If you were asked what daylighting is, how would you answer?
Instinctively, you might think of the sun providing light, and explain how you experience this and why having more access to daylight is good. But would this really answer what it is?
To design with daylight and achieve desired outcomes, it's important to first understand what daylight is before it enters a building: its components, and the effect those components have on our ability to influence daylight in our built environment.
WHAT IS DAYLIGHTING?
KEY LEARNINGS
- Be able to define daylighting.
- Understand the components of daylight.
Defining ‘daylighting’ Daylighting is the controlled use of natural light in and around buildings1.
At its core, daylighting is the practice of placing apertures (windows/doors), or other transparent media and reflective surfaces, to bring daylight into a building. When done well, this helps to create a comfortable, safe and healthy indoor environment that optimises not only a building’s energy use, but the well-being of the people that use it.
One of the most familiar aspects of daylighting is the effective illumination it provides for occupants to carry out tasks in a space. In other words: how much natural light there is, or will be, in a room.
However, daylighting encompasses much more than this. To take full advantage of it, we can start by better understanding daylight itself.
It’s not all sunshine: what is daylight? Daylight has three components, all of which should be taken into account when thinking about how to use daylight within buildings.2
Direct sunlight Direct sunlight has a very high intensity, producing an illuminance level on the surface of the earth that can exceed 100,000 lux.3
Its other main feature is its constant movement. The brightness of direct sunlight varies by season, time of day, location, and sky conditions. Thoughtful architectural design is required, especially in sunny climates, to manage allowance, diffusion, shade, and reflections.
Photography: Milena Villalba. Architects: AR3 Gualguasplliteras, MDBA
Direct sunlight condition and climate responsive architectural solution. Photography: Milena Villalba
Site location example Comparing the sky conditions in Rome and Oslo gives a simple illustration of how site location affects the availability of direct sunlight.
At a northerly latitude, Oslo experiences clear skies for around 33% of the year and overcast skies for around 28%. By contrast, the skies are clear in Rome for around 65% of the year – twice as much as Oslo. Rome experiences overcast skies for only 13% of the year, on average.4
It may seem obvious that the number of cloudy days in your project’s location will impact the availability of daylight but how do you consider it in building design?
If your site receives minimal direct sunlight for 66% of the year (Oslo), does the orientation of its spaces have the same impact compared to a project in a location where the sun is shining for 65% of the year (Rome)?
When working across borders it is essential to question the fundamental assumptions we make about daylight and ensure the impact of the local climate is truly understood and translated into sensitive design responses.
Skylight In addition to direct sunlight, the atmosphere and clouds act to scatter sunlight, creating a soft and diffuse light known as skylight. The illuminance level produced by an overcast sky might reach 10,000 lux in the winter, and as high as around 30,000 lux on a bright overcast day in the summer.5
A diffuse sky is often the main source of useful daylight in cloudy climates.
Skylight in overcast condition. Architects: Zaha Hadid
Skylight in sunny conditions. Architects: Steven Holl
Reflected light Both sunlight and skylight are reflected by ‘surface features’ including the ground, terrain, trees, vegetation, and neighbouring buildings. The surface reflectance of the surroundings influences the total amount of reflected light reaching a building facade. In densely-built environments, light reflected from the ground and surroundings can be a major contributor to indoor daylight.
Reflected sunlight from a building facade and ground surface. Architects: Steven Holl
The components of daylight.
Daylight in buildings The daylight that reaches a building’s façade comprises of all the characteristics above: direct sunlight, diffuse skylight, and reflected light. It is therefore a mix of intense and directional light, and soft and diffuse light, with 15% or more being made up by reflected light, depending on the surroundings.8
Assessing the availability of the different components of daylight, and creatively balancing their dynamics and potential against the spatial needs of a project, dictates whether interior daylighting is ‘good’ or not.
» Read on: What is good daylighting?
Direct sunlight
Photographer: Jeff Goldberg. Architect: Rick Joy Image source
Diffuse skylight
Reflected light
Direct sunlight
Photographer: Jeff Goldberg. Architect: Rick Joy Image source
Diffuse skylight
Reflected light
1 Reinhart, C (2014). Daylighting Handbook I, p.23. 2 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, p.14. 3 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, p.15. 4 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, p.32. 5 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, p.15. 6 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, p.33. 7 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, p.33. 8 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, p.15