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The Society of Light and Lighting



THE LIGHTING MANIFESTO Four leading figures call for change

SPECTRAL ANALYSIS Controlling colour to save energy


September/October 2020

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 Rory Marples MSLL 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 LL6 2020 IS 14 AUGUST PUBLISHED BY The Society of Light and Lighting 222 Balham High Road London SW12 9BS www.sll.org.uk ISSN 2632-2838 Š 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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Certain lighting metrics may have been arrived at arbitrarily, or at least remain difficult to get to the bottom of decades later, and their basis may be long overtaken by technology and practice, but still they persist. A natural conservatism combined with slow-moving bureaucracies inevitably militate against change. But because something is customary it does not mean that it is correct. There has been endless discussion for years about the wisdom of allowing the horizontal plane to be the central plank, as it were, of lighting metrics in the workplace. That the horizontal plane is not the be all and end all has been acknowledged and there have been modifications to guidance. The importance of the vertical surface has been recognised and emphasised. But somehow we can't shake off the tyranny of the desk top. Despite the fact that the working plane is now the

computer screen, self-illuminated and vertical, and despite the millions of square metres of carpet that are needlessly and wastefully lit, to cite just two arguments against it. How do you turn the juggernaut of traditional thinking around? In their Ambient Lighting Manifesto (p5), four lighting heavyweights, Peter Boyce, Kit Cuttle, Kevin Kelly and Peter Raynham, are calling for a paradigm shift in lighting practice. This is generally a time for change and reassessment of our thinking. Perhaps lighting metrics will become part of that reevaluation.


CURRENT SLL LIGHTING GUIDES SLL Lighting Guide 0: Introduction to Light and Lighting (2017) SLL Lighting Guide 1: The Industrial Environment (2018) 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 (2018) 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)


Secretary’s column/Contents

September/October 2020



Twitter: @sll100

• To apply for the card email sll@cibse.org

• For membership upgrade: www.cibse.org/societyof-light-and-lighting-sll/ membership/guidanceand-subscriptions

of the work of CIE-UK, and to take advantage of this excellent offer you can email sll@cibse.org with the subject 'CIE Publications' and we will then send you the discount code. The publications can be purchased on the CIE publications website but you will need the code from the SLL for the discount. As you know, the SLL had to cancel the Lighting Research and Technology symposium, Applying Light for Human Health, originally scheduled for this summer. However, we are very pleased (there’s a definite pleased theme about this Secretary’s Column) to confirm that we will be presenting an SLL Light and Health week from 2-6 November. Each day will see 60 minutes of presentations from leaders in the field of lighting research, supply and design. Each of the five sessions will also include a 30-minute live Q&A session with the speakers. We will confirm the specifics relating to the topics and speakers soon, along with booking information. Do check the website for upcoming SLL online events as well as past presentations for you to download.








THE AMBIENT LIGHTING MANIFESTO Peter Boyce, Kit Cuttle, Kevin Kelly and Peter Raynham call for a paradigm shift in lighting practice


ON THE RIGHT WAVELENGTH Alp Durmus outlines the concept of an adaptive optimisable lighting system that could save energy

11 DOES Vλλ SPD MEASURE UP (3)? David Loe concludes his investigation into an alternative illumination metric

13 ULTRA CAUTION WITH ULTRAVIOLET The CIE warns against the uncontrolled use of UV-C lighting prompted by the coronavirus pandemic

15 ON THE ROAD Iain Carlile looks at four of the most recent LR&T papers, all of which focus on street lighting

16 EVENTS COVER: Kistefos (The Twist) art space, Jevnaker, Norway, lighting design by Light Bureau, winner of an IALD Award of Excellence 2020


‘ECS is the sole ID and competence card scheme for electrotechnical operatives that is recognised by the industry’

© Tomasz Majewski

We are delighted that the society has partnered with the Electrotechnical Certification Scheme (ECS) to introduce the Lighting Professional Related Discipline ECS card (see p4). Administered by the Joint Industry Board (JIB) in England, Wales and Northern Ireland, ECS is the sole ID and competence card scheme for electrotechnical operatives that is recognised and endorsed by the industry. SLL corporate members who wish to attend or work on construction sites in Scotland should contact the Scottish JIB which administers the scheme in Scotland. The Lighting Professional ECS card will allow SLL corporate members access to construction sites to carry out their work. The card lasts for three years and SLL membership must be maintained during that time for the card to be valid. All corporate members of the society – Associate Member (AMSLL), Member (MSLL) and Fellow (FSLL) – can apply for the card (see above right). Affiliate members should consider upgrading their membership to corporate grades before applying for the card. The criteria for upgrading membership can be found on the website (see above right) under the heading 'Guidance to applicants for election and transfer'. There you will see the experience or education and experience criteria for the various grades of membership. We will then be able to inform you of the centres where you can book your assessment and training procedures. We are also pleased to give SLL members the option of opting out of receiving the hard copy of Light Lines. In its place you will receive an email every two months with the link to the latest online edition. If you wish to do this please email sll@cibse.org with the subject 'Light Lines Opt-Out'. We are also able to confirm that SLL members can now receive a 66.6 per cent discount on all CIE publications. The society has been a long-time supporter



