The Society of Light and Lighting
LIGHT LINES
VOLUME 13 ISSUE 4 JULY/AUGUST 2020
BUILD BACK BETTER Rethinking the future
PLANE TRUTHS Rethinking the metrics
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July/August 2020
Editorial
FROM THE EDITOR SECRETARY Brendan Keely FSLL bkeely@cibse.org SLL COORDINATOR Juliet Rennie Tel: 020 8772 3685 jrennie@cibse.org EDITOR Jill Entwistle jillentwistle@yahoo.com COMMUNICATIONS COMMITTEE: Linda Salamoun MSLL (chair) Iain Carlile FSLL Jill Entwistle Chris Fordham MSLL Rebecca Hodge Eliot Horsman MSLL Stewart Langdown FSLL Bruce Weil Gethyn Williams 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 LL5 2020 IS 17 JULY PUBLISHED BY The Society of Light and Lighting 222 Balham High Road London SW12 9BS www.sll.org.uk ISSN 2632-2838 © 2020 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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Positive outcomes do emerge from catastrophe. Clouds and silver linings. Throughout lockdown it has been hard not to relish the respite from pollution and petrol fumes, the sound of birdsong, the sense, as someone put it, of the Earth starting to breathe again. Of course that's easy to say if you're not holed up in some crowded urban tenement with little prospect of earning any money. Most countries will emerge with economies seriously damaged if not in tatters. Will our rush to recoup lost capital trample over already inadequate efforts to stop climate change? Or do we have sufficient vision and motivation to see that economic renewal can sit easily with a less rapacious approach to the planet and its people? Why does one preclude the other? Why can't one drive the other? They were the questions effectively posed by new SLL president Bob Bohannon in his address in May. This was an opportunity for reevalution.
'The Covid-19 lockdown has, temporarily, cut CO2 emissions, but it has also triggered a huge economic contraction,' he said. 'Some governments are calling to harness their economic recovery to plans to boost low carbon design and technology. They call this Build Back Better.' This universal message should also be an aspiration for the society, he said. Overall the SLL needed to promote the value of light. 'The more the wider public realises what light does, the more our clients are likely to engage with us and move away from the lowest common denominator, price-driven discussion.'
JILL ENTWISTLE JILLENTWISTLE @YAHOO.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: Lighting for Healthcare Premises (2019) 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) SLL Lighting Guide 17: Lighting for Retail Premises (2018) SLL Lighting Guide 18: Lighting for Licensed Premises (2018) SLL Lighting Guide 19: Lighting for Extreme Conditions (2019) Guide to Limiting Obtrusive Light (2012) Code for Lighting (2012) Commissioning Code L (2018) SLL Lighting Handbook (2018) sll.org.uk
July/August 2020
Secretary’s column/Contents
Contents
FROM THE SECRETARY At the time of writing the UK is still in lockdown and with no face-to-face meetings we are trying to get as much online content to you as we can. SLL coordinator Juliet Rennie has created an online learning and content diary identifying all webinars and presentations that we know of. If you think we’ve missed something or you have something coming up that you would like adding to the list, please do get in touch with us. In addition, if there is a topic or some subject area you would like the SLL and its members to consider covering please again let us know. We can’t promise anything but we will do all that we can. The 2019/2020 LightBytes Light and Wellness season moved online in May and June via webinar. We thank the Sponsors in Partnership and the speakers who enabled the series to take place face-to-face in Birmingham, Dublin, Manchester and Leeds, and eventually online: Soraa, Thorlux (Richard Caple), Xicato (Roger Sexton) and Zumtobel (Graeme Shaw). Also a big thank you goes to Dr Eleonora Brembilla for joining the series with her focus on daylight. Many of the planned events in the regions that were cancelled, including LightBytes Online, can be found online (see box above right). These events include Sophie Parry with the West Midlands Region discussing Well v2: requirements for electric lighting; Nic Bukorovic alongside the contributors presenting the new LG2: Lighting for Healthcare Premises; the Alternative Route to CEng with Katerina Konsta and Kristina Allison, and Henrik Clausen and the South West Region presenting Light, Health and Wellbeing in the Workplace. We were due to have the SLL 2020 AGM and Awards at the Ortus Centre in Camberwell, London, on 21 May and, as we mentioned in the last edition of Light Lines, that
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Diary: www.cibse.org/society-oflight-and-lighting-sll/sll-events/ upcoming-webinars-and-onlinecontent Cancelled events now online: www.cibse.org/society-of-lightand-lighting-sll/sll-events/pastpresentations
obviously could not take place. Instead, we had an online event with outgoing president Jim Shove reviewing his year and handing over the presidency to Bob Bohannon. President elect Ruth Kelly Waskett chaired the event and we thank her, and Jim for his year as president, and welcome the new SLL president Bob Bohannon (see p5 for a summary of his address). The online event can be viewed using the same past events website (see above). We are hopeful that the events with our partner Clarion can still take place later this year. The Lighting Design Awards are scheduled for 22 September, and LuxLive, alongside the Lux Awards, is planned to take place on 11-12 November. Fingers crossed, a strong wind, some magic and who knows?
