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Introduction
Published in Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe, Visual and Non-Visual Effects of Light, 2020
Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe
Although for a long time it has been widely known that sunlight is one of the most important regulators of human physiological functions related to circadian rhythm, in-depth research into the biological mechanism of the non-visual effect of light began in the late 20th and early 21st centuries, with the discovery of a new photoreceptor on the retina called the intrinsically photosensitive retinal ganglion cell (ipRGC). A rapid development of research related to the human non-visual response to light was launched. It has been proved that light has the ability to change circadian rhythms, i.e. to change the time periods in circadian cycles, which may result in shifting the phases of physiological cycles. Light also affects a number of physiological reactions, such as the regulation of hormone secretion (e.g. it can inhibit the pineal hormone responsible for melatonin secretion at night), affects the level of body temperature, induces the pupillary reflex, raises subjective alertness, and, under certain conditions, changes the bioelectrical brain activity indicating sleepiness or alertness. That is why the non-visual effects of light are so important for human functioning.
Assessing the Effects of Polychromatic Light Exposure on Mood in Adults: A Systematic Review Contrasting α-opic Equivalent Daylight Illuminances
Published in LEUKOS, 2023
Ashley Nixon, Rebecca Robillard, Chloe Leveille, Alan B. Douglass, Meggan Porteous, Jennifer A. Veitch
In addition to stimulating visual perception, light influences many physiological and psychological processes, including cognition, sleep, and mood (Cajochen 2007; Duffy and Czeisler 2009; Golden et al. 2005). Light intensity, spectrum, duration, and timing are all thought to play a role in these effects (Prayag et al. 2019). Over recent years, researchers have revealed the prominent involvement of intrinsically photosensitive retinal ganglion cells (ipRGCs) in regulating circadian rhythms, melatonin secretion, and other biological processes. ipRGCs express melanopsin, a photopigment. They also receive synaptic input from other retinal photoreceptors (S-, M-, L-cones and rods) and contribute to diverse physiological and behavioral functions (Belenky et al. 2003; Brown et al. 2021; Dacey et al. 2005; Jusuf et al. 2007; Schmidt and Kofuji 2010; Wong et al. 2007). Direct pathways linking ipRGCs and various brain regions involved in emotional processing have also been found in both animal (Fernandez et al. 2018; Hattar et al. 2006; Huang et al. 2019; Legates et al. 2014) and human (Vandewalle et al. 2010; Weil et al. 2022) studies. While many studies focused on the melanopsin system, all photoreceptor systems interact closely and their relative contribution to the effects of light on mood in healthy humans remains poorly understood. Furthermore, because indoor lighting is typically polychromatic (i.e., white appearing and inclusive of many wavelengths), there is a need to move beyond monochromatic light comparisons, which are often used in studies that examine fundamental processes.
A Review of Human Physiological Responses to Light: Implications for the Development of Integrative Lighting Solutions
Published in LEUKOS, 2022
Céline Vetter, P. Morgan Pattison, Kevin Houser, Michael Herf, Andrew J. K. Phillips, Kenneth P. Wright, Debra J. Skene, George C. Brainard, Diane B. Boivin, Gena Glickman
The physiological effects of light are mediated by the eye in humans. Light entering the eye stimulates retinal photoreceptors that convert photic information into neuronal signals, which get transmitted via ganglion cells to various regions of the brain (Fig. 1). For many years, it was thought that there were only two classes of photoreceptors in the human eye—the rods and cones; however, another very different photoreceptor type was discovered in the mammalian eye about two decades ago. These retinal photoreceptors are specialized ganglion cells that contain the photopigment melanopsin and are intrinsically sensitive to light, and were therefore called intrinsically photosensitive retinal ganglion cells (ipRGCs) (Berson et al. 2002; Hattar et al. 2002; Provencio et al. 1998, 2000).