Psychology

I don't know, but I imagine, that the airlines employ the services of many different professionals in designing their aircraft.   Among those will be behavioural psychologists I'm sure.

If you pause to think about it, you could become a bit uncomfortable about the way that the airlines create a pattern for the day that sometimes will encourage you to sleep daytime so that your body clock has the best chance of adjusting.

So the stars come out and the lights go out.   When "morning" comes, the light will slowly come up a warm sunrise glow.   And on some aircraft there is even a piped dawn chorus....

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