BRENDAN KEELY BKEELY @CIBSE.ORG
'If there is a topic or something you want the SLL and its members to consider covering online, please let us know'
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EDITORIAL
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SECRETARY’S COLUMN
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NEWS
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REBUILDING THE FUTURE
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PLANE RETHINKING
Covid-19 has presented an opportunity to reevaluate, says new SLL president Bob Bohannon – and build back better
Kit Cuttle on the evolution of lighting in the workplace, and how the LiDOS procedure addresses 'fundamentally flawed' current lighting practice
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WELL VERSED
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THROUGH THE AGES
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EVENTS
Keith Miller reviews CIBSE's recently introduced document on health and wellbeing, focusing on the crucial role played by lighting
Iain Carlile finds past and present concerns in the latest online papers from Lighting Research and Technology
COVER: Chapel of Notre Dame du Haut, Ronchamp, France, by Le Corbusier. Photo by Henry Plummer, one of this year's three winners of the Daylight Award (see p4)
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July/August 2020
News
THE LATEST NEWS AND STORIES
COMPANY CLAIMS NEW LIGHTING METRIC
DAYLIGHT AWARD HONOURS THREE LAUREATES Finnish architect Juha Leiviskä, UK neuroscientist Prof Russell Foster and US architect, writer and photographer Henry Plummer (pictured from left to right) are this year's recipients of the Daylight Award. Plummer's was an extraordinary award for lifetime achievement, made only this year and marking the 40th anniversary of the first Daylight Award, given to Danish architect Jørn Utzon. Leiviskä received the award for works of architecture 'that demonstrate a unique ability to make daylight an integral element of his buildings,' said the judges, while Foster, instrumental in the discovery of the third photoreceptor in the eye, was honoured 'for his clinical studies in humans addressing important questions regarding light'. Henry Plummer received his lifetime achievement award for 'recording daylight phenomena in his brilliant photography and writing'. 'Whether elucidating the neural effects of light or invoking the poetic essence of light, the laureates of the 2020 Daylight Award demonstrate to us the power of natural light,' said the jury. The Daylight Award, conferred biennially, was established by the philanthropic foundations Villum Fonden, Velux Fonden and Velux Stiftung, and has two categories, research and architecture. It supports daylight research and daylight in architecture, for the benefit of human health, well-being and the environment, placing specific emphasis on the interrelation between theory and practice. For more details, go to www.thedaylightaward.com
ON THE LIGHTER SIDE... Lighting made out of weird stuff number... something. Actually not as weird as some of the ones we've had, like mushrooms, fish skins and cow's innards, but another example of how lighting plus apparently prosaic object can yield surprising results in the right hands. Montreal-based artist Elisabeth Picard forges together hundreds of zip-ties – more than 300,000 since she began using them in 2011 – to create glowing sculptures. Each tie is dyed with pastels, earth tones, and sometimes UVreactive fluorescent colours. The artist likens the results to 'landscapes, minerals, plants, micro-organisms and sea creatures'.
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US LED company Bridgelux says it has developed a metric to measure the natural quality of artificial light. The Average Spectral Difference measure will enable the objective comparison of naturalness between different light sources, says the company. ‘Standard lighting quality metrics such as the colour rendering index (CRI) and the colour metric TM-30 do not fully address the naturalness question,' said Bridgelux. Unlike these measures, where higher values indicate higher quality light, ‘ASD provides an objective measurement of how closely a light source matches natural light over the visible spectrum, averaging the differences of the spectral peaks and valleys between a light source and a standardised natural light source of the same CCT.' Natural Light
ThriveTM
80 CRI
90 CRI
98 CRI
0%
9%
28%
20%
18%
Ra
100
98
83
91
98
Rf
100
98
84
91
94
100
101
93
97
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Evaluation metric
ASD CRI TM-30
Rg
TWO 'OUTSTANDING' CANDIDATES WIN JSSF SCHOLARSHIP FUNDING Stella Destephanis Murray, studying for an MSc in architecture and architectural engineering at Penn State University, and Krina Christopolou, in her final year of postgraduate RIBA II studies at the Bartlett School of Architecture, UCL, are the recipients of the Jonathan Speirs Scholarship Fund 2019/2020. Sydney Nguyen, studying at California Polytechnic State University, and Meryem Ozmen, on an interior architecture degree programme at Northumbria University, were both commended. 'Both the winners made outstanding submissions which clearly expressed their phenomenal passion and drive to use light as a major part of their ongoing studies, as well as their intended future careers,' said JSSF chair John Roake. 'Competition was delightfully fierce this year, so much so that the board agreed that two further candidates, Sydney Nguyen and Meryem Ozmen, also merited our support by way of a commendation and a bursary.' For more details go to www.jssf.org.uk
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AGM: President's address
REBUILDING THE FUTURE The Covid-19 outbreak has delivered a shattering blow but, said new SLL president Bob Bohannon, it is an opportunity to reevaluate – and build back better
he president’s role in this year of all years, said Bob Bohannon, was to enable 'the amazing talent within the society to deliver on the objectives and challenges facing us all'. Coronavirus, he continued, 'has given many of us a chance to reevaluate what is important. Clear skies or cheap air travel? Quiet streets, clean air and the sound of birdsong, or the freedom to drive?' It was an opportunity to address issues such as climate change from an industry perspective. 'The Covid-19 lockdown has, temporarily,
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cut CO2 emissions, but it has also triggered a huge economic contraction,' said Bohannon. 'Some governments are calling to harness their economic recovery to plans to boost low carbon design and technology. They call this Build Back Better.' Citing how NASA's ICE Sat 2 was using light in the form of LiDAR to measure climate change, specifically the ice loss from the Arctic and Antarctic ice sheets, Bohannon said the evidence was 'terrifying', showing that the Thwaites and Crosson ice shelves have lost 5m and 3m of ice each year
for the past 16 years. 'In total Greenland and Antarctica have lost more than 300 gigatons of ice a year. Just one gigaton will fill 400,000 Olympic-sized swimming pools.' 'We might have the data,' he said, 'but to put it simply we are losing the war against climate change.' He quoted Seth Scott, CEO of climate change consultant ProBorea, who wrote in a Greenbiz article, that 'Sustainability currently consists of 99 per cent cost savings and one per cent environmental savings‌ a focus on energy efficiency has distracted our
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AGM: President's address
industry from the original goal – an impact on the environment.' Over the past five to 10 years much of the lighting industry has embraced 'a laser focus on luminaire efficiency and the return on investment of replacing legacy light sources with LED,' said Bohannon. 'Lower prices improve ROI, and this, and the design and build procurement method, drove down prices.' The benefit, he said, was that the lighting sector of building services has delivered huge reductions in emitted CO2. But there have been costs, he added. 'Importing a lowest-possible-cost, 30,000 hour, 600 x 600 LED panel without any serviceable components, on a container ship from the other side of the world, which burns high sulphur content bunker fuel spewing sulphur dioxide, nitrogen oxide and particulates, is maybe not the most environmentally sound way of delivering light. Even if it does score well in SBEM. 'As the late US ecologist Prof Barry Commoner, wrote, "The first law of ecology is that everything is connected to everything else".' Much of the current industry design and build structure is predicated on short-term saving of capital cost to deliver buildings that perform for about as long as the warranty or retention period lasts, said Bohannon. 'We all have our own horror stories on value engineering, or simply the selling of products so cheap that they are effectively a light fitting in name only. I was told the story of builders finding the product quality of cheap wholesaler LED downlights so poor that they were losing money on having to return to new installations to replace failed luminaires. Their problems were compounded by the difficulty of getting
