Sunlight, Outdoor Light, and Light Therapy in Disease Management

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Original Editors - Ziya Altug

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Introduction[edit | edit source]

A lack of bright light and sunshine may lead to various medical disorders. This brief review highlights the role and practical application of light therapy, sunlight, and outdoor light exposure as an adjunct in managing pain, depression, and mood.

Outdoor Light

Since antiquity, many ancient cultures have worshipped the sun for a variety of reasons. Hippocrates wrote the first texts about the sun's benefits on mental health and mood and named this therapy "Heliotherapy."[1] Taber's Cyclopedic Medical Dictionary defines heliotherapy as "exposure to sunlight for therapeutic purposes" and phototherapy as "exposure to sunlight or to ultraviolet light for therapeutic purposes."[2] Phototherapy may be used to treat conditions such as extensive atopic dermatitis, extensive psoriasis, seasonal and nonseasonal depression, seasonal bipolar disorders, and neonatal hyperbilirubinemia.[3] From about the middle of the 19th century to the middle of the 20th century, sunlight, in combination with isolation, proper hygiene, fresh air, good nutrition, and physical exercise, was used to control and treat tuberculosis.[4] Moreover, Niels Ryberg Finsen (1860-1904) earned a Nobel Prize in Medicine in 1903 for his work on phototherapy to treat diseases such as lupus vulgaris.[5]

Light Therapy in Medicine[edit | edit source]

Outdoor Exercise

Sensible sunshine exposure plays an essential role in overall health. Michael F. Holick, Ph.D., MD, a researcher at the Boston University Medical Center, indicates that "vitamin D is the sunshine vitamin" and sunlight plays a role in vitamin synthesis.[6][7][8][9]Sunlight exposure may improve overall health,[10]control infections,[11]improve life expectancy,[12]reduce cognitive impairment,[13]help manage influenza pandemics[14][15]enhance the immune system,[16]manage coronavirus,[17]and improve employee mental health.[18]

Moreover, sunlight may have bactericidal potential[19]and help reduce fungal contamination in contaminated clothes.[20]Light therapy may be used to manage seasonal affective disorder,[21]for major depressive disorders and bipolar depression without seasonal pattern,[22]beneficial for improving sleep-wake cycles in individuals with Parkinson's disease,[23]and for multiple sclerosis-related fatigue.[24]

Light Therapy for Mood Disorders[edit | edit source]

An article by Turner and Mainster[25] in the British Journal of Ophthalmology indicates that the eyes play a vital role in good health. The authors state that “Bright light (≥2500 lux), particularly from bluer sources such as outdoor daylight, can reduce or eliminate insomnia and depression; immediately increase brain serotonin, mood, alertness, and cognitive function.” A study in Biological Psychiatry in 1994[26] indicates that “many Americans may be receiving insufficient light exposure to maintain optimal mood.” Interestingly, the subjects in this study were located in sunny San Diego, California, and 40 to 64 years old. According to Figueiro and colleagues,[27] “Light can also elicit an acute alerting effect on people, similar to a ‘cup of coffee.’” A longitudinal study in the Journal of Neural Transmission in 2007[28] concluded that blue light increases alertness and information processing speed.

Light Therapy for Pain Management[edit | edit source]

A randomized study in Pain Medicine in 2014[29] indicates that light therapy could not only improve depressive symptoms but also reduce pain intensity in individuals with chronic nonspecific back pain. The authors say that this effect may be due to pain and depression sharing similar pathophysiological pathways. Another study by Burgess and colleagues[30] shows that morning light therapy may help U.S. veterans with chronic low back pain. Another research study by the same lead author[31] shows that light therapy may be feasible as an adjunctive treatment for fibromyalgia. Table 1 summarizes the benefits of sunshine and sunlight and Table 2 outlines light levels in outdoor and indoor environments.

Table 1 - Benefits of sunshine and sunlight [4][6][8][9][14][16][19][20]

  • Source of vitamin D
  • Source of natural bright light to improve mood and seasonal and nonseasonal depression
  • Treating medical conditions such as tuberculosis and psoriasis
  • Controlling infections
  • Improve immune system
  • Bactericidal potential
  • Potential to reduce fungal contamination


Table 2 - Light levels in outdoor and indoor environments.

