major annual celebration. Unesco has given us the chance, but it is up to us to engage and make it work.

Luckily, the lighting community has passion, enthusiasm and commitment, and I have no doubt that our International Day of Light will become a tremendous success.

John Dudley is chair of the International Day of Light 2018 Steering Committee

International Day of Light: facts The International Day of Light is administered from the International Basic Science Programme (IBSP) of Unesco by a steering committee that includes representatives from Unesco as well as bodies such as the American Institute of Physics (AIP), the European Centres for Outreach in Photonics (ECOP), the European Physical Society (EPS), the IALD, the CIE, lightsources.org and The Optical Society (OSA) among many others. It will be held on 16 May every year, the anniversary of the first successful operation of a laser in 1960.

For more details go to www.lightday.org

LR&T essentials

Body of evidence Dummies can be helpful for field studies, discovers Iain Carlile

Four of the most recently published papers in Lighting Research and Technology consider field study measurements, LED lighting and conservation of photographic artworks, and the effects of dynamic and static CCT on human performance.

A paper by Lo and Steemers investigates how the effects of lighting experiments performed in real locations can vary with the presence of dummies (to represent an occupied space).

An experiment was performed in the historical context of King’s College Chapel in Cambridge, where two field surveys of concert lighting were undertaken, one with the chapel empty and one with it occupied. In each situation photometric data was recorded from six different viewing positions under three different electric lighting conditions.

Comparing the two studies, the authors found that the data collected from the occupied space more accurately represented the luminance and light distribution, and therefore provided a more accurate description of the visual scene.

The authors recommend the use of occupied spaces for field studies in order to gain a more complete understanding of the luminous environment. They suggest the use of dummies as a simple and inexpensive construct, giving greater control over the experimental set-up when compared to using real people.

Luo et al’s paper considers light damage to museum displays, specifically comparing the use of LEDs and halogen sources for the illumination of contemporary photographic artworks. While LED sources have become more popular for lighting artworks, the authors note that there is no advanced evaluation of colour fading or a colour-change test for

contemporary works. An accelerated ageing test was used to assess the effects of the light sources on C-Print, Cibachrome and inkjet prints. The authors present a colour fading model for assessing museum LED lighting to predict the colour difference in contemporary photographic materials for both short-term and long-term exhibitions. They also provide a revised light dosage classification for modern photographic materials.

Ye et al present a study into the use of dynamic CCT changes on human performance. Their study investigated different cycle times and ranges of CCT with respect to human alertness and task performance. During a 4.5 hour session each of the 10 participants was exposed to six conditions of dynamic light. Measurements of brain activity (using an electroencephalogram), critical flicker frequency, cognitive task performance and alertness/sleepiness questionnaires were used to assess the human responses to the varying lighting states during the sessions.

From the results the authors found that under a higher CCT range (6000K- 12,000K) the participants appeared to be more alert and performed better, although this led to more eye fatigue. There was little effect from different CCT cycle times.

Nagare, Plitnick and Figueiro undertook a study to investigate how light exposure duration affects melatonin suppression and whether adolescents (aged 13-18) are more susceptible to short-wavelength blue light than adults (aged 32-51). A total of 12 adolescents and 12 adults participated in the study. Each participant was exposed to three lighting conditions: a <5 lux control, warm 2700K, and cool 5600K, delivering a circadian stimulus of 0.25 at eye level. The authors’ analysis of the results indicates that a longer duration exposure suppressed melatonin to a greater degree.

In addition the authors found that there was a significant interaction between spectrum and the participant’s age – for adolescents (but not the adults) melatonin suppression was greater after exposure to the 5600K light source (43 per cent) than the 2700K light source (29 per cent), suggesting an increased sensitivity to short-wavelength radiation.

Iain Carlile, MSLL, is an associate of DPA Lighting

Lighting Research and Technology: OnlineFirst In advance of being published in the print version of Lighting Research and Technology (LR&T), all papers accepted for publishing are available online.

SLL members can gain access to these papers via the SLL website (www.sll.org.uk) Measuring light in field experiments using dummies and objects: A study of concert lighting VWL Lo and KA Steemers Museum lighting with LEDs: Evaluation of lighting damage to contemporary photographic materials H-W Luo, C-J Chou, H-s Chen and MR Luo The effect of dynamic correlated colour temperature changes on alertness and performance M Ye, SQ Zheng, ML Wang and M Ronnier Luo

Experimental set-up in King’s College Chapel, where two field surveys of concert lighting were undertaken (Lo and Steemers)

Effect of exposure duration and light spectra on nighttime melatonin suppression in adolescents and adults R Nagare, B Plitnick and MQ Figueiro

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EVENTS...EVENTS...EVENTS...EVENTS...EVENTS...EVENTS...EVENTS...EVENTS...EVENTS...EVENTS...EVENTS

2018 3 May Lighting Design Awards 2018 Venue: London Hilton, Park Lane http://awards.lighting.co.uk 8-10 May Lightfair Exhibition and Conference Venue: McCormick Place, Chicago www.lightfair.com 9 May IALD International Lighting Design Awards Venue: Revel Fulton Market, Chicago www.iald.org 10 May SLL Lighting Knowledge Series: LightBytes Venue: Fifteen Ninety Nine, Glasgow sll@cibse.org 10 May WELL Building Standard (organised by SLL and CIBSE Scotland) Speaker: Helen Loomes Venue: Teacher Building, Glasgow sll@cibse.org 10 May LG15: Transport Buildings – the key considerations Speakers: Keith Miller and Carolina Florian, GIA Equation Venue: Arup, Manchester sll@cibse.org 16 May LR&T Symposium (and International Day of Light celebration evening) Venue: Darwin Building (symposium) and South Cloisters (IDL), UCL, London www.sll.org.uk/www.lightday.org 17 May CIBSE training: Lighting Design Principles and Application Venue: CIBSE, Balham, SW12 training@cibse.org 23 May How to be Brilliant (ILP) Speaker: Lisa Hammond, director, Gravity Design Associates Venue: Body and Soul, London EC1 jess@theilp.org.uk 24 May SLL AGM, Awards and Presidential Address Venue: Haberdasher’s Hall, EC1 sll@cibse.org 7 June SLL Lighting Knowledge Series: LightBytes Venue: Barbican Centre, London EC2 sll@cibse.org

16 May: LR&T Symposium and IDL celebration evening, Darwin Building, UCL

17-22 June 16th International Symposium on the Science and Technology of Lighting Venue: University of Sheffield www.is16.org

Lighting Knowledge Series: LightBytes The Lighting Knowledge Series is kindly sponsored by Fagerhult, Trilux, Xicato and Zumtobel. For venues and booking details: www.sll.org.uk

21 June CIBSE training: Lighting – Legislation and Energy Efficiency Venue: CIBSE, Balham, SW12 training@cibse.org 27-28 June Smart City Event Venue: Zuiderstrandtheater The Hague, Netherlands www.smart-circle.org/smartcity/ 4 July CIBSE training: Emergency Lighting to Comply with Fire Safety Requirements Venue: CIBSE, Balham, SW12 training@cibse.org 13-14 September Symposium on Promotion and Protection of the Night Sky Location: Capraia Island, Italy http://capraianightsky2018.com 4 October CIBSE training: Lighting Design Principles and Application Venue: CIBSE, Balham, SW12 training@cibse.org 25-27 October Professional Lighting Design Conference Venue: Marina Bay Sands, Singapore https://pld-c.com 14-15 November LuxLive Venue: ExCel London http://luxlive.co.uk

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 training@thelia.org.uk For up-to-date information follow us on Twitter @sll100