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Light-Hygiene: using light and dark cycles in such a manner as to affect health. The experience of light and dark cycles that agree with a natural solar timing pattern could be referred to as good light-hygiene. There is an exception to this idea. Naturally occurring good light-hygiene for humans becomes incrementally more improbable as one moves increasingly towards the North or South Pole. The equator is perfect for human light-hygiene, providing 12 hours of darkness and 12 hours of light, which lighting pattern does not trigger the need for winter or summer adaptations within a person’s metabolism. However, those who live between the equator and a pole may have a moderately challenged good light-hygiene — mainly during the seasonal short-lived length-of-day (L.O.D.) peaks of summer and valleys of winter season. Living away from the equator will stimulate varying degrees of seasonal metabolic summer and winter adaptions. The seasonal peak lengths of day and night last a short time, and, if they are not too extreme (for example, around the Great Lakes area the peak L.O.D. duration is 15 hours, as opposed to Alaska where the peak duration is 24 hours), the biological strain and resultant metabolic adaption stimulated by this light-hygiene compromise may not be very detrimental to some. To others, even these relatively short-lived L.O.D. duration peaks and valleys are very biologically and/or mentally devastating even during the months surrounding the extremes of the peaks and valleys.

Humans are capable of both winter and summer adaption. In the winter, the long nights signal the body to make more melatonin, to sleep longer and to grow more brown fat that burns energy for heating. In the summer, the long days signal the body to desire less sleep and increase the drive to eat more carbs for the storage of energy that will be needed later for the winter when the brown fat cells are providing heat. But despite this ability to adapt, not everyone is equally adaptable.

For the lengths-of-daylight away from the equator, we would NATURALLY experience a swinging back and forth throughout a year from “too short” to “just right,” followed by “too long” before reversing direction back toward “just right,” followed by “too short” again. Humans have some ability to adapt to this, but humans can not adapt to a perpetual summer lasting a year long. That is what artificial light can create, a perpetual summer, with artificial long days that are too long for 365 days of the year. This stops the swinging of the lengths-of-days, and prevents winter-adaption which otherwise would have helped humans to recover naturally from our summer drive to eat more carbs.

Good light-hygiene from natural solar timing is either the 50/50% balance of day and night occurring daily at the equator or the swinging back and forth between short and long days throughout an entire year (such as we experience around the Great Lakes)  which still mathematically averages as a 50/50% balance of day and night, but for the entire year instead of for a 24-hour cycle . Good light-hygiene also implies that the swinging of the length-of-days is tolerable to a particular person, which tolerability varies from person to person and is further complicated by how far that person is from the equator.

A common example of poor light-hygiene is the usage of artificial lighting in the evenings which constitutes a perpetual-summer-stimulation that even exceeds the maximum short-lived summer peak L.O.D. in the Great Lakes area (maximum day length 15 hours) by simulating a 16-hour long day, for all 365 days of the year (assuming that a person is in darkness for only 8 hours).

We want good light-hygiene, the natural solar timing pattern (that is tolerable), to be the driver of the timing phases of our Circadian Rhythm, as each human cell’s Circadian Rhythm is programmed for about a 24-hour cycle, roughly divided into two equal halves. Click Circadian Rhythm to follow a logical sequence of explanation.


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