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The hype around LEDs stems from two primary benefits. First, LEDs are brighter than traditional lights, and many cities feel that the increased brightness improves public safety. Second, LEDs are more energy efficient than earlier generation bulbs, bringing both financial and environmental benefits to converting cities.
Unfortunately, exposure to blue-rich light at night can lead to decreased melatonin secretion in humans. Melatonin is a hormone secreted at night by the pineal gland that helps balance the reproductive, thyroid, and adrenal hormones and regulates the body’s circadian rhythm of sleeping and waking. Lower Melatonin levels have been tenuously linked to increased risk of cancer.
Luckily for Bay Area residents, Oakland, Berkeley, and San Francisco have all chosen to install LEDs on the yellow side of the spectrum. The yellow-rich LEDs are still brighter than the streetlights they are replacing, but are less likely to disrupt either people or wildlife than blue-rich LEDs. “Most of the cities that have been doing a really good job [using yellow-rich LEDs] are in California,” says Parks
Melatonin deprivation may speed the rate of brain aging, according to the University of Maryland Medical Center.
Melatonin deprivation may raise blood pressure and lead to kidney damage, according to a study published in the November 2010 issue of the "Journal of Pineal Research
While light of any kind can suppress the secretion of melatonin, blue light does so more powerfully. In an experiment, researchers exposed people to 6.5 hours of light—either blue or green. The blue light suppressed melatonin for about twice as long as the green light and shifted circadian rhythms by twice as much.
You see, during the day, our brains can't get enough of light sources that rely heavily on the blue color wavelength such as energy-efficient bulbs and electronic screens (laptops, smartphones, tablets, etc.)
Think of it as light-based brain candy — those cool blues keep us alert, awake, on-the-move. But at night, when our bodies are naturally winding down, the blues are best to be avoided as they can disrupt natural sleep patterns and overall health.