Red Lights At Night Better Than White When It Comes To Mood
August 7, 2013

Red Lights At Night Better Than White When It Comes To Mood

Brett Smith for - Your Universe Online

People working the graveyard shift may want to literally see red because according to a new study -- the color of light animals are exposed to at night can affect mood regulation.

Study researchers from The Ohio State University found hamsters that were exposed to blue lights at night experienced the worst mood disruptions, followed closely by white lights, when compared to hamsters that spent their nights in a dim red light.

"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," said study co-author Randy Nelson, professor of neuroscience and psychology at the university.

According to the study, which was published in The Journal of Neuroscience, the scientists examined special retina cells called ipRGCs. These cells don't play a major role in vision, but still sense light and send signals to a part of the brain affects the body's circadian rhythm, an internal clock that determines the sleep cycle. Previous research has suggested that these cells also have 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," said co-author Tracy Bedrosian, currently a postdoctoral researcher at the Salk Institute. "This may be why light at night seems to be linked to depression in some people."

While we may think of red and blue as colors of the rainbow, they are actually different wavelengths of light that our brain processes into what we think of as colors. Going into the study, the scientists said they knew ipRGCs react differently to different types of light.

"These cells are most sensitive to blue wavelengths and least sensitive to red wavelengths," Nelson said. "We wanted to see how exposure to these different color wavelengths affected the hamsters."

In one part of the study, the team conditioned adult female Siberian hamsters to four weeks each of nights with no light, dim red light, dim white light or dim blue light. Several tests were used to check the hamsters for signs of depression.

One test checked to see if the hamsters drank less-than-normal amounts of sugar water, a sign of a mood disorder. The team found that hamsters that were exposed to nighttime darkness drank the most sugar water. Those exposed to dim red light drank the next most, while those exposed to dim white or blue light drank considerably less than the others.

After conducting the mood-analysis tests, the team examined the hippocampus regions of the hamsters' brains. The scientists found that the rodents that spent the night in dim blue or white light had a noticeably reduced density of dendritic spines compared to those spending their night in total darkness or dim red light. These brain structures send chemical messages from one cell to another and a lowered density has been linked to depression, according to Nelson.

"The behavior tests and changes in brain structure in hamsters both suggest that the color of lights may play a key role in mood," he said.

"In nearly every measure we had, hamsters exposed to blue light were the worst off, followed by those exposed to white light," Nelson added. "While total darkness was best, red light was not nearly as bad as the other wavelengths we studied."

Bedrosian said the effects of nighttime lights could apply to humans as well.

"If you need a night light in the bathroom or bedroom, it may be better to have one that gives off red light rather than white light," she said.