The physiological and psychological effects of windows and daylight

Traditionally, lighting designers have concentrated on creating lighting conditions that are suitable for the visual tasks performed in a room and simultaneously meet individual needs. Following the discovery of light sensitive photocells in our eyes in 2001, considerable attention has focused on the possibility of using daylight to achieve a healthy lit environment. Daylight is rich in the part of the spectrum that seem most important to these light sensitive processes. The science moved rapidly in the following ten to fifteen years.

In 2011 it was again time for a review of the state of the art on the health and well-being effects of daylight and windows.

The VELUX Group commissioned NRC Construction to review the literature, focusing on the effects of daylight in residences. The conclusions may be broadly summarized as:


• Human well-being relies on regular exposure to light and dark each day. 
• Daylight is the most energy-efficient means to deliver the light exposure. 
• Uncontrolled daylight also can cause high contrast and thermal discomfort. 
• Uncontrolled daylight also can cause problems; glare from the sun reduces visibility and causes visual and thermal discomfort. 
• The optimal pattern of light and dark exposure—as well as the limits at which daylight control is needed—varies by race, age, and individual differences. 
• The desire for daylight also depends on how building openings affect the appearance of the space, on the function of the space, and on cultural norms about privacy, enclosure and view. 
• A view of the outdoors is also a contributor to well-being, particularly if it is a nature scene or similar pleasing sight. Windowless spaces create monotonous conditions that may be stressful.
• Using daylight is sustainable only when balanced against the effects of windows and skylights on the building envelope, ventilation, and overall energy balance.