'The one clear, irrefutable message that keeps coming through is the benefits of daylight' 6
replacements from the same batch. Their solution: use GU10 downlights, where they can easily replace the GU10 LED sources. Progress? I think not.' Most important of all, continued Bohannon, was the end user’s lighting aspirations. 'How does light better enable their organisation, be it a school, office, hospital or shop to meet their objectives? If they don’t know this, or if we haven’t explained it to them, then why should we be surprised that they simply buy the cheapest.' With so many people working from home, we have come to question the daily commute, the need for offices and for driving or flying to meetings, said Bohannon. 'How many of us, working in home studies, on kitchen tables, in bedrooms or garden sheds will now see the obsession with delivering 500 lux, wall-to-wall, so that even the waste bin in the corner is bathed in light, as simply ridiculous. No matter how efficient the luminaire, such a scheme is surely now ludicrous,' he said. Bohannon moved on to the related issue of daylighting. A lot of the society’s time had been spent on 'circadian lighting', he said, yet the one clear, irrefutable message that keeps coming through is the benefits of daylight. He cited Eleanora Brembilla, research associate in Advanced Building Daylight Modelling at Loughborough University and one of this year's LightBytes speakers, who had made a plea that access to daylight needs to rapidly move up the planner's agenda. Interestingly, the London Plan addresses daylight, he said. 'To me it seems ironic that there have been lengthy discussions about human-centric ar tificial lighting and much less about natural daylight.' Overall the SLL needed to promote the value of light, said Bohannon. 'The more the wider public realises what light does, the more our clients are likely to engage with us and move away from the lowest common denominator, price-driven discussion.' Safety, integrity, resilience were all watchwords. 'We need high-quality teaching within our profession and our society to promote competence,' he added. CIBSE and the SLL are now home to 'a remarkable, multicultural pool of young lighting talent from countries across the world', as far af ield as India, Mexico, the Middle East, Hong Kong and Australasia, he said. 'Many of these young designers and
engineers may now be facing harsh financial times again. We need to be relevant to them, to help them, to keep up their energy and their motivation.' It was not a task that he could achieve alone nor could it be done in just a single year, said Bohannon. 'I’m simply not smart enough, creative enough to do it. I don’t have enough time in a year. But you can. The Society of Light and Lighting is one of the world's largest learned lighting societies. We have brilliant academics, daylighters, product designers, lighters, managers, engineers, sales people, students and teachers in our ranks. If I can do one small thing this year, it is to help you, the society, Build Back Better.'
Background Bob Bohannon has 30 years' experience in lighting, designing and delivering lighting schemes including major projects such as London's Royal Albert Hall and St Pancras Station. Now director of lighting consultant LuxRapide, he began in the early 1980s with a BSc Hons in business studies from Bradford University School of Management. He subsequently moved into lighting, gaining an LIF Advanced Certificate in the late 1980s and an MSc in Light and Lighting at UCL in 1993. He became a lighting designer with BDP, moving on to become general manager of Sill Lighting UK for nearly 18 years. Prior to his current company, he helped establish lighting consultant Lux Populi in this country as UK director. A strong believer in both environmental and corporate social responsibility, he is committed to reduce the environmental impact of his activities for the sake of generations to follow.
This year's presidential address was given online on 21 May. It was preceded by a message from outgoing SLL president Jim Shove before he handed over the role to Bob Bohannon. The event was chaired by SLL vice president and president elect Ruth Kelly Waskett. The address can be seen in full at www.sll.org.uk
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July/August 2020
Lighting metrics
PLANE RETHINKING Kit Cuttle examines how lighting in the workplace evolved, and expands on the LiDOS procedure, outlining how it addresses 'fundamentally flawed' current lighting practice t F ig 1: at the time of Harrison and Anderson this would have exemplified a well-lit workplace, with high ceiling, tall windows, clearly defined work plane. The electric lighting is off. The daylight distribution determines the functional layout
t the Annual Convention of the IESNA held in Chicago, 20-23 October 1919, W Harrison and EA Anderson presented their paper, Coefficients of Utilization, in which they stated the formula for what we now know as the lumen method. Harrison and Anderson defined the coefficient of utilisation, which we now refer to as the utilisation factor, as 'the proportion of useful light flux', indicating that only luminous flux that finds its way, either directly or indirectly, on to the horizontal working plane is useful: the rest is useless and wasted. This notion has not passed unchallenged. In presenting the Diamond Jubilee Lecture to the IES of Great Britain in 1969, JM Waldram stated: 'In its latest edition the Code is beginning to break away from the crudities of illumination on the horizontal plane, to foreshadow the methods by which
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we may specify, predict and provide both the brightness on all surfaces in the interior, and modelling effects for its features and contents. A new era of lighting design is beginning, whereby the appearance of ordinary interiors may be designed with some of the care hitherto reserved for buildings of special architectural importance.' So, where are we now? European Standard EN 12464-1 Indoor Work Places is perhaps the most widely referred to indoor lighting standard in the world, and it defines the purpose of lighting as being 'to enable people to perform visual tasks efficiently and accurately', for which the prime criterion is 'a maintained illuminance over the task area on the reference surface' for which “the task area shall be illuminated as uniformly as possible.' While these considerations are, arguably, relevant for lighting indoor workplaces (as indicated by the title) the standard then
proceeds to present a schedule of minimum average maintained illuminance values for all manner of indoor applications, including circulation spaces, restaurants, theatres, cinemas, and even indoor car parks. For many of these applications there is no identifiable visual task and the horizontal working plane lives on as the de facto measurement plane for verifying compliance with the standard. Choose for yourself an indoor space to be in when someone hands you a light meter and asks you to check the illuminance. How would you proceed? You would check that you were not in a shaded position before holding the meter in front of you at about waist height – what are you doing? You are locating the meter on the horizontal working plane. Once you have a reading you know that that is not enough as you need the average horizontal working plane value. Even if you do not go to the extent of gridding the space and accurately determining the value, it is clear that Harrison and Anderson’s century-old concept governs not only how you measure illumination but how you think of illumination quantity. Half a century ago, Waldram saw the shortcomings of the horizontal working plane and predicted its demise, but that has not happened. Why not?
