Overlighting has two main safety concerns, glaring and exaggerated darkness.
Glaring on the Eyes:
After issues of safety, light pollution has a wide range of negative effects on human health such as disrupting our circadian rhythms, messing with our melatonin levels, and generally contributing to sleeping disorders.
Melatonin is a naturally occurring hormone which is released by darkness and inhibited by light. It serves many functions in the human body, primarily regulating the daily cycles of our systemic activities. Reduction or elimination of light at night can help maintain a robust melatonin rhythm. While any kind of light can interfere with melatonin production, the short wavelength, blue portion of the spectrum is the most potent for melatonin suppression in humans.
Other Emerging Research:
The scientific community is studying the range and complexity of circadian disruption and the role of melatonin suppression from too much artificial light at night. Scientists are finding an undisputed connection between sufficient sleep and good health. Moreover, they are recognizing the importance of exposure to daylight during the day and darkness at night to maintain a routine circadian rhythm. The World Health Organization now lists “shiftwork that involves circadian disruption” as a probable carcinogen and the American Medical Association has recognized it as a carcinogen and health risk.
On 15 June 2009, the American Medical Association also adopted resolutions that support the reduction of light pollution and glare and advocate for use of energy efficient, fully shielded outdoor lighting. Ongoing research continues to probe the connection between natural darkness and human health.