Sunlight Obstruction Syndrome (SOS) is only half the story

The adverse effects of artificial light at night are actually greater than those of sunlight deprivation

Chris Patrick, an Irish-born clinical pharmacist living in Brisbane, Australia, recently coined an interesting new term, “Sunlight Obstruction Syndrome”¹. While SOS is not an approved medical diagnosis, it does effectively convey one of the key messages about light and health. And we need catchy terms to capture the attention of the general public and make them aware that exposure to the right light at the right time is a vital part of good health.

Sunlight Obstructed Lives

We spend our days mostly indoors in rooms where UV and near infrared blocking windows filter out over half the natural light spectrum, and where the design of our interior space keeps us in near-twilight levels of daytime illumination. Indoor artificial lighting, predominantly from blue-pump LEDs, delivers only a narrow fraction of the natural spectrum - a pale imitation of natural light. Unlike our ancestors, who typically spent far more time outdoors exposed to natural daylight, we live in a sunlight-obstructed world.

Infographic from Chris Patrick

As the infographic shows, Sunlight Obstruction Syndrome can be associated with a wide variety of chronic illnesses that are common in today's world and that shorten our lifespan. And yet, Sunlight Obstruction Syndrome is only half of the story. Exposure to Artificial Light At Night, or “ALAN”, contributes to the same panoply of disease and ill health.

Both SOS and ALAN cause the circadian disruption that underlies all this human pathology. Exposure to natural daylight boosts the amplitude of our circadian rhythms and helps keep us synchronized to the natural day-night cycle. When we live indoors we are deprived of adequate natural daylight, and our circadian rhythms dampen and lose their tight association with the Earth's rotation.

Similarly, artificial light at night sends a confusing signal that it is still daytime outside, dampens our circadian rhythms, and disassociates the internal synchrony of the circadian clocks in every cell of our body. There is a huge literature reviewed in my book, THE LIGHT DOCTOR, that shows that ALAN is a major cause of obesity, diabetes, heart disease, cancer and multiple other chronic conditions that shorten our healthy lifespan.

Which is more harmful SOS or ALAN?

One way to understand the relative contributions of SOS and ALAN are the studies where day and night light exposure has been tracked 24 hours a day for multiple days and correlated with the development of ill health.

In the 85,000 older adults participating the the UK Biobank study, those who were exposed to the most ALAN had a 30% greater incidence of psychiatric illness such as major depressive disorders, whereas those who had the least sunlight exposure (greatest SOS) had a 20% increase in major depressive disorders². So while both SOS and ALAN contribute to significant chronic ill health, the adverse health impact of ALAN was even greater than that of SOS.

Similarly, SOS and ALAN both shorten lifespan, but the effects of ALAN on mortality are greater. Among the 89,000 people in the UK Biobank study, the people exposed to the most artificial light at night had a 46% increased risk of cardiometabolic mortality. In contrast, the people exposed to the least daylight had a 39% increased risk of cardiometabolic death.³

Similarly in a study of 831 children, whose light exposure was monitored 24 hours a day for 5 consecutive days, both decreased exposure to bright light during the day and increased exposure to ALAN were associated with increased obesity. However reducing exposure to bright LAN was more beneficial for weight control compared to increased exposure to bright daytime light ( i.e. reduced SOS)⁴

Of course, the combined adverse health impacts of SOS and ALAN are greater than that of either alone. So it is vitally important to increase both natural outdoor daylight exposure and to reduce the use of blue-rich light at night.

Limitations of the SOS Message

Sunlight Obstruction Syndrome (SOS) is a catchy term and flags the importance of getting outside every day in natural daylight. However, it could lead to the conclusion that simply seeking sunshine is the key to good health. So here are some qualifications.

You don’t need direct sunshine, daylight on a cloudy day is sufficient.

Sunlight can be obstructed by clouds, and that is not a problem. Even on an overcast cloudy day there is plenty of broad-spectrum light intensity for boosting your health. Getting outdoors every day is the key, rain or shine.

Getting up to greet the sunrise is not required, or even a good idea

The first half of the morning is the most effective time to seek daylight to provide the sky-blue wavelengths for syncing the circadian clock, and the far red and infrared rays to boost mitochondrial energy production. Some people make it a point to get up early enough to greet the rising sun, but this not always a good idea. During the summer months the sun may rise before 6 am, and light at that time will progressively advance the circadian clock more than is desirable and you will end up awakening too early.

Sunlight exposure reduces the risk of circadian disruption but does not eliminate it

As discussed above getting exposed to outdoor daylight each day is vital for good health, but also make sure you avoid all blue-containing light in the evenings before bed.

Too much sunshine increases other health risks

Moderation in all things applies to seeking sunlight. There are substantial risks of sunburn, skin cancers and other health problems from excessive sunlight exposure without the use of sunblock lotions. Excessive sunlight can also cause eye damage, so protecting the eyes from 425-450 nm violet-blue light when the sun is bright is also important.

Further Resources

For more remarkable insights into what we have done to ourselves by moving indoors and switching on narrow-spectrum blue-rich LED lights, see my book THE LIGHT DOCTOR.

Remember the light we see is as important our health as the food we eat, the water we drink, and the air we breathe.

Sources

1. Patrick C (2025) SOS: Sunlight Obstruction Syndrome https://www.linkedin.com/posts/cpatrick88_sos-sunlight-obstruction-syndrome-is-the-activity-7338074993488023552-2Icr?utm_source=share&utm_medium=member_desktop&rcm=ACoAAAKJjAYBIdaRjpN02Rg4-HuTno9_SuCtT3c

2. Burns AC et al (2023) Day and night light exposure are associated with psychiatric disorders: an objective light study in >85,000 people. Nature Mental Health. 1: 853–862 https://doi.org/10.1038/s44220-023-00135-8

3. Windred, D.P., Burns, A.C., Lane, J.M., Olivier, P., Rutter, M.K., Saxena, R., Phillips, A.J. and Cain, S.W., 2024. Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in> 88,000 individuals. Proceedings of the National Academy of Sciences, 121(43), p.e2405924121.

4. Ding W. et al (2025) Personal 24-hour light exposure pattern with obesity and adiposity-related parameters in school-aged children: A cross-sectional study based on compositional data analysis. Environmental Research 275, 15 June 2025, 121422 https://doi.org/10.1016/j.envres.2025.121422