A POTTED HISTORY OF CURRENT LIGHTING PRACTICE
Figure 1 shows an example of good workplace lighting from Harrison and Anderson’s era – high ceiling, tall windows, and daylight well distributed over a clearly defined horizontal working plane. The electric lighting is there to provide back-up illumination whenever the preferred source of illumination is insufficient. While this back-up illumination is uniform, it is the directional characteristic of daylight that sets the layout of this workplace. Nobody wants to face the light or to have their back to it, and this determines the arrangement of furniture and people. We move on to the 1960s, and Figure 2 shows that while the ceiling has come down a bit and the electric lighting is now on whenever the space is occupied, it is the daylight distribution that still determines the office layout. Note that all of the staff are trained keyboard operators and the planners have them neatly organised. Of course, the lighting technology is different, but it is the visual task that has undergone radical change. Not only is the task plane now almost vertical, but the effect of illumination is to reduce the visibility of detail, and for the CRT displays of that era the effect was pronounced.
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Lighting metrics
p F ig 2: the 1960s – lighting distribution is unchanged, but now layout is set to minimise task illuminance
p F ig 3: the 1970s and chaos – everyone has a screen. There is permanent use of electric lighting and daylight is demoted
p F ig 4: the 1990s and the planners take control. Daylight and views outside are virtually eliminated. Maximum flux is directed on to the horizontal plane and other surfaces are ignored – a dismal, oppressive workplace
p F ig 5: the 21st century and the free range office with creative interaction – but what about task illuminance?
However, as far as lighting practice was concerned, that did not matter. Standards continued to specify minimum task illuminance values in full knowledge that this would be interpreted as horizontal working plane illuminance, and so illumination quantity would be maintained with minimal illumination incident on the task plane. Yes, for the past 60 years, recommendations for good office lighting practice have been directed to maintaining ambient illumination while minimising task illuminance. During the 1970s everybody had to have their own PC and Figure 3 captures the shambles that erupted. The ceilings are down again, the lighting is permanently on, and the windows have reduced to view-out slots. Even so, it can be seen that the windows continue to dictate the furniture layout but an overall sense of disorder pervades. This could not pass without attention. In the 1990s the planners took control, and
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the dismal effect of their intervention is shown in Figure 4. Ceiling heights are sufficient only to permit minimal headroom, and while windows have not been eliminated the view of them has been. Office workers are isolated in separate cells composed of sound- and light-absorbing panels where they are supposed to appreciate the visual comfort afforded by the strongly directional overhead lighting. If farm animals were kept in such conditions it would cause outrage. This situation could not persist. Figure 5 shows free-range office workers creatively interacting in their new millennium office. Constraining walls are minimised, and the abundant daylight imposes no layout restrictions. When daylight fades the electric lighting will create an entirely different light distribution and changed appearance of the space. This may be managed to relate to peoples’ circadian cycles. The slightly light-hearted tone of this survey should not detract from the stark
finding that the metrics that we use to measure, specify and predict indoor lighting are out of step with how people respond to the visible effects of lighting on the appearance of their surroundings. Without metrics that relate to human response we have no useful measure of the effectiveness of lighting, and without a measure of the effectiveness of lighting we have no valid measure of the efficiency of lighting. It is as fundamental as that. The basis of general lighting practice is fundamentally flawed.
THE LIDOS PROCEDURE
The Lighting Design Objectives (LiDOs) Procedure is based on two concepts that relate to how people respond to the visible effects of lighting on the appearance of their surroundings, and for this two corresponding illumination metrics are employed. The first of these concepts is perceived brightness of illumination (PBI), which is a scale
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Lighting metrics
of overall visual assessments of 'How brightlylit' or 'How dimly-lit' an indoor space appears. Research has shown that assessments of PBI relate to ambient illuminance, this being the average indirect flux density within the volume of an enclosed space. Mean room surface exitance (MRSE) provides a useful measure of ambient illuminance (lux) and Table 1 shows a tentative proposal for the PBI/MRSE relationship. It may be noted that PBI has an associated metric: perceived adequacy of illumination (PAI), which specifies the minimum ambient illuminance to provide for overall visual assessment of a space appearing to be adequately lit for its purpose. Research is continuing to establish a schedule of MRSE values for PAI in various categories of indoor spaces. The other concept is visual emphasis (VE), which is a scale of visual assessments of how diversity of illumination may impart visual prominence to selected target surfaces, which may comprise either objects within a room or room surfaces. These assessments may be related to the target/ambient illuminance ratio (TAIR) where the target illuminance is the sum of direct illuminance and MRSE. Table 2 shows a tentative proposal for the relationship. These concepts and metrics come together in the LiDOs Procedure, the outline of which is shown in Figure 6. The practitioner starts any lighting project by listing lighting design objectives to be achieved in each space. These may range from specifying an ambient illuminance to be provided to a detailed description of how lighting is to influence the appearance of a complex space and its contents. Examples of such complex spaces might range from an art gallery to an airport terminal or a manufacturing facility. Perceived brightness of illumination (PBI)
MRSE (lux)
PBI-7
Very brightly lit
800
PBI-6
Brightly lit
430
PBI-5
Slightly brightly lit
230
PBI-4
Neither brightly lit nor dimly lit
120
PBI-3
Slightly dimly lit
65
PBI-2
Dimly lit
35
PBI-1
Very dimly lit
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Lighting Design Objectives (LiDOs)
Illumination Efficiency
Illumination Hierarchy
Ambient Illumination
Perceived Adequacy of Illumination (PAI)
Perceived Brightness of Illumination (PBI)
Target Illumination
Flux Utilization
p F igure 6
Visual Emphasis
Direct Flux Distribution (DFD)
q T able 2
MRSE
TAIR
direct flux (lm) to be delivered on to each target surface. This specification comes with a promise: deliver these direct flux quantities on to the corresponding surfaces and the specified lighting design objectives relating to both illumination quantity and distribution will be achieved.
