10 Jun Lighting colour affects sleep and wakefulness
A team of researchers from Oxford Univeristy, were aiming to understand have shown how different colours of light could affect our ability to sleep. The lead researcher, 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). On the other hand, green light 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.
The researchers also found that while exposure to all three colours of light increased the level of corticosterone stress hormone in ordinary mice, blue light caused a much higher rise. In mice without melanopsin, the response to blue light was greatly reduced. Blocking the effect of corticosterone reduced the sleep-delaying effect, suggesting that the production of this hormone in response to light actively inhibits sleep.
‘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.’