Gaining an understanding of the fundamentals of daylight allows for the setting of daylighting goals, that will (ideally) have your client’s full backing and excitement of the difference that good daylighting will make to their project. To achieve the project ambitions, some deep thinking and analysis is needed of the project site and its surroundings. What opportunities are there to make the best use of the daylight available? What possible risks and constraints could impact on the eventual design?
GOOD DAYLIGHTING STARTS WITH CONTEXT
KEY LEARNINGS
- Understand key physical and non-physical context elements that directly influence daylighting in a project.
- Establish sun angles specific to your project location and understand how these change throughout the year.
- Understand the concept of daylight availability, the key factors influencing it (variation of global illuminance values, visible sky component), and how this can inform contextual design responses to achieve good daylighting.
Why context is so important?
The way we understand things as human beings is frequently based on context. First, we try to comprehend the background scenarios, before deciding on what to believe, what to take into consideration, or what to do next.
In architecture, context is the sum of the external elements that influence the building and site. Analysis and evaluation of context gives an idea of what is existing before we introduce a new element to it, it also can determine (or at least influence) the architectural style, the selection of materials, and the site layout. When it comes to daylight, a thorough evaluation of context gives the boundary conditions for daylighting design.
Leth & Gori Architects, Copenhagen, Denmark
"Our point of departure is always that no place is empty. The light is already there. The shadows are already there. The land, the city, the people. They are all basic conditions of the site on which a project is built.”
The elements of context in architecture
The elements of context are both physical and non-physical.
Neighbouring buildings, roads, land contour, access to water, surrounding ecosystems, weather, and climate; are common examples of physical contextual elements. Whilst political, legal, social, economic and cultural factors are examples of the non-physical.
Whether physical or non-physical, many of these elements will have direct or indirect consequences, both positive and negative, on the possibilities for daylighting in the project. Each element needs to be well understood to create a quality synthesis and project proposal that balances the priorities agreed upon.
Several parameters provide the fundamental context needed for optimally positioning and shaping a building on a given site in relation to daylighting:
- Latitude (daylight availability & sun angles)
- Climate (need for specific shading responses etc.)
- Prevailing weather
- Neighbouring buildings (height, material properties & views) and potential future development
- Neighbouring natural features (topography, height and type of vegetation eg. deciduous, bodies of water and possible reflections)
- Legal requirements (boundary setbacks, privacy regulation)
Secondary considerations in relation to daylight include all other site observations that will certainly impact siting choices, but which typically impact daylighting in a more secondary way:
- Movement over and around the site (traffic, people, animals, water – how this could affect building form and position of daylight openings)
- Political and socio-cultural contexts that may influence a style of building (will a highly experimental form be accepted?)
- Availability of building materials, products, and skilled craftsperson’s
- And many more!
In this daylighting guide, we have also talked about the quality of light in a space, something that is not easily measured but rather must be observed and understood in a more intuitive way. The quality of light is influenced to a large degree by the site location and local climate so observations of the ‘behaviour’ of light that results on a specific site, can set the foundations needed for harnessing its potential through your architectural response.
Where is the sun? Starting with what may seem to be the obvious, the sun’s position in the sky changes during the day as the earth rotates. And, as we move through the seasons, that daily variation alters throughout the year.
A building’s position (in terms of latitude) determines the angles at which it is exposed to sunlight and how these change throughout the day and year. This directly influences daylight availability and will also have an impact on visual comfort.
You can establish your projects sun angles by using the following formula:
1. Solar Elevation Angle at noon Equinox (21 March & 21 September) = 90 minus latitude of location
2. Solar Elevation Angle at noon 21 June = 90 minus latitude of location plus 23,5
3. Solar Elevation Angle at noon 21 December = 90 minus latitude of location minus 23,5
Whilst most of the daylighting concepts discussed so far can be applied to any location in the world, an obvious distinction to make at this point, is that if your site is located in the Northern hemisphere, throughout the day, the sun will predominantly be to the south whilst if it is in the Southern hemisphere, the sun will be to the north. It is also important to understand that the difference between south and north exposures are more intense the farther you are from equator. This means that the implications of having a ‘south’ facing facade will be amplified the further north of the equator you are and vice versa.
Position of the sun at the Equator
Position of the sun at the northern hemisphere
Although understanding sun angles and considering daylight availability across different sites can feel like a highly pragmatic exercise, as designers there are immense opportunities to discover in re-understanding these concepts through a more poetic lens as a path to new project inspiration.
Niall McLaughlin, Daylight Talk
“...is the thing that brings all of the life-giving energy to the earth, sets up the climate, affects the geology and is a fundamental part of our being. "
“Daylight is a natural consequence of the fact that we are circling a star; our world is in constant orbit around a star which is beaming radiation at us, is the thing that brings all of the life-giving energy to the earth, sets up the climate, affects the geology and is a fundamental part of our being. In fact, it would be difficult for us to say that we can live outside that paradigm, so deeply does it affect every aspect of our being that we have to think of daylight as being, probably, the deepest ground of our own existence.”
How bright is daylight? Daylight effectively provides illumination that is an order of magnitude greater than artificial lighting. Most artificially lit interiors have less than 500 lux, with only a few non-residential building uses requiring 750 to 1000 lux. In comparison, a clear blue sky (without the direct sun) will in general provide a total illuminance of 30,000 lux to a surface (with direct sunlight providing levels that can exceed 100,000 lux)1.