APPLYING THE LIDOS SPREADSHEET
Visual emphasis (VE)
TAIR
VE-5
Emphatic
40
VE-4
Strong
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VE-3
Distinct
3
VE-2
Noticeable
1.5
VE-1
None
<1.5
The LiDOS may be as simple or as complex as circumstances demand, and always should include either the PAI or the PBI criterion specified by MRSE. Then for each space there comes a question. Are there any features that would benefit from being given visual emphasis? Examples of such features might range from architectural elements to artworks, merchandise, visual tasks, direction indicators or safety hazards. If the answer is no, then the illumination efficiency track is followed with the aim of satisfying the PAI criterion with optimal efficiency. This involves maximising flux utilance by directing direct flux from the luminaires on to relatively high reflectance room surfaces. If the answer is yes, then the illumination hierarchy track is followed with the aim of first satisfying the PBI criterion, and then creating an ordered distribution of visual emphasis for the space and its contents. This involves specifying a TAIR distribution for directing direct flux from the luminaires on to selected target surfaces. For either track, the outcome is a direct flux distribution (DFD) that specifies the
Application of the LiDOs Procedure is facilitated by use of the LiDOPs spreadsheet (instructions for downloading are given at the end of the article). The hotel reception foyer shown in Figure 7 is an example of a space for which the question, 'Are there any features that would benefit from being given visual emphasis?' would receive a 'Yes' response, and so the illumination hierarchy track (see Figure 6) is to be given priority. As shown in Figure 8, guests enter through the glazed doors in wall three so that Figure 7 shows their first view, although for some added interest a mural has been added to wall two and a water feature positioned near the centre of the space for this worked example. Suppose yourself to be developing a lighting proposal for this space. Chart 1 shows the spreadsheet for which you have filled in the principal room with its areas and reflectance values. Only the shaded cells are to be filled in and as you are doing this the spreadsheet automatically completes the surface absorption column: the total surface absorption is shown in the box below to be 232.6 sqm. This is the measure of the roomâ&#x20AC;&#x2122;s capacity to absorb light (actually, the area of a perfect absorber having the same capacity). That is the tedious part of the procedure completed and now you give consideration to the LiDOs. How brightly lit, or dimly lit, is this space to appear? You may want this to vary according to the time of day, but for now you give attention to the daytime appearance. You opt for a slightly bright appearance and, referring to Table 1, you select an MRSE level of 230 lux. That value is inserted into the cell
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Wall 1
Lifts
Wall 4
Wall 2
LOUNGE
Water feature Reception counter Mural
p F ig 7: the hotel reception used as a model for the LiDOS Procedure and schematic of the same space (Fig 8)
near the top of the spreadsheet and instantly a required total first reflected flux (FRF) value of 53,507lm appears in the lower box. This is the quantity of reflected direct flux that is required to generate the 230 lux of ambient illumination in this space. Next you give attention to the target surfaces and Chart 2 shows how the TAIR column is filled in to indicate a chosen distribution of visual emphasis. Start by ignoring the ceiling and attending to the walls. These are to have an attractive woodgrain finish, and you decide on a VE-1 ‘noticeable’ level of visual emphasis (see Table 2). You enter a 1.5 value in the TAIR column for wall one, and immediately the spreadsheet indicates that the direct surface illuminance needs to be 115 lux; and to provide that, 3772 lumens of direct flux on to this wall is required which will produce 1697 lumens of first reflected flux (FRF). Also, (but this is not shown in Chart 2) the box below would indicate that this FRF contributes three per cent of the total required FRF. (I would suggest downloading the spreadsheet and following the workings on-screen.) You move on and add a TAIR value of 1.5 for wall 2, and this adds 1537lm to the target surfaces FRF, raising the total contribution to six per cent. Then you come to the mural. It is a colourful work, and the client wants it to be a welcoming and memorable feature of the hotel. You decide on a visual emphasis between VE-2 ‘distinct’ and VE-3 ‘strong’, and you enter a TAIR value of 5. At this point the spreadsheet would show that the target surfaces FRF contribution jumps to 22 per cent of the required total FRF. There is no point in directing flux on to
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CIRCULATION
u Fig 8
wall 3 as so much of it will be lost to the outdoors, but wall 4 gets similar treatment to the two previous walls. Continuing down the column, the water feature is selected for VE-3 ‘strong’ visual emphasis, and other objects are accorded values to complete your envisaged illumination hierarchy. As is shown in spreadsheet 2, the target surfaces produce 30,637lm of FRF, which is 57 per cent of the total required FRF. This leaves you with the task of making up the remaining 43 per cent. You now switch from the illumination hierarchy mode of thinking to giving priority to illumination efficiency (see Figure 6). The key to optimising flux utilisation for providing MRSE is to maximise first reflected flux by providing luminaires that direct flux on to high-reflectance target surfaces. For this, you turn your attention to the ceiling and try some trial-and-error experimentation. Entering a value of 1.5 in the ceiling TAIR cell causes the target surfaces first reflected flux (FRF) to rise to 78 per cent of the required total FRF value (not shown), and as is shown in Chart 3, increasing the TAIR value to 2.0 puts you right on target: the target surfaces FRF provides 100 per cent of the required total FRF. This means that if each target surface receives the indicated value of direct surface illuminance, then the resulting first reflected flux will generate the chosen value of MRSE. You should now give careful attention to this lighting distribution, and it needs to be talked through with the client. It might satisfy his or her expectations for how lighting would influence the appearance of this space, but are you entirely satisfied? The treatment of the principal selected features appears to work well, but the visual emphasis for the woodgrain
