What is the Origin of Light at Night?

The study of light's effect on human physiology and the circadian system has a long history, but the term gained clinical relevance with the proliferation of artificial light sources and the increased understanding of chronobiology in the late 20th century. The phrase is a direct, descriptive term for the environmental exposure being studied. Research has identified the specific wavelengths of light responsible for circadian disruption.

What is the Mechanism of Light at Night?

The primary mechanism involves the suppression of melatonin, a key chronobiotic hormone, through the stimulation of intrinsically photosensitive retinal ganglion cells (ipRGCs) in the eye. These cells, particularly sensitive to blue-wavelength light, project to the suprachiasmatic nucleus (SCN), the master clock, which then signals the pineal gland to halt melatonin production. This hormonal suppression disrupts the internal circadian timing system, which in turn can negatively affect glucose regulation, immune function, and the nocturnal repair processes essential for longevity.

Light at Night

Meaning

Light at Night (LAN) refers to any exposure to artificial illumination during the biological night, a period when the human body’s circadian rhythm expects darkness. This environmental factor is a significant disruptor of the body’s natural sleep-wake cycle and a potent inhibitor of melatonin secretion from the pineal gland. Clinically, LAN is recognized as a modifiable risk factor that can negatively impact hormonal balance, metabolic health, and sleep quality. It is a modern challenge to ancient biological programming.