Just what colour is time?

New research suggests colour is a reliable sensory mechanism for telling the time of day. By constructing an artificial sky, a research team at the University of Manchester found that colour of light – rather than brightness – affects the body clock of mammals.

Research leader, Dr Timothy Brown said: “This is the first time that we’ve been able to test the theory that colour affects the body clock in mammals. It has always been very hard to separate the change in colour to the change in brightness but using new experimental tools and a psychophysics approach we were successful.”

In the study, published in the journal PLOS Biology, the team first looked at the change in light around dawn and dusk to examine colour alternations of light. Next, the scientists recorded the electrical activity from the body clock of mice while showing them different visual stimuli. They discovered that many of the cells involved in the visual process are more sensitive to changes in colour between blue and yellow than to changes in brightness.

The team then used measurements of the changes in the colour spectra to construct an artificial sky which simulated daily alternations of colours and brightness. Next, the scientists measured the body temperature in mice – placed beneath the recreated sky – and found that when colour of light was changed, their body clock was working optimally.

However, when the brightness of the sky was changed and there was no alteration in colour, the mice demonstrated higher activity before dusk. This indicated that their body clock wasn’t properly aligned to the day night cycle.

“What’s exciting about our research is that the same findings can be applied to humans. So in theory colour could be used to manipulate our clock, which could be useful for shift workers or travellers wanting to minimise jet lag,” said Dr Brown.