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The design of building envelopes can have a significant
effect on lighting in a building, and on the wellbeing of its occupants. This
CPD, in partnership with Velux Commercial, explains.
As good as some artificial lighting is, no electric light source has yet been created that can match the quality of natural light or mimic the variation in its spectrum throughout the course of a day, a season, or a year. All of which puts a focus on ‘daylighting’, or the controlled use of natural light in and around buildings.
Humans have evolved circadian rhythms and our building
designs should reflect the importance of those rhythms. It is possible to
create indoor environments that not only provide a good visual experience and
high levels of visual comfort, but which are also in tune with the physiology
of the occupants. This CPD article looks at the role of natural light in human
health and how commercial buildings can be designed to achieve genuinely
‘human-centric’ daylighting throughout the building fabric.
Daylight and everyday life
The non-visual aspect of light is every bit as critical to
how the body functions during the day as the light we use to see.
This is where circadian rhythms enter the equation, the human body’s natural response to changing light levels including the production of different hormones at different times. The hormone melatonin governs our pattern of wakefulness and sleep and the type of light to which we expose ourselves plays a role in managing the cycle.
Exposure to ‘cooler’, more distributed, blue-rich light
during the day suppresses the production of melatonin and maintains alertness
by effectively encouraging the production of serotonin, dopamine and cortisol.
Following this with ‘warmer’ and more focused light during the evening
stimulates the release of melatonin and helps people to feel sleepy.
Good lighting and true ‘human-centric’ lighting combine both
visual and non-visual aspects to stimulate the correct physiological responses
and promote good health.
Daylight for health
Usually, we do not receive enough daylight and often the
24-hour nature of society then exposes us to too much light during the hours of
During the day, humans need light that is high in ‘melanopic
content’ followed by light that is low in melanopic content during the evening
(and then darkness). This is why exposure to natural light is so important when
thinking about building design.
When it comes to quantity, indoor light is typically a whole
order of magnitude lower than outdoor light. A sunny summer’s day can provide
an illuminance of up to 100,000 lux. Even on a grey and cloudy day 5,000 lux of
illuminance is possible. By contrast, indoor lighting might be designed to
offer just 200 or 300 lux.
The impact of being indoors
It is popularly held that people spend around 90% of all our
time indoors. The light we are usually exposed to indoors, as well as offering
a much lower illuminance than natural light, is not dynamic. It has a constant
colour temperature and our bodies do not respond to it in the same way.
The circadian rhythm is still evident in people with a
‘typical’ 9 to 5 office job, but its peaks and troughs are not as pronounced.
Feelings of sluggishness are likely as well as making it harder to get to
sleep. By contrast, seeing daylight early in the day appears to start the
process of getting the body ready for sleep later that night and can even
mitigate exposure to bright light later in the day.
Lighting and building design
Commercial pressures on building design commonly result in
office buildings where around a third of employees have no access to daylight.
European building standards have helped to avoid a similar crisis in occupant
comfort and the publication of EN 17037 should ensure that daylighting only
improves in buildings throughout Europe.
There is little doubt that daylight should be a significant
component of a building design that claims to embrace human-centric lighting.
This section looks at how different parts of a building may be designed to
properly account for daylight and to provide naturally well-lit spaces.
Tall buildings with fully glazed facades will always possess
a ‘wow’ factor. But it is important to ensure a building that isn’t just
attractive from the outside, but also provides a comfortable internal
All too often, fully glazed buildings offer little
consideration for the heating and cooling loads, and energy demand that such a
design imposes. Occupants will have a good view to the outside, but at what
cost in terms of over-exposure to daylight and glare, and reliance on
mechanical systems for internal temperatures and ventilation?
A glazed facade might look like a clever or intricate design,
but intelligent design involves delivering a healthy interior without consuming
more resources than a building needs to. That means selecting the appropriate
size and location of window openings to maximise daylight while minimising heat
It may sound strange to think about floors as part of
daylighting, but they do have a role to play. Shiny and bright surfaces can
cause glare, but light colours improve visual comfort.
Then there is the size of the floor area itself and, more
specifically, the depth to which it penetrates the building interior. Sometimes
referred to as the floor plate, the deeper the floor area and the further that
parts of it are from the facade windows the harder it is to serve with an
appropriate level of daylight.
Where floor areas are too large or deep, or where site
constraints or external obstructions restrict access to daylight, facade
glazing alone is unlikely to meet the daylighting requirements of a building.
This is where roof glazing solutions come in.
Good use of unobstructed roof glazing can help to achieve better illumination and balance glare from facade glazing. Like the walls of a building, orientation influences the availability and quality of daylight in the interior.
It is also worth considering that roof areas may offer
glazing options where there is a restriction on what can be done with the
walls. While it’s tempting to think that new-build projects tend to offer
unrestricted possibilities, there are often constraints – and the constraints on
a refurbishment project can be even more onerous. While the quality of a view
through roof glazing may not be as varied as can be achieved with facade
glazing, it is better placed to offer an unrestricted view of the sky and help
further a sense of connection with the outdoors.
Generally speaking, an atrium is a way of bringing the
outside in – a space that is sheltered from the elements while giving building
users a connection to the external environment.
The glazing to an atrium therefore falls under different
criteria to the roof glazing described above. Where ‘standard’ roof glazing is
primarily intended to light an individual space, an atrium can also offer the
potential to ‘harvest’ daylight. It brings natural light into a large central
space, from where other parts of the building can then benefit without needing
direct access to facade glazing.
Terraces and outdoor spaces
However well designed a building is, when it comes to access
to daylight there is no substitute for being outside. Ensuring the availability
of high-quality outdoor space can help encourage people to leave a building and
enjoy access to daylight.
A roof terrace has the potential advantage of offering
unobstructed access to daylight at any time of day (subject to the position and
height of any surrounding buildings). There is arguably greater scope for the
design of outdoor spaces at ground level, providing not only daylight but also
contact with nature that may have its own mental health benefits.
For example, rather than the path between an office building
and its car park being across a featureless expanse of grey roads and
pavements, could it be a short wooded walk instead?
For any building’s lighting strategy to be considered truly human-centric, it should incorporate daylight as much as possible to provide well-lit, dynamic and comfortable internal spaces. Not only does daylight provide a higher level of illumination, it also helps maintain the circadian rhythms of the building’s occupants.
EN 17037: The European Daylight Standard
The new standard addresses the provision of daylight in
EN 17037, which came into effect at the end of 2019, is the
first European Standard to deal exclusively with the design and provision of
daylight in buildings.
What does this standard cover?
To achieve its multiple aims in respect of daylighting and
occupant comfort, EN 17037 covers four different areas:
Daylight provision, or illuminance levels, allows users to carry out tasks and plays a part in determining the likelihood of artificial lighting being switched on. Assessment can be via either climate-based modelling or daylight factor calculations.
Assessment of window views
Building users should have a large, clear view of the outside. EN 17037 considers the width and outside distance of the view, as well as landscape ‘layers’ (sky, landscape and ground). The view should be perceived to be clear, undistorted and neutrally coloured.
Access to sunlight
Calculating access – or exposure – to sunlight is a comfort and health factor for users of dwellings, nurseries and hospital wards. Daily sunlight exposure can be established through detailed calculation or table values.
Prevention of glare
Prevention of glare is concerned with removing the probability of glare for building users, especially those who do not choose where they sit. It uses a detailed calculation of daylight glare probability (DGP), or a standard table of values for sun-screening materials.
VELUX Commercial has a dedicated EN 17037 white paper covering everything you need to know about this daylight standard. It is available here