Chemically, the human body is performing several different functions at every second of the day – from breaking down food, to converting oxygen to CO2, to promoting chemical reactions (in the form of hormones) triggered by our senses. Two hormones that are driving factors in our day-to-day-lives, melatonin and cortisol, are affected by the amount of light we receive from the sun throughout the day.
Chemical Imbalance Through Lighting
Melatonin and cortisol are the natural sleep-and-wake hormones in the body. An imbalance between these two hormones causes us to feel fatigued, unable to perform efficiently, and can be triggered by the absence of bluish-white light normally received from the sun. On the flip side, an imbalance of these hormones can also be caused by taking-in too much blue-white light before going to sleep; whether from streetlights, cell phones and tablets, or leaving the television on. The results depend on what spectrum content of the light, and how much is entering our eyes at any given time.
The Hidden Photoreceptor
In the human eye, there are two visual photoreceptors, rods and cones, which are responsible for detecting light and objects as they move through our vision; however, there is a third photoreceptor in the human eye that is nonvisual, called the ipRGC (intrinsically photosensitive Retinal Ganglion Cells). Compared to rods and cones, the ipRGC are sluggish and more responsive to light over time, providing a stable representation of ambient light intensity. The ipRGC are very receptive to blue-white light, and as such, play a major role in synchronizing our circadian rhythm or body clock. When we receive sunlight in the morning our bodies respond by producing cortisol. This response is due to input from the ipRGC telling the brain “it’s daytime, you should be awake and alert.” In that respect, the absence of blue-white light causes the brain to produce melatonin - the hormone related to sleep. In a typical day-night cycle decreasing blue hues, and increasing red-orange-yellow hues in the sky, lower cortisol production while increasing melatonin production. This chemical change is essentially telling our brains to “prepare for rest.”
When we don’t have the proper balance of light throughout the day, the chemistry of our body is out of sync, which can lead to physical and mental health risks. Uneven exposure to light and its effects on human health are often seen during winter months in areas moderately-to-extremely north or south of the equator. One negative effect many people suffer from, seasonal affective disorder (or SAD), causes people to feel unmotivated, tired, and depressed. With less bright-white light reaching their eyes, less cortisol is produced, therefore causing fewer stimulants in the body to promote the feeling of energy and happiness. Understanding how light affects our circadian rhythm and the chemistry of our body, it becomes easier to understand how the correct type of lighting in homes, schools, hospitals, and prisons is crucial. In the correct lighting, students focus better in class, hospitals have more alert night staff, and prisons have fewer outbursts with inmates.
At Energy Performance Lighting, we’re dedicated to providing a healthier artificially-lit environment for everyone. Our focus is on the scientific connection between light and human health, while delivering energy savings unmatched by any competitor.
Source: Dijk D-J, Archer SN (2009) Light, Sleep, and Circadian Rhythms: Together Again. PLoS Biol 7(6): e1000145. doi:10.1371/journal.pbio.1000145