September/October 2020



SLL PARTNERS WITH ECS TO CREATE COMPETENCE CARD The SLL has partnered with the Electrotechnical Certification Scheme (ECS) to introduce the Lighting Professional Related Discipline ECS card. Run by the Joint Industry Board (JIB) in England, Wales and Northern Ireland, ECS is the only ID and competence card scheme for electrotechnical operatives recognised by the industry. It allows those working in specialised electrotechnical disciplines, but who do not carry out any electrical installation work, to attend and work on construction sites. Applicants must pass or already have ECS Health, Safety and Environmental Assessment and attend an Electrical Safety Awareness training day and assessment. The card is valid for three years during which time the applicant must remain a member of the SLL. The cost is £40, with additional fees of £40 for the ECS Health, Safety and Environmental Assessment. The Electrical Safety Awareness training day and assessment cost is dependent on the organiser and venue. Application is open to SLL Associate Members (AMSLL), Members (MSLL) and Fellows (FSLL). SLL Affiliates are unable to apply, but have the opportunity to upgrade their membership. 'The construction industry places a huge degree of importance on ECS cards' said Jay Parmar, chief executive of the JIB. The agreement has taken 12 months to bring to fruition. 'The card provides our members with the very practical benefit of being able to access and work on construction sites as a recognised professional,' said SLL president Bob Bohannon. 'This very useful new benefit for SLL members will create safer workplaces for all.' Anyone wishing to apply or who needs more information on becoming AMSLL, MSLL or FSLL should email: sll@cibse.org SLL members who wish to attend or work on construction sites in Scotland should contact the Scottish JIB

ON THE LIGHTER SIDE... Zoom has become ubiquitous during lockdown so not surprisingly it has found its way into a light art installation. Scream the House Down by artist Marcus Lyall was installed in an empty office building in London Bridge before travelling to New York, Hong Kong, Russia and beyond. The coloured light spectacle was triggered by members of the public joining a Zoom call and screaming at the installation. The louder and longer, the bigger the response from the building. Highly cathartic. 'The artwork was a place to direct


your frustrations and tensions, without judgement and without affecting the people around you,' said Lyall. www.illuminateproductions. co.uk/screamthehousedown

Scientists at the Circadian Light Research Center in Stoneham, Massachusetts, say they have pinpointed the narrow band of blue light that synchronises circadian rhythms during the day and disrupts them at night. According to their study, published online in June in the Journal of Biological Rhythms, the critical band falls between 438-493nm with a peak at 477nm, which they have dubbed 'circadian blue'. The study used polychromatic rather than monochromatic light. 'Our goal was to define the exact wavelengths of light that trigger the human circadian system in real-world lighting conditions,' said Dr Martin Moore-Ede, a former professor at Harvard Medical School and CEO at Circadian ZircLight, a company that arose from research into human circadian rhythms at Harvard Medical School and the University of Toronto. The 34 study subjects were exposed to a different LED or fluorescent white light spectra for 12 hours each test, during which melatonin levels were measured. 'We found melatonin suppression levels varied widely depending on the light source’s unique spectral characteristics,' said Dr Anneke Heitman, study co-author. 'This data enabled us to isolate the impact of individual wavelengths of light and determine the colour of circadian blue.' Previous research into the spectral sensitivity of the body clock has been carried out in dark-adapted conditions with short exposures to monochromatic lights, said Dr Moore-Ede. 'However, we spend the vast majority of our time in a light-adapted state, exposed to white polychromatic light. Our study reflects how we interact with light in the real-world.' Based on the findings, Circadian ZircLight has built and patented spectrally engineered day and night LEDs, licensing the technology to leading lighting companies. For the full study, go to: https://journals.sagepub.com/doi/ full/10.1177/0748730420923164


Light Fields III by Zumtobel

September/October 2020

THE AMBIENT LIGHTING MANIFESTO Peter Boyce, Kit Cuttle, Kevin Kelly and Peter Raynham call for a paradigm shift in lighting practice

Kevin Kelly

Twitter: @sll100

Kit Cuttle

Peter Boyce

Peter Raynham



September/October 2020

rogress in society, science and technology often depends on a paradigm shift – think Germaine Greer, Albert Einstein and Tim Berners-Lee. We believe interior lighting, as generally practised, is ripe for a paradigm shift. We believe that the paradigm shift required is to stop designing lighting to deliver a specified uniform illuminance on a horizontal working plane, and to start giving priority to lighting the space rather than just focusing on the visual tasks.


There are four reasons for this belief: • The way information is delivered has changed. Today, a lot of the information necessary for task performance is delivered through self-luminous screens. Unlike paper-based tasks, information on screen does not require task illumination for it to be visible. This means much lighting is being designed to fulfill needs that no longer exist. • The number of tasks that require visibility of fine detail is much reduced. This has occurred partly through the wider availability of good quality photocopying and printing, and partly through the growth in machine vision, computer power and robotics. Again, this means much lighting is designed to fulfill needs that no longer exist. • Light is now recognised as generating both visual and non-visual responses, both being important for human health and wellbeing. This recognition is directing attention away from lighting the task to the light received at the eye. This means lighting designed to deliver a set illuminance on a hypothetical horizontal working plane is largely irrelevant to what should be the main functions of lighting: making the whole space visible and supporting human health • Continuing to define good lighting by nominal task illuminance delivered to a horizontal working plane means we will miss an opportunity to ensure lighting will make a real contribution to enhancing human health and happiness. It may also lead to a waste of energy and financial resources, and cause damage to the environment.


CURRENT PRACTICE Lighting as currently practised is an activity undertaken by a number of different groups ranging from professional lighting designers, through lighting equipment manufacturers, architects and building services engineers to electrical contractors. These groups have different levels of expertise and different income streams, meaning the amount of time they can spend on a lighting design varies, but they do have two things in common. First, they all use software to develop their designs, some more sophisticated than others. Second, they mostly follow the illuminance standards produced by authoritative bodies, both national and international. Even professional lighting designers do this, because to do otherwise poses a risk of litigation should the client be dissatisfied. The consequences of current practice are many and varied. By designing lighting for a nominal task illuminance on a horizontal working plane, one consequence is that light is being delivered where it is not needed at a level that is not necessary. In other words, energy is being wasted. Excessive energy consumption has implications for climate change. Further, unless lighting practice frees itself from the chains of illuminance on a horizontal working plane, there is a risk that lighting will be seen as a simple commodity where innovation and creativity are limited and price is everything. The implications for the lighting industry are not attractive.

THE OBJECTIVE To achieve the desired paradigm shift, what is required is to change the lighting standards produced by authoritative bodies such as ISO, CEN, CIE and SLL from illuminances and illuminance uniformity on a horizontal plane to minimum ambient illuminances. Ambient illuminance is defined as the average flux density of the indirect flux field within the volume of a space.

‘Ambient lighting is real human-centric lighting’

As such, it involves consideration of the distribution of light throughout the space and can be expected to relate to peoples’ perceptions of the space. It would also be a better approach to quantifying the nonvisual impact of lighting as it provides an estimate of the amount of light that will be received by the eyes. Ambient lighting is real human-centric lighting. A design method suitable for this paradigm shift, the Lighting Design Objectives (LiDOs) procedure, already exists (Light Lines, July/August, 2020). The LiDOs procedure first requires the practitioner to specify the objectives of the lighting installation. Once this is done, the ambient illuminance can be determined and target surfaces to receive direct flux selected, enabling objectives to be met by adjusting the target/ambient illuminance ratio values. This can cover situations ranging from where visually difficult tasks occur and the ambient illuminance is insufficient to creating distributions of emphasis to achieve envisaged visual effects. It is worth noting that the LiDOs procedure is very flexible and does not limit the possible outcomes. It even allows a uniform illuminance across a horizontal working plane to be produced if that is the objective.

HOW TO GET THERE To achieve such a paradigm shift we will need to gain the support of a number of different groups: lighting designers, lighting manufacturers, lighting regulators, professional lighting societies and architects. Among the questions that will have to be addressed are: • How will lighting practice be changed? • Will the change increase energy consumption? • What are the costs of ambient lighting compared with the current practice? • What are the opportunities for the lighting industry? • Will it lead to architects and lighting designers working more closely together? • Can design software be rewritten to support the LIDOs procedure? • What form should lighting standards take? • How can daylighting be incorporated into the LiDOs procedure?



September/October 2020

 S  an Francisco offices of international law firm Covington, lighting design by Fisher Marantz Stone: 'start giving priority to lighting the space rather than just focusing on the visual tasks'

‘It will never happen unless all those involved lift up their eyes from the horizontal working plane’

© Jason O'Rear

efficiency may be literally turned upside down – and needs further investigation. 6 Given the conservative nature of the authorities which prepare lighting recommendations it is likely that a transitional phase will be required if the movement from standards based on task illuminance on a horizontal working plane to standards based on ambient illuminance is to succeed.

There are a number of activities needed before the desired paradigm shift can occur: 1 Research aimed at identifying suitable metrics for quantifying ambient lighting and appropriate levels of these metrics for inclusion in standards is essential. 2 Research is needed to establish that giving priority to ambient lighting results in a better human response to an interior than current practice, both on

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first sight and after prolonged exposure. 3 Development of a reliable and robust ambient illuminance meter. 4 Research is required to estimate the financial and energy costs of implementing an ambient lighting approach relative to current practice, including any attempts to influence human health with light. 5 The present understanding of lighting

A transitional lighting standard would be one in which application tables are given in terms based on current practice (illuminance and uniformity) and in terms suitable for ambient lighting (MRSE, MICI, TAIR and so on). This would allow lighting practitioners to use whichever approach they thought was best suited for a given project. Lighting regulators, such as those revising EN 12464-1, should prepare for this transition by providing information on the ambient lighting approach as soon as possible.

CODA There is a long way to go before a shift from working plane lighting to ambient lighting can be justified and made to occur. However, it will never happen unless all those involved lift up their eyes from the horizontal working plane and see the opportunities for better lighting practice presented by ambient lighting.


Research: spectral optimisation

September/October 2020

ON THE RIGHT WAVELENGTH Alp Durmus outlines the concept of an adaptive optimisable lighting system and examines the applications orldwide energy consumption contributes to two of the biggest challenges facing humanity: resource scarcity and climate change. Pressured by the increasing energy demand of a growing population, governments, manufacturers and the lighting industry have been tackling this issue by promoting energy-efficient light sources, such as solid-state lighting (SSL) devices. SSL devices offer several advantages over previous lighting technologies, such as compact size, longer lifetime, directionality, high efficacy, ease of control of light output and high colour quality. However, one of the most significant contributions of SSL devices could be considered system and control compatibility due to their semiconductor nature. Generating light through semiconductor devices introduced us to a whole new range of capabilities, generally known as smart lighting. Smart lighting is a growing industry with the potential of reaching a market value of US$21bn by 20231. A smart lighting system aims to reduce the energy consumed by lighting by sensing environmental factors (for example, occupant presence) and controlling the light output (for example, dimming). The earlier smart lighting applications were rudimentary in terms of the light output control and integration of sensor data, but an increasing number of different technologies has been proposed to resolve connectivity and control issues. Despite the complexity of intelligent lighting systems, the basic functions are very simple: quality lighting, user satisfaction and energy efficiency. Lighting quality and energy efficiency can



be measured through the physical properties of a light source. The spectral power distribution (SPD, aka spectrum) is the radiant power emitted from a light source as a function of wavelength. It is possible to calculate the colour quality of light sources, such as chromaticity (for example, CCT, Duv, chromaticity coordinates) and colour rendering metrics (CRI, ANSI/IES TM-30), as well as energy efficiency (or the luminous efficacy of radiation) using light source SPD. The colour appearance of an object is a product of interactions between the light source spectrum, the object’s spectral reflectance and the human visual system. An object reflects some of the incident light on its surface, and the reflected light reaches observers to be perceived as the colour of the object. However, the light that is not reflected is absorbed by the object and turns into heat; it is wasted for lighting purposes. Since the output of the SSL devices, such as LEDs, can be adjusted, it is possible to create a lighting system by optimising the light source SPD to reduce the amount of light absorbed by objects. For example, a red object reflects light in the longer wavelengths (perceived red), but the shorter wavelength radiation (perceived blue) is absorbed by the object. Therefore, eliminating the light absorption by not emitting the short wavelengths can tremendously increase energy efficiency. A spectrally optimisable absorptionminimising lighting system consists of sensors that detect the 'colours' (reflectance characteristics) of objects and emit optimised light to each coloured part of an object, as shown in Figure 1. Although a 3D real-time implementation of this

concept would be the ultimate goal, an early adaptation of such a lighting system could be used for illuminating 2D structures, such as paintings and facades.

ARCHITECTURAL APPLICATIONS: SAVING ENERGY Earlier investigations of the absorptionminimisation concept were based on computational simulations that identify the maximum theoretical energy savings. These simulations were not limited to the commercially available light source SPDs. Results indicate that the energy consumed by lighting to illuminate a series of coloured test samples could be reduced by up to 71 per cent if theoretical light source SPDs with two spectral peaks were generated2. Energy savings gained by light optimisation did not compromise the colour quality of the objects. In this study, reflectance characteristics (object colours) were

ď ą F  ig 1: a spectrally optimisable lighting system can detect the colours of objects through a sensor (top right corner) and emit optimised lighting to each coloured part of an object in the environment


Research: spectral optimisation

September/October 2020

grouped according to their spectral shapes. Expectedly, green objects resulted in relatively higher energy savings, due to the increased sensitivity of the human visual system to the middle wavelengths. Extending on the computation work, we tested the spectral optimisation concept by using real light sources and everyday objects to quantify energy savings and colour shifts. Nine commercially available narrow-band LEDs were optimised to illuminate commonly found objects that are known for their colour appearance (for example, tomato representing red hue)3. A balanced set of objects were chosen that circulate the whole hue circle. In the visual experiments, observers found the colour appearance of the fruits and vegetables equally natural and attractive under both optimised lighting conditions and reference phosphor-coated white LEDs. While energy savings were not as high as the previous studies, the visual experiments showed that the absorption-minimisation concept can deliver energy-efficient lighting without causing visual distortions. Higher energy savings could also be achieved if the saturation of the objects were increased since people prefer saturated objects (to a certain extent) and remember the colour of the objects to be more saturated than their original appearance4. While the colour quality of the visual environment is critical for user satisfaction, other aspects of the human visual experience can also be incorporated into an intelligent lighting system. For example, a light projection system can be optimised to reduce visual clarity, scene preference and perceived brightness. Quantifying the visual aspects beyond colour requires evidencebased models that estimate human visual response to the visual environment. For example, image quality assessment measures have been adopted from imaging applications to the architectural domain to quantify the visual clarity of scenes5.

The change in the chemical composition of the molecules due to light absorption (photochemical action) can be decelerated, if not completely prevented, by optimising the light spectrum for object reflectance. Earlier applications of the absorption minimisation concept on artwork suggest that it is possible to reduce damage caused by optical radiation and energy consumption by up to 55 per cent with perceptible but small colour shifts6. More advanced optimisation techniques can enable similar damage and energy consumption reductions without causing any perceptible colour shifts in the appearance of mono-coloured paintings7. These studies were conducted using single-coloured paintings, and artworks are typically more complex in terms of colour, form, and structure, so the intelligent lighting system should address spatial qualities of the stimuli as well as spectral qualities. To address the spatial complexity issue, a light projection prototype has been developed, consisting of a CCD camera, an RGB projector and a computer8. Joaquin Sorolla’s painting, Women Walking on the Beach, was illuminated pixel by pixel with an RGB projector to restore its appearance and minimise future damage. Damage caused by optical radiation was reduced by up to 67 per cent in certain parts of

the painting, and 37 per cent on average. There is more work to be done to further reduce the light absorption, and assess the visual appearance of artwork under optimised lighting by expert (conservators, curators) and non-expert observers.

CHALLENGES AND FUTURE IMPLICATIONS The intelligent lighting systems that are based on environmental sensing and light optimisation offer unprecedented opportunities. However, an advanced integrative lighting system will require computational power, precision optics and reflectance recovery – in real-time. Although the precision, spectral control and speed needed for this projection system seem enormous, there are encouraging advancements in the field of sensing and projection technologies. For example, some of the functionalities of the proposed lighting system already exist in different forms. Indoor positioning through visible light positioning (VLP) allows the location of objects and people inside a building by using sensory information collected from mobile devices, while visible light communication (VLC) can be used to transmit data via modulating LED outputs9.


 Fig 2: 3D projection mapping at the Vivid Sydney light festival in Australia


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© Pixabay License

Absorption-minimisation lighting can offer advantages beyond energy efficiency. Light that is absorbed by objects turns into heat and can cause irreversible damage to light-sensitive objects, such as paintings.


Research: spectral optimisation

While the position, orientation and speed of objects in space are important factors, the light source spectrum and optical surface characteristics of objects are more fundamental to the proposed system. It is possible to 'extract' the spectral characteristics of light sources and object spectral reflectance by using common CCD cameras, or even colour encoded projectors10,11. These devices can offer Wi-Fi or Bluetooth connectivity to cloud storage and enable real-time operation and connection to other semiconductor devices. Real-time motion, object and surface recognition, object tracking and light-mapping systems are already realised in various forms, and they can be used by advanced integrative lighting systems. The light output control complements the sensing technologies in an integrative lighting system. Tunable, high-precision light projection systems are crucial for the spectrally optimisable lighting systems. Projection mapping, also known as video mapping, is a popular method, used to illuminate complex objects in the real world. Examples of projection mapping are commonly found in festivals in urban environments all over the globe. One of the most well-known examples is the Sydney Opera House at the Vivid Sydney lighting festival in Australia, as shown in Figure 2 (previous page). Designers of the projection mapping create a spatial map of the surface of a target area (a building facade, for example), and generate images or animations that may result in optical illusions, highlight dimensions or depth, or add a notion of movement to static surfaces. In architectural spaces, the projection mapping applications would not require the same resolution, luminous flux, or contrast, as used by these outdoor examples where light is projected at high distances. The colour quality of the projection system is an essential factor when it is used in the built environment. It is possible to control a projection system independent of the existing lighting conditions, object colour and texture, projector position and brightness, by using several projectors12 . A multi-projector approach can enable high consistency of image geometry, intensity and colour, which are crucial for the perceived quality of the environmental scenes. Increasing progress in the field of optics will hopefully provide even finer control over the light output of a projection system.


September/October 2020

FINAL THOUGHTS Optimising light source output by considering the environmental characteristics has the potential to create efficient and good quality lighting. The absorptionminimisation concept is a technology-neutral way of reducing energy consumption without causing perceptual distortions in the visual perception. Although today LEDs are widely used in the lighting industry, emerging technologies, such as quantum dots and lasers, can also be used in an integrative adaptive lighting system. Despite the current engineering limitations, there is enough experimental data supporting the successful application of the proposed concept in architectural spaces. As often stated, future studies should investigate the spatial and temporal characteristics of the system in real-time, and the preference and acceptability of the results by conducting visual experiments.

References 1 Rohan, S (2018) Smart Lighting Market worth 20.98 Billion USD by 2023. Retrieved from https:// www.marketsandmarkets.com/ PressReleases/smart-lighting.asp 2 Durmus, D and Davis, W (2015) Absorption-Minimizing Spectral Power Distributions. Light, Energy and the Environment (Optical Society of America, OSA Technical Digest (online), 2015), paper JTu5A.2. 3 Durmus, D and Davis, W (2017) Object color naturalness and attractiveness with spectrally optimized illumination. Optics Express, 25(11), 12839-12850. 4 Siple, P and Springer, RM (1983). Memory and preference for the colors of objects. Perception and psychophysics, 34(4), 363-370. 5 Durmus, D (2020). Spatial frequency and the performance of imagebased visual complexity metrics. IEEE Access, 8, 100111-111119. 6 Abdalla, D, Duis, A, Durmus, D and Davis, W (2016). Customisation of light source spectrum to minimise light absorbed by artwork. In Proc. CIE Lighting Quality Energy Efficiency (pp. 22-31). 7 Durmus, D, Abdalla, D, Duis, A and Davis, W (2020). Spectral optimization to minimize light absorbed by artwork. Leukos, 16(1), 45-54.

Alp Durmus is assistant professor at the Department of Architectural Engineering, Pennsylvania State University

8 D Vázquez, AA FernándezBalbuena, H Canabal, C Muro, D Durmus, W Davis, A Benítez and S Mayorga. (2020) Energy optimization of a light projection system for buildings that virtually restores artworks. Digital Applications in Archaeology and Cultural Heritage, 16, e00128. 9 Chew, I, Karunatilaka, D, Tan, CP and Kalavally, V (2017). Smart lighting: The way forward? Reviewing the past to shape the future. Energy and Buildings, 149, 180-191. 10 Botero-Valencia, JS, ValenciaAguirre, J, Durmus, D and Davis, W (2019). Multi-channel low-cost light spectrum measurement using a multilayer perceptron. Energy and Buildings, 199, 579-587. 11 Chen, SY, Li, YF, Guan, Q and Xiao, G (2006). Real-time three-dimensional surface measurement by color encoded light projection. Applied Physics Letters, 89(11), 111108. 12 Bimber, O and Emmerling, A (2006). Multifocal projection: A multiprojector technique for increasing focal depth. IEEE Transactions on Visualization and Computer Graphics, 12(4), 658-667.


Lighting metrics

September/October 2020


DOES Vλ SPD MEASURE UP? David Loe concludes his investigation into an alternative illumination metric art 1 of these investigations suggested a basis of illumination metrology that embraced human evolution with respect to sight, as well as a degree of logic which also included a suggested system for measuring the quality of colour rendering. In Part 2, a pilot experiment was carried out using the Farnsworth-Munsell 100-hue test to rate the light source colour rendering quality based on human subjective colour selection performance. Three different light sources were used including two LED sources and natural daylight. The result was that there was no significant difference in their colour rendering quality yet their spectral distributions were very different. However, the consideration arose that the task size within the human field of view equates to a conical zone of approximately five degrees, a zone covered by foveal vision, and an SPD Vλ which the earlier experiment showed to be, in terms of colour vision, limited (virtually monochromatic with yellow-red spectral distribution). Therefore perhaps the result should not be surprising. Incidentally, a 1973 study by a group at UCL, led by RG Hopkinson and E Rowlands, and entitled ‘Visual Performance in Illumination of Differing Spectral Quality’, examined visual performance measured under a range of different lamp colour rendering qualities and illuminances. It involved a collection of Landolt ring tasks, both simple and complex, with a range of coloured tasks. Again, tasks which involved foveal vision. The result was that when the illuminance was 300 lux or greater the colour rendering performances were very similar. Since these two studies provided similar visual performance results, it seems


