Daylight! Are we giving ourselves enough of it? Circadian rhythms work to coordinate our daily cycles of behavior, alertness, sleep, and physiology throughout the 24-hour day/night cycle. The natural pattern of light and darkness is the most prominent cue for keeping our internal biological clocks in sync with the outside world, which is very important for maintaining mental, physical, and emotional health. Since indoor light isn’t always enough to keep our systems in check, we should consider daylighting a necessary, freely accessible natural tool to enhance our health and overall wellbeing.
Light and the human circadian system
Our eyes contain light receptors called rods and cones. Rods allow us to see in dim light and near-darkness while cones allow us to navigate through daytime vision accounting for colors, movements, shapes, and edges.
Did you know that there are other light receptors in our eyes that work alongside rods and cones to maintain our circadian system so that it can function properly depending on whether it is day or night? They are called intrinsically photosensitive retinal ganglion cells. This is a major recent discovery, unknown for well more than century since the rods and cones were identified as underlying vision. This new research has revealed that these cells are naturally sensitive to light because of a light-sensitive protein called melanopsin. These cells also respond to rods and cones through synapses — basically the same way that neurons in the brain communicate with one another.
Because rods, cones, and the photosensitive retinal ganglion cells are sensitive to light, our exposure to light (or lack of light) affects us in many ways across day and night — such as changes in mood, energy, learning, memory, pupil size, and the release of melatonin which helps us sleep, to name a few.
Isn’t it amazing how much our systems are impacted by the simple cycle of day and night?
Daylight vs. indoor light
The main difference between daylight and indoor light is that daylight tends to have a higher intensity than most indoor light — with the exception being light therapy lamps which work to mimic the properties of natural daylight. Another difference is that although indoor artificial light has many obvious benefits, such as allowing us to work and study during later hours, it doesn’t offer our bodies the light it needs to function in sync with our circadian cycle of alertness and concentration.
Essentially, daylight is like physical exercise in that they are both needed for maintaining our health. Even getting 30 minutes to an hour of daylight could be enough to keep our systems running in check. Ideally one would pair a healthy diet, physical exercise, enough daylight exposure, and a regular sleep pattern together for the best results. This schedule of activities is really not complicated, though it takes an initial commitment that quickly turns rewarding and habits forming.
United Kingdom (UK) light study
A study based in the UK, including data from about half a million people, found that, on average, people spent about 2.5 hours outside during the day. For each extra hour spent outside, the study found that participants experienced:
Greater odds — or increased levels — of
- ease of getting up in the morning
Lower odds — or fewer symptoms — of
- need to take antidepressant medication
- anhedonia — not being able to feel pleasure
- low mood
- neuroticism — a trait that reflects feelings of anger, anxiety, self‐consciousness, irritability, emotional instability, and depression
So, what’s the takeaway?
Daylight has definite positive effects on our mental, physical, and emotional health. We should consider it necessary for our ability to function optimally.
It is essential that we:
- get a reasonable amount of daylight exposure, complemented by indoor light therapy devices when needed.
- sleep on a consistent schedule, allowing enough sleep time to ward off slumping during the day, complemented by intelligent napping if needed.
- exercise regularly on a schedule that does not interfere with sleep.
Marwan Hamed is a public health practitioner and freelance writer for CET.