18 minute read
HUMAN LIGHTS
The Lighting Research and Technology Symposium this month will focus on the theme of lighting and human health. Based on their presentations, John Mardaljevic and Peter Raynham examine the roles of natural light and electric lighting respectively
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Let’s begin by imagining that we know just how much ‘natural lighting’ (daylight) is necessary for human health – of course, we don’t, but let’s pretend for now that we do. Just how much is likely to be some absolute measure of (daylight) illumination received at the eye. It will be an amount, or perhaps a varying amount over time (sometimes called a profile). Whatever the amount, or profile, it probably won’t be of the common or garden lux variety; rather, it’ll be one of the (now several) non-image forming light metrics. That’s another way of saying that the spectral character of the illumination needs to be accounted for. Maybe the changes in the spectral character of daylight need to be tracked also, in order to properly effect circadian lighting.
At this point, you might be thinking: 'Hold on a moment, isn’t daylight "circadian" to begin with?' You would, of course, be quite correct. In fact, it would be perfectly reasonable to call for a halt in this progression of reasoning much earlier on. And, instead, begin to ask rather more fundamental questions, for which we need answers before we can even begin to progress meaningfully with any of the above.
Although not explicitly indicated, the title refers to natural illumination inside buildings. As long as we spend moderate amounts of time outdoors, we probably don’t have to worry about getting too little natural light. Unless our intention is to synthesise vitamin D from exposure to sunlight — but (mercifully) that is outside the scope of this short article. Prepandemic, we were probably all spending far too great a proportion of our waking lives indoors. For many, the ‘lockdown’ may have afforded the opportunity to take daytime walks that, under normalcy, would not have happened. It’s also likely that many swapped a dingy spot in a deep-plan office for a better-daylit home alternative (even if what they sit on in the kitchen isn’t quite as comfy as the expensive ergonomic chair which their lower-back has fond memories of). Whichever way, pre-, during or (fingerscrossed) post-pandemic, it is the daylight inside buildings that is important to us. E
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Thus we look to guidelines, recommendations and/or standards to ensure that the buildings which we occupy provide the natural illumination that we need. Or, from a buyer’s perspective, ‘want’ rather than ‘need’. The 2012 Future Homes Commission survey showed that '63 per cent [of potential UK house-buyers] rated natural light as the most important aspect of a home'. A need that many (in the UK at least) feel is not being met by much of the modern housing stock on the market. And so many of us choose to buy energyinefficient Victorian homes that possess, among other things, splendid daylighting from large windows. We cannot, alas, choose either our workplaces or the schools our children go to based primarily on their perceived daylighting properties. Instead, we must rely on guidelines, standards and so on to provide for that.
View of sky and ground across a window aperture
Planning guidelines in particular can be a major determinant of the daylighting potential of the final building.
In the 1920s, Percy Waldram determined what was intended to be a precise and objective measure of an 'ordinary notion' of sufficiency for daylight illumination. Instead of using the actual (absolute) measures of illumination – as recorded by the instruments Waldram used in the study – he instead defined the provision of daylight in terms of a relative measure called the sky factor (assuming a uniform luminance sky). The daylight factor is essentially an evolution of the sky factor, though accounting for reflected light, glazing transmission and based on the CIE standard overcast sky luminance pattern (codified by the CIE in 1955). In the mid-1990s, climate-based daylight modelling (CBDM) was first demonstrated and proven to be capable of high accuracy, in other words the Four-Component method was validated using the BRE-IDMP dataset. CBDM is now a commonplace simulation tool to predict performance measures for the evaluation of building designs.
CBDM would appear to open the door to being able to predict just how much light arrives at the eye, and when. However, all building performance simulation (BPS) is subject to the performance gap (PG) where the disparity between, say, predicted and actual energy use could be large, for example, a factor of two or more. The magnitude of the energy performance gap is well documented because, once the building has been occupied, the meters reveal actual consumption against which prediction can be compared.
Despite the disparities between simulated and actual performance, BPS is still carried out on a routine basis to evaluate building design options because it is generally believed that BPS will help drive the design in the right direction. While the (possibly illusory) absolute target might be the end goal, it is largely the relative outcomes between design options that drive building design. Illumination quantities, however, are never routinely measured, except for conservation purposes in museums and so on. So the performance gap between, say, climate-based daylight predictions and actual daylight levels in real, occupied buildings has never been quantified. Nevertheless, as noted, validation studies provide confidence that BPS is effective for design refinement/optimisation even if absolute accuracy is elusive.
