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The energy source both in terms of fuel and electricity on my ship is nuclear fusion. Very precise nuclear fusion: there is no helium fusion until there is absolutely 100% helium in the main fusion tank and in the 6 other fusion tanks, so the ship only needs fuel once. Then they can fly through space via nuclear fusion forever.

Note that because of artificial gravity and cosmic ray protection, the people won't get space sickness or any other side effects of being in space.

Through the whole generation ship there is artificial sunlight. Some people are nocturnal. This requires invisible UV lights on the nocturnal side of the sleeping quarters so that every day crew members get vitamin D while they sleep. They will be burnt by UV, deal with it.

But the nocturnal side of the human (there are some aliens that are also nocturnal or diurnal although for different reasons) sleeping quarters requires absolutely no infrared or visible light, just UV.

The artificial sunlight on the ship covers this range:

Sunlight

Now how do they get this spectrum on a generation ship with green energy? LEDs, of course. They produce it at the exact type ratios shown here (7% ultraviolet, 44% visible light, 37% near infrared, 11% far infrared, the other 1% isn't important and would probably be just a bit more visible light in the case of the LEDs).

The visible spectrum is done using white LEDs(Pretty obvious).

With artificial sunlight, plants and animals can be taken care of, so they have chickens for eggs, cows for milk, etc.

But is this artificial sunlight the best way to mimic daytime in space? And for the nocturnal people, is UV during sleep the best way to get vitamin D?

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  • $\begingroup$ Are you saying fly forever as in for a very long time or actual forever? The latter may not be possible - $\endgroup$ – Zxyrra Nov 18 '16 at 3:08
  • $\begingroup$ what is the problem? What is the question? Habits of humans who are nocturnal? I can tell you they do not need UV, not during the sleep, not during not sleep. Sun bath once a week or month for 5 minutes is more then enough for them. Try to define the problem more articulate way, maybe. $\endgroup$ – MolbOrg Nov 18 '16 at 3:12
  • $\begingroup$ @MolbOrg Question is last sentence and articulate. $\endgroup$ – Zxyrra Nov 18 '16 at 3:13
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Is this artificial sunlight the best way to mimic daytime in space?

Yes. How else would you mimic daytime? You need a circadian rhythm of day and night, and it would obviously be best to provide a light spectrum similar to what is available on earth. Maybe turn down the UV a little bit to ensure no sunburn and no melanoma. If you have LEDs that can do that, then you have the best solution.

Is UV during sleep the best way to get Vitamin D

No. First, if you have UV light present during your daytime hours, why do you need it at night? Second, if you need a circadian rhythm (as humans do) you would not want to cycle the ship between day and night, you would want to cycle the people between day and night compartments: day for their working hours and night for their sleeping hours. That way they get 12 hours of sunlight with UV and shouldn't have any vitamin D problems.

There is a throwaway mention of nocturnal (?) aliens (???). Its not really clarified, but if they are nocturnal humans from earth with its day-night cycle, then they can sleep during the day, so they can sleep in daylit compartments and get UV. If they are nocturnal aliens, they would either not need vitamin-D or they would have some other way to get it.

So even if you aren't getting enough Vitamin-D due to low UV level to reduce melanoma or whatever reason, there are still vitamin-D supplements that are easy enough to add to your food, they are quite common today in milk and other things.

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    $\begingroup$ Well the nocturnal humans are there for a purpose. When they reach the destination planet and start forming a civilization, there will have to be humans watching out for predators with all senses day and night. So some humans have to be nocturnal or at least not deep sleepers. The nocturnal aliens are different in a lot of ways but 1 difference is they are born nocturnal or diurnal unlike us humans where nocturnal vs diurnal is adaptive. The nocturnal aliens are again there for a purpose, namely to keep the generation ship running while other aliens sleep. $\endgroup$ – Caters Nov 18 '16 at 3:52
  • $\begingroup$ If these humans have the technology to travel the starts in generation ship, how do they not have the technology to build predator proof living places? You can't build a generation ship, but you also don't have to worry about predators. $\endgroup$ – kingledion Nov 18 '16 at 3:57
  • $\begingroup$ But it isn't the humans that have the technology. The humans are simply using it. It is the aliens that actually have the technology and have had it for thousands of years. $\endgroup$ – Caters Nov 18 '16 at 4:01
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    $\begingroup$ @Caters These commends may be useful in the original question. My answer is still applicable as it stands. $\endgroup$ – kingledion Nov 18 '16 at 4:14
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    $\begingroup$ @Caters Why do you need nocturnal aliens , to keep ship running while you sleep? Here on earth we have shift work 1st,2nd, and 3rd. It maybe inconvenient for awhile, but people today do it all the time. Police workers and hospital worker work night all the time. Get shot at 3am you can't wait till 8am for treatment. $\endgroup$ – cybernard Nov 19 '16 at 4:01
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First, about the vitamin D. While it is true that in the absence of dietary supplements people need some amount of sunlight in order to get their vitamin D, the actual requirement is tiny -- a few minutes now and then. After all, there are people who live beyond the Arctic circle. And vitamin D can be manufactured very easily -- much easier than scrubbing the CO2 from the ship's air, much easier than keeping molds under control etc. Just one more tiny problem for the life support system.

About light spectrum. A perfect imitation of the spectrum of solar light is useless. For human color vision you don't have to reproduce the visible spectrum faithfully, you only need LED light with good CRI (Color Reproduction Index); there is absolutely no need to reproduce the spectrum outside the visible range. For growing plants, you would very much prefer to concentrate luminous energy in those bands which are absorbed by clorophyll. The human eye is most sensitive to green wavelengths, yet clorophyll does not use them at all -- that's why leaves appear green, because green light is reflected. So in the hothouses where plants are grown you would not waste energy producing green light.

Finally, circadian rhythm on a ship. There is actually a lot of experience with circadian rhythm on enclosed ships, coming from submarines. During the Cold War, both Russia and America maintained fleets of nuclear-powered ballistic missile submarines; such a submarine dives at the beginning of the patrol and remains submerged for a long time. The crew does not see the outside world for months. The practical experience is that the human body performs best when a 24 hour cycle is adopted (see for example, http://www.usnews.com/opinion/blogs/world-report/2014/05/08/us-navy-benefits-from-a-better-sleep-schedule), but that it can adapt to an 18-hour cycle (see http://dspace.rubicon-foundation.org/xmlui/bitstream/handle/123456789/5511/17393936.pdf?sequence=1) with no major problems, and there is no need to have a night-and-day cycle for the entire ship -- the ship as a whole can remain always alert, only individual crew members need cycles of work, rest and sleep; this saves on the requirements for sleeping spaces, leisure spaces etc.

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  • $\begingroup$ This is why I separated them(both humans and aliens) into nocturnal and diurnal to begin with was so that the ship would not have to stop at some point in space. $\endgroup$ – Caters Nov 18 '16 at 22:54
  • $\begingroup$ The entire point is that on an enclosed ship there are no nocturnal and diurnal shifts, but the ship is always in the same state -- there is no day and there is no night -- and each individual member of the crew cycles through their dayly routine together with their shift-mates, offset by 6 and 12 or by 8 and 16 hours from the other shifts, with the crew generally divided into three shifts which come on watch one after the other. $\endgroup$ – AlexP Nov 18 '16 at 23:18

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