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 LL4 2025 IS 23 MAY
PUBLISHED BY
The Society of Light and Lighting 91-94 Saffron Hill London EC1N 8QP www.sll.org.uk ISSN 2632-2838
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 Designed and printed in the UK
Since the discovery of the third photoreceptor in the eye, the focus has been on the blue end of the lighting spectrum (peaking at 460nm in terms of melatonin suppression).
However, research has increasingly revealed the importance of red and infrared wavelengths to human health. In Unseen Benefits (p7) Dr Martin Moore-Ede, who as a Harvard professor led the team that located the suprachiasmatic nucleus, the biological clock in the human brain, looks at its significance.
There are diverse areas where deep red and infrared light have been shown to have beneficial effects. Near infrared light has been found to reverse the deteriorations of mitochondrial function that result from ageing and disease, for example.
A study at the University of Pittsburgh published earlier this year found that exposure to 617nm red light could reduce the size of blood clots with implications for treating and preventing heart attacks and strokes, while
irradiating human skin with 670nm red light for 15 minutes has been found to beneficially affect glucose tolerance.
Ironically, our adoption of energy-saving measures has had unforeseen repercussions in this area. 'We live in an infrared-deprived world,' says Moore-Ede, citing the growing use of IRblocking E-Glass in buildings and LED sources that have little deep red and no infrared (unlike wood fires, candles and incandescent lamps).
The solution though is not exclusively artificial. 'The richest source of near-infrared light is sunlight, or even daylight on a cloudy day,' says Moore-Ede.
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 Lighting (2023)
SLL Lighting Guide 5: Lighting for Education (2011)
SLL Lighting Guide 6: The Exterior Environment (2016)
SLL Lighting Guide 7: Office Lighting (2023)
SLL Lighting Guide 8: Lighting for Museums and Galleries (2021)
SLL Lighting Guide 9: Lighting for Communal Residential Buildings (2022)
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 (2022)
SLL Lighting Guide 13: Places of Worship (2018)
SLL Lighting Guide 14: Control of Electric Lighting (2023)
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)
SLL Lighting Guide 20: Lighting and Facilities Management (2020)
SLL Lighting Guide 21: Protecting the Night-time Environment (2021)
SLL Lighting Guide 22: Lighting for Control Rooms (2022)
Guide to Limiting Obtrusive Light (2012) Code for Lighting (2022)
Commissioning Code L (2018)
SLL Lighting Handbook (2018)
CIBSE TM66: Creating a Circular Economy in the Lighting Industry (2021)
CIBSE TM65.2: Embodied Carbon in Building Services – Lighting (2023)
FROM THE SECRETARY
Thank you to everyone who joined us at the SLL conference, Illuminating the Future: Balancing Light and Dark Nightscapes. The event took place at the end of March at Senate House, University of London. Thank you to SLL immediate past president Helen Loomes for organising the conference, and working with the speakers to deliver such an informative event.
We look forward to the SLL AGM on the evening of Thursday 20 May at the Barbican, London. The AGM will be followed by the presentation of the SLL Annual Awards. Kristina Allison, the incoming president, will then give her address, outlining her vision for the year ahead, and we will have a chance to thank outgoing president Dan Lister for his work over the previous 12 months. We will then move on to the Barbican’s Garden Terrace for socialising and networking.
SLL will partner with the LIA’s TECH-X, a brand new conference designed to bring the entire lighting industry together. Taking place on Wednesday 10 September at Convene 133 Houndsditch, this event will feature multiple stages with diverse tracks, covering everything from connected lighting and design innovations to critical regulatory updates.
Staying with the LIA, the SLL will again partner with the ICEL Conference which will take place at Cavendish Conference Centre, London, on Thursday 11 September.
Meanwhile Recolight will host the Circularity Live Conference, which we are also partnering once more, on 25September at the Minster Building, London.
SLL Ready Steady Light will return on 14October for its 30thyear in association with Rose Bruford College and the IALD. We are very excited to be celebrating this anniversary and welcome the teams to the college in Sidcup for what promises to be a great day and evening. We will inform everyone when the team entry registrations are available.
The SLL will join the Society of Public Health Engineers (SoPHE) and CIBSE Healthcare Group at the Healthcare Estates conference and exhibition on 21-22October at Manchester Central. We enjoyed our first experience of the event in 2024 and look forward to returning with our CIBSE colleagues and friends.
The SLL will also partner and exhibit at LiGHT 25 on 19-20November at the Business Design Centre, Islington, London. SLL speakers will also
• For more on TECH-X: www.thelia.org.uk/memberservices/events/tech-x.html
• For more details of ICEL: www.thelia.org.uk/resource/ icel-emergency-lightingconference-2025-guidingthe-future-of-emergencylighting.html
• To submit applications for the Jan Heap Bursary: www.cibse.org/sll-jean-heap
• For information on Ready Steady Light: www.cibse.org/ready-steadylight
feature in the conference programmes. The 2024 exhibition and conference was excellent, and such a success that the organisers have opened up a new Tech Zone.
The SLL Young Lighter 2025 deadline for submissions passed at the end of April. Thank you to all who submitted entries to the competition, we will announce the shortlisted entrants soon.