For the reasons given above, it would be unwise to prescribe any performancebased daylight metrics as a basis for planning, since decisions could be readily challenged in court as ‘unsound’ because of the (unknowable) performance gap. Perhaps, for planning, we need to take a step back from complex BPS and reconsider some of the fundamental principles of daylighting.
First and foremost: what is the skylight and sunlight potential of the building apertures? This consideration should take place at the early design stage using only a 3D model of the building envelope, but including whatever geometrical complexity is necessary to obtain a reliable result, for example, window reveals, overhangs, balconies, external obstructions. Ideally, the underlying method(s) used to determine measures of skylight/sunlight potential should be purely geometrical, and therefore not subject to the performance gap. Notwithstanding this requirement, it should be possible to then make reliable estimations of the daylighting performance potential of the apertures.
This radical shift in the way we evaluate building apertures is, I believe, needed because the intrinsic uncertainties in BPS are being overlooked in the rush to sate an appetite for ever more impressive-sounding claims regarding the prediction of metrics for non-image forming effects, wellbeing and so on. We need to give the ‘head’ a chance to catch-up with the fast moving ‘feet’.
John Mardaljevic is professor of building daylight modelling at Loughborough University
Autodesk, Boston, lighting by Lam Partners: European workplace guidance due out next year will include advice and suggest possible metrics for mean room surface exitance, together with visual lightness and interest
To provide the electric lighting necessary to support human health we must first understand which bits of health we can support and what sort of level of proof we need to make a health claim. The two main ways of collecting evidence for a claimed health benefit are double blind trials and large epidemiological studies. In the area of lighting both these methods are virtually impossible so it is going to be very hard to claim a health benefit for lighting in a rigorous way. However, we all know that good lighting in a room can make you feel better, but this is a feeling and so may be described as an improvement in wellbeing rather than a direct health benefit.
On the other side of the coin we know that inferior lighting that perhaps causes glare or is annoying due to flicker can be bad for us and cause headaches. Also there are claims that insufficient illuminance for
a given task can cause myopia in children. So perhaps the first thing for electric lighting to do is to avoid these problems by following the existing codes and guidance.
There are two potential ways for lighting to make us feel better: one route could be described as psychological and the other route is physiological. This distinction is somewhat tenuous like the way glare is split into discomfort and disability flavours. The physiological impact of light has been studied a great deal recently, and the mechanisms and pathways involved are documented if not fully understood. However, work on the physiological areas of the problem has detracted from the more traditional studies of the psychological impact of light and, more widely, the whole discipline of environmental psychology is being squeezed out in the focus on neuroscience.
However, psychological benefits of good lighting are there. The problem is pinning down which bit of the lit environment generates the benefits. So again the problem needs to be approached from the negative perspective. If a room looks gloomy and the people in it do not think there is adequate illumination then there is not going to be any psychological uplift associated with the light. This brings in the concept of Perceived Adequacy of Illumination (PAI). This concept was used by Kit Cuttle in his paper Towards the Third Stage of the Lighting Profession. In that paper Cuttle also introduced the metric mean room surface exitance (MRSE). This metric is useful but applying it in certain situations can be hard so a parallel metric of mean indirect cubic illuminance (MICI) has also been developed. Researchers such as James Duff and Longyu Guan have tested the relationship between the two metrics and found that MRSE is a very good predictor of PAI.