Outdoor Light Levels[25]

Bright sunlight, noon
Cloudy bright day
Overcast day
Very overcast day
Sun rising over the horizon


100,000 lux
25,000 lux
10,000 lux
2,000 lux
800 lux

Indoor Light Levels[25]

Candle[1]
Offices, kitchens
Living room
Average nursing home
Typical Seasonal Affective Disorder (SAD) treatment [1]


1 lux
200-500 lux
50-200 lux
50 lux
2,500 lux (2 hours per day) or 5,000 lux (1 hour) or 10,000 lux (30 minutes per day)

Adapted from Choukroun et al[1], Turner et al[25]

  • Lux is a unit of light intensity equivalent to 1 lumen/m2.[2]


Safety Considerations[edit | edit source]

In general, light therapy is safe for the eyes. However, individuals using light therapy should undergo a periodic ophthalmologic examination.[32][33][34]

Using a Light Therapy Box

Precautions for light therapy include headache, light sensitivity or photosensitivity, migraines (due to photophobia and photosensitivity), photosensitive skin, use of photosensitizing medications (e.g., psychiatric neuroleptic drugs, psoralen drugs, antiarrhythmic drugs, antimalarial drugs, antirheumatic drugs, St. John's Wort), and ocular abnormalities.[35] Clinicians should also be aware that individuals using light therapy may experience side effects such as anxiety, blurred vision, daytime drowsiness, dryness of the eyes, eye strain, fatigue, headaches, hyperactivity, insomnia, irritability, nausea, or a sunburn-type reaction.[32] [36]

Practical Application[edit | edit source]

Outdoor activity, exercise, and work help achieve optimal light exposure[37]. Table 3 outlines sample outdoor activities, sports, exercises, winter exercises, and indoor exercises to improve bright light exposure. Researchers have found suboptimal lighting practices in the home,[32] work,[38] and school39[39] can affect performance,[38] depression,[32][40] sleep,[41][42][43][43][44] and myopia.[45]

Table 3 - Sample outdoor activities to increase light exposure.

Locations for Outdoor Activity
  • Balcony
  • Patio
  • Backyard
  • Home gazebo
  • Park
  • Trail
  • Fitness courts (e.g., pullup bars, rope, parallel bars, rings)
Outdoor Activities
  • Biking
  • Hiking
  • Outdoor calisthenics
  • Outdoor Pilates
  • Outdoor tai chi
  • Outdoor yoga
  • Walking
Outdoor Sports
  • Basketball
  • Pickleball
  • Softball
  • Table tennis
  • Tennis
  • Volleyball
Winter Activities
  • Cross-country skiing
  • Ice skating
  • Outdoor trail biking
  • Outdoor walking
  • Skiing
  • Sled riding
  • Snowshoe walking
  • Snowboarding


Tables 4, 5, and 6 outline practical self-management strategies that may be used to enhance light exposure at home, work, or school.

Table 4 - Practical self-management strategies for increased light exposure in the home.

  • Get enough natural outdoor light during the day, especially in the morning.
  • Have your breakfast near a window or on a balcony, porch, patio, or in your backyard gazebo.
  • Open the curtains to let in as much outdoor light as possible, especially in the morning.
  • Consider remodeling the home to add more windows or skylights or enlarging existing windows.
  • Consider adding a sundeck or a gazebo to the backyard for exercise, meditation, relaxation, or reading.
  • Consider painting walls with light shades or tones (e.g., white) and purchase furniture with light colors.
  • Create a reading, relaxation, or healing space in the home that has sunlight streaming in. For reading, it's best if the sunlight is behind the person.
  • Place the home computer or workstation to face out a large window where a person can gaze off into the distance periodically. However, the homeowner should avoid facing direct sunlight.
  • Wash home windows and trim the bushes and trees near the windows to allow for more light to enter the home.
  • To prevent sleep problems, turn off cellphones and computers several hours before bedtime.
  • Sit on a balcony, patio, porch, or in the backyard, and do some bird watching or gaze at the horizon or trees in the distance for light and relaxation.

For optimal benefits, homeowners may need to consider remodeling their homes to allow more interaction with the outdoor environment. See a sleep medicine or lighting specialist for additional guidance.