There is still a little time to submit your applications for the SLL Jean Heap Bursary 2025. The deadline day for entry is Tuesday 6May (see box for link).
The application process for the SLL Member grade of membership (MSLL) has been completely changed (see LL Jan/Feb 25). The new application enables early career lighters to apply for MSLL via a set of competencies, and no longer relies on the years of experience or lighting education with years of experience.
We encourage everyone to look at the new application process which is completely online, and which allows you to submit your information in stages. If you would like to discuss the application process please do contact us (sll@cibse.org).
COVER: The recently opened VillejuifGustave Roussy station, designed by architect Dominique Perrault, and one of 68 new stations planned for the Grand Paris Express project.Around 50m below street level, its multi-layered roof structure allows natural light to filter down to the platforms below
Dominique Perrault Architecte
A €3.87m Horizon Europe-funded initiative has been launched aimed at redefining darkness 'as a valuable cultural, aesthetic and ecological resource within urban landscapes'.
The Art of Darkness project brings together diverse partners, including LUCI, the international network of cities concerned with urban lighting for social, cultural and economic development.
Over the next three years the project will unite research institutions, cities and creative professionals. It will conduct five artistic pilot trials in cultural heritage sites across five countries –Denmark, Estonia, Finland, France and Italy – with the aim of developing design strategies and solutions that enable 'sustainable, aesthetic and socially feasible dark-time experiences'.
The project integrates diverse disciplines such as architecture, lighting design, light art, cultural heritage, environmental psychology, cultural anthropology, and engineering to explore and showcase the potential of darkness in urban landscapes.
Other partners include LUCI’s city members Montpellier Metropolitan Municipality, the cities of Oulu, Finland, and Tallinn, Estonia, its associated member Eindhoven University of Technology, as well as the University of Bologna, Aalborg University, Tallinn University of Technology, and the Finnish Light Art Society FLASH. The project will be coordinated by the University of Oulu. www.luciassociation.org/the-art-of-darkness-project-kicks-off
ON THE LIGHTER SIDE…
A shout out to Montreal's Lumino which celebrated its 15th anniversary this winter, running from November to March. The largest yet, it featured 30 works of light art by Quebec artists throughout public spaces in the city.
One of them was Chaleur Humaine (pictured), a piece in the Place Pasteur by Anne Lagacé that resembles a suspended sun.
By no means a parochial event, the international arm of organiser Quartier des Spectacles Partnership has now
taken Lumino installations to 100 cities in 14 countries on five continents. www.luminomtl.com/en
ONLY CONNECT
The LIA is launching a new, oneday lighting conference. TECH-X, partnered by the SLL, aims to set 'a bold new standard in the sector'.
Based on feedback from past LIA events, it will be a multi-disciplinary forum, with multiple stages covering diverse lighting themes. These will include connected lighting solutions, innovations in lighting design and updates on essential standards and regulations.
The LIA has also teamed up with BEAMA, the UK manufacturing trade association for the electrotechnical sector, to present the 2050 Connected Conference, a two-day event designed to drive action on net zero and circularity in the built environment and energy supply chains.
'More than just an event, it is a catalyst for action, offering a unique platform for manufacturers, government and the wider supply chain to address shared challenges,' says the LIA.
Featuring government and industry experts, the first day will focus on manufacturers, while day two will bring together manufacturers, distributors, specifiers, contractors, energy companies, facility managers, architects and consulting engineers.
'No one manufacturer can decarbonise alone, it requires a whole supply chain to transform and innovate,' said Yselkla Farmer, CEO of BEAMA.
'The transition to a net zero and circular economy requires more than just regulatory compliance,' added Ayça Donaghy, LIA CEO. 'It demands a fundamental shift in how industries collaborate and innovate.'
The 2050 Connected Conference will take place on 1-2 July 2025 at the Royal College of Physicians, London. More details at: www.thelia.org.uk/ member-services/events/2050connected-conference.html
Tech-X (Technical Excellence Conference) will take place on 10 September at Convene 133 Houndsditch, London EC3
Photo-Henrika Pihlajaniemi
NIGHT VISIONS
Peter Raynham considers the complexity of public lighting and identifies problems that are looming
Richard Feynman famously remarked, 'If you think you understand quantum mechanics, you don’t understand quantum mechanics'. Lighting has now grown to a level of complexity whereby Feynman’s
remark about quantum mechanics could equally be applied.
One of the most difficult issues with lighting is that a full description of the light field and its impacts is too complex to be useful when discussing the subject. A full description of the light field depends on knowing the luminance distribution about every point in space, knowing
the spectrum of the light and knowing how that light has changed over time.
There are two angles needed to define the luminance distribution about a point and three coordinates needed to describe the location of a point in space, so including time and spectrum, this is a sevendimensional problem. There is also a variation in response to the light field between people, and when considering environmental impacts there is a whole range of organisms that need to be considered.
As it is not possible to consider all of the issues at one time,
lighting is approached by a series of simplifications. These methods are often based on research but the simplifications can lead to problems. Moreover, investigating new lightrelated phenomena without considering which elements of the light field are important is a pathway to more problems.
In lighting practice it is common to only consider lighting falling on to or being reflected from surfaces. The properties of a source spectrum are often reduced to photopic lumens, CCT and Ra. This approach works reasonably well when providing sufficient light to make tasks visible, but when trying to control glare and obtrusive light there is no good solution, and a series of control limits and metrics of limited value are used.
