What color is the light you sleep with? You may say that you don’t sleep with any lights on. But if you take a closer look, you’re likely to see some light coming from your alarm clock…cell-phone charger…computer…e-reader…night-light…and/or bedroom TV.

Problem: The color of the light you’re exposed to at night, even while you’re sleeping, may affect how you feel during the day—and not in a good way. In fact, certain colors are linked to signs of depression, a new study reveals.

Good news: You can minimize your risk by making your room truly dark or, if you need a bit of illumination, by using the right kind of clock or night light, a new study suggests.


It’s thought that exposure to light at night interferes with the release of hormones that affect mood and various physiological functions. Researchers wanted to explore whether certain colors of light would be better or worse than others in this regard. The experiments were conducted on hamsters, but these mammals share enough physiological similarities with humans that the findings might well apply to us, too.

For four weeks, all the hamsters were exposed to bright light (similar to normal daytime lighting) for 16 hours each day. However, their nighttime-light exposure differed. One group was exposed to no light at night, while three other groups were exposed to either dim white light…dim blue light…or dim red light. Then the hamsters were given various tests to assess depression-like symptoms. The tests were done during daytime, away from any immediate effects of nighttime light.

First the hamsters were placed in tanks filled with room-temperature water for 10 minutes. (From previous studies, the researchers knew that hamsters normally swim vigorously during this challenge—but those who demonstrate various depression-like behaviors are likely to just float passively.) In this study, hamsters that had slept in the dark spent almost all their time swimming (happy hamsters!)…while those that had been exposed to white or blue light at night spent the least time swimming (not so happy). Most interesting of all, those that had been exposed to red light at night spent significantly more time swimming than the other light-exposed hamsters—indicating that red light did not affect mood nearly as negatively as white or blue light did.

Another measure of depression is anhedonia, the inability to derive pleasure from normally enjoyable activities. For hamsters, drinking sugar water is very pleasurable. Findings: Hamsters not exposed to any light at night consumed the most sugar water, followed closely by those exposed to red light…whereas those exposed to white or blue light consumed only about half as much. So again, red did best among the colors of light, coming in second only to darkness.

Finally, the researchers looked at the hamsters’ brains, particularly the neurons in the hippocampus, an area known to be involved in mood regulation. The hamsters that had spent their nights in blue or white light had significantly reduced density of dendritic spines (hairlike growths on brain cells that are used to send chemical messages between cells), another sign that has been linked to depression. The dark-night hamsters showed the highest density of these dendritic spines…with the red-light hamsters again coming in a close second.


What explains these results? Researchers suspect that specialized light-sensitive cells of the retina, called ipRGCs, are responsible. These cells, which detect the unique wavelengths emitted by various colors, are most sensitive to blue wavelengths and least sensitive to red wavelengths. The ipRGCs also send messages to the part of the brain that helps regulate circadian rhythm. When circadian rhythm is disrupted—by nighttime light or some other factor—the body feels the effects physically and psychologically. In addition, ipRGCs send messages to the brain’s limbic system, which controls mood and emotion. All these factors help explain why red light at night had fewer detrimental effects on mood than other colors of light.

Good-mood lighting at night: It’s best if you can keep your bedroom totally dark, and to do that, besides having light-blocking shades or curtains on your windows, you’ll need to turn off, cover or remove all electronics and other light-emitting objects at night. (The one exception is your smoke alarm/carbon monoxide detector, for obvious reasons.) If you want to have a clock immediately readable at all times or if you need a small night-light (for instance, to illuminate the way to the bathroom), use a clock that emits red light…or use a red bulb in your night light. It’s a simple enough thing to try…and you might just start feeling better because of it!