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reasonable to assume that it is only when the whole visual field is used, a cone width of around 40-degree diameter, that colour identification can be achieved. However, this may be difficult to test and hence the calculation processes suggested in Parts 1 and 2 may be the only alternative. However, because Vλ with its limited range of colour cannot be used for colour vision it can show luminance patterns (subjective brightness patterns), which through shadows and highlights can define three-dimensional form, or volume, as described by the artist David Hockney. Therefore, perhaps there are two types of human sight operating in parallel and depending on the task in hand, which the brain selects as the combination required for the particular visual task. Figure 1 seeks to demonstrate this possibility, though not by using human sight directly. The three images represent the two parts of sight together with the sum of the parts: a) A black and white photograph demonstrates the possible performance of foveal vision, in other words of no or very limited colour, and through shading and highlights indicates the shape of the objects. b) A water colour sketch which aims to show only the outline of the objects and their colour as detected by the full visual field. c) A colour photograph showing normal vision as a combination of foveal vision with full field vision of cones of around 40 degrees wide.

 F  ig 1: demonstrating images which when combined make up human sight. Image (a) demonstrates the monochrome image as seen by the fovea (Vλ). In reality the image would be yellow-red in colour. Image (b) is a watercolour attempt to show the approximate colours of the objects in profile. Image (c) attempts to show the combination (a) + (b) = (c) human sight




All of this suggests that sight is about luminance patterns which are defined by illumination, either directly by a light source,

E 11

Lighting metrics

September/October 2020

 F  ig 2: example of illumination for an art gallery with a low background luminance and hence a low visual adaptation. This enables the illuminance on the artwork to be at a level that minimises damage

It will need more work from neurologists and other scientists to investigate these suggestions and to put it to the test. Designers would also need to consider its effect on design, with their experience of illumination both in terms of function and appearance. Light source manufacturers also need to consider it since they will need to provide light sources with better colour performance.


or by any intervening surface reflectance or transparency. These, together with the human colour observational experience in the above proposal, suggests at least a simplistic hypothesis which needs further investigation.

ILLUMINATION LUMINANCE DESIGN There remains the possibility that some illumination situations, through their luminance patterns, can be a form of pleasure or distaste, and of comfort and discomfort, as well as providing the most appropriate illumination for the particular task or industry. Yet in many cases they are based on a uniform planer task illuminance and glare index which, in their defence, allows the same task illumination conditions, normally over a horizontal plane over a wide area. However, there are many designers who go beyond the basics, and design lighting schemes based on appearance, particularly of illumination on vertical surfaces, which may or may not enhance performance. And this is an area that still needs considerable investigation.

HUMAN SIGHT AND THE PROCESS OF ADAPTATION A further problem with using human sight within the testing process is that of both colour and luminance adaptation. Note the various examples of ‘apparent’ colour-changing illusions, which can demonstrate dramatic colour changes where none exist, except within the brain. Also note that human sight will try to adapt to the range of luminances within a particular scene with an attempt to minimise discomfort glare or to enable a good quality of sight in a low light condition.


Note how in an art gallery the ideal is to provide a task illuminance to minimise conservation problems. And to provide a low level of background illumination, perhaps by the average luminance within the human visual field, relative to the illumination on the artwork can provide visual satisfaction with less potential problems of damage to the artwork (Figure 2). Considering that natural daylight has a spectral distribution embracing all the colours of the rainbow it is suggested as the spectrum of illumination metrology and named DVλ (see Parts 1 and 2). This is particularly as the DVλ spectral distribution includes the zone covered by Vλ, which is the spectral distribution currently used for task illumination.

INSTRUMENTATION If the suggestions provided in this study are considered to be feasible then there remains a need for instrumentation which can measure luminance distributions over a field of the human eye, in other words a 40-degree cone with the spectral response of DVλ. And small enough to be helpful in the field. However, with modern technology based on digital camera technology, this should not be impossible. It could also be engineered with an attachment so it can be converted into the measure of planer illuminance.

WHERE NEXT? This study proposes that a better system of illumination measurements could be developed based on an improved understanding of human sight leading to a better system of illumination metrology.

A further consideration regarding the above is an article in Lighting Journal June 2015 by researcher Dr Erez Ribak et al of the Technion-Israel Institute of Physics and Medicine. It reports that in 1906 the Nobel Prize for Physiology and Medicine was awarded jointly to Santiago Ramón y Cajal and Camillo Golgi in recognition of their work on the structure of the nervous system. Among many other discoveries, they discerned the structure, shape and organisation of the various human neural cells. In particular, they discovered neural tissue in the retina for detecting images that enables colourful sight in daylight and grey at night. A question they posed was why are the neurons in front of the photoreceptors? The neurons are very thin, approximately 0.25mm, and near transparent. Further work carried out more recently by Professor Andreas Reichenbach in Leipzig focused on the Muller cells, concluding that they can serve as light guides – according to the recent research of Ribak et al, specifically colour light guides to the retina. At the very least, this limited analysis of human light and colour sensitivity raises the possibility that the two elements of sight mentioned in the main article, the fovea, which is near monochromatic, and the colour element, operate in parallel.

