Did you know that lighting has an effect on your health? In this article, we discuss the connection between light and our well-being.

A millennial medical discovery
At the start of the new millennium, medical scientists discovered a third type of photoreceptor cells in our eyes. Previously, it was believed that the only photoreceptor cells in the eye were rods and cones. Now, we know that the ganglion cells in the retina of the eye are also photosensitive i.e: sensitive to light. These cells have a nerve connection to the biological clock located in the brain. This, in turn, has a nerve connection with the gland responsible for the regulation of some hormones in our body. The revelation here is the direct connection between light, bodily timing and hormones. Therefore, lighting not only has a visual effect but also a non-visual biological effect. This proves that lighting is actually important for our health.

Circadian rhythms
The earth’s rotation on its own axis in 24 hours results in a 24-hour rhythm of light and dark. This rhythm regulates a number of our bodily processes, such as the sleep-wake rhythm and the rhythm according to which certain hormones are produced. These 24-hour rhythms are called Circadian Rhythms.

Another bodily process that is regulated by the earth’s light-dark rhythm is body temperature. The figure below depicts the circadian rhythm of our body temperature.

Double plot (2 x 24 hours) of typical daily rhythms of body temperature (relative scale)


A healthy person’s body temperature fluctuates in the day and night by about 0.4 degrees centigrade, under the influence of the natural light-dark rhythm.

In a similar manner, the energy hormone cortisol and the sleep hormone melatonin is controlled by this light-dark mechanism over the course of the day and night. These two hormones are responsible for regulating our degree of alertness and sleep. The figure below shows the regulation of these hormones over 2 x 24-hour periods.

Double plot (2 x 24 hours) of typical daily rhythms of cortisol (blue) and melatonin (grey)


One of the roles of cortisol is to increase blood sugar levels, in order to supply the body with energy. Cortisol levels increase in the morning, to give the body energy for the day, and subsequently decrease gradually towards the evening, when less energy is required. On the other hand, the sleep hormone melatonin drops in the morning, reducing sleepiness. It then rises again when it becomes dark in order to facilitate sleep. This sleep effect is strengthened as cortisol is then at its minimum. It is for this reason that it is recommended not to watch TV or use your mobile phone at least a half-hour before bed. This is because screens give off blue light, which photoreceptor cells in our eyes detect as daylight, thereby inhibiting the production of the sleep hormone, making it more challenging to fall asleep immediately.

blue light
Illustration of the blue light from screens which inhibit the production of the sleep hormone


Besides the regulation of bodily processes such as the sleep-wake cycle, the natural 24-hour rhythm of light and dark also ensures our biological clock maintains the 24-hour rhythm. The morning light synchronizes our internal body clock to the earth’s 24-hour light-dark cycle. Without this synchronization, we would gradually adopt the wrong rhythm of alertness and sleepiness. Eventually, this would lead to a period with alertness during the dark hours and sleepiness during the daylight hours – a phenomenon which you have likely experienced when ‘jet-lagged’.

Click here to learn more about the effects of light and how it influences the human body and system.

Circadian lighting
Circadian lighting has been developed with the circadian rhythm in mind. It is based on the concept that electric light can be used to support human health by minimizing its effect on the human circadian rhythm. Circadian lighting therefore mimics the natural changes in light, supporting the body’s biological clock.

Click here to read about our Circadian Rhythm lighting installation for Growthpoint.