Table 5 - Practical self-management strategies for increased light exposure at work

  • If a person has windows in their office, position the desk to face out the window. Being able to look away from a computer monitor and into the distance may help reduce eye strain. However, the office worker should avoid facing direct sunlight.
  • Arrange all workstations at the perimeter of the office to face out windows.
  • Place vending machines, water dispensers, and photocopiers near windows.
  • Have meetings in well-lit rooms with large windows and natural outdoor light.
  • Consider holding small group meetings while walking outside on a sunny day.
  • Consider adding skylights to areas with many workstations.
  • Open window blinds and trim back bushes and trees covering office windows.
  • Eat lunch outdoors (at a picnic table or sit on a portable chair), even if a person sits under a tree or in the shade. If a person can't go outside due to heat, cold, allergies, or pollution, sit near a window in the cafeteria and do some bird watching or gaze at the horizon or trees in the distance.
  • After eating your lunch, take a 10 to 15-minute walk. Exercise outdoors before work, during lunch, or after work. Short bout exercise has been shown to be effective for improving health and enhancing exercise adherence in overweight and obese adults.[46][47]
  • Go outdoors during work breaks. Even on an overcast day, being outdoors provides more light than the typical indoor office lighting (see Table 2 for lux levels).

For optimal benefits, companies may need to consider remodeling their buildings to allow more interaction with the outdoor environment. See a sleep medicine or lighting specialist for additional guidance.


Table 6 - Practical self-management strategies for increased light exposure at school.

  • Open the blinds and curtains to allow natural outdoor light to enter.
  • Have children sit near the windows. However, the students should avoid facing direct sunlight.
  • Take recess outdoors.
  • Include activities that involve outdoor projects such as gardening and sports.
  • Encourage children to eat outdoors, even if it's under a tree or in the shade. If the children can't go outside due to heat, cold, allergies, or pollution, have them sit near a window in the cafeteria and do some bird watching or gaze into the distance.
  • Include more outdoor recess breaks and outdoor physical education classes. According to some researchers, higher levels of total time spent outdoors may be associated with less myopia.[45]

For optimal benefits, schools may need to consider remodeling their buildings to allow more interaction with the outdoor environment. See a sleep medicine or lighting specialist for additional guidance.

Assessment Tools[edit | edit source]

  • Morningness-Eveningness Questionnaire (MEQ) Horne JA, Ostberg O. A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. Int J Chronobiol. 1976;4(2):97-110. https://pubmed.ncbi.nlm.nih.gov/1027738/
  • Munich ChronoType Questionnaire (MCTQ Roenneberg T, Wirz-Justice A, Merrow M. Life between clocks: daily temporal patterns of human chronotypes. J Biol Rhythms. 2003;18(1):80-90. doi:10.1177/0748730402239679 https://pubmed.ncbi.nlm.nih.gov/12568247/
  • Seasonal Health Questionnaire (SHQ) Thompson C, Cowan A. The Seasonal Health Questionnaire: a preliminary validation of a new instrument to screen for seasonal affective disorder. J Affect Disord. 2001;64(1):89-98. doi:10.1016/s0165-0327(00)00208-1 https://pubmed.ncbi.nlm.nih.gov/11292523/
  • Seasonal Pattern Assessment Questionnaire (SPAQ) Mersch PP, Vastenburg NC, Meesters Y, et al. The reliability and validity of the Seasonal Pattern Assessment Questionnaire: a comparison between patient groups. J Affect Disord. 2004;80(2-3):209-219. doi:10.1016/S0165-0327(03)00114-9 https://pubmed.ncbi.nlm.nih.gov/15207934/
  • Murray G. The Seasonal Pattern Assessment Questionnaire as a measure of mood seasonality: a prospective validation study. Psychiatry Res. 2003;120(1):53-59. doi:10.1016/s0165-1781(03)00147-1 https://pubmed.ncbi.nlm.nih.gov/14500114/
  • Rosenthal N., Bradt G., Wehr T. Seasonal Pattern Assessment Questionnaire (SPAQ) Bethesda, MD, USA: National Institute of Mental Health; 1984

Related Articles[edit | edit source]

Resources[edit | edit source]

References [edit | edit source]

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