For an experience that commands a quarter to a third of our lives, surprisingly little is known about how our bodies and brains sense the need to sleep, then automatically adjust and discharge that need so that we can function day in and day out.
The molecular clock doesn’t only regulate the amount and quality of sleep we get. It has a big hand in overall physical and mental health as well. Body temperature, heart rate, hormone levels, immune response, mood, alertness, cognitive performance, auditory reaction times—all have their moments in the sun, as solar time is biologically etched within us.
Blue light is part of the visible light spectrum; exposure to it in the morning is physically vitalizing and mood-enhancing. It sets the human rhythm, kicking off biological day. Even small amounts of it, studies show, suppress production of melatonin, the circadian-tied hormone that ushers in biological night, building up as light diminishes and promoting sleepiness.
Brain function is especially tied to the timing and type of light exposure because photoreceptors in the human eye—retinal ganglion cells—communicate directly with the brain, sending signals to the SCN master clock. By virtue of a unique constituent protein called melanopsin, photoreceptors at the front of the eye are most sensitive to blue-light wavelengths.