We are outside animals: why windows are critical for human health

Twinsburg, Ohio
outside animals
by Helen Sanders, Ph.D
outside animals
photo credit: Emma Simpson on Unsplash

“Daylight is a drug and nature is the dispensing physician”, according to Deborah Burnett of Benya-Burnett Consulting. Nature delivers daylight 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]. 

Healing impacts

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]. 

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].  

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].


[1] For an overview of daylight and circadian rhythms see for example http://thedaylightsite.com/body-clocks-light-sleep-and-health/

[2] See, for example, P. Bhatti et. al (2013). Nightshift work and Risk of Ovarian Cancer, Occup. Environ. Med. 2013;70:231-237. https://www.ncbi.nlm.nih.gov/pubmed/23343856

[3] Human Spaces, Report on the global impacts of biophilic design. https://greenplantsforgreenbuildings.org/wp-content/uploads/2015/08/Human-Spaces-Report-Biophilic-Global_Impact_Biophilic_Design.pdf

[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, https://www.nrel.gov/docs/fy02osti/30769.pdf

[5] Heschong Mahone Group, Inc. (2003). Windows and Offices: A Study of Office Worker Performance and the Indoor Environment –CEC Pier 2003. http://h-m-g.com/downloads/Daylighting/A-9_Windows_Offices_2.6.10.pdf

[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, https://www.usgbc.org/resources/daylighting-bias-and-biophilia-quantifying-impact-daylighting-occupants-health

[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.  http://www.terrapinbrightgreen.com/wp-content/uploads/2012/06/The-Economics-of-Biophilia_Terrapin-Bright-Green-2012e.pdf

[11] Daylighting in Schools: Improving Student Performance and Health at a Price Schools Can Afford, NREL Report 28049, https://www.nrel.gov/docs/fy00osti/28049.pdf

[12] Daylighting in Schools, Heschong Mahone Group, 1999, http://h-m-g.com/downloads/Daylighting/schoolc.pdf

[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. http://h-m-g.com/downloads/Daylighting/A-7_Windows_Classrooms_2.4.10.pdf

[15] Seppanen et al., Room Temperature and Productivity in office work, LBNL report 60952, http://eta-publications.lbl.gov/sites/default/files/lbnl-60952.pdf

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