Dayighting Metrics III:
Circadian Stimulus (CS)

Developed by the Lighting Research Center (LRC), the new Circadian Stimulus (CS) metric quantifies for the first time the effect of light on our circadian system, establishing a relationship between exposure to a certain light source and the suppression of the generation of melatonin in our body.

What is melatonin?

Melatonin is a hormone whose concentration in the body varies with changes in exposure to ambient light. Its production begins with the light of sunset, reaching the maximum level in the dark and preparing the brain to initiate sleep, while the first lights of dawn make the body stop generating melatonin preparing us for awakening.

The synthesis of melatonin is carried out from serotonin, a neurotransmitter in our nervous system that influences behavioral processes such as mood, perception, anger and memory, also involving other agents such as vitamin B and folic acid.

In addition to influencing our immune system, memory, learning and aging, melatonin is the main marker of our biological clock, regulating our sleep/wake cycle.

Circadian Stimulus

So does light influence our well-being? The LRC focused the answer to this question on the ability of a light source to suppress the generation of melatonin, boosting our biological clock and keeping us active during exposure to that light.

The CS quantifies this capacity considering one hour of exposure and values ranging from CS = 0.1 to CS = 0.7, the maximum theoretically achievable melatonin suppression.

According to the LRC, an exposure of CS = 0.3 for at least one hour in the morning could be enough to adjust the circadian system, affecting positively our behavior. Similarly, it raises the need to have a lower CS in the evening than in the central hours of the day, which can be achieved by modifying the SPD of the light source or its illuminance (always measured in the vertical plane).


* References:
. M Karasek, K Winczyk (“Melatonin in humans“, 2006)
. MS Rea, MS Figueiro (“Light as a circadian stimulus for architectural lighting“, 2016)



David Rodríguez

Director of Operations at Lledó Energía.

Physicist and Electronic Engineer. WELL AP.

Professionally and personally involved in energy efficiency and sustainable building, with more than 15 years of experience in Photovoltaics and Daylighting.

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