Red night lights better for health than white or blue

The colour of the light can make a big difference, when it comes to some of the health hazards of light at night, a new study suggests.

In a 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, Randy Nelson, co-author of the study and professor of neuroscience and psychology at The Ohio State University, said.

"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 specialized 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.

Other research suggests these light-sensitive cells also send messages to parts of the brain that play a role in mood and emotion.

"Light at night may result in parts of the brain regulating mood receiving signals during times of the day when they shouldn't," co-author Tracy Bedrosian, a former graduate student at Ohio State who is now a postdoctoral researcher at the Salk Institute, said.

"This may be why light at night seems to be linked to depression in some people," the researcher said.

The study is published in The Journal of Neuroscience.