Our knowledge of the impact of the light spectrum on people is still very limited. Some 30 years ago we only really considered photopic light and the human brightness response. Then around 25 years ago scotopic and mesopic vision came to the fore,
making the consideration of road lighting more complex. Then came the melanopic response to light and its importance in a range of physiological responses including resetting the body clock.
Finally, a few years ago it was found that red light and infrared radiation can stimulate mitochondriaimproving metabolism. This has impacts on vision, as retinal cells can become more sensitive and, as red light can penetrate the skin, the metabolism of the whole body can be affected. At this stage an action spectrum has not been established and so it is necessary to rely on arguments based on
evolutionary biochemistry to suggest that any part of the solar spectrum may be important.
One of the major issues at present is the increasing number of complaints about the glare and dazzle from vehicle lights, with more commentators putting the blame on new LED lights on cars. But is it really that simple? There are numerous other factors that may be involved in this problem, including: changes in road lighting, changes in road surface quality, changes in light spectrum and changes in the demographics of people who drive at night.
The results of a series of road lighting experiments conducted by Schmidt-Clausen and Bindels¹ show that reducing background illumination has the potential to change a situation where glare is acceptable to one where it is somewhere between disturbing and unbearable. Thus the change to LED street lighting, which controls the light much better than HID sources and thus reduces spill light on to buildings, may be making the glare worse.
We now know that red light stimulates the retinal cells and can improve the speed at which cells are de-bleached. Thus, the absence of red light may slow the recovery from dazzle. Modern headlights are only required to have 28 per cent of the red light of traditional tungsten halogen sources and they have no requirements in the infrared.
One feature of glare response is that it is very variable. Both Schmidt-Clausen and Bindels, and Jia² found that the luminous stimulus to create a given glare response varied by 1000 to one across subjects. This difference in response was further studied by Furlan, Bargary et al³ and they found neurological differences in subjects that related to their responses.
Similarly, there is a wide range of responses to disability glare with a six to one difference between subjects being reported. These varying responses demonstrate how difficult it is to provide a system of public lighting that can meet everybody’s needs.
It is also not just the glare that limits people's use of the streets at night, as illuminance is also important. What's more, it is not just a problem of lighting, there are much larger social and psychological issues in play. This gives rise to the under use of town centres at night by older people which in turn leads to the night-time economy being focused on young people. So even if it was possible to improve the lighting to encourage older people to use the streets at night, ultimately there would be little to attract them in our towns.
One additional complicating factor for public lighting at present is the hand back of the current PFI lighting schemes. The PFI projects that started around 20 years ago allowed local authorities to delegate their public lighting to a contractor who would renew the lighting equipment and maintain the lighting for a period of 25 years. There are 31 PFI contracts in England and most of them will be ending over the next 10 years. The process to end a PFI is not simple, however, and there are many potential problems.
Perhaps the most worrying issue is that many local authorities no longer have a person who is competent in dealing with street lighting and so they may not understand the lighting assets that are being returned to them or how to manage them going forward. There are also a whole range of further issues associated with how well the inventory of the equipment matches the equipment that is installed, and the expected residual life of the equipment that is being transferred. The current advice is that a seven-year programme of hand-back should be used. The net result of this process is that neither the PFI contractor nor the local authority is going to want to take on anything new until the transfer is over, so big changes in lighting strategy are not going to happen for quite a while in the areas affected.
This article is based on a presentation by Peter Raynham, emeritus professor at UCL, at the SLL conference, Illuminating the Future: Balancing Light and Dark Landscapes, on 27 March
REFERENCES
1 Schmidt-Clausen & Bindels, Assessment of discomfort glare in motor vehicle lighting, LR&T, Vol 6,2 1974
2 Yingxin Jia,Astudy of mechanisms for discomfort glare, PhD thesis, School of Health Sciences, City University, 2014
3 Furlan, Bargary et al, Cortical hyperexcitability and sensitivity to discomfort glare, DOI: 10.1016/j. neuropsychologia.2015.02.006
It is human nature to focus only on what we can see, and that is certainly true of
the light in our world. Only 39 per cent of natural daylight is visible to the human eye. The majority (54 per cent) of sunlight is
� 54 per cent of the solar light spectrum comprises near-infrared light (750–1400nm) that penetrates most deeply into human tissue between 700–900nm in the tissue transparency window
invisible infrared light, which we experience as warmth, and the remainder (seven per cent) is invisible ultraviolet light. Recent research reveals just how important this infrared light is to our health.
We live in an infrared-deprived world where the average person spends only seven per cent of their time outdoors. The increasing use of E-Glass, which blocks infrared rays to keep buildings cool, and LED lights that provide only a narrow range of visible light wavelengths with little deep red, and no infrared, narrow the light spectrum we experience indoors in the name of energy efficiency. We are no longer exposed to the near-infrared light generated by the wood fires, candles and incandescent light bulbs of past years¹.
TISSUE TRANSPARENCY WINDOW
Of particular interest is deep red light from 650-750nm, and near-infrared light in the 750-900nm range, which can penetrate multiple centimetres deep into the body. This 'tissue transparency window' is limited by haemoglobin absorption at the lower end and by water absorption of infrared wavelengths at the upper end².
