Red light may be best at night: study

Working in night shifts? Ensure your office has red lights!
Exposure to red light in office may decrease health risk in night shift workers, a new study suggests.
In the study involving hamsters, researchers found that blue light had the worst effects on mood-related measures, followed closely by white light.
But hamsters exposed to red light at night had significantly less evidence of depressive-like symptoms and changes in the brain linked to depression, compared to those that experienced blue or white light.
The only hamsters that fared better than those exposed to red light were those that had total darkness at night.

The findings may have important implications for humans, particularly those whose work on night shifts makes them susceptible to mood disorders, said Randy Nelson, co-author of the study from The Ohio State University.

"Our findings suggest that if we could use red light when appropriate for night-shift workers, it may not have some of the negative effects on their health that white light does," Nelson said.
The research examined the role of specialised photosensitive cells in the retina - called ipRGCs - that don't have a major role in vision, but detect light and send messages to a part of the brain that helps regulate the body's circadian clock. This is the body's master clock that helps determine when people feel sleepy and awake.

"Light at night may result in parts of the brain regulating mood receiving signals during times of the day when they shouldn't," said co-author Tracy Bedrosian.
"This may be why light at night seems to be linked to depression in some people," said Bedrosian.
What people experience as different colours of light are actually lights of different wavelengths. The ipRGCs don't appear to react to light of different wavelengths in the same way, researchers said.
"These cells are most sensitive to blue wavelengths and least sensitive to red wavelengths. We wanted to see how exposure to these different colour wavelengths affected the hamsters," Nelson said

In one experiment, the researchers exposed adult female Siberian hamsters to four weeks each of nighttime conditions with no light, dim red light, dim white light (similar to that found in normal light bulbs) or dim blue light.
They then did several tests with the hamsters that are used to check for depressive-like symptoms. For example, if the hamsters drink less-than-normal amounts of sugar water - a treat they normally enjoy - that is seen as evidence of a mood problem.
Results showed that hamsters that were kept in the dark at night drank the most sugar water, followed closely by those exposed to red light. Those that lived with dim white or blue light at night drank significantly less of the sugar water than the others.

The study was published in The Journal of Neuroscience.