The colour blue is generally recognised for its calming effects, but a recent study has found that may not be the case when it comes to evening lighting.
A new study by the Ohio State University has found that exposure to blue light at night can lower people's moods and encourage depressive symptoms.
The research also revealed that white light had a less depressive effect than blue light on mood and performance. Red light fared even better, while absolute darkness faring the best.
The study was conducted on hamsters but has highlighted important information that could be applied to humans, particularly those who work the graveyard shift.
Lighting in interior design has long been recognised for its effects on human mood and behaviour and is now strategically adjusted to create ambiance, influence mood and increase productivity. Ohio State researchers believe hospitals and workplaces that operate 24 hours should be lit with red light in the evening.
"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 lead researcher, professor Randy Nelson.
The study focused on ipRGCs - specialised cells in the eye’s retina that detect light and send messages to the circadian clock region of the brain, which regulates the body’s day versus night cycle.
One analysis explored the hamsters' reduced consumption of sugar water, which is a sign of a mood disorder. The study revealed that the hamsters exposed to nighttime darkness drank the most, followed by those exposed to dim red light. When exposed to dim white or blue light, the consumption of sugar water was considerably reduced.
The next test examined the hippocampus regions of the hamsters’ brains and found the hamsters that spent the night in dim blue or white light had a noticeably reduced density of dendritic spines (brain structures) compared to those exposed to total darkness or dim red light.
"These cells are most sensitive to blue wavelengths and least sensitive to red wavelengths," said Nelson. "We wanted to see how exposure to these different colour wavelengths affected the hamsters."
"The behaviour tests and changes in brain structure in hamsters both suggest that the colour of lights may play a key role in mood," Nelson added. "In nearly every measure we had, hamsters exposed to blue light were the worst off, followed by those exposed to white light. While total darkness was best, red light was not nearly as bad as the other wavelengths we studied."
Humans also react to different colour wavelengths, and light at night could cause mood problems both at night and during the day, according to co-author Dr Tracy Bedrosian.
“This may be why light at night seems to be linked to depression in some people,” she said.
Nelson and Bedrosian believe the results of their study could be applicable to humans and extend beyond shift workers to people who may experience lower moods in winter.
As architects and interior designers move toward the benefits of implementing natural light for its daytime benefits, the study highlights that spaces that operate in the evening also require well-designed lighting to support their users and that colour can indeed matter.
"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," Bedrosian said.