The depth of penetration into tissue depends on the wavelength of the red or infrared light and its intensity. Red light in the 650-670nm range is effective in reducing skin dermatitis after radiation³, and in restoring retinal function in the ageing eye⁴. It has also been very effective in restoring mitochondrial function in small insects such as drosophila and bees. However, to reach deeper tissue nearinfrared light must be used. The peak tissue transmission is at around 850nm, where infrared light, depending on its intensity, and how much melanin pigment is in the person’s skin, may penetrate up to 8cm of depth⁵.
YOU DON’T HAVE TO GET UNDRESSED
Infrared light at 850nm penetrates normal clothing (for example, vest + shirt + sweater) 100 times more effectively than red light at 660nm. Unlike ultraviolet and blue light which are blocked by clothing, you can
get the full health benefits of infrared light with your normal clothes on. Dense fabrics such as denim and ski outfits block infrared while cotton and polyester let most of the infrared reach your body⁶.
When red and near-infrared light penetrates the body, it stimulates the mitochondria within the cells.
Mitochondria are the small intracellular organelles that use glucose and oxygen to produce chemical energy in the form of adenosine triphosphate (ATP) which powers metabolism. As people naturally age, or are impacted by disease, mitochondrial ATP production declines and the mitochondria also produce reactive oxygen species that contribute to systematic inflammation. Exposure to nearinfrared light can reverse these deteriorations of mitochondrial function.
One of the key enzymes in ATP production is mitochondrial cytochrome c oxidase. Its peak sensitivity to infrared light is around 835nm⁷. This is close to the infrared wavelengths that penetrate to the maximum depths.
TIME OF DAY MATTERS
The greatest response of mitochondria to red and near-infrared light exposure is in the morning hours. This is when the circadian rhythm of natural ATP production is at its peak⁸. Exposures to the same dose of red light in the afternoon and evening hours have little or no effect.
Interestingly, the morning is the time of day when the solar spectrum contains the greatest relative proportion of nearinfrared light.
REMOTE EFFECTS
Red and near-infrared light does not have to penetrate deep into the body to have systemic effects. For example, irradiating human skin with 670nm red light for 15 minutes can have a substantial effect on glucose tolerance. The rise in blood glucose levels after drinking a sugar drink was reduced by 28 per cent in people previously treated with this red light shone on their backs. Similarly, irradiating the back of a mouse with red light can improve their retinal function.
This suggests that red and near-infrared light causes chemical changes in circulating cytokines and other molecules that may transit the benefits of red and near-infrared light beyond the specific areas that are irradiated. In addition, red and nearinfrared light stimulates the production of intracellular melatonin, which is an antioxidant.
TRANSITION TO HUMAN MEDICINE
Studies in animal models have shown the benefits of correcting mitochondrial malfunction using near-infrared light in a number of conditions, including brain injury, Parkinson’s disease and multiple sclerosis. As yet, there have been relatively few clinical studies in human subjects, although this is a promising active area of research. Should our indoor lighting provide near-infrared light?
Our indoor lights, as we discussed earlier, used to provide near-infrared from wood fires, candles and incandescent light bulbs, which emit 88 per cent infrared light. Are the dosages we receive from these indoor light sources high enough to matter for our health?
A recent study indicates the answer may be yes. LED lights with added near-infrared in the 800-1000nm range were shown to have a calming and relaxing effect, as compared to LED lights without added infrared⁹. The measure they used was heart rate variability, a marker of sympathetic versus parasympathetic nervous activity. This is part of our body’s autonomic control system which can either activate us in times of danger or challenge (sympathetic nervous system), or calm us down when we are safe and can relax (parasympathetic nervous system).
The study volunteers had a significant increase in relaxation measured by heart rate variability, and an increased subjective sense of pleasure when the lights contained infrared wavelengths.
In the US, even though incandescent light
REFERENCES
bulbs are banned because they cannot meet the 2023 US Department of Energy (DOE) energy standard of 45lm/W, alternatives are available. For example, NIRA A18 and BR30 light bulbs supplement an LED chip with an incandescent filament to provide visible light plus near-infrared light up to 300nm. The challenge is that the near-infrared in the spectrum is treated as wasted watts by DOE regulations so while they can achieve 50lm/W, these light bulbs cannot meet the 125 lumens per watt minimum standard that comes into effect in 2028.
This is one of the reasons why we have petitioned the US DOE to create a new product class of General Wellness Light Bulbs that would not be subject to the 125lm/W minimum.
In the meantime, get outdoors in the mornings. The richest source of nearinfrared light is sunlight, or even daylight on a cloudy day. Mornings are the time of day when the relative infrared content of daylight is highest, and the time when the boosting effect of infrared light on mitochondrial energy production is at its most effective.
