Green light gives a go ahead for sleep too

​Washington D.C: If you thought that a calming blue color would help you sleep better, then think again. Turns out, green is the go-to lighting hue.

A research team from the Oxford University has shown how different colours of light could affect our ability to sleep.

The researchers, led by Dr Stuart Peirson, were aiming to understand why exposing mice to bright light caused two - physically incompatible - responses.

Dr Peirson explained, "When we expose mice to light during the night, it causes them to fall asleep. Yet, at the same time, it also increases levels of corticosterone, a stress hormone produced by the adrenal gland that causes arousal - wakefulness. We wanted to understand how these two effects were related and how they were linked to a blue light-sensitive pigment called melanopsin, known to play a key role in setting our body clock."

The team exposed mice to three different colours of light - violet, blue and green. Based on the existing data about the role of melanopsin in sleep, they expected that the blue light would induce sleep fastest as the wavelength of the blue light (470 nanometres - nm) was closest to the peak sensitivity of the pigment (around 480nm).

However, it was green light that produced rapid sleep onset - between 1 and 3 minutes. Blue and violet light delayed sleep - the onset of sleep taking between 16 and 19 minutes for blue and between 5 and 10 minutes for violet.

Dr Peirson said that the results meant that mice exposed to blue light had less sleep than those exposed to violet and green light. We confirmed the effect by testing mice using green and blue light at a time when they would usually be less active.'

An obvious caveat of this study is that mice are a nocturnal species that are active during the night. As such, green light may be expected to increase wakefulness rather than increasing sleep in humans. The researchers would therefore predict that blue light will further enhance the wake-promoting effects of light by elevating adrenal stress hormones.

Dr Peirson concluded that the results also add to our understanding of the effects of light emitting devices on humans, where recent studies have shown that the blue light from these devices delays sleep. "However, as we have shown that there are different pathways in the brain, by which different colours of light have different effects on sleep or wakefulness, we need to understand how the overall colour balance of artificial light could affect people's alertness and sleep."

The study appears in PLOS Biology.