Daylighting design is an essential aspect for creating brighter, healthier buildings for everyone. Considering that daylight has a unique ability to shape the experience of a space, it is important for architects and designers to take it into account in order to build healthier, more sustainable buildings. Good daylighting design can improve the health, mood, cognitive abilities and productivity of the occupants of homes, schools or workplaces, while reducing the energy consumption of the building.
We explore a few key factors that can influence daylight availability in buildings and how to account for them in your next project.
Climate and latitude
The prevailing climatic conditions of a building site define the overall preconditions for its daylighting design in terms of sunlight availability, visual comfort, thermal comfort and energy performance.
The location latitude determines the solar altitude for any given time of day and year. The summer and winter solar altitude properties are important design inputs for the availability and control of direct sunlight. For example, the figure below shows the difference in outdoor illuminance (lux) levels and length of daytime between northern and southern European locations.
External obstruction
External obstructions from surrounding elements on the building site (buildings, vegetation, ground surface, etc.) can have a tremendous impact on the amount of daylight that reaches interiors, direct sunlight availability and the quality of window views. It is a crucial element to consider when analyzing the daylight performance of a building design. The figure below shows the significant difference in obstruction levels between rural and urban environments, underlining the need for rigorous daylight planning when designing in dense urban environments.
Building geometry
The geometry of a building influences its capacity to deliver adequate levels of daylight to interior spaces. When the building is deep, daylighting solely via facade windows has its limitations. No matter how much glass there is in the facade, it will only be possible to achieve an adequate daylight distribution a few meters from the facade (in spaces with typical ceiling heights). The figure below shows the daylight factor (DF) levels obtained in a deep room with 3 different window configurations.
Material properties
The colour and reflectance of room surfaces are part of the daylighting strategy. Dark surfaces reflect less light than bright surfaces, and the result is likely to be an unsatisfactory luminous environment in which there is little indirect or reflected light. Bright vertical surfaces inside the room are generally preferred to dark ones, but shading devices used to control sunlight should use darker materials in order to limit the risk of glare when prominently positioned in the field of view of building occupants. The figure below shows the impact of surface colour and reflectance on luminance levels.
Window orientation, size and position
The orientation of windows influences the availability and qualities of daylight in interiors, most notably with regards to the presence of direct sunlight. Roof windows installed on a flat or low roof pitch are less sensitive to orientation if they have an unobstructed view of the sky.
The amount of daylight entering a room is directly linked to the total glazing area of the windows in the room and the visible transmittance value of the glazing. As a rule of thumb, double glazing (with no coating) lets in approx. 80% of the light, while triple glazing (with no coating) lets in approx. 70% of the light.
The positioning of windows will influence the distribution of daylight in the room and determine the amount of 'useful' daylight. Window position should also account for the relation between the view to the outside and the eye level of the occupants.
VELUX Daylight Visualizer is a free easy-to-use and powerful daylighting simulation tool that can be used to evaluate the impact of all these factors on the daylight performance of your building projects. The figure below shows how daylight conditions are improved by the addition of roof lights in a school project in Germany.
