Circadian rhythm

Circadian rhythm

Human beings have an internal clock that is intrinsic in our brain, which shifts between alertness and sleepiness at regular intervals. This phenomenon is known as circadian rhythm and it has a central role in sleep/wake cycle regulation.

The release of melatonin which promotes sleep onset is regulated by the central circadian rhythm generator. (Khullar, A. 2012, The Role of Melatonin in the Circadian Rhythm Sleep-Wake Cycle, Psychiatric Times, available at

For millenia humans have lived synchronised with the natural cycle of light and dark, with the majority waking up after sunrise and sleeping after sunset.

In modern society we spend a lot of our waking day indoors, taking the car or bus from home to work, being in an office underneath artificial light and in front of computer monitors and phone screens.

In a short time humans in the developed world have faced a massive transformation in our habits with the result of delaying and shifting “natural” sleep patterns.

“Electric lighting disrupted our behavioral dependence on the day-night cycles of the sun, and facilitated alterations in our circadian sleep-wake cycles. Recent research has begun to identify the physiologic consequences of unnatural light exposure and subsequently altered circadian rhythms..”

Brainard J., Gobel M., Scott B., Koeppen M,. Eckle T. (2015) Health Implications of Disrupted Circadian Rhythms and the Potential for Daylight as Therapy Anesthesiology, Available at

The same study found that the consequences of a distruptive circadian rhythm, include ailments including myocardial infarction, stroke, sepsis, obesity, stress and gene mutation.

The problem of distruption of a person’s circadian rhythm has been recognised most in the health and care field.

In a study conducet by Anjali Joseph, The Impact of Light on Outcomes in Healthcare Settings ( he suggests that when the shift of the healthcare workers doesn’t match with the daylight clock, they “...can feel drowsy, tired, and distracted”. Moreover it would result in -”...fatigue and a complete inability to perform during the night shift” .

A solution to this problem has been reported by LEDs Magazine, where in a Danish hospital they got rid of the blue wavelengths at night to create an amber hue during the night shift . A very positive result has been observed from the nurses reporting a better quality of sleep. (LEDs Magazine, September 2018, Circadian Lighting has Danish Night Nurses Sleeping Better)

These studies are being reflected in consumer products, such as the Apple iPhone which introduced a “Night Shift” mode, which reduces the phone screen’s blue light output, which is recognised the most problematic wavelenght of light for sleep distruption, to an amber light screen

However, a study by the Lighting Research Center has found that while this setting may slightly reduce the effect of screen exposure on melatonin production, the screen’s brightness still has an effect on sleep disruption. (New LRC Study Evaluates the Effectiveness of Apple’s iPad Night Shift Application, vailable at

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