For decades, scientists have known that daylight is essential to human health. Back in 1948, the British Medical Journal poked fun at a group of engineers who tried to convince doctors that artificial light was superior to sunlight.
By the 1980s, insufficient daylight came to be seen as a possible factor in “sick building syndrome,” a set of symptoms afflicting some office workers. A number of subsequent studies have bolstered the link.
Scholars more recently have established that workers in windowless offices are less happy and less healthy than their colleagues with steady sources of daylight. Workers without daylight are more stressed, too. By contrast, workers with windows are more satisfied; students who sit near windows perform better.
But is there a connection, as some contend, between daylight and worker productivity?
Sadness and stress
Absenteeism costs the American economy about $225.8 billion annually, according to the Centers for Disease Control and Prevention; that’s $1,685 per worker. Major causes of absenteeism and “presenteeism” (reduced performance and productivity at work) are stress and depression. And both of these ailments have been associated with a lack of daylight.
In one widely cited 1992 study, Swedish researchers compared students in classrooms with windows and students studying under only florescent lights. They found that students without daylight produced less of a hormone that helps the body deal with stress and infection. “Work in classrooms without daylight may upset the basic hormone pattern, and this in turn may influence the children’s ability to concentrate or cooperate, and also eventually have an impact on annual body growth and sick leave,” the researchers wrote in the Journal of Environmental Psychology. “Windowless classrooms should be avoided for permanent use.”
Nurses in a Turkish hospital were subjects in another study, published in 2005. About half of 141 nurses had more than three hours of daylight exposure per day; about half had less. Those with more than three hours were less stressed and more satisfied with their work. Another study of nurses found them 95 percent more likely to make medical errors in mid-winter than in the fall, when there is more light.
Other research has compared workers in the Arctic during winter, when daylight hours are extremely short, and the tropics, where the length of the day is largely consistent year-round. It found workers in the Arctic winter feel they are not getting enough sleep. They are also more prone to depression — a finding backed by extensive research on seasonal affective disorder (SAD), when some people grow depressed during the shorter winter days.
For those suffering bipolar disorder, strong midday light may have therapeutic qualities. A 2017 study in the American Journal of Psychiatry found bright light between noon and 230 p.m. may decrease mood swings and depression in bipolar patients.
Health and sleep
Replacing daylight with artificial lamps appears to affect the brain’s production of melatonin, a hormone that regulates sleep, enhances immune function and may prevent some forms of cancer. Studies have found lower melatonin levels in night-shift workers and day workers in windowless workspaces; both groups sleep worse than workers with access to daylight. A 2010 study of eighth-grade students found that lack of exposure to morning daylight may delay bedtime that evening, cutting into their sleep.
A poor night’s sleep can negatively impact overall health, memory and attention span. A 2014 study in the Journal of Clinical Sleep Medicine, led by Mohamed Boubekri of the University of Illinois at Urbana-Champaign, examined the quality of office workers’ sleep and found evidence that workers who spend most of their days in rooms without windows sleep worse than those with windows nearby. Moreover, they reported lower scores on all eight factors measured by the short-form health survey (SF-36), an established test of overall physical and mental health.
A 2012 study of patients’ average length of stay in a Korean hospital found significant benefits correlated with brighter rooms, especially ones with ample daylight. Patients recovering in rooms facing southeast left the hospital between 16 and 41 percent faster than patients in rooms facing northwest (which receive less direct sunlight in the northern hemisphere). The researchers, led by an engineer at the Missouri University of Science and Technology, also conclude that morning light may be more beneficial to patients’ health than afternoon light.
Some research has claimed that sustainably designed offices — that is, offices in buildings that are relatively energy efficient, filter air and maximize the use of natural light — improve worker productivity. A number of design standards, such as WELL certification by the International WELL Building Institute in Washington, D.C., are often touted for boosting productivity. But while the evidence is extensive that design features such as windows can improve workers’ health and happiness, a 2016 literature review challenges claims that design can impact output. There is “no agreed definition of productivity in an office environment,” the paper notes.
Students, however, because they take tests regularly, are easier to measure. A paper funded by the state of California found broad performance improvement among students in classrooms with the most natural light. The 2002 study looked at 21,000 students in three school districts (in California, Washington state and Colorado). Some scholars have questioned the paper’s methodology while acknowledging the findings merit further study: The paper suggests that students in classrooms with the most daylight progressed 20 percent faster in math over one year compared to their peers with less light, and 26 percent faster in reading.