This leads to the very good question, why are MRSE and PAI related? As first approximation you would expect the total amount of light arriving at a person’s eye to be a predictor of how light they perceived E
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Schroders HQ, London, lighting by GIA Equation: 'we all know that good lighting in a room can make you feel better, but this is a feeling and so may be described as an improvement in wellbeing rather than a direct health benefit'
a space to be. So perhaps it might be worth find that your result tends to follow MRSE. speculating about what is happening. If you This is perhaps why MRSE is a predictor of think about what is driving a visual response PAI, but this is just a supposition. then the obvious answer is your retina. If we think about the physiological responses So retinal illuminance is likely to be key to to light then the same argument may well eliciting a given assessment of the adequacy apply so perhaps we need to do some of illuminance. Moreover, it is common for serious testing of spatial response functions. the retina and the front end of the visual The one clear element is that ambient light system to respond in a logarithmic way. in whatever form you assess it is important It is also likely that our assessment of and should be promoted in lighting design. illuminance adequacy is related to some While it might not yet be the time to write it form of summation of the input received into normative parts of standards and guides, across the retina. So the total stimulus is it is going to be an informative part of the going to be related to the sum of the logs next edition of EN12464-1, the European of the retinal illuminance on a given area Standard for lighting in indoor workplaces. multiplied by the given area. The document, due to come out next year,
Retinal illuminance is a function of luminance provides advice and suggests possible metrics in the field of view and the size of the pupil, including: illuminance on the walls and and the retinal area illuminated is a function ceilings, mean ambient illuminance and mean of the solid angle subtended at the eye by the room surface exitance, together with visual source. If you sum the logs of the lightness and interest. source luminances multiplied Once we have by the associated solid design rules that angles for a range can help of situations you ‘The one clear element achieve
is that ambient light in whatever form you assess it is important and should be 8 promoted in lighting design’
perceived adequacy of illumination we can then move on to a consideration of elements that make us feel even better. This could be the use of biophilic elements such as green walls or just a nice view from a window. However, adding extra elements to a space where the illumination is considered not to be adequate is not likely to improve things.
Returning to the physiological impacts of light then the key one we all think of is circadian entrainment. Most people are able to maintain their entrainment by a short period outside during the course of the day. For these people the physiological benefits of an enhanced electric light regime are somewhat limited. So it is mainly people who cannot get outside, such as people in care, that can benefit from more light indoors. However, the evidence base for any spatial metric of light is very limited and the use of spectrally weighted corneal irradiance almost certainly wrong. It may well be a solid angle weighted log of radiance function that is needed. However, this is speculation.
Peter Raynham is professor of the lit environment, UCL Institute for Environmental Design and Engineering
The sessions at the LR&T Symposium featuring John Mardaljevic and Peter Raynham will be on Thursday 5 November, starting at 1pm
APPLYING LIGHT FOR HUMAN HEALTH: PROGRAMME
ollowing the cancellation F of the Lighting Research and Technology Symposium in June, the SLL is hosting an online version this month. With the theme Applying Light for Human Health, it will run every day from 2-6 November, and will feature 90-minute sessions on each of the five days.
The thinking behind the theme of the symposium is to help define the parameters for the ways in which lighting can contribute to health and wellbeing, according to the SLL.
Following the discovery of the intrinsically photosensitive retinal ganglion cells (ipRGC) in the human retina there has been a great deal of research on the non-visual effects of light. While this effort has resulted in an increase in understanding it has also produced several claims for lighting systems that will enhance human health, says the SLL.
This has caused anxiety among lighting designers and manufacturers, according to the SLL, giving rise to concern that 'the claimed benefits may not be evident in practice, or worse, they may be detrimental to human health. Alternatively, if true, hesitation to embrace new applications may see them being left behind.'
Instrumental in planning the 2020 Symposium has been former LR&T editor in chief, Dr Peter Boyce. 'The aim of this symposium is to transfer knowledge from the laboratory to the field. The hope is that this will enable lighting to safely and successfully expand its contribution to human health.'
