If we wake up with nature and the rising sun, have our activity and main meal at mid-day and don't stay up late with TV & computer screens, our waking & sleeping cycles will be balanced and we'll have good energy during the day and strong digestive fire (agni).

The pineal gland in the brain, which senses when the sun sets, produces proper melatonin for sleep & protects the health. This gland is connected to our sense of sight & will not secrete properly when artificial light is bright & long at night ~ especially "blue light."

The Problem with Artificial Light ~ livescience.com

"The body's biological clock works in rhythms that are set by the amount of light and dark the body is exposed to. This is called the circadian rhythm. Circadian rhythms control the timing of many physiological processes. They determine sleeping and feeding patterns, as well as brain activity, hormone production and cell regeneration. When the body is exposed to only to the natural light of the sun, the hypothalamus area of the brain sets its sleep patterns according to when it is light outside and to when it is dark……..When artificial light is added to a human's day, the body's natural rhythms become confused. The retina can now receive light no matter what time of day it is, so the body doesn't know when to get ready for sleep. A study published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism found that, when compared with dim light, exposure to room light during the night suppressed melatonin by around 85 percent in trials.

Blue light and sleep patterns

Fluorescent and LEDs bulbs create a two-fold problem when it comes to sleep. First, they produce artificial light. Second, they produce blue light. Blue light wavelengths produced by electronics and overhead lights boost attention, reaction times and mood, according to Harvard Medical School. Research has found that exposure to blue light suppresses the production of melatonin more than any other type of light. It is believed that the shorter wavelengths in blue light is what causes the body to produce less melatonin because the body is more sensitive to this type of light.