1 Moore-Ede M (2024) The Light Doctor: Using Light to Boost Health, Improve Sleep and Live Longer. Circadian Books
2 Fosbury R and Jeffrey G (2024) Life-life interactions beyond photosynthesis. https://herschelsociety.org.uk/wp-content/uploads/ 2024/02/The-Astrophysics-of-Earth_v3.3.pdf
3 Zhang et al (2018) Application of red light phototherapy in the treatment of radioactive dermatitis in patients with head and neck cancer. World Journal of Surgical Oncology 16:222 https://doi.org/10.1186/ s12957-018-1522-3
4 Shinhmar H, et al (2021) Weeklong improved colour contrasts sensitivity after single 670nm exposures associated with enhanced mitochondrial function. Sci Rep 2021 Nov 24;11(1):22872. doi: 10.1038/ s41598-021-02311-1. PMID: 34819619
5 Zimmerman S and Reiter RJ (2019) Melatonin and the Optics of the Human Body, Melatonin Res. 2 (1) 138-160; doi: 10.32794/mr11250016)
6 Saleem A et al (2013) Near Infrared transmission through various clothing fabrics. J Textile Sci Eng 3:2 DOI: 10.4172/2165-8064.1000129
7 Mason MG et al (2014) Re-evaluation of the near infrared spectra of mitochondrial cytochrome c oxidase: Implications for non-invasive in vivo monitoring of tissues. Biochimica et Biophysica Acta 1837: 1882–1891 http://dx.doi.org/10.1016/j.bbabio.2014.08.005
8 Shinhmar H et al (2022) Shifting patterns of cellular energy production (adenosine triphosphate) over the day and key timings for the effect of optical manipulation. J Biophotonics. 15:e202200093. DOI: 10.1002/ jbio.202200093
9 Roddick CM et al (2024) Effects of near-infrared radiation in ambient lighting on cognitive performance, emotion, and heart rate variability Journal of Environmental Psychology 100: 102484
As a professor at Harvard Medical School (1975–1998), Dr Moore-Ede led the team that located the suprachiasmatic nucleus, the biological clock in the human brain. He has a first class honours degree in physiology from the University of London, and medical degrees from Guy’s Hospital Medical School, and a PhD in Physiology from Harvard University. He has published 10 books – including The Clocks That Time Us: Physiology of the Circadian Timing System, and The Light Doctor – and more than 180 scientific papers. He is director of the Circadian Light Research Center in Boston, which he founded in 2010. As well as advising corporate clients, he has testified before Congressional committees and advised government agencies on the health and safety of the 24/7 workforce in the US, Canada and Europe.
For further information on The Light Doctor: www.amazon.com/Light-DoctorMartin-Moore-Ede/dp/ B0D54SHWS4
Alot of photometric data in the form of LDT (luminaire data transfer) and IES (Illumination
Engineering Society) files pass across our desks, but unfortunately we find that the majority of them are problematic.
Lighting designers use advanced tools such as Relux and Dialux to produce incredibly detailed lighting designs with near photorealistic renderings of the lighting effects. They use the glare tables and glare calculations in the programmes and yet they base them on bad input data.
One part of the problem is that the lighting design programmes have made it possible to
� Visualisation of internal communication spaces at the rejuvenated Battersea Power Station, part of an award-winning scheme by Speirs Major Light Architecture: the correct photometric data is key to accurate rendering
import and use any valid data file, though they are quite specific in saying that they accept no responsibility for the quality and accuracy of the data used in their calculations. They must have got so fed up with poorly formatted files being rejected by their programmes that over the years they have made it possible to import virtually anything. We can only conclude that most users believe that if it imports into Relux and Dialux it must be right, but nothing could be further from the truth.
The following are some of the common things we see in photometric data files used for lighting design:
UPLIGHT THAT SHOULD NOT BE THERE
These days most goniophotometers collect data in absolute calibrated intensities, with the lumen output calculated by summing the intensities over the spherical data collection field. Any goniophotometer will measure some stray light during the test as it is impossible even in a good, well-run laboratory to make the surfaces of the test area and the gonio itself completely non-reflective. A properly run lab will carry out a few extra readings to establish the extent of this stray light. With these extra readings it is possible to process the raw gonio data to remove the stray light.
We have seen uncorrected photometric data for sealed-back, downlight-only high bay and low bay luminaires with four to six per cent uplight – in other words at least four to
six per cent over the declaration of lumen output. It is actually worse than this as there will also be stray light in the downward intensities so the ultimate lumen output error will be higher than the non-existent uplight percentage.
Does it matter if there are marginal amounts of uplight or stray light that should not be there? Well, yes it does: stray light incorrectly increases lumen output so all luminaire efficacy calculations (lumens per Watt) required by the Building Regulations will produce values that are too high.
Including non-existent uplight in glare calculations when calculating the RUG (UGR) table will produce values in the standard glare table that are too low.
INCORRECT OR MISSING DIMENSIONS
We see a lot of photometric data files with missing or incorrect dimensions. LDT files describe two sets of dimensions, physical and luminous.
The first set of dimensions gives the physical size of the luminaire. Does it matter if these dimensions are wrong? Again, yes it does. If physical dimensions are wrong, then your luminaire layout plan is worthless. We are placing luminaires close to other services –sprinklers, AC ducting and vents, signage and so on. If the luminaire size is wrong then you can’t tell if your layout will work.
The second set of dimensions gives the size of the luminous portion of the luminaire.The main value dependent on these dimensions being correct is the RUG (UGR) table. If the luminous size is wrong the values in the standard glare table are incorrect.
