Blue Wavelengths are Responsible for the Harmful Effects of Light at Night

Recent research shows that the harmful effects of light at night are largely mediated by certain blue wavelengths which are detected by newly-discovered melanopsin photoreceptors in the retina ganglion cells in the eye.

Light falling on the human eye serves at least two distinct functions. The most obvious function  is vision, using the rods and cones in the retina to see images of the world. A second and less well-known function is the non-image forming “time-keeping” connection that regulates the activity of biological clocks, important brain hormones, and certain aspects of behavior. The time-keeping pathway involves a different set of cells in the retina of the eye with a different photopigment (melanopsin) that is especially sensitive to blue light. This pathway directly feeds into a biological clock in the brain (the “suprachiasmatic nucleus” or “SCN”) which is  responsible for generating circadian rhythms.  When the time-keeping pathway is activated by these wavelengths of blue light, it triggers the SCN to regulate specific hormones such as melatonin and cortisol.  Melatonin released by the pineal gland is a critical suppressor of tumor growth. Cortisol, the so-called “stress hormone,” is a master molecule that influences many other critical hormones including insulin which regulate the body’s health and metabolism. Normal sleep, restfulness, alertness, and health are orchestrated by these and other molecules in exquisitely precise rhythms in response to the cycles of light and darkness.

Blue Light at Night and Biological Clock
                                                             (c) 2014 CIRCADIAN ZircLight
Blue light during the day is critical to synchronizing our circadian rhythms, but we are not designed to see blue light at night. Many of the adverse effects of chronic light exposure at night appear to be mediated by abnormal nighttime stimulation of this time-keeping pathway by the blue light wavelengths in the light spectrum. When this pathway is disrupted by exposure to white light or only blue light at night, it initiates a chain reaction that results in decreased energy, mood, performance and vigilance and increased risk of errors, accidents, injuries, absenteeism and workplace turnover. Over the long- term, continuous light exposure at night results in sustained hormonal dysregulation leading to significant health consequences including sleep disorders, diabetes, heart disease, depression and even certain types of cancer (e.g., breast, prostate and colon cancers).

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