I think I've found the scientific explanation. Well, not the explanation but the answer to this problem.
The influence of different light spectra on the suppression of pineal melatonin content in the syrian hamster
Quote:
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Red light is the least capable of suppressing pineal melatonin
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(Pileal melatonin is one of the things that makes you sleep)
Is the least capable, so "contrario sensu" it still has some effect.