We see a lot of data for luminaires with some light emitted horizontally and upwards where the luminous height in the file is zero in all four planes. This is physically impossible and should yield a false glare table. However, lighting design programmes do not sense check your data. They perform the calculations and produce values in the standard glare table that are incorrect.
Glare is a hot (misunderstood) topic present on nearly all specifications. Getting the glare table calculated correctly is very important. There is another wrinkle here. IES files only describe the luminous dimensions, and there is no way for an IES file to provide physical dimensions. There are several problems with this:
• If the file is correct, the dimensions in the IES file are the luminous dimensions: the physical size of the luminaire is usually larger than the luminous size, so your layout will not tell you if your luminaire bangs into the AC ducts. An IES file for a luminaire with no luminous height will have a height/
thickness of zero so will not be visible in your layout from certain points of view, which could be a bit of a problem for suspended or surface downlights.
• If the file is wrong and the dimensions are the physical size: the luminous size of the luminaire is usually smaller than the physical size, so the values in the standard glare table will be incorrect. Increasing the luminous area gives lower values in the glare table. Surely no unscrupulous manufacturer would ever do this intentionally to get a better UGR table...?
Lighting design programmes offer a workaround for this problem by providing a facility to edit the dimensions of luminaires, but this is an extra step for the lighting planner which can be avoided by using correctly formatted LDT files instead of IES files. There is quite simply less work required to do the job properly.
NO SYMMETRY OR INCORRECT SYMMETRY
A photometric data file for use in lighting design is supposed to represent the average performance of an average luminaire of that type (except for emergency lighting where there are legal constraints).
Most photometric data files we see have no symmetry applied to them. If manufacturers are developing a luminaire, they would want the test data from the prototypes to be ‘warts and all’ so they could see if it has been manufactured correctly. If the luminaire is meant to have some symmetry and the test data does not, either the test set-up was incorrect or the test sample was wrong, either way the developer would want to know.
Photometric data released to clients/ users should be the average/mean data of the production run of that luminaire, which requires a symmetry to be applied. Not only does this give the necessary average performance, it will also show the product in the best possible light (no pun intended) as the design will show the expected symmetry. It seems this distinction between development data and product data has been lost, and most labs are only issuing non-symmetric files and leaving the manufacturer to apply any symmetry.
TOO MUCH/NOT ENOUGH DETAIL
Photometric tests should be performed using data steps small enough to record the full details of the luminaire distribution, including any unexpected anomalies. Routine tests would be in one-degree steps in elevation and five-degree steps in azimuth, with the ability to reduce this step size when required. This is test data, it is not suitable for release for use with lighting design software.
Lighting design programmes calculate the average effect of a luminaire over a small area, then repeat the calculation for the next small area. The size of the area is determined by many parameters but is typically in the range of 0.2sqm to 10sqm. Visual representations, and maximum and minimum values are obtained by using the results from each of these areas, while the main calculations are based on the combined effect of all these small areas in the lighting scheme. Each area requires the calculation of an average intensity from the luminaire at various angles – the more detailed the file, the longer it is going to take to calculate the average.
The released data for lighting design purposes should have the correct data steps appropriate to the distribution. For instance, a dense, opal downlight that has an almost perfectly lambertian distribution (output is proportional to the cosine of the angle) can be described with 19 data steps (0-90 degrees in five-degree steps), and each elevation angle is relevant to all azimuth angles. This is a small calculation load for the programme.
If, however, a test data file is provided with, say, 0-180 degrees in one-degree steps in elevation and five-degree steps in azimuth, the programme must calculate not from 19 data steps but from 13,032 data steps, which increases the calculation load on the programme and so slows scheme calculation down without having any effect on its accuracy. Providing extra detail is not harmful but it is wasteful and unnecessary and will slow the light planner down.
Trying to design with a symmetric 10-degree FWHM (Full Width Half Maximum) spotlight with five-degree elevation data steps is wrong, misleading and potentially very inaccurate. There would only be three data points that are significant – zero, five and 10 degrees – with no detail about what happens between each point. This luminaire would require data in 0.5degree or possibly 0.1-degree elevation steps to describe the beam shape correctly.
A lot of LED streetlights have very sharply delineated peak intensities in elevation over a relatively small azimuth spread. The old CIE streetlight data format expected variable intensity steps in both azimuth and elevation with maximum detail being 2.5 degrees in elevation and five degrees in azimuth over the peak, relaxing to 15 degrees in both directions well away from the peak.
We have seen LED streetlights that require even smaller steps in both planes. Missing the peak intensity due to wide data steps in streetlighting is very poor practice. It results in incorrect values for threshold increment (TI) and both longitudinal and overall uniformity.
The same requirements for detail apply to narrow-beam floodlights, and some extreme emergency luminaires that have a very narrow peak and a sharp run back above and below
the peak. Don’t forget designers have statutory responsibilities under safety legislation when designing emergency lighting installations and can be held criminally responsible for their designs. Missing peaks and troughs in the data will also result in lumen output errors and therefore incorrect results for luminaire efficacy calculations (lumens per Watt) required by the Building Regulations.
A polar curve showing straight lines is a pretty good indication that the data steps are too wide to correctly describe the luminaire. If a detailed file shows a very jagged polar curve, the lighting designer may decide not to use that luminaire in a scheme as the visual effect when installed may result in stripes on the floor not shown in the average calculations of the lighting design programme.
