Authored by Dr. Helen Sanders, PhD., Technoform North America

“Daylight is a drug and nature is the dispensing physician”, according to Deborah Burnett of Benya-Burnett Consulting. Nature delivers daylighting of the right type (color), in the right dose (intensity), at the right time to manage our mood, help us sleep better at night, manage our weight and help us ward off disease. Over centuries humans have evolved with the cycle of day and night [1].

The body’s natural processes, such as the immune, cardiovascular and metabolic systems and the sleep-wake cycle, depend on this light-dark cycle to function properly.  Daylight at the right time improves our mood, helps us sleep better at night, manages our weight, and helps us ward off disease. We are truly “outside animals”. However, according to the U.S. Environmental Protection Agency (EPA), we now spend 90% of our time indoors, effectively isolating us from that which keeps us healthy.

Working, studying or healing in buildings only dimly lit with static output electric light may not provide enough intensity, nor spectral color or intensity variation to regulate our body’s core functions.  Also, when humans are exposed to light intensity or type at the wrong time of the day their circadian rhythms can be disrupted, negatively impacting health [2].


Views matter and views of nature matter even more

The ability of building occupants to view the outside environment is also important. Physiologically it helps relax and re-focus eyes to the horizon.  It reduces stress by satisfying the need for safety by providing the ability to see approaching danger.  Views of nature are especially important.  While the benefits to physical and mental health are only just being understood, our interactions with nature reduce stress and irritability by increasing relaxation while simultaneously reducing our fight or flight cognitive functions. According to the Global Impact of Biophilic Design in the Workplace, views of greenery and water through windows have been linked to lower levels of stress for employees compared to those without a window [3].

In the work-place, data demonstrating the positive impact of daylight and views on occupant well-being and productivity is overwhelming and much of it is close to 20 years old [4].  Access to daylight and views is correlated with double digit improvements in productivity and cognitive test scores, better quality of life, vitality and sleep, reduced sick leave and staff turnover, and increases in the number of applicants for open positions [4-7].


Healing impacts

Knowledge of the positive impact of daylight and views on healing is not new either. Florence Nightingale figured this out, promoting the power of direct sunlight for mood improvement, sanitation and healing through her 1859 “Notes on Hospitals” [8].  More recently, there have been over fifty studies demonstrating the positive influence of daylight in hospitals, for patients, visitors and staff alike.

Benefits for patients include reduced hospital stays, less pain felt, less pain medication taken, and improved outcomes.  Reductions in stay length have the potential to save $93M annually [9]. Moreover, medical staff experienced improved alertness, fewer sick days, higher retention and, critically, fewer dispensing errors.

Roger Ulrich, whose seminal research reported 8.5% shorter hospital stays for post-operative patients with a view of nature, asserts that “larger windows should be provided to permit more exposure to daylight and restorative nature views in patient rooms and other spaces where depression, pain and stress are problems” [10].


Improved learning

Daylight and views are positives for both students and teachers too [4, 11-14].  Healthy growth, improved dental health, greater well-being, increased attendance from both students and staff, higher student achievement, better behavior, and teacher retention have been widely documented [4, 11-14].  Good daylighting reduces eye strain, relieving the visual stress associated with reading, and improving information processing and learning ability.  In the most touted study, the Heschong Mahone Group (HMG), reported that students with the most daylight progressed 20% and 26% faster on math and reading tests respectively, compared to their peers in the least daylit classrooms [7].

A teacher commented “When I’ve had it with the kids and I can’t answer another question, I just take a minute, look out the window at the view, and then I’m OK. I’m calm and ready to go back into the fray”, indicating the importance of windows to stress reduction both children and teachers.

Another study, correlating behavior, health and the stress hormone cortisol with daylighting levels, indicated that the lack of daylight may impair the basic hormone patterns, inhibiting a child’s ability to concentrate or collaborate with peers, and potentially impacting their growth and attendance [13]. The positive correlation of daylight with attendance and health has been repeated in subsequent studies.

According to HMG, with better daylit classrooms with quality views, “schools could be saving up to one month of instructional time for the reading and math curriculum that could be used for other areas of learning”.

Contrary to previous belief, daylight and views can help children concentrate.  Research has shown that students in windowless classrooms are more hostile, hesitant and maladjusted, and tended to be less interested in their work.


Uncomfortable daylight

Although there are proven benefits from daylight, there are several studies that show that these benefits disappear if the occupants experience visual or thermal discomfort.  Productivity reportedly drops by approximately 1% for every 1oF the temperature moves away from the optimum 71-72oF [15].  And in schools and offices window glare effectively self-cancels the positive benefits from the view [5, 14].



The key to creating healthy environments conducive to healing, learning and productive work is the creation of comfortable, well daylit environments with views to outside nature.  To achieve this, as part of a climate specific daylight design fenestration must be specified with high thermal performance to manage conductive heat gains and losses and keep the radiant temperature of its surfaces in a comfortable range. This means wide thermal breaks, warm-edge spacer, dual or triple pane insulating glass with high performance low emissivity coatings. Use of passive and/or active design strategies that effectively control direct solar heat gain and glare are also needed.

The workplace is the leading cause of stress for U.S. adults, with connections to cardiovascular disorders and mental health issues.  Other immune and metabolic system diseases such as cancer, diabetes and obesity are also leading causes of illness and death.  With these issues impacting so many lives, provision of comfortable and plentiful daylight and views in all buildings should be a public health imperative.  It also begs the question: Should windows be mandated by our building codes as a health requirement for all classrooms, offices and patient rooms?





[1] For an overview of daylight and circadian rhythms see for example:


[2] See for example, P. Bhatti et. al (2013). Nightshift work and Risk of Ovarian Cancer, Occup. Environ. Med. 2013;70:231-237.


[3] Human Spaces, Report on the global impacts of biophilic design.


[4] For an extensive literature review work prior to 2002 see Edwards & Torcellini – A literature review of the effects of natural light on building occupants, 2002, NREL report 30769,


[5] Heschong Mahone Group, Inc. (2003). Windows and Offices: A Study of Office Worker Performance and the Indoor Environment –CEC Pier 2003.


[6] Cheung et al. Impact of workplace daylight exposure on sleep, physical activity and quality of life, 2013


[7] I. Elzeyadi, Daylighting – Bias and Biophilia: Quantifying the Impact of Daylighting on Occupants Health, 2011,


[8] Florence Nightingale, Notes on Hospitals, 1859, Dover Publications


[9] Roger Ulrich “Biophilic Theory and Research for Healthcare” in Biophilic Design, edited by Stephen Kellert, Judith Heerwagen and Martin Mador, 87-105. New York, Wiley 2008.


[10] The Economics of Biophilia, Terrapin Bright Green, 2012.


[11] Daylighting in Schools: Improving Student Performance and Health at a Price Schools Can Afford, NREL Report 28049,


[12] Daylighting in Schools, Heschong Mahone Group, 1999,


[13] Kuller, R. and C. Lindsten, “Health and Behavior of Children in Classrooms with and without Windows, Journal of Environmental Psychology, 12, pp. 305-317, 1992


[14] Heschong Mahone Group, Windows and Classrooms:  A Study of Student Performance and the Indoor Environment, for the California Energy Commission, 2003.


[15] Seppanen et al., Room Temperature and Productivity in office work, LBNL report 60952,


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