LED street lights mess up your circadian rhythm
How can you tell which street lights are responsible for your less-than-stellar mornings? To understand the difference in the quality of light, look at the photo above. The overpass is lit by the older, tungsten-orange-style lights, while the roadway below is lit by a newer LED. The latter is clearer and more brightly lit. Great for roads, bad for bedtime.
To be clear, not all LEDs are created equal. LEDs are easily configurable to be any number of shades and intensities. In this case, it's the hyper-intense bluish-white light, chosen for its clarity, that's a problem. This is the same light emission you get from your television. These blue LEDs have been associated with suppressing melatonin at a much higher rate than traditional street lights. Hence, the alarming revelation that street lights might be keeping you up at night.
This is the exact reason Apple unveiled Night Shift with iOS 9.3.