Wall 3
walls was supposed to be ‘noticeable’, and its TAIR value is less than that of the ceiling. Might the appearance of the ceiling be distracting? You raise the TAIR values for walls 1, 2 and 4 to a value of 2.5, and this causes the target surface FRF value increase to 117 per cent of the required total FRF value (this is not shown). So, it is back to the ceiling again and some more experimentation. As shown in Chart 4, after some experimentation you arrive at the finding that a ceiling TAIR value of 1.6 brings the illumination distribution back in balance. You now have the basis of a working specification. The crucial data is the direct flux distribution (DFD) column. It tells you that if the target surfaces receive the specified levels of direct flux, the reflected flux will generate the ambient illumination (MRSE) that corresponds to the chosen ‘how brightly-lit’ appearance. In combination with that, the distribution of direct flux will achieve the balance of visual emphasis defined by the distribution of TAIR values. In this way, you will achieve your specified LiDOs that relate to ambient and target illumination. Providing the DFD involves selecting suitable luminaire locations and applying conventional illumination engineering principles to specify correct light source wattages, but the design process does not stop there. The quality of the lighting solution will ultimately depend on your attention to detail. For example, how the lighting over the reception counter reveals the people behind the counter will influence the sense of welcome felt by new arrivals at the hotel, and at the same time it will influence how the receptionists are able to cope with the paperwork on the counter top. If you write a LiDO for each of these, one would call for diffused side lighting
sll.org.uk
July/August 2020
Lighting metrics
Room Surface
Surface Area m^2
Surface reflectance
Surface absorption m^2
TAIR Direct surface DFD illuminance lx lm
Target surface FRF lm
Room Surface
Surface Area m^2
Surface reflectance
Surface absorption m^2
TAIR Direct surface DFD illuminance lx lm
Target surface FRF lm
Ceiling
131.6
0.75
32.9
1
0
0
0
Ceiling
131.6
0.75
32.9
1
0
0
0
Wall 1
32.8 29.7
0.45 0.45
18.0 16.3
1 1
0 0
0 0
0 0
Wall 1
32.8 29.7
0.45 0.45
18.0 16.3
1.5 1.5
115 115
3772 3416
1697 1537
0.65 0.45
4.9 3.6
1 1
0 0
0 0
0 0
Mural
Wall 3, solid
14 6.6
Wall 3, solid
14 6.6
0.65 0.45
4.9 3.6
5 1
920 0
12880 0
8372 0
Wall 3, glazed
26.2
0.1
23.6
1
0
0
0
Wall 3, glazed
26.2
0.1
23.6
1
0
0
0
Wall 4
27.2 14
0.45 0.25
15.0 10.5
1 1
0 0
0 0
0 0
Wall 4
27.2 14
0.45 0.25
15.0 10.5
1.5 5
115 920
3128 12880
1408 3220
Wall 2,
mural
excluding
Mural
mural
excluding
55.4
0.25
41.6
1
0
0
0
Reception counter Circulation
55.4
0.25
41.6
1.5
115
6371
1593
Water feature
4.6
0.75
1.2
1
0
0
0
Water feature
4.6
0.75
1.2
10
2070
9522
7142
Lounge
70.7
0.12
62.2
1
0
0
0
Lounge
70.7
0.12
62.2
3
460
32522
3903
Lift doors
4.8
0.4
2.9
1
0
0
0
Lift doors
4.8
0.4
2.9
5
920
4416
1766
Reception counter Circulation
Room surface absorption Total direct flux Required total first reflected flux Target surfaces first reflected flux FRF difference
p C hart 1
232.6 m^2 0 lm 53507 lm 100% 0 lm 0% 53507 lm 100%
Room surface absorption Total direct flux Required total first reflected flux Target surfaces first reflected flux FRF difference
p C hart 2
232.6 m^2 88907 lm 53507 lm 100% 30637 lm 57% 22870 lm 43%
Room Surface
Surface Area m^2
Surface reflectance
Surface absorption m^2
TAIR Direct surface DFD illuminance lx lm
Target surface FRF lm
Room Surface
Surface Area m^2
Surface reflectance
Surface absorption m^2
TAIR Direct surface DFD illuminance lx lm
Target surface FRF lm
Ceiling
131.6
0.75
32.9
2
230
30268
22701
Ceiling
131.6
0.75
32.9
1.6
138
18161
13621
Wall 1
32.8 29.7
0.45 0.45
18.0 16.3
1.5 1.5
115 115
3772 3416
1697 1537
Wall 1
32.8 29.7
0.45 0.45
18.0 16.3
2.5 2.5
345 345
11316 10247
5092 4611
Wall 3, solid
14 6.6
0.65 0.45
4.9 3.6
5 1
920 0
12880 0
8372 0
Wall 3, solid
14 6.6
0.65 0.45
4.9 3.6
5 1
920 0
12880 0
8372 0
Wall 3, glazed
26.2
0.1
23.6
1
0
0
0
Wall 3, glazed
26.2
0.1
23.6
1
0
0
0
Wall 4
27.2 14
0.45 0.25
15.0 10.5
1.5 5
115 920
3128 12880
1408 3220
Wall 4
27.2 14
0.45 0.25
15.0 10.5
2.5 5
345 920
9384 12880
4223 3220
Wall 2, mural
excluding
Mural
Reception counter Circulation
Wall 2,
mural
excluding
Mural
55.4
0.25
41.6
1.5
115
6371
1593
Reception counter Circulation
55.4
0.25
41.6
1.5
115
6371
1593
Water feature
4.6
0.75
1.2
10
2070
9522
7142
Water feature
4.6
0.75
1.2
10
2070
9522
7142
Lounge
70.7
0.12
62.2
3
460
32522
3903
Lounge
70.7
0.12
62.2
3
460
32522
3903
Lift doors
4.8
0.4
2.9
5
920
4416
1766
Lift doors
4.8
0.4
2.9
5
920
4416
1766
p C hart 3
Room surface absorption Total direct flux Required total first reflected flux Target surfaces first reflected flux FRF difference
LiDos 190826 Spreadsheet Project Hotel Reception name: area MRSE
Wall 2,
230 lm/m^2
and the other for directional downlighting. Lighting quality inevitably depends on the practitioner’s skill in identifying LiDOs and resolving their often-conflicting requirements. This requires thoughtful attention to the finer points of lighting’s power to influence not only the appearance of peoples’ surroundings, but also the appearance of the people themselves.
