Designing and simulating daylight

Images courtesy Stantec

By Marc Trudeau, Architect AIBC, LEED AP
The benefits of daylight are well-documented. For building occupants, it offers a range of positive physiological effects, which, in turn, translates into tangible benefits such as higher productivity, reduced employee sick time, improved employee morale, and lower lighting costs for businesses.

Building occupants, owners, and policy-makers are increasingly aware of these benefits and are asking for buildings to be well-lit by natural light. Daylighting design and simulation is the way to make this happen—to quantifiably understand how light enters a building and to determine how to achieve the project’s daylight goals.

Daylighting is emphasized in green building standards, such as the Leadership in Energy and Environmental Design (LEED) rating system. Daylight targets based on LEED are even being included as requirements for projects not pursuing certification. In this author’s own work, an increase in the Canadian public-private partnership (P3) projects specifying daylight performance thresholds has been seen. These are clear indicators to the rising importance of daylight in design.

LEED v4 allows for credit using Illuminating Engineering Society’s (IES) metric for measuring daylight sufficiency, employing spatial daylight autonomy (sDA) and annual sunlight exposure (ASE). LEED also allows for compliance using illuminance simulation and field measurement.

While the field measurement is relatively straightforward to implement, credit achievement cannot be determined until the project is built and occupied. Daylight simulation allows immediate feedback during an iterative design process and gives the project team flexibility to evaluate the interaction between daylighting, and building energy performance targets. The sDA daylight target is new in LEED v4, though, so it is unclear to many in the building industry how challenging this will be for buildings in Canada. (The article is adapted from the author’s presentation at the 2016 Canada Green Building Council (CaGBC) National Conference, held in Toronto. It includes daylight simulation results as presented at the eSim 2016 Conference, held in Hamilton.)

Benefits and challenges
Daylight and windows offer numerous positive effects for occupant well-being and building performance relating to:

  • circadian rhythms (high light levels promote alertness and help control the sleep-wake cycle) (See J.M. Zeitzer et al’s Temporal Dynamics of 
Late-night Photic Stimulation of the Human Circadian Timing System,” which appeared in the American Journal of Physiology [2005]);
  • connecting occupants with outdoors;
  • reducing electric lighting use;
  • solar heating (i.e. reduced need for building 
space heat);
  • quality views;
  • beauty of light and shadow; and
  • colour quality and visual appeal.

Several research studies have looked at the benefits of daylight to specific building types and occupant groups. In one study, hospital patients in rooms with more sunlight reported less pain and stress and took 22 per cent less analgesic medications, resulting in a 21 per cent reduction in medication costs. (See J.M. Walch et al’s article, “The Effect of Sunlight on Post-operative Analgesic Medication Usage: A Prospective Study of Patients Undergoing Spinal Surgery” in Psychosomatic Medicine (2005).) In another study, comparing office and call-centre workers with best views to those with none, calls were processed six to 12 per cent faster and occupants performed 10 to 25 per cent better on tests of mental function and memory recall. (To read the 2003 report, “A Study of Office Worker Performance and the Indoor Environment: 
CEC PIER,” visit

Daylight research studies such as these are challenging to do well because there are many variables and results are often based on subjective human responses. Therefore, the methods and results of these studies need to be considered critically.

Finding relevant and carefully done research is worth the effort because occupant well-being gets to the purpose of why buildings exist. Continuing with the example of medication costs within a hospital, the benefit to patient well-being will be extremely important because it relates to the facility’s fundamental role in improving health. As well, the operational cost benefits to a hospital could 
be substantial.

Balanced against these benefits, daylight and windows also bring design challenges and can cause negative effects:

  • glare (i.e. visual discomfort due to high light contrast);
  • excessive solar gains (i.e. increased need for building space cooling);
  • sound and room acoustic issues;
  • distracting views; and
  • privacy concerns.

In the design phase, the benefits and challenges of windows need to be evaluated using design tools and expertise. Daylight consultants can use simulations to quantify glare and the amount of daylight entering a space, using tools such as interior renderings and illuminance analyses. Energy consultants can use energy models to estimate the savings from electric light use and determine the appropriate balance between helpful solar heating and detrimental solar gains. Acoustic consultants can give guidance on strategies to manage sound and room acoustics. Finally, architectural designers must bring all this information together, giving careful thought to the form and materiality of the project to create an inspiring result.

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