FILE NAME AND CATALOGUE NUMBER
We believe it is a relatively simple matter to make the file name and catalogue number match in some way. This makes it easy for designers to find a particular product data file from a list. We see a surprising number of files where the file name has no relationship to the catalogue number, and in some cases catalogue number and file name that are supposed to match are different, so the lighting planner cannot be sure which data to use. Manufacturers and laboratories should make it easy for designers to find and verify their data and be sure which product it refers to.
While we are on the subject, another peeve is ridiculously long file names/catalogue numbers. Exporting LDT files from a particular website produces catalogue numbers of 300 characters and more. The LDT file format specifies a maximum of 78 characters for luminaire name and luminaire number, while the subsequent ELX format specifies a maximum of 24 characters. The default maximum expected length for lighting design programmes is now 40 characters. While lighting design programmes may tolerate more characters, they often do not have enough room on the screen to display everything.
The LDT file format specifies a maximum of eight characters for the file name, the subsequent ELX format specifies a maximum of 12 characters. While both limits are currently ignored by lighting design programmes, there are still several applications that stick to the Windows path length and line length limit of 256 characters. It’s annoying to have to edit the file name/ catalogue number just to read the file and means lighting designers are required to do more work to use a particular product. Perhaps this is us being ‘old school’ as we were brought up on 8.3 format for file names, but if you need more than 20 characters for a file name or catalogue number then perhaps you are not really in control.
You might think none of this really matters –the files downloaded go into Relux and Dialux and produce answers, so what? But, as suppliers to designers and users, shouldn’t manufacturers and test laboratories ensure that the data presented is in the best possible format, helping their clients make effective and efficient use of their products?
Richard Hayes is director of independent technical services consultant 42 Partners, founded in 1992, and Dan Griffiths is technical operations manager at the Lighting Industry Association (LIA)
� Most goniophotometers collect data in absolute calibrated intensities, with the lumen output calculated by summing the intensities over the spherical data collection field
Previous studies have shown that the correlated colour temperature (CCT) of light significantly influences individuals when studying or working. However, there is little research on the impact of CCT on stress and task performance, particularly in terms of subjective preference and experience.
A study by Erkan et al investigates the relationship between CCT, participants’ thermal sensation vote (TSV), stress levels and task performance.
Participants had to complete a variety of paperbased tasks, including puzzles and questionnaires, under varying colour temperatures: 2700K, 4000K and 6500K. The participants' heart rate variability was monitored, and they were also fitted with an electroencephalogram (EEG) to objectively assess stress levels. The study primarily focused on EEG alpha and theta waves.
The authors also list some of the limitations of the test methodology, such as possible variations due to CRI. Also, the time of day was not taken into account. However, the overall results show that under the 2700K conditions, participants reported higher thermal comfort and better cognitive task performance rates.
B Kim et al have looked at context-aware
presets for office lounges, otherwise known as break-out spaces. Previous studies have shown the benefit of different lighting scenes but they are not often achieved in practice due to users not actively changing the settings. Again, smart lighting systems or those driven by AI using multiple sensors have been proposed but not widely adopted. Common concerns are the initial cost and the technical expertise required for installation.
The authors first developed lighting solutions for five different scenarios: empty, relaxation, discussion, chatting and party. They then developed a simple algorithm that detects the number of users, their movement and their sound volume (dB) by using an omni-directional microphone and a single webcam. With this information, the algorithm suggests appropriate lighting settings. This was tested on two types of office and user assessments evaluated. The conclusion was that the adaptive presets enriched the users’ experience.
There is a discussion on how best to improve the algorithm, revolving around the trade-off between simplicity and accuracy. The aim is to optimise the algorithm for different contexts such as schools and residential spaces.
As soon as you begin to learn about daylighting
⊳ Brain maps showing the change according to the alpha power value of successful/ unsuccessful participants at different CCT levels (Erkan et al)
or colour rendering, one of the first aspects you encounter is Daylight Illuminant D65, a standardised reference light source used in design and research with a colour temperature of 6500K. It is often used to describe the colour of the daylight. However, you soon learn that it represents the colour of an overcast sky and fails to capture the variability and richness of actual daylight. In particular, the blue of clear skies.
Recent research shows that the spectral composition of the light influences our mood, perception and physiological responses. This is affected by sun position and weather conditions, as well as geographical location.
A short paper by M Knoop et al, Our skies are too grey: Where is the colour?, describes a programme to collect worldwide spectral daylight measurements. This is to emphasise the need for localised data to appropriately represent daylight in different locations.
Some research on the subject was done in the early 1960s, and later confirmed by TV researcher Anya Hohnbaum who travelled the world for travel company Expedia to find the best blue sky. It was found to be in Brazil.
Alan Tulla is a former president of the SLL and principal of the independent consultancy Alan Tulla Lighting
Lighting Research and Technology: OnlineFirst In advance of being published in the print version of Lighting Research and Technology (LR&T), all papers accepted for publishing are available online. SLL members can gain access to these papers via the SLL website (www.sll.org.uk)
Effects of Lighting on task performance, stress and thermal sensation in working environments
I Erkan, S Simsek, AB Avci, G Akyol
Context aware lighting for office lounge with simple algorithm
B Kim, G Yi, H-J Suk Our skies are too grey: Where is the colour?
