As humans, we are naturally inclined to sleep when it is dark and be awake when it is light. For most of human history, we have lived by the light provided by nature, and our sleep cycles have been governed by the presence or absence of light throughout the day and night cycle. Only recently in historical terms have we had access to artificial light when it is dark outside, allowing us to live and work 24 hours a day.

Circadian rhythms – your body’s master clock

By the time we are six months old, our circadian rhythm is fully developed, but it needs to be synchronised every day or it will start to drift out of sync. This is because our biological circadian rhythm is not perfectly aligned with the 24-hour day cycle of the Earth spinning a single rotation. The cycle within our bodies is approximately 24.5 hours, so it needs to be reset daily. Circadian rhythms help regulate our sleep patterns and many other critical daily bodily processes, acting as our body’s master clock.

Melatonin secretion and light

Melatonin, a hormone that makes you sleepy, is created when the body receives triggers from incoming light through non-visual receptors in our eyes. At night, when there is less light, our bodies make more melatonin, making us drowsy and allowing us to move into the sleep cycle successfully. If we expose ourselves to triggering light at night, melatonin secretion will be suppressed, and our body clock will be set back, reducing our capacity to sleep. The time within a day when our circadian rhythm is synchronised is critical to the biological resetting process.

Resetting your circadian rhythm – the type and amount of light

Other critical factors for resetting our circadian rhythm are the type and amount of light. Light with higher wavelengths (towards the blue spectrum) will suppress melatonin secretion, which will delay our bodies’ entry into the sleep cycle. High-frequency light should be avoided late in the day before we want to sleep, but encouraged early in the day because it helps to activate our synchronisation.

The amount of light, intensity, and duration will all impact the effectiveness of the trigger. Ideally, we should be exposed to high light levels early in the day and progressively reduce our exposure throughout the day, just as we experience in the natural world. 

Modern lighting and its conflict with sleep

It is clear that light is fundamental to sleep, and the way that most of us live in the modern world can conflict with this basic biological process. Most of us spend substantially less time outside during daylight hours than we would have throughout history. Furthermore, we extend the presence of light into the night, potentially confusing our biological triggers.

Parts of the human population increasingly work at night, attempting to live against our natural circadian rhythms. When we are having difficulty sleeping, light should be considered a potential factor, allowing us to restrict or enhance our light exposure at particular times.

Lighting design that considers our circadian rhythm

Lighting designers are beginning to understand better how to design lighting for spaces that positively respond to these biological processes. We need to make a wider audience aware of this knowledge and embed it in a design consciousness for future spaces and how we live. Consideration of our circadian rhythms can and should be a fundamental design principle, just as circadian rhythms are fundamental to biological life on Earth. 

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