Some people prefer being awake at the crack of dawn, and some people love to burn the midnight oil. But whether you are a lark (morning person) or an owl (nighttime lover), it may surprise you to know that we are all affected by light and dark in similar ways.
All animals have a built-in circadian rhythm - a biological cycle that responds to environmental stimuli. One of the most important cues that affects the circadian rhythm is daylight. Light stimulates the release of hormones and metabolites that makes us more alert and reactive, increasing our energy and muscle strength. By contrast, darkness stimulates hormones, such as melatonin, that makes us tired and sleepy.
Given that we know exposure to light and dark truly affects our internal systems, it's alarming to think of how many brightly lit gadgets we now use before trying to fall asleep. Thus, if you feel groggy or unrested in the morning, your blue phone screen the night before may be to blame.