M Knoop, P Balakrishnan, L Bellia, UJ Blaszczak, AK Diakite-Kortlever, D Dumortier, J Hernandez-Andres, M Inanici, P Kenny, MB Kobav, S Liang, T Luo, M Maskarenj, P O'Mahoney, C Pierson, AThorseth, P Xue
Like many island dwellers I am hopelessly drawn to water and the sea. For me, nature is one of my biggest inspirations and, as a lighting designer, natural light, and all its nuanced qualities, has a massive influence on my professional and personal life. When the two are brought together the result is something beautiful, ethereal and perfect. It wasn’t until I started to try to compile this list that I realised just how many images I have of light and water. I am also in awe at the beauty we, as humans can create in the form of art, architecture, music and literature. While we can make amazing advances in science and technology to improve our lives, cure illnesses and explore the depths of the oceans or the far reaches of space, the really good stuff comes when we create, design, write and compose. It enriches our lives and nourishes the soul.
Sydney Harbour
Go to any large city on the water and at night this mesmerising kaleidoscopic dance will take place. There is something otherworldly when artificial lighting is reflected in water, especially if it is agitated or moving. I love the way that the lights of the bars, restaurants and vibrant nightlife along the harbourside melded together in the water, creating this stunning abstract image. I loved the effect so much I actually took three images and rotated them through 90 degrees to create my own Rothko-inspired triptych.
Yosemite 'Firefall'
There is a rare phenomenon where the perfect timing of the right sunlight at the right angle creates the illusion of fire. The first magical occurence is at Horsetail Fall on El Capitan in Yosemite, every February (pictured). From some angles, it appears that lava is spewing over the cliff. The second is Nicola D’Antino's Fontana Luminosa in L’Aquila, Italy. When the sun is at the right angle and you are in exactly the right location, the two bronze women appear to be pouring molten lava from their Abruzzese cauldron.
Sunlight and water
The Solent (other stretches of water are available)
Taken with an old iPhone one morning in 2012 out sailing on a chilly November day. A dark, moody sky gathered and an unpleasant storm blew in. We rode it out, to be greeted by the sunlight punching through the clouds like a celestial ray of hope, perfectly framing one of the fleet who had just managed to get their spinnaker up. When light punctures a stormy sky it reminds us the storm will pass and there is hope of better times beyond. A lovely metaphor for life.
Venice
The perfect storm of natural light, water, architecture, art and culture. From the dark back streets and the narrow alleyways to the moment you emerge without warning into an open piazza flooded with natural light. And everywhere there is that magical interplay of light, water and shadow. Venice is beautiful at any time, but I would pick February on the build up to Carnivale, when the mists rising off the canals diffuse the daylight to give the whole city an ethereal glow. It is both haunting and romantic. 1 4 5 3 2
This effect is completely different to the sun breaking through clouds, or the illusion of fire, and is a perfect demonstration of the powerful, transformative effect of light. While we can use artificial light to transform the look of a space, convey an emotion or tell a story, nature was there first. Those subtle nuances we try to recreate as lighting designers are often borrowed from observations of the natural world. The refraction and disruption of light through water to create a rainbow is a fascinating reminder of the complexities of light.
James Poore, FSLL, is the newly appointed regional director lighting at Aecom
James Poore
Adobe Stock
James Poore
StockCake
James Poore
Events 2025
For details of all upcoming webinars, go to: www.cibse.org/societyof-light-and-lighting-sll/sll-events/upcoming-webinars-and-onlinecontent
For previously recorded CPD webinars (including regional webinars), go to: https://www.cibse.org/get-involved/societies/society-of-lightand-lighting-sll/sll-events/on-demand-webinars-past-presentations
EVENTS
SLL AGM, AWARDS & PRESIDENTIAL ADDRESS
Date: 20 May
Venue: The Barbican, London www.cibse.org/whats-on/search-events/sll-agm-awardspresidential-address-2025/
TECH-X
TECHNICAL EXCELLENCE CONFERENCE
(organised by the LIA and supported by the SLL)
Date: 10 September
Venue: Convene 133 Houndsditch, London EC3 www.thelia.org.uk/member-services/events/tech-x.html
ICEL CONFERENCE
(organised by the LIA and supported by the SLL)
Date: 11 September
Venue: Cavendish Conference Centre, London W1 www.thelia.org.uk/member-services/events/icel-emergencylighting-conference.html
CIRCULARITY LIVE CONFERENCE
(organised by Recolight and supported by the SLL)
Date: 25 September
Venue: Minster Building, London EC3 www.recolight.co.uk/circular-lighting-live/
READY STEADY LIGHT
(organised by the SLL with Rose Bruford College and the IALD)
Date: 14 October
Venue: Rose Bruford College, Sidcup, Kent www.cibse.org/ready-steady-light
HEALTHCARE ESTATES CONFERENCE AND EXHIBITION
(organised by the Society of Public Health Engineers (SoPHE) and CIBSE Healthcare Group, and supported by the SLL)
Date: 21-22 October
Venue: Manchester Central www.healthcare-estates.com/
LET DIPLOMA IN LIGHTING DESIGN
For details and registration: www.lightingeducationtrust.org