Probed less often by researchers is the relationship between daylight and moral behavior. But in 2013, two Taiwanese researchers writing in the Journal of Environmental Psychology described three experiments that appear to show people acting more ethically in well-lit rooms than in dingy ones — in one of the tests, for example, doling out more money to strangers from a common pot. The researchers found “brighter surroundings can induce people to act less selfishly and increase the likelihood of honesty.”
Lastly, scholars have also focused on shoppers, finding that windows allowing daylight into stores may even boost sales.
- Alimoglu, Mustafa Kemal; et al. “Daylight Exposure and the Other Predictors of Burnout Among Nurses in a University Hospital.” International Journal of Nursing Studies, 2005. doi: 1016/j.ijnurstu.2004.09.001.
- Blask, David E. “Melatonin, Sleep Disturbance and Cancer Risk.” Sleep Medicine Reviews, 2009. doi: 10.1016/j.smrv.2008.07.007.
- Boubekri, M.; et al. “Impact of Windows and Daylight Exposure on Overall Health and Sleep Quality of Office Workers: A Case-Control Pilot Study.” Journal of Clinical Sleep Medicine, 2014. doi: 10.5664/jcsm.3780.
- Byrd, Hugh; Rasheed, Eziaku Onyeizu. “The Productivity Paradox in Green Buildings.” Sustainability, 2016. doi: 10.3390/su8040347.
- Choi, Joon-Ho; Beltran, Liliana O.; Kim, Hway-Suh. “Impacts of Indoor Daylight Environments on Patient Average Length of Stay (ALOS) in a Healthcare Facility.” Building and Environment, 2012. doi: 10.1016/j.buildenv.2011.10.010.
- Cuttle, C.; Brandston, H. “Evaluation of Retail Lighting.” Journal of the Illuminating Engineering Society, 1995. doi: 10.1080/00994480.1995.10748117.
- Figueiro, Mariana G.; Rea, Mark S. “Lack of Short-Wavelength Light During the School Day Delays Dim Light Melatonin Onset (DLMO) in Middle School Students.” Neuroendocrinology Letters, 2010.
- Gumenyuk, Valentina; Roth, Thomas; Drake, Christopher L. “Circadian Phase, Sleepiness, and Light Exposure Assessment in Night Workers with and Without Shift Work Disorder.” Chronobiology International, 2012. doi: 3109/07420528.2012.699356.
- Jennings, J.; et al. “Can Dynamic Light Improve Melatonin Production and Quality of Sleep?” Critical Care, 2014. doi: 10.1186/cc13204.
- Karami, Zohre; et al. “Effect of Daylight on Melatonin and Subjective General Health Factors in Elderly People.” Iranian Journal of Public Health, 2016.
- Kukec, Andreja; Dovjak, Mateja. “Prevention and Control of Sick Building Syndrome (SBS). Part 1: Identification of Risk Factors.” International Journal of Sanitary Engineering Research, 2014.
- Küller, Rikard; Lindsten, Carin. “Health and Behavior of Children in Classrooms with and Without Windows.” Journal of Environmental Psychology, 1992. doi: 10.1016/S0272-4944(05)80079-9.
- Marmot, A. F.; et al. “Building Health: An Epidemiological Study of ‘Sick Building Syndrome’ in the Whitehall II Study.” BMJ Occupational and Environmental Medicine, 2006. doi: 1136/oem.2005.022889.
- Marqueze, Elaine Cristina. “Natural Light Exposure, Sleep and Depression among Day Workers and Shiftworkers at Arctic and Equatorial Latitudes.” PLoS One, 2015. doi: 10.1371/journal.pone.0122078.
- Roseman, C.; Booker, J.M. “Workload and Environmental Factors in Hospital Medication Errors.” Nursing Research, 1995. doi: 10.1097/00006199-199507000-00007.
- Sit, Dorothy K.; et al. “Adjunctive Bright Light Therapy for Bipolar Depression: A Randomized Double-Blind Placebo-Controlled Trial.” The American Journal of Psychiatry, 2017. doi: 10.1176/appi.ajp.2017.16101200.
- Wright Jr., Kenneth P.; et al. “Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle.” Current Biology, 2013. doi: 10.1016/j.cub.2013.06.039.
- Wurtman, Richard J. “The Effects of Light on the Human Body.” Scientific American, 1975.