MARK STEVENSON – MARKETING LEAD, THORLUX LIGHTING, UK CIRCADIAN LIGHTING


Circadian rhythm and human-centric lighting


The importance of the human body’s natural circadian rhythm means that human- centric lighting ought to be a key component of patient care, as Mark Stevenson, marketing lead at Thorlux Lighting, explains.


Our relationship with light is fundamental to our existence on this planet. Light from the Sun and its accompanying heat energy were the catalysts for evolution on Earth, from single-celled protozoa to human beings. The knowledge that ‘light is life’ seems almost intrinsic to us; indeed, the Sun itself has been an object of veneration and deification throughout human history. In the modern era, we understand more


than ever the effect of light on the human body. Research at the genetic level continues to uncover the intricate mechanisms driving our biological clocks. However, the importance of quality light exposure at the right time is well established. Coupled with this knowledge, we can


also control and fine-tune artificial lighting as never before. How can we use this to create better indoor environments for people? And what benefits could this knowledge provide to the healthcare sector?


The circadian rhythm First, it is necessary to understand how light interacts with the body. In common with all mammals (and


many other animals and plants), humans are governed by an irresistible internal clock known as the circadian rhythm. Chronobiology – the study of natural


cycles and periodic or repeating functions within living organisms – has demonstrated that differing lengths of biological rhythms are at work in nature. For example, infradian rhythms are long loops, such as annual crop cycles or the migration patterns of birds. In contrast, ultradian rhythms can be as brief as a single heartbeat. However, the


circadian rhythm exerts the most influence over our lives. As the composition of its name suggests (circa –


60


approximate; diem – day), the circadian rhythm is a roughly 24-hour cycle that dictates processes in the human body, such as alertness, sleep, hunger, and body temperature. It governs the behaviour of more than 40 per cent of genes in the human body. And light is one of the main drivers of the circadian rhythm.


A brief history of


chronobiological research In 1729, the French naturalist and polymath Jean Jacques d’Ortous de Mairan (1678-1771) was the first scientist to observe what we now refer to as the circadian rhythm. Intrigued by the opening and closing of mimosa plants in reaction to the presence of sunlight, he performed a simple experiment wherein he kept the plants in constant darkness


Mark Stevenson


Mark Stevenson is a marketing lead at Thorlux Lighting in Redditch,


Worcestershire, UK. He is a graduate of the University of Wolverhampton and has worked at Thorlux since 2022. Founded in 1936, Thorlux is known


globally and provides professional lighting and control systems for architectural,


medical, commercial, floodlighting, industrial, and hazardous area applications.


and recorded their behaviour. De Mairan observed that they continued to open and close their leaves rhythmically, even when sunlight was absent. While de Mairan did not reach the


correct conclusion from his experiment – inferring that the plants could sense the Sun without seeing it, rather than being driven by an internal clock regulating behaviour throughout the day-night cycle – this was the first step towards our modern understanding of the circadian rhythm. The British biologist Colin Pittendrigh


(1918-1996) established the modern field of chronobiology when, in the early 1950s, he described the circadian clock of Drosophila flies. This research provided the first models of how circadian rhythms in an organism entrain (synchronise) to local light-dark cycles. With this established, inquiry into the biological clock in humans and across nature could begin in earnest. Technological advances in DNA and gene sequencing research in the 1990s helped identify the genes that govern circadian rhythms and the effects they generate to move our bodies through the various stages of the cycle. These technological breakthroughs enabled the groundbreaking work of geneticists Jeffrey Hall, Michael Rosbash, and Michael Young. In 2017, all three were


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