MONDAY 2 NOVEMBER
1PM-2.30PM 1 How Light Exposure Affects Human
Health: Russell Foster, professor of circadian neuroscience and head of the Department of Opthalmology,
Oxford University (30 mins) 2 What Manufacturers Need to
Know: Peter Thorns, head of
Strategic Lighting Applications,
Thorn Lighting (15 mins) 3 What Lighting Designers Need to
Know: Florence Lam, Arup Fellow and global lighting design leader (15 mins) 4 Live Q&A
TUESDAY 3 NOVEMBER
1PM-2.30PM 5 Lighting for Day Work and Schools:
Mariana Figueiro, director of Center for Healthy Ageing, Institute for
Health, chief of Division of Sleep and
Circadian Medicine, Robert Wood
Johnson Medical School, Rutgers
Institute for Health (20 mins) 6 Nightshift Work: Arne Lowden, sleep and stress researcher,
Stockholm University (20 mins) 7 Lighting for Homes: Luc Schlangen, senior researcher, director of global standardisation, principal scientist and programme manager for light and health, Eindhoven University of Technology (20 mins) 8 Live Q&A
For more information contact sll@cibse.org
WEDNESDAY 4 NOVEMBER
1PM-2.30PM 9 Lighting for Sleep: Mark Rea, professor of architecture and cognitive sciences
LRC, Rensselaer Polytechnic Institute (20 mins) 10 Lighting Instability, Headaches and
Migraines: Arnold Wilkins, emeritus professor at Essex University (20 mins) 11 Lighting for People with Dementia:
Mariana Figueiro (20 mins) 12 Live Q&A
THURSDAY 5 NOVEMBER
1PM-2.30PM 13 How can natural lighting necessary for human health be implemented?:
John Mardaljevic, professor of building daylight modelling at Loughborough
University (30 mins) 14 How can electric lighting necessary for human health be implemented?:
Peter Raynham, professor of the lit environment, UCL Institute for
Environmental Design and Engineering (30 mins) 15 Live Q&A
FRIDAY 6 NOVEMBER
1PM-2.30PM 16 The Future of Lighting and Health:
John O’Hagan, Public Health England, visiting professor in laser and optical radiation safety at Loughborough
University, vice-president standards,
CIE (30 mins) 17 Live Q&A with speakers from all sessions
WORKING The �carpet bombing’ approach was sold as being energy efficient, and indeed lighting has been well in advance of many building MODEL services in terms of energy efficiency improvements. With the migration to LED over the past five to 10 years, lighting has focused on output efficiency The popularity of working from home, the time (and C02) saved from not commuting offices will becomes hubs and meeting zones, places where the crucial networking and organisation culture are experienced, but with much work done from home.
The government is calling for a doubling of resource productivity by the year 2050. This requires changes in luminaire construction (for example, replaceable drivers to ensure extended service life and reusable bodies), but also changes in procurement and application. THE PAST IS ANOTHER COUNTRY When we look back it often surprises us what poor building performance figures we accepted, the obvious example being the tungsten light bulb with its abysmal energy efficiency. The low energy (the energy efficacy of the luminaire itself), in other words a product-led strategy. The improvements in luminaire efficacy It is time to rethink the office – how it is lit are now suffering diminishing returns while scheme quality has been and how we buy it, says Bob Bohannon compromised. The resultant schemes are bland, boring and unpopular. M any reading this article will be working from home, proof positive of humankind’s innate compact fluorescent lamp alternative had its drawbacks, but now everybody’s go-to technology is the LED. However, we still moves in and not unreasonably wishes to arrange the space according to their own organisational objectives. The result is that ability to rapidly adapt to regularly accept a similarly questionable very often a new and almost unused lighting changing circumstances – in this case the risks standard practice in our office procurement – scheme is thrown straight in the skip, with of Coronavirus transmission. The economic the CAT A fit-out. the likely destination of the near-new light shock from lockdown has prompted the In the UK, a very large proportion of offices fittings being the shredder for raw material need to stimulate the economy. However, are speculative developments, built before the recycling. If they do not rearrange the rather than seek to merely regain ‘business as end occupant is either identified or consulted lighting, but do install acoustic partitions or usual’, the call has been to Build Back Better on their needs. Some in the development and cellular offices the occupier will quickly find – restabilising our future economy on much real estate sectors consider that in order to that some areas fall below British Standards more sustainable lines. let the building, every office floor must be fully or SLL minima – employers are now at risk.
The office is changing: sustainability is fitted out with ceilings and lighting – known CAT A was conceived at a time when more important to the investment decision as the CAT A fit-out. If you do not know the there was not the widespread investor and this is increasingly reflected in the client, what they do or where they will sit, interest in sustainability, energy and carbon Global Real Estate Sustainability Benchmark then the lighting design becomes dangerously metrics that we have today. The CAT A (GRESB) rating, tenant decisions and the simple – light everything, a blanket 400 lux paradigm can, indeed must, now itself need for corporate social responsibility. wall-to-wall, corner to corner, so that the bin be consigned to the skip and revisited The government has adopted a target of in the corner gets the same amount of light as to better align with current regulatory, 2050 to reach net zero carbon emissions. a prime desk top. sustainability and investment requirements. will have large impacts on office use and office design. It is widely thought that many Comcast Technology Center, Philadelphia, lighting by Tillotson Design Associates: future schemes must combine lighting for sustainability and people
The problem arises when the tenant
