LIVING IN CIRCADIAN DISRUPTION
For hundreds of thousands of years, we have evolved within the circadian rhythm, attuned to light in the cyclical patterns provided by Sun and Moon. This rhythm of light is intimately tied into our body – influencing hormone production, the regulation of sleep and mood, cell regeneration and many other vital processes. However, within an evolutionary blip the Earth has been blanketed in fluorescent lights, satellites, screens and LEDs, illuminating our previously dark and wonderous nights. Electric light has become domestically available only since the early 20th century, and has expanded its presence into almost every previously dark-sky territory. With this rapid and unnatural expansion has come a great dissociation – as our slow, analogue bodies attempt to assimilate to the mass 'illumination'.
Researchers are just beginning to understand some of the disruptive effects of this widespread phenomenon, but it has yet to reach a level of general awareness. "Circadian disruption in turn produces a wealth of downstream effects, including dysregulation of key hormones." Circadian rhythm is being tied to so many important functions," says Joseph Takahashi, a neurobiologist at the University of Texas Southwestern. "We're just beginning to discover all the molecular pathways that this gene network regulates. It's not just the sleep-wake cycle. There are system-wide, drastic changes.”" According to one researcher, most people are living in a state of "circadian fog".
WHY IS CANDLELIGHT DIFFERENT?
[lux = lumens/sqm - a unit of measurement for the intensity of light within a given space ]
The full moon illuminates a clear night at a level of 0.1-1 lux, depending on where you are in the world. In contrast, a typical living room is illuminated nightly between 100-300 lux, up to 3000 times more light than we are evolutionarily built for at night. Even a single computer or tablet contributes ~40lux, which is still very disruptive to our circadian rhythm by diminishing the production of melatonin. However, a single candle from 1 metre away only produces ~1 lux, much closer to the nightly lux range that we have evolved within. 
It is not only the lux level that is causing disruption, but also the type of light. Screens (LCD and LED's) and fluorescents contain a much higher level of blue light, which is a short-waved, high-energy form of light near the UV zone of the light spectrum. This blue light is being linked to major disruptions in melatonin and other hormones  and can even influence changes in insulin resistance  and prostate cancer prevalence . Candlelight however, emits a more gentle light between the infrared to yellow zone of the light spectrum. This light is longer-waved, low-energy and has less impact on our melatonin production.
It makes perfect sense that candlelight, an ancient and widely used form of illumination, that burns natural waxes, is better for us. Using a candle is akin to bringing the fires that we all used to gather around (and some of us still do) inside, in miniaturized form. Fire connects us to our deep human ancestry, and our bodies recognize that.
CHALLENGE – For a week, try using only candlelight at night (and avoid looking at your phone, or use a nightmode filter) and see how your sleep and mood is affected.
 Screens May Be Terrible for You, and Now We Know Why https://www.wired.com/2015/03/artificial-light-may-be-unhealthy/
 Circadian rhythm disruption and mental health - https://www.nature.com/articles/s41398-020-0694-0/
 “The secretion of melatonin is tightly controlled by light; <3 lux of light exposure at night is effective in suppressing the onset of melatonin secretion and shortens melatonin secretion duration in humans50,51. Thus, via suppression of melatonin rhythm, light at night has the potential to substantially alter physiology and behavior." Circadian rhythm disruption and mental health - https://www.nature.com/articles/s41398-020-0694-0/
 A New Study Delves Into How Blue Light Affects Your Metabolism –https://www.chronobiology.com/new-study-delves-blue-light-affects-metabolism/
 Night work and the risk of cancer among men – https://pubmed.ncbi.nlm.nih.gov/23035019/