However, the ‘brightness’ of daylight and consequently the ‘daylight availability’ on a site is affected by location. The measure to indicate this is ‘global illuminance’ – it consists of the total amount of light (illuminance, lux) received from the visible hemisphere (the sky) including both direct sunlight and indirect skylight. Global illuminance varies significantly with latitude (for reasons including sun angle and daylight hours) as well as the predominant local weather conditions.
Whilst global illuminance on a site receiving direct sunlight can exceed 100,000 lux, the same site on a cloudy day would typically see global illuminance values of around 10,000 lux in the winter, and as high as around 30,000 lux in the summer. This means that the average amount of daylight available on a site in a sunny climate will of course greatly exceed that of a site located in a predominantly cloudy climate.
DAYLIGHT COMPARISONS: ROME, PARIS AND OSLO
Why is this important? As there is variation in global illuminance across latitude and climatic zones, it directly impacts daylight availability and in turn will affect what percentage of the available daylight needs to enter a building to achieve appropriate lux levels within a space. In EN 17037’s assessment of daylight provision, this is addressed in both verification methods. Given that site location is so influential in the availability of daylight, it is highly optimal to set daylighting goals that will be measured on real climatic data.
Furthermore, as global illuminance is essentially measuring the light being received from the sky, it of course points to the importance of understanding the amount of visible sky. The amount of visible sky (and the orientation of it) determines more precisely the daylight availability for a specific space and subsequently prepares you to take informed decisions around optimal spatial planning and later daylight openings.
Know your neighbours: ensuring visible sky for your project
Much like site location discussed above, daylight availability is heavily dependent on visible sky and the presence of obstructions. Whilst it may be simple to understand that neighbouring buildings can create overshadowing on a site, are you aware of the metrics that can help you to make informed planning decisions based on this?
Neighbouring buildings (and natural features like topography and vegetation) create what is called a ‘visible sky obstruction’ which directly impacts the availability of daylight on a site.
This visible sky obstruction can be assessed through three common metrics.
VERTICAL SKY COMPONENT
‘Vertical sky component’, expresses how much light reaches a façade, as a percentage of the direct skylight available from an overcast sky2. The calculation is typically simulated as it considers direct skylight 3 dimensionally. It is typically made as a spot measure from the centre point of a window. The total available light in vertical sky component is calculated based on the CIE standard overcast sky.
OBSTRUCTION ANGLE
‘Obstruction angle’, assesses the angle from horizontal at the point of measurement, to the top of a neighbouring obstruction. The obstruction angle is more useful as a rule of thumb as it is a simple 2-dimensional measure. An angle of above 45 degrees should be investigated further to ensure adequate daylight availability (see further recommendations in table below)3.
VISIBLE SKY ANGLE
Visible sky angle, is the vertical angle between the lowest and highest points of the sky that are visible from the centre of the window. This is particularly useful for taking into account the angle of a potential opening which can significantly benefit the daylighting potential4.
Vertical glazing
Sloping glazing
Some simple guidelines that can assist you in your planning process are outlined below5.
Remember to consider your possible future neighbours and how this could impact the future daylighting in your project. Furthermore, if you believe that building occupants have a fundamental right to accessing daylight in a reasonable way it is important to consider how you can minimise the impact that your own project will have on your neighbours’ access to daylight.
Whilst all assessment criteria of the EN 17037 (daylight provision, access to sunlight, the potential for glare, and views) will be affected by the presence, or absence, of neighbouring obstruction, the visible sky component (or obstruction angle) is a good starting indicator to kick of your planning.
What planning tools can help me? Digital tools are available to assist designers in quickly understanding the climatic conditions of their site and to help with making strategic planning decisions in the early stages of projects. These tools allow designers to make the best use of the available conditions for the site, they can save time and money by avoiding substantial changes later in the project, and they will allow you to effectively communicate your ideas to clients while also demonstrating the benefits of their daylighting ambition.
“Daylighting design should be approached in a more holistic way: developing solutions that are part of the architectural concept, while meeting visual, thermal, and energy needs. Furthermore, daylighting should be a major focus area of the design process, right from the early stages, and should be comprehensively studied on all scales from urban design to building components.” Anna Pellegrino, Associate professor and PhD in energetics at Politecnico de Torino, Italy.
Keep an eye out for new tools to help you with early-stage daylighting assessments » Spacemaker
Progressing from planning to design Once some basic principles and ideas have been established for a project, based on the client's program and site specifics such as geography, latitude, climate, and neighbouring developments, you can move into a more detailed level of planning and design.
» Read on: Design
1 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, p.15. 2 Littlefair, P. King, S. Howlett, G. Ticleanu, C. and Longfield, A. (2022). Site Layout Planning for Daylight and Sunlight: A Guide to Good Practice. BRE Electronic Publications, p6-14. 3 Littlefair, P. King, S. Howlett, G. Ticleanu, C. and Longfield, A. (2022). Site Layout Planning for Daylight and Sunlight: A Guide to Good Practice. BRE Electronic Publications, p6-14. 4 Littlefair, P. King, S. Howlett, G. Ticleanu, C. and Longfield, A. (2022). Site Layout Planning for Daylight and Sunlight: A Guide to Good Practice. BRE Electronic Publications, p6-14. 5 King, S., 2017. Daylight and Sunlight in Housing. [online] Goodhomes.org.uk. Available at: <https://goodhomes.org.uk/wp-content/uploads/2017/07/New-Homes-and-Our-Health-Stephanie-King-BRE.pdf> [Accessed 11 October 2022].