The city of Seattle was one of the first in the US to make the switch to LED street lighting. This was huge from an efficiency perspective - the LED lights are 30% more efficient than the high-pressure sodium lights they replaced.

However, there was an unintended consequence: residents began to complain about the harsh blue-white light - and lots of research shows that the blue component to white light is especially disruptive to your natural sleep cycle. The city has since switched to "warmer" lights on new installations, but the existing ones will stay put until they burn out.... (More)