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Finding it hard to sleep? Stay away from blue and violet

world Updated: Jun 09, 2016 08:17 IST

LONDON: Different colours of light may affect your ability to sleep: green may produce the most rapid onset of sleep, while blue and violet may delay it the most, says a new study from the University of Oxford.

Researchers led by Stuart Peirson from Oxford’s Sleep and Circadian Neuroscience Institute came to the conclusion on the basis of a study on sleep patterns of mice. Exposing the mice to bright light caused two – physically incompatible – responses.

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

However, it was green light that produced rapid sleep onset – between one and three minutes. Blue and violet light delayed sleep – the onset of sleep taking between 16 and 19 minutes for blue and between five and 10 minutes for violet, a university release said on Wednesday. The study was published in “PLOS Biology ”.

Peirson said: “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.

“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.”

To investigate the role of melanopsin, the team performed the same test on mice lacking the pigment. For these mice, the colours had opposite effects – blue caused rapid sleep onset, while green and violet significantly delayed sleep, showing melanopsin is necessary for substantial wavelength-dependent effects of light on sleep.