Scientists from Oxford University have researched how different colors of light could affect our ability to sleep. Last year, the team tested green, blue, and violet light on mice. They found that green light produced rapid sleep onset -- between 1 and 3 minutes while blue and violet delayed sleep. When the mice were exposed to violet light, it took them 5-10 minutes to fall asleep. Blue light made them the sleepiest with the onset of sleep taking between 16 and 19 minutes.
The researchers believe this all has to do with a blue light-sensitive pigment called melanopsin. These light-detecting pigments operate in the retina and seem to affect how we react to different kinds of light. There was also a connection between blue light and corticosterone, a stress hormone produced by the adrenal gland the causes arousal and wakefulness. We could therefore predict that blue light will enhance the wake-promoting effects of light by elevating adrenal stress hormones.
An obvious caveat of this study is that mice are nocturnal, but humans are not. So it very well could mean that green is not the magic color for us. Perhaps green light increases wakefulness rather than sleep. If there's one thing we do know for sure, blue light should be avoided at night. Short-wavelength blue light (emitted from the sun, electronic devices, and fluorescent lighting) shifts the circadian clock, alerts the brain, and suppresses melatonin production. This is why you should avoid looking at your phone before bed. For better sleep, consider powering down your devices at least an hour before bed. Turn it off and you'll rest easy!