Melanopic EDI (Melanopic Equivalent Daylight Illuminance) is a method used to measure how electric lighting affects our circadian rhythm. But why is this method important?
Light is as essential to our lives as food, water, and air. Since ancient times, the Earth has followed the same rhythm, where the day begins when the sun rises and ends when the sun sets. Everything on our planet depends on this rhythm, even we humans are biologically programmed to adhere to it.
For a long time, science believed that it was the visual perception of humans that determined day and night. However, scientific experiments with blind individuals challenged this notion. Surprisingly, these experiments revealed that the eye does much more than just see. Just as our ears are responsible for both our hearing and balance, our eyes play a crucial role in both our visual perception and circadian rhythm regulation.
Within the eye reside specialized light-sensitive cells known as ipRGC cells (Intrinsically Photosensitive Retinal Ganglion Cells). When exposed to bright daylight, these cells send signals to a small centre in our brain, signalling that it is daytime and time to be active. Paradoxically, it is within this intense daylight that we also build up the urge to sleep, which we experience in the evening and fulfil at night.
As the light fades during the afternoon and evening, fatigue starts to creep in. This tiredness is accumulated throughout the day, where the ipRGC cells have been exposed to intense light. Without this bright daytime period, we do not achieve the same level of beneficial fatigue that promotes a good night's sleep.
Our circadian rhythm receives information from these microscopic light-sensitive cells in our eyes, which are not part of our visual perception. It is our circadian rhythm that governs (almost) all physiological processes in our body. Therefore, a stable circadian rhythm is crucial for human life and health, but a good alignment of our circadian rhythm only occurs when we are exposed to the right light at the right time.
It is a well-known fact that humans, from an evolutionary standpoint, require bright light during the day and darkness at night to function and thrive. However, there is a minor challenge.
Today, we find ourselves indoors for over 90% of the time, posing a challenge to our circadian rhythm. The issue arises because we predominantly inhabit buildings with static artificial lighting, maintaining the same colour and intensity throughout the day. In simpler terms, the lighting we are surrounded by is designed based on visual parameters rather than biological ones. This means that indoor lighting is tailored to meet our visual needs for seeing, but it does not consider the amount of light required to keep us healthy. Our visual light requirements and our biological light needs, however, are vastly different.
Humans do not necessarily have a visual need for bright light during the daytime to see and navigate buildings – especially if there are plenty of windows providing ample natural light. However, biologically, we often require much more and much stronger light than what is typically installed. Conversely, at night, we need sufficient light to see the spaces we move in, but biologically, we require very little, preferably no light at all. Spending time indoors means that our bodies often lack adequate light during the day and are exposed to excessive light in the evening and at night. This issue is further exacerbated by the tendency of most people to turn off the lights during the day and turn them up in the evening and nighttime, which contrasts sharply with the natural rhythm outside that we should be following.
In the end, humans often find themselves in a predicament where indoor lighting, switched on during the day, fails to signal our bodies that it is indeed daytime. We also spend insufficient time outdoors to receive vital signals from the sun's rays. Come evening, the abundance of light in the spaces we inhabit leaves our bodies uncertain if it's truly nighttime. This disruption hinders and diminishes sleep quality, impairing the body's ability to coordinate essential processes. It all boils down to our indoor-centric lifestyles, where our bodies miss out on the crucial rhythm provided by natural daylight, exacerbated by static indoor lighting making matters worse.
Melanopic EDI allows us to become aware of the subconscious impact light has on our circadian rhythm. While we may not consciously notice the constant regulation of our internal clock in our brain and body, we certainly feel the consequences when this rhythm is disrupted. An altered circadian rhythm can lead to a variety of physical and mental health issues, including sleep problems, depression, stress, cardiovascular diseases, and even cancer. Therefore, it is crucial to incorporate knowledge of our biology and circadian rhythm when designing lighting in the built environment. By utilizing Melanopic EDI in lighting implementation, we can create lighting environments that not only cater to our visual light needs but also support our biological requirements, which are essential for our overall health and well-being.