See SLL Newsletter March/April 2018 and Light Lines March/April 2020 for full details of the first and second studies: • https://issuu.com/ matrixprint/docs/ sll_mar_apr_18 • https://issuu.com/ matrixprint/docs/2987_sll_ light_lines_march_2020_ issuu?fr=sNzBhYjE2MjEw



September/October 2020

ULTRA CAUTION WITH ULTRAVIOLET In a recent position statement, the CIE has warned against the uncontrolled use of UV-C lighting prompted by the coronavirus pandemic he CIE has warned against the use of UV disinfection lamps to disinfect hands or any other area of skin unless clinically justified. While it acknowledges that products which emit UV-C are 'extremely useful' to disinfect air and surfaces or sterilise water, it follows WHO (World Health Organisation) advice in advocating caution. 'UV-C can be very hazardous to humans and animals, and therefore can only be used in properly constructed products that meet safety regulations, or in very controlled circumstances where safety is taken into account as the first priority, ensuring that the limits of exposure as specified in ICNIRP (2004) and IEC/CIE (2006) are not exceeded,' says the CIE in


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its recently issued position statement. 'For proper UV assessment and risk management, appropriate UV measurements are essential.' The current pandemic has accelerated the search for environmental controls to contain or mitigate the spread of coronavirus (SARSCoV 2), and there has been widespread publicity for the potential use of UV lighting as a disinfector and steriliser. Germicidal UV radiation (GUV) can reduce both contact spread and airborne transmission of infectious agents such as bacteria and viruses. GUV within the UV-C range (200nm–280nm), primarily 254nm, has been used successfully and safely for more than 70 years, says the CIE. 'However, GUV must be knowledgably applied with appropriate attention to dose and safety.

Inappropriate GUV application can present human health and safety issues, and produce insufficient deactivation of infectious agents. Application in the home is not advisable, and GUV should never be used to disinfect the skin, except when clinically justified.' UV-C has been used successfully for water disinfection for many years, says the statement, and UV-C disinfection is routinely incorporated into air-handling units to manage the build-up of biofilms and to disinfect air (CIE, 2003). UV-C sources were commonly used in several countries to sterilise operating theatres and other rooms overnight until the availability of antibiotics and vaccines together with the introduction of polymer materials in healthcare settings made its use less necessary.




The CIE refers to the resurgence of interest in the use of whole room UV-C exposure devices for healthcare environments intended to disinfect the air and accessible surfaces. 'Such devices can either be placed in a specific room location for a period of time, or they can be robotic units that move around the environment to minimise shadow effects. For surface disinfection, in addition to the option to place a UV-C source in the room, it is possible to place a UV-C source close to a surface.' The CIE says that 'there is growing evidence that the use of UV-C as an adjunct to standard manual cleaning in hospitals can be effective in practice, although more specific application guidelines still need to be developed as well as standard testing procedures.' Upper air disinfection UV-C sources are usually mounted above head-height in rooms and operate continuously to disinfect circulating air. Their use in this way has been recommended by the WHO as a means for tuberculosis infection prevention and control, for example. Outlining the risks associated with UVC, the statement points out that most people do not get exposed to it naturally. UV-C from the sun is primarily filtered by the atmosphere, even at high altitudes, and human exposure to it typically arises from artificial sources. UV-C only penetrates the outermost layers of the skin and doesn't penetrate deeper than the surface layer of the cornea of the eye. However, exposure of the eye to UV-C can result in photokeratitis, a painful condition that feels as if sand has been rubbed on to the eye, and when the skin gets exposed to high levels of UV-C, it can cause reddening similar to sunburn (erythema). There is some evidence, says the CIE, that repeated exposure of the skin to UV-C levels that cause erythema may compromise the body’s immune system. While ultraviolet radiation is generally considered to be carcinogenic, there is no evidence that UV-C alone causes cancer in humans. 'While the UV radiation from low-pressure mercury UVGI lamps has been identified as a potential carcinogen, the relative risk of skin cancer is significantly less than the risk from other sources (such as the sun) to which a worker will be routinely exposed,' the CIE concluded in an earlier Technical Report (CIE 187: 2010).


September/October 2020

Some UV-C products may additionally emit UV-B or UV-A, says the CIE, 'and some UV disinfection sources declared as UV-C sources may not even emit UV-C'. This may increase the risk of skin cancer if protective measures are not taken. In normal use, however, UV sources secured inside ductwork for recirculated air or used for water sterilisation 'should not present a risk of exposure to people'. The position statement also looks at how UV-C is measured in situ, usually using handheld UV-C radiometers. The CIE stresses the importance of accredited laboratory calibration, and applying any recommended correction factors. 'The calibration report is usually only valid for the UV-C source used in the calibration,' it adds. 'Significant errors may result when measuring other source types with the instrument.' Ideally, says the CIE, the instrument will be calibrated using a source with a similar spectral composition to those to be measured by the user, 'in order to reduce spectral mismatch errors'. Finally, the CIE touches on the current proliferation of UV-C consumer products, often handheld, promising efficient disinfection of surfaces and air. Specific guidance on the safety of consumer products is the responsibility of other bodies, it says, and the position statement only covers the wider issue of the safe use and application of UV radiation for germicidal disinfection. However, it expresses concern 'that users of such devices may be exposed to harmful amounts of UV-C. Moreover, consumers may use/handle UV products inappropriately – and therefore not achieve effective disinfection – or they might be buying products that do not actually emit UV-C'. For the full position statement complete with references go to: http://cie.co.at/ publications/cie-position-statementuse-ultraviolet-uv-radiation-managerisk-covid-19-transmission For earlier statements on UV go to: https://www.cibse.org/news-and-policy/ april-2020/cie-releases-two-keypublications-on-uv-disinfecti The LuxLive Digital Kicker Conference on UV-C lighting will take place on 22 September. Go to https://luxlive.co.uk for the latest information

