Posted on: 29 - 3 - 2023

Circadian Lighting: Evidence-Based Design vs Standards Based Design

If you read our 2022 wrap up, I was critical of our industry’s inability to capitalise on the demand for proper circadian lighting. Unfortunately, this problem is not new, nor is it going away, so in this blog post, I will explore a way forward with the intersection of evidence-based design and our circadian rhythm.

Firstly, to look forwards, we must look back and understand how we ended up where we are currently. Back in 1924 (celebrating a century next year), evidence of the human visual perception of light was discovered in the form of the photopic lumen. This scientific research has been documented and implemented into numerous standards since.


In recent years there has been growing interest in using evidence-based design (EBD) and how this can impact human health. Evidence-based design is the process of using scientific research to inform and guide the design of buildings for people. In a modern world where everything happens at a faster pace, there is greater access to information and human well-being is a priority for organisations means the use of standards based design can lag behind the best possible outcomes. Human well-being is a priority for organisations, so using standards-based design can lag the best possible outcomes. While well designed and carefully thought out by experts in their field, standards take considerable time to develop and document. Moving ahead of standards-based design into an evidence-based design can enable progressive designers to deliver better client results with links to improved occupant satisfaction and well-being, reduced absenteeism, improved productivity, and better health outcomes.


Next, I will briefly define a circadian rhythm (if you know this already, skip to the next paragraph). The circadian rhythm is our internal body clock that regulates our sleep-wake cycle and other bodily functions such as digestion, hormone production, and metabolism. Our natural circadian rhythm aligns approximately to 24 hours. I say approximately as each person exists on a spectrum. Some have a faster clock, and others a slower one. We need the brightness of a day and darkness of a night to entrain our circadian rhythm in a typical 24-hour cycle. The problem we are addressing in this blog is that modern lifestyle and indoor environments, both day and night, result in constant twilight, and we miss the bright day and dark night signals our brain needs to maintain a healthy circadian rhythm. To make matters worse, most people don’t know it’s happening.


In the last 20–30 years, scientific research has discovered evidence linking light to our circadian rhythm, and experts have provided recommendations for what we should do about it. This started with discovering the IPRGCs (intrinsically photosensitive retinal ganglion cells) and their response to light exposure in the blue part of the spectrum at 490nm (close in appearance to the blue sky). Most recently, the following paper was published by PLOS biology; ‘Recommendations for daytime, evening and night-time indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults’. This paper was written by an international group of experts in the fields of sleep, circadian rhythms, and light physiology and provides practical recommendations for how to design indoor lighting to support optimal health and sleep.


The evidence linking light and human health is conclusive and expert consensus on how to design effective circadian lighting for people has been published. This means designers can confidently move from standards-based design to evidence-based design for the benefit of human health and well-being because it’s the right thing to do.


Reflecting on this blog, it’s not far until we tick over to 2024, nearly 100 years since the photopic lumen changed lighting forever. Clients want circadian lighting for the betterment of their people, but they don’t know what that means, and until now, it’s been impossible to know what to do. So now it’s nearly 2024, the evidence is there, and once again, it’s time for evidence to change lighting forever.


By James Duder

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