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Humans (even programmers :-) ) are used to having some access to natural light, but in a colony in space, on the dark side of a tidally-locked planet, or underground (for example) this won't happen. Are there known (documented) effects on people's health (physical and psychological) as a result of living in such an environment, where all light is artificial?

Assume the timing of lighting changes is under inhabitants' control, and that any lighting technologies currently known can be applied.

I'm not asking about temporary situations (like winter in Antarctica) but about living in such an environment for years.

I'm aware of Seasonal Affective Disorder (SAD) and that it can be mitigated by special lamps producing light in a particular range of the spectrum. What else could go wrong in this environment? Assume the use of dietary supplements to make up for the loss of Vitamin D through sunlight.

Because they will have access to light (just not sunlight) I'm assuming that their vision won't degrade (a la Wells's Morlocks), but if that's wrong, please correct me.

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  • $\begingroup$ The experienced of people who work in the Antarctic during the winter months would be useful. $\endgroup$ – RonJohn Mar 16 '18 at 22:47
  • $\begingroup$ Is there any specific part of 'natural' sunlight that you expect can't be copied by technology? It's just light from a glowing thing, filtered through atmosphere - Xenon arc lamps are even hotter, and water filtering etc can be done, so we can match sunlight in both intensity and spectrum. $\endgroup$ – bukwyrm Mar 19 at 8:24
  • $\begingroup$ If you're writing a story in such a setting, why not go spend a winter in northern Alaska while writing? $\endgroup$ – workerjoe Mar 19 at 13:33
  • $\begingroup$ @Joe I'd love to, but there are these little matters of my job, family, and finances. :-) $\endgroup$ – Monica Cellio Mar 19 at 14:06
  • $\begingroup$ @TheDyingOfLight good idea. I'll edit to add that and remove mentions of moons, and then clean up these comments. $\endgroup$ – Monica Cellio Mar 20 at 14:08
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Physical health

Sunlight is popularly regarded as beneficial due to the production of vitamin D, but also popularly regarded as non essential since vitamin D can also be gained from diet or supplements. However, the process of producing vitamin D uses up specific raw materials. Those materials, if not used up to make vitamin D, are instead used to make a form of cholesterol. Sunlight exposure leads to lower blood cholesterol. The chemical processes are discussed more in this paper.

More recently other studies have shown further benefits to exposure to ultra violet rays, and it has been suggested that the risk of skin cancer is outweighed by the risks involved with low sun exposure. There are suggestions of benefits to blood pressure and heart health.

Some of these studies were carried out using artificial ultra violet sources, so the benefits do not depend on it coming specifically from Earth's sun. The hypothetical habitat would benefit from having ultra violet lamps, ideally at a frequency or frequencies that bring the benefits without damaging skin cells and risking cancer, if such frequencies can be found through further study. The lamps could either be in treatment rooms which inhabitants would regularly visit, or the general lighting could include enough ultra violet light that everyday life would involve sufficient exposure without having to put time aside for it. This would probably depend on the cost of producing such light. If it's cheap it may as well be everywhere.

Psychological health

As explained in DonyorM's answer blue light is involved in sleep regulation. Studies that deprive people of access to a day/night cycle with which to reset their circadian rhythms are short term, so the effects of long term exposure to such conditions have not been studied. However, there are people who are blind and have no light reception with which to reset their body clocks. Reading up on non-24-hour sleep-wake disorder may help you get a better idea of the long term effects. This would be helpful if you are writing a story in which you want to explore the effects on a society of not having sunlight, but less useful if you just want to decide whether your characters need sunlight - if you want to write about a healthy colony you probably already have enough reasons to include artificial sunlight without having to read further.

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  • $\begingroup$ It would also be worth adding to the psychological health bit some detail on Seasonal Affective Disorder (SAD). It's far more common than people think, and is currently thought to be caused by reduced exposure to sunlight: nhs.uk/conditions/seasonal-affective-disorder-sad Expect people to be tired and depressed. $\endgroup$ – Ynneadwraith Mar 19 at 11:30
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Artificial light could be used instead of sunlight. Much of the basis for this answer comes from this article. The article is mostly about sleep cycles, but it includes some pertinent information.

External cues keep the body in sync.

That's the biggest thing. To be completely successful in mimicking life on Earth, artificial light must fade and come back in a rhythmic manner. This sets are body clock and gives us cues to work with. These cues may not necessarily be every 24 hours, but they do need to be regular. Studies have shown that getting light at the wrong times can mess up your body. (This is true on Earth too).

There would also need to be the proper spectrum of light. Our body especially responds to blue light, which is what sunlight is primarily composed of. Blue light stops the production of melanin, which is what puts us to sleep.

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  • $\begingroup$ It's worth noting that studies investigating the uninterrupted circadian rhythms of people show that we tend to settle into a regular slightly longer than 24-hour cycle in the absence of other stimuli (light/regular food times etc.), to no apparent ill effect. $\endgroup$ – Ynneadwraith Mar 20 at 14:14
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Yes, living without sunlight can affect the human body and mind negatively. I say can because as mentioned in Githubphagocyte's answer, blind people may be affected differently, and different individuals would experience different effects based on their psychological makeup and physical preparedness.

The best first-person account I can direct you to is that of Michael Siffre, an experienced French caver who voluntarily conducted personal experiments involving isolation in underground caves for extended lengths of time. This was to further understanding of how humans may react to being outside of external cues for sleep/wake cycles and the psychological effects of isolation that may be experienced during space travel. In 1962 he spent two months in a glacial ice cave 375 feet underground, and in 1972 was sponsored by NASA to spend six months in a cave in Texas. The entire time he maintained telephone contact with his research assistants, relating his sleeping, waking and eating times

If you can read French, you can find and read the detailed results of his experiments yourself, but basically: He maintained a normal 24-hour circadian rhythm for the first month, but thereafter varied randomly between 18 and 52 hours. After almost three months in the Texas experiment, he started suffering from depression and contemplated suicide. In both experiments he experienced perturbations in his sense of time, and subsequent short term memory loss (apparently short-term memory is highly dependent on time cues). I don't recall anything interesting regarding his physical health, other than his suffering from hypothermia in the first experiment, as I assume he was well-stocked for nutritional needs otherwise, so no ill effects from vitamin D deficiencies.

Wikipedia article: http://en.wikipedia.org/wiki/Michel_Siffre

Interview with Cabinet magazine here: http://www.cabinetmagazine.org/issues/30/foer.php

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  • $\begingroup$ I'd think long-term hypothermia is likely to cause Polar T3 syndrome, the effects of which look a lot like SAD, as well as what's described above. $\endgroup$ – T.E.D. Nov 23 '16 at 14:42
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Far from being an expert in the filed, but according to that review by Aries et al. from 2013, so far no real conclusion can be drawn about the effect of the specific daylight to our health. Specifically, they conclude

There is only limited statistically significant and well-documented scientific proof for the link between daylight and its potential health consequences, despite the omnipresent attention this supposed relation is receiving.

In most cases the observed effects could be explained by other factor than light directly.

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I am not a doctor but can assure you that I suffer from S.A.D. and am very depressed in the winter without sun. I have tried sun lamps and I take Vitamin D supplements and neither of these actually make me feel any better. I have depression, a lack of energy, trouble getting to sleep and I do not actually want to get out of bed during the cold grey months. The minute the makes a real appearance (even when it is cold) I soak up some of those rays and feel better, energized, and enthusiastic within minutes. Without the sun I only go through the motions and do what can not be avoided, anyone who thinks we can live without light is nuts. We just like plants and other animals need sun and water to live.

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