Correlated color temperature and light intensity: Complementary features in non-visual light field

Abstract

An appropriate exposure to the light-dark cycle, with high irradiances during the day and darkness during the night is essential to keep our physiology on time. However, considering the increasing exposure to artificial light at night and its potential harmful effects on health (i.e. chronodisruption and associated health conditions), it is essential to understand the non-visual effects of light in humans. Melatonin suppression is considered the gold standard for nocturnal light effects, and the activation of intrinsically photosensitive retinal ganglion cells (ipRGCs) through the assessment of pupillary light reflex (PLR) has been recently gaining attention. Also, some theoretical models for melatonin suppression and retinal photoreceptors activation have been proposed. Our aim in this study was to determine the influence of correlated color temperature (CCT) on melatonin suppression and PLR, considering two commercial light sources, as well as to explore the possible correlation between both processes. Also, the contribution of irradiance (associated to CCT) was explored through mathematical modelling on a wider range of light sources. For that, melatonin suppression and PLR were experimentally assessed on 16 healthy and young volunteers under two light conditions (warmer, CCT 3000 K; and cooler, CCT 5700 K, at ~5·1018 photons/cm2/sec). Our experimental results yielded greater post-stimulus constriction under the cooler (5700 K, 13.3 ± 1.9%) than under the warmer light (3000 K, 8.7 ± 1.2%) (p < 0.01), although no significant differences were found between both conditions in terms of melatonin suppression. Interestingly, we failed to demonstrate correlation between PLR and melatonin suppression. Although methodological limitations cannot be discarded, this could be due to the existence of different subpopulations of Type 1 ipRGCs differentially contributing to PLR and melatonin suppression, which opens the way for further research on ipRGCs projection in humans. The application of theoretical modelling suggested that CCT should not be considered separately from irradiance when designing nocturnal/diurnal illumination systems. Further experimental studies on wider ranges of CCTs and light intensities are needed to confirm these conclusions.

Dimming the Lights to Support the Overall Human Wellbeing In An Urban Context

“…Following the bright light exposure protocol participants are exposed to dim light again to assess whether melatonin suppression is continuous even after acute bright light exposure. They reported that under both bright light settings melatonin suppression was higher than dim light settings and at the 5700K setting the suppression was slightly higher than 3000K setting [14]. In another study Nagare, Rea & Figueiro questioned whether the position and the colour of the light source would affect the melatonin suppression level.…”

The Complex Effects of Light on Metabolism in Humans

“…Light with a 1900 K color temperature containing a spectrum ranging from 500 to 650 nm of yellow–orange–red light (1900 K) in 40 individuals (18–25 yrs) induced significantly higher levels of melatonin compared to light exposure to color temperatures at 3000, 4000, and 6600 K [ 116 ]. However, differences were not observed between color temperatures at 3000 and 5700 K in 16 individuals (9 females; 23.8 ± 3.1 yrs) [ 117 ]. Glutamate secretion, which is indicative of cognitive ability, was also promoted by 1900 K after two hours of light exposure [ 116 ].…”