CONCLUSIONS
There is no need for the lighting profession to persist with the mismatch between peoples’ responses to the visual effects of lighting and the technology that governs lighting practice. The LiDOs Procedure is proposed as a first step towards relating lighting practice to
Twitter: @sll100
232.6 m^2 119175 lm 53507 lm 100% 53338 lm 100% 169 lm 0%
p C hart 4
peoples’ expectations for how lighting may influence the appearance of their surroundings. It is envisaged that as use of the procedure develops, so will its scope be expanded by additional LiDOs being incorporated. There are currently several professional lighting practices making use of the procedure and the feedback gained from those practices is proving invaluable in developing procedures for coping with practical issues encountered in application. More widespread use in general lighting practice depends on more research to more reliably define the response functions in terms of the new metrics, but the author has for some years been collaborating with a few academic institutions working towards that end. However, the crucial step would be for lighting standards to switch to specifying minimum illuminance levels in terms of ambient
Room surface absorption Total direct flux Required total first reflected flux Target surfaces first reflected flux FRF difference
232.6 m^2 127698 lm 5350 lm 100% 53542 lm 100% -34 lm 0%
illuminance. This would lead to substantial changes ranging from lighting design software to measurement and verification procedures, including assessment of lighting energy efficiency and luminaire performance. This article is based on a paper presented by Dr Kit Cuttle, FSLL FIESANZ FIESNA, at the IESANZ Conference in Melbourne, 21-22 November 2019, and has appeared in Lighting journal published by the IESANZ For more information on the LiDOs Procedure, go to https://tinyurl.com/LiDOsProcedure where there is further discussion of design implications; an explanation of the technical basis of the procedure; a link for downloading the spreadsheet, and a bibliography that includes research studies relating to LiDOs concepts
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Guidance
WELL VERSED Keith Miller reviews CIBSE's recently introduced document on health and wellbeing, focusing on the crucial role of lighting otions of health and wellbeing are increasingly being put at the heart of all conversations about good design. This topic often takes centre stage in design for the built environment, both in the design of interiors, and for the external environment and the public realm. The publication of CIBSE’s new Technical Memorandum TM40: Health and Wellbeing in Building Services is therefore very timely. The document is aimed at engineers and other professionals responsible for the design and management of the built environment. It considers the effects of internal and external environments on health, comfort and cognitive performance. The focus is not just on providing design guidance, but also on facilities management and performance in use. The scope of TM40 includes performance criteria for humidity, air quality, thermal conditions, light, acoustics, electro-magnetic fields and water quality. The document sets the scene by analysing health and wellbeing in the context of internationally recognised determinants of health and how the environment has a significant influence on health outcomes. For example, it is estimated that 23 per cent of deaths are due to modifiable environmental factors alone. It uses Maslow’s hierarchy of needs to illustrate how human needs can translate into a similar hierarchy in the workplace. The scope of TM40 focuses on the middle ground of this hierarchy, which is the creation of environments that support health, comfort and cognitive performance. The document is well structured and consistent, with each section describing the health and wellbeing context, regulatory framework, performance criteria, guidance and recommendations, and emerging themes.
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Hufton + Crow
N
p D aylight design: Jumaa Mosque, Doha, lighting design by GIA Equation
Principal author Julie Godefroy is a chartered engineer, sustainability consultant and full-time CIBSE technical manager. She has introduced each chapter with a summary of 'key takeaways' which consider the health and wellbeing impacts and objectives for building professionals, guidance during the design, construction and operational stages of a project, and notes on the overlap of each topic with other environmental issues. In terms of light and lighting, this technical memorandum is intended to be complementary to existing guidance published by SLL, such as the Code for Lighting; LG10: Daylighting, and LG7: Offices. It considers the different ways in which light affects our health and wellbeing, through the visual system, through its impact on circadian rhythms, as well as visible and non-visible radiation.
The health and safety aspects of providing suitable levels of illuminance are considered alongside detrimental effects such as glare, flicker and excessive luminance ratios in the field of view. The importance of exposure to natural light and good daylight design is a significant part of the Light and Lighting chapter, which contains recommendations on the design of building form and layout, window design, and balancing daylight, sunlight, thermal requirements and glare control. The significant positive impacts of daylight are highlighted alongside negative effects that may arise from its lack, such as sleep disorder, depression and possible links to Alzheimer’s disease. Emerging research relating to the health impacts of absence of daylight exposure such as cardiovascular
sll.org.uk
July/August 2020
Guidance
SOFT NEEDS Inspiration
Self Actualisation
Productivity
Self- esteem
Wellbeing
Love and belonging
Safety
HARD NEEDS
NEEDS A WORKPLACE SHOULD COVER
Health, employment, property, family and social ability Air, food, water, shelter, clothing, sleep
NEEDS OF A HUMAN BEING
of light on the circadian system and physiological processes. Lighting engineering and photometry are designed around the human visual system, and consider luminance and illuminance, light source stability, colour spectrum and direction. This impact on the circadian system also includes colour spectrum and light direction, but it is measured in a very different way and these effects are less well understood. TM40 notes the following: •
•
•
The effects of light on the circadian system at two different hours can be opposite Internal time, duration and sequence (that is light exposure history) all affect human responses to daylight Clock time and working hours affect when a person is required to do a particular task requiring lighting
This par t of the document concludes by pointing out that this is an active area of research with much remaining uncer tainty; a viewpoint that is in line with the SLL Circadian Lighting Position Statement, which was issued in April 2019 The publication also looks at the negative impacts of flicker and stroboscopic effects, alongside flicker prevention measures. It identifies special user groups that are
city
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Safety and security
velo
– Constitution of the World Health Organisation (WHO, 1946)
Friendship, family, intimacy, sense of connection
Air
‘Health is a state of complete physical, mental and social wellbeing, and not merely the absence of disease or infirmity. The enjoyment of the highest attainable standard of health is one of the fundamental rights of every human being without distinction of race, religion, political belief, economic or social condition.'
Confidence, achievement, respect for others, the need to be a unique individual
Physiological needs
Health
and digestive problems, and possible links to cancer, are also mentioned. In terms of electric light, TM40 looks at lighting and visual performance. The document notes that lighting was rated among the most important physical indoor environment parameters (beyond furniture and spatial arrangement) with an average estimated effect on task performance of around 10 per cent. In addition to facilitating identified visual tasks, the way that light affects the overall appearance and pleasantness of a visual scene is discussed, alongside ways in which lighting can be used to aid intuitive wayfinding, direct movement and facilitate communication. Architectural lighting is acknowledged as something that contributes to our wellbeing and enjoyment of a place by providing visual interest, emphasis, accent, colour and variety which complement buildings, landscapes and the public realm. The document also addresses the effects
Morality, creativity, spontaneity, acceptance, inner potential
p Factors contributing to indoor environmental quality (TM40)
particularly sensitive to the effects of light, such as those individuals who suffer from photosensitive epilepsy, migraine and autism spectrum disorder. There is also a section examining the positive and negative effects of light as electromagnetic radiation, the health benefits of light as radiation, phototherapy and the use of light as a purification device. TM40 then summarises the regulatory framework within the UK, which generally embodies best practice lighting design principles. Obtrusive light and light pollution is also mentioned with reference to the Clean Neighbourhoods and Environment Act, 2005.
