Blue light is a specific frequency band of electromagnetic radiation within the visible spectrum. While visible light tends to appear a white-ish, yellow color, the visible spectrum spans from violet through red (the colors of the rainbow). Blue light falls on the end of high energy, short wavelength light that can cause damage and disruptions to the biological systems in all living things.
If you recall here, light through the eye drives wakefulness via the absorption of photoreceptors in the retinal cells to generate a signal that stimulates the SCN (our master clock) in the brain. The SCN then sets the pace for all organ clocks to begin their daily cycles of function. It just so turns out that the photoreceptor in the retinal cells called melanopsin are highly sensitive specifically to the blue light frequencies. This makes sense from an evolutionary perspective because as the sun rises, the blue light frequencies are the highest energy wavelengths emitted by the sun, and blue light tends to scatter more than the other band of frequencies thus making our sky appear blue. A blue sky is indicative to the brain that it is daytime. After the sun sets, the sky darkens and our brain perceives nighttime approaching. This is the signal required for the brain to begin releasing a hormone called melatonin which not only helps drive the sleep cycle, but restores natural anti-oxidants and facilitates full body regeneration. Darkness at night is critical in allowing the SCN to set the tone for sleep by slowing down the organ clocks to allow regeneration to take place so we can function optimally for the next day.
Our ancestors often used candles and firelight at night to stay awake longer, although fire contains very little blue light and would only minimally disrupt melatonin secretion and the sleep cycle. However, modern life uses new technology LED and fluorescent lighting which emit large spikes of blue light frequencies that are absorbed by the melanopsin photoreceptors all hours of the day. This disrupts the circadian rhythm, lowers melatonin and delays the sleep cycle which is our period for regeneration. When this occurs chronically, our organs degenerate faster than normal and we age prematurely. Given that the circadian rhythm regulates every function in our body to help us adapt to our environment, we begin to experience diseases tied to malfunctioning of the organs due to chronic degeneration. In fact, the WHO has classified working night-shift to be “probably” carcinogenic in 2007 due to chronic circadian rhythm disruption.
Because of how critical the circadian rhythm is for controlling energy flow and allowing us to adapt to our environment and thrive, any chronic disruption to this natural rhythm will ultimately lead to diseases of aging. Our exposure to chronic blue light in the modern world is top of the list for environmental stressors we face. We must limit our blue light exposure and protect ourselves as best we can. Living in sync with the natural light cycle in our environment is what we are adapted to, but with the simple flick of a switch or a reach for our favorite gadgets, we can lose control of our health rapidly.
IMG sources: https://www.univie.ac.at/geographie/fachdidaktik/FD/site/external_htmls/imagers.gsfc.nasa.gov/ems/visible.html https://www.sott.net/article/371530-Is-Artificial-Light-at-Night-Making-You-and-Your-Kids-Fat-Sick https://www.popularmechanics.com/technology/gadgets/reviews/g164/incandescent-vs-compact-fluorescent-vs-led-ultimate-light-bulb-test/