Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: Petrochemicals on 21/11/2023 21:47:19
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Are humans biologically synchronised with the seasons? Mankind has has millions of years to evolve, some at the equator and some at the polar regions, but all places experience seasons, be it cold, dry, hot or wet. Some people are known to utilise light sources to improve their own feeling during dark months, people become joyous and active in the summer and can develop nesting characteristics in the winter in line with the activity in nature. I wonder whether this behavior is entirely psychological or is there more to it?
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There is some physiology involved. It seems than an absence of blue light produces "seasonal affective disorder" in many people, leading to lethargy and even clinical depression. It is thought that the problem is due to the production of excessive melatonin and reduced serotonin but I can't claim to understand the connection between the retina and the hypothalamus.
I worked with a company to optimise the spectrum and dosimetry of "SAD lights", trying to maximise the beneficial effect without inducing blue light disruption to color vision, which has been found inter alia to affect the performance of airline pilots reading modern full-color instruments after flying in the "blue bowl".
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Interesting, Alan. I had previously thought that the lack of short wavelength blue light was that part of the spectrum which when missing was responsible for increased melatonin secretion from the pineal gland. I am definitely slowed down mentally at this time of the year and I struggle with some mental tasks that would not tax me in brighter times. Fortunately it does not progress to depression as it does with some people. Could you expand on the problem with pilots and the spectrum of displays, please.
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Different phenomenon, same cause. If you google "blue light hazard" you will come across all sorts of assertions and denials of permanent retinal damage caused by exposure to intense blue light including the "unshaded daylight" above the cloud layer. Suffice it to say that the International Commission on NonIonising Radiation Protection recognises a number of effects including disturbance of circadian rhythm and possible macular damage, and has published guidance on safe acute and continuous exposure levels across the visible spectrum.
The finding that intrigued me was a temporary and possibly cumulative loss of color discrimination at "unshaded daylight" levels of exposure. This work dates from the 1990s and compared the color vision of military (short sorties, low level, with a helmet and visor) and airline (long sectors above cloud, no protective eyewear) pilots. Despite being in almost every other matter recruited from identical groups, airline pilots definitely showed decreased color discrimination compared with military pilots at similar ages, and the temporary acute effect (immediately after exposure) was enough to raise a concern about the conspicuity of "glass cockpit" displays. Guidance from unions and aviation authorities was to always wear sunglasses when flying in the "blue bowl".