“Characterizing the potential of daylight to fulfil non-visual requirements" by Martine Knoop
Lecturer at the Chair of Lighting Technology
Technische Universität Berlin
Lecture from the 7th VELUX Daylight Symposium “Healthy & climate-friendly architecture– from knowledge to practice” that took place in Berlin on 3-4 May 2017. For more information visit http://thedaylightsite.com
Daylight is very effective in fulfilling visual and non-visual requirements in the built environment. It differentiates from electric lighting in several aspects. The dynamics in light levels and the spectral power distribution, with a strong short wavelength component, are said to be specific beneficial characteristics of the natural light source. Additionally, directionality of light seems to be of importance. Daylight from windows realizes a spatial light distribution in indoor spaces, which results in higher illumination of vertical surfaces.
Increased luminance of walls positively affects room appearance and user well-being, and higher vertical illuminances at eye level are associated with less fatigue in office spaces. Furthermore, inferior and nasal illumination is said to be more effective in inducing non-visual effects. Non-visual lighting requirements are various, but several psychological and physiological responses are affected by the spectral power distribution, light levels and directionality of the light. At present, daylight planning considers a minimum daylight coefficient (a constant) or the course of the daylight coefficient on a horizontal plane in the room, not reflecting the dynamics or absolute lighting levels, nor considering spatial light distribution.
The correlated colour temperature of the light is usually set to 6500K, or colorimetric characterization of daylight is based on measurements combining diffuse (skylight) and direct light (sunlight), even though research has shown that the spectral power distribution of specific regions of the sky (sky patches) can vary largely. To properly evaluate the impact of daylight on human beings in buildings and support healthy lighting design, it is required to consider the colorimetric characteristics of sky patches separately, and to include information on the directionality and origin of the light, additionally to horizontal and vertical illuminance levels in a room.
These parameters are influenced by sun position and the prevailing sky conditions, which provide the specific dynamics for all three considered aspects. The presentation will show a differentiated view on characterisation of daylight provision, using spectral information of many sky patches and the quantification of light direction. The spectral information is based on spatially resolved spectral power distribution measurements of daylight with a sky scanner of the TU Berlin. The quantification of light direction is investigated in a further research pro-ject at the TU Berlin, and provides an insight into the influence of season and sky condition on the directionality and diffuseness of the daylight. The impact of spectral power distribution and directionality of light on non-visual effects is studied by two additional PhD students. The approach will show the potential of daylight to induce non-visual effects through consideration of specific daylight characteristics.
Whereas the approach uses detailed spectral and directional information for now, amsimplification of the assessment will be studied in a subsequent project, to ensure applicability in the design process and development of lighting controls for healthy daylighting. Martine Knoop is Lecturer at the Chair of Lighting Technology, Technische Universität Berlin, Germany. In this role, she is responsible for research and education on indoor lighting, daylighting and colorimetry. After studying architecture and building physics at Delft University of Technology, she finalized her PhD in 2000, dealing with glare from windows and acceptance studies in daylit rooms. Before taking up her assignment at the TU Berlin, she was a senior application specialist of Philips Lighting, the Netherlands and parttime visiting professor at Eindhoven University of Technology. Her current research focuses on the unique characteristics of daylight responsible for the user preference for this light source, in order to promote and improve daylight design, as well as to develop new adaptive electric lighting solutions, to enhance user well-being and performance in indoor spaces.