What is GUV? Ultraviolet radiation is that part of the optical radiation spectrum that has more energy (shorter wavelengths) than visible radiation, which we experience as light. GUV is ultraviolet radiation that is used for germicidal purposes. Based on the biological impact of ultraviolet radiation on biological materials, the UV spectrum is divided into regions, defined by the CIE as: UV-A: wavelength range 315nm-400nm UV-B: wavelength range 280 nm-315 nm UV-C: wavelength range 100 nm-280 nm The UV-C part of the UV spectrum has the highest energy. While it is possible to damage some microorganisms and viruses with most of the ultraviolet radiation spectrum, UV-C is the most effective and hence UV-C is most commonly used as GUV. The radiant exposure required for the deactivation of an infectious agent by 90 per cent (in air or on a surface) depends on the environmental conditions (such as relative humidity) and the kind of infectious agent. It typically ranges between 20 J/sqm and 200 J/sqm for mercury lamps predominantly emitting radiation at 254nm (CIE, 2003). Previously, GUV of 254nm has been shown to be effective in disinfecting surfaces contaminated with the Ebola virus. Other studies have demonstrated the effectiveness of GUV during an influenza outbreak in the Livermore Veterans Hospital, California. However, despite ongoing research, at present there is no published data on the effectiveness of GUV against SARS-CoV 2. – CIE Position Statement


LR&T essentials

September/October 2020

ON THE ROAD Iain Carlile looks at four of the most recent online Lighting Research and Technology papers, all of which focus on street lighting themes n the first of the papers, Sakar et al consider the changing technologies of street lighting and the effect that supply power quality may have, resulting in the incorrect operation of the lighting and potential safety issues. The authors note that while much research in this respect has been done on traditional street lighting using high-pressuresodium (HPS) lamps, little research existed on voltage dips with LED street lighting. An experiment was conducted in which artificial voltage dips were applied to incandescent, HPS and LED sources, and the results compared against proposed metrics. These included performance metrics (flicker and light intensity) and transient characteristics (overshoot, response delay and response time). When compared to incandescent and HPS lamps, LED sources exhibited uncoordinated light intensity drops, being longer or shifted with respect to the voltage dip. From the outcome of the study, the authors recommend that LED street lights need testing prior to installation to prevent unexpected consequences. Given that an increasing number of HPS street lighting installations are being changed over to LED, the authors make recommendations for standardisation committees to implement an assessment method for lighting equipment. A paper by Fotios et al investigates how ambient light conditions (daylight versus after





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dark) may affect road traffic collisions (RTC). Four analyses of RTCs were carried out in order to compare differences between the methods of analysis. These involved a repeated analysis of RTCs in the UK in daylight and darkness, to test reproducibility, an Odds Ratio analysis, a defined case hour analysis, and a whole year analysis. From the results, the authors conclude that previous studies may have underestimated the detrimental effect that darkness has on the risk of RTCs. In another paper, Robbins and Fotios note that, with respect to road lighting, there are two separate bodies of research showing how changes in lighting conditions affect hazard detection, and that driving is impaired by distraction. However, the two bodies of research have yet to be integrated, which is critical for lighting design recommendations, since distraction may affect the optimal lighting conditions. In order to progress this, the authors investigated what could be considered the critical types of distraction, so that these may be simulated in future lighting research. Two methods were used to identify the prevalence of driving distractions. The first method involved interviews with drivers following collision, while the second method used observation of drivers on real roads. From the analysis of the data, prevalent distractions were identified as auditory, such as conversations with other passengers

Voltage/current sensor

ď ´  Fig 1: Schematic of test set-up for voltage dips (Sakar et al)

and listening to music. The authors therefore recommend appropriate auditory distractions be incorporated into future experiments studying the effects of lighting and hazard detection. Cao et al present a study of the effect of driving speed on visual performance under mesopic vision. The experiment was conducted using a driving simulator, in which the effect of two different variables was studied: detection rate (DR) and detection distance (DD). From the results of the study, it was found that driving speed has a significant effect on both DR and DD, with an increase in driving speed resulting in a significant decrease of both values. Based upon the results of the experiment, the authors propose a new model, the Simulator-based Visual Performance model, which describes the effect on visual performance of driving speed, target contrast, distance and their interactions. 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) Susceptibility of LED street lamps to voltage dips S Sakar, A Bagheri, S RĂśnnberg and MHJ Bollen A comparison of approaches for investigating the impact of ambient light on road traffic collisions S Fotios, CJ Robbins and J Uttley Road lighting and distraction whilst driving: Establishing the significant types of distraction CJ Robbins and S Fotios Effect of driving speed on target visibility under mesopic conditions using a driving simulator D Cao, Y Tu, Z Wang, L Wang, L Liu, Z Chen, D Lou, X Zhu and C Teunissen


Events 2020

For up-to-date information on all SLL events please visit the website: www.sll.org.uk

16-18 SEPTEMBER [d]arc room livestream Conference, workshop and product demonstrations www.darcroom.com 22 SEPTEMBER LuxLive Digital Kicker Conference Online event on UV-C lighting https://luxlive.co.uk 6-11 NOVEMBER Applying Light for Human Health: Lighting Research and Technology Symposium (online event) www.sll.org.uk 11-12 NOVEMBER LuxLive Digital Festival Online event with overall theme of health and wellbeing with four strands: Emergency Lighting, Smart Lighting, Workplace, and Lightspace Festival https://luxlive.co.uk

12 NOVEMBER Lux Awards Online event https://luxawards.co.uk

19 NOVEMBER Lighting Design Awards Venue: Troxy, London E1 https://awards.lighting.co.uk 24-25 NOVEMBER Build2Perform (CIBSE event) Venue: Olympia London www.build2perform.co.uk



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SLL Light Lines September/October 2020