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E
July/August 2020
Guidance
James Newton
ighting to enhance architecture: Knightsbridge Estate, L London, lighting design by GIA Equation
10000
8000
7000
6000
5000
4000
3000
2000
1000
800
700
600
500
400
300
200
100
All wavelengths in nm
Eyes: photokeratitis and photoconjuctivitis Skin: erythema and skin cancer Eyes: cataracts Skin: elastosis
Eyes: cataracts
Eyes: pigment darkening Eyes: photoretinal damage (blue light hazard) Eyes: retina burn Skin: burn Eyes: corneal burn
p Wavelength bands for various types of optical hazard
The next section of the document considers lighting performance criteria while noting that the World Health Organisation (WHO) recognises light, both natural and electric, as a determinant of health. The Light and Lighting section of TM40 concludes with a section on lighting design guidance for both daylight and electric light design. There is also a useful table which compares EU regulations
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and UK regulations with CIBSE and SLL recommendations. What is really refreshing about this technical memorandum is that lighting design guidelines are not, as is customary, seen in isolation. Instead they are presented holistically, in a clear and concise way, in the contex t of a general technical publication, alongside other building ser vices issues.
Keith Miller, MSLL, is director of GIA Equation and a member of the SLL's technical and publications committee. He has provided advice on lighting design issues and emerging trends for TM40 SLL members can download TM40 from the CIBSE Knowledge Portal (www.cibse.org/ Knowledge/CIBSE-TM/TM40-2019-HealthIssues-and-Wellbeing-in-Building-Services)
sll.org.uk
July/August 2020
LR&T essentials
THROUGH THE AGES Iain Carlile finds past and present concerns in the most recent online papers from Lighting Research and Technology ain et al have examined how the circadian effect can change due to age-related changes in the eye. The study measured corneal illuminance and the human eye’s spectral transmittance, with age-related change, at different spectral power distribution (SPD) values. These values were created using red-green-blue-warm-white (RGBWW) colour-mixing LEDs to create five different SPDs with CCT/CRI values of 2700K/95 Ra, 4000K/96.6 Ra, 5000K/96.8 Ra, 6500K/95.6 Ra and 8000K/93.5 Ra. The results showed that, as a general trend, the effect of the circadian stimulus (CS) increased with CCT from 4000K to 8000K at the same age, but at 2700K CCT a higher circadian impact was noted compared to that of 4000K for the same age groups. It was also noted that at consistent CCT the CS value increased with corneal illumination but decreased with age. Also, at the same corneal illuminance the CS value of different age groups may be the same at different CCT values. The authors suggest that their results could be used to create personalised video display terminals and that interior lighting could be tailored from the perspective of circadian effect. However, they note that there are many other factors related to age that might also have an impact. Vries et al present a study on lighting in the office environment. They investigate changes in desk, and therefore task illuminance, while maintaining a constant wall luminance, and the impact this has on a user’s performance, mental state and perception of the surrounding space. A simulated office space was created with five workstations in an open-plan style layout,
or mental state of office occupants. They recommend that a more comprehensive approach to office lighting design is needed. Bertenshaw’s paper provides a historical review of the standardisation of light and photometry. He looks at the technological challenges and solutions that were faced in creating reproducible standards and measurement of light from the 18th to 21st century, exploring some of the social, political and economic reasons for doings so. He looks at the evolution of lighting from candles, through to gas lighting and incandescence, setting out the different historical standards for each, and on to the current radiometric definitions.
I
Twitter: @sll100
p A diorama of William Murdoch demonstrating gas lighting at his home in Redruth, Cornwall, c1794 (from The standardisation of light and photometry – A historical review)
and daylight was excluded by using opaque blinds. The space was lit with ceiling-recessed 600 x 600mm office-style luminaires, with adjustable spotlights providing wall illumination. All luminaires were dimmable, with ceiling fittings used to adjust the desk illuminance, and spotlight wallwashers raised/dimmed to ensure a constant wall luminance between the different experimental conditions. Three different desk illumination conditions were used: 150 lux, 500 lux and 1500 lux, at a uniformity of 0.8. It was found that visual acuity of paperbased tasks and perceived brightness increased significantly with higher desk illuminance, however the room’s attractiveness did not. Illuminance at the eye rose significantly with increased desk illuminance but had only minor effects on subjective alertness and cognitive performance. The authors conclude that while task illuminance for visual acuity is an appropriate design parameter, it has little to no impact on the attractiveness of a space, nor the cognitive
Iain Carlile FSLL is a past president of the SLL and a senior associate at dpa lighting consultants
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) Teasing apart office illumination: Isolating the effects of task illuminance on office workers A de Vries, JL Souman and YAW de Kort Change of circadian effect with colour temperature and eye spectral transmittance at different ages HJ Tian, T Chen, Y Hu, T Guan and MP Cai The standardisation of light and photometry – A historical review DR Bertenshaw
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July/August 2020
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Events 2020
For up-to-date information on all SLL events please visit the website: www.sll.org.uk
22 SEPTEMBER Lighting Design Awards Venue: Troxy, Commercial Road, London E1 https://awards.lighting.co.uk 11-12 NOVEMBER LuxLive Venue: ExCeL, London https://luxlive.co.uk
12 NOVEMBER Lux Awards 2020 Venue: London Hilton Park Lane (tbc) https://luxawards.co.uk
24-25 NOVEMBER Build2Perform (CIBSE event) Venue: Olympia London www.build2perform.co.uk LightBytes The LightBytes Series is kindly sponsored by Soraa, Thorlux Lighting, Xicato and Zumtobel. For venues and booking details: www.sll.org.uk
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