Came across an interesting pod cast by Russell Foster, Professor of Circadian Neuroscience at Oxford University. He was speaking on the Naked Scientist website about the effects of the LEDs on sleep and alertness. Our brains have receptors called photosensitive ganglion cells which regulate non-visual responses to light by measuring brightness.
It has been said as a species we are sleep 1. to 2 hours less each night due to the invention of the the electric light bulb. Find out more of the link below: