Numerous studies are beginning to suggest that excessive exposure to white light emitting diodes (LEDs), especially at night, may have adverse effects on our brain’s circadian rhythms. Specifically, these perturbations to our biological clocks can disrupt sleep patterns and reduce the production of hormones such as melatonin, an antioxidant compound that protects DNA from damage, by as much as 25% according to model-based calculations headed by Mark Rea, director of the Lighting Research Center at Rensselaer Polytechnic Institute in Troy, N.Y.

From the source article by Ben P. Stein:

LEDs have been in practical use since they were first introduced in the 1960s as light indicators in electrical components and alphanumeric displays in early handheld calculators. As the cost of manufacturing LEDs dramatically dropped upon larger-scale commercialization, LEDs have increasingly become integrated into consumer and non-consumer products such as radio-alarm clocks, smartphone displays, flat-panel televisions, and traffic light signals. Furthermore, white light LEDs—which emit blue-rich light—have begun to replace the traditional incandescent or compact fluorescent lights used in home lighting, car headlights, and streetlamps because of advantages in increased illumination and energy-efficiency.

While organizations such as the International Dark-Sky Association urge caution on using white LEDs for outdoor nighttime lighting and some scientists are already calling for regulations to ban the outdoor use of blue-rich light, others estimate that the effects are small and caution that more rigorous scientific studies are needed before determining if white LED light has any health impacts at all. Some scientists argue that other factors, such as sleep deprivation and abnormalities in a person's overall 24-hour pattern of exposure to light and dark, may do much more to disrupt circadian rhythms. Epidemiological studies have linked circadian disruptions to health problems, such as cancer, cardiovascular disease, and obesity, and scientists are trying to determine if light at night—and blue-rich LEDs—are a cause.

Aside from the potential negative impacts of white LEDs on human health, other scientists like Abraham Haim of the University of Haifa in Israel also draw concerns over the excess usage of white LED lighting and its contribution to environmental light pollution. Similar to studies in humans, Haim has found that the delicate circadian rhythms of nocturnal animals are also affected by blue-emitting light. As a solution, Haim and his colleagues not only suggest a “total ban of the outdoor emission of light at wavelengths” in the blue visible spectrum but to also revert back to using older low-pressure sodium lamps that produce yellow-orange colored lights.

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