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Lighting affects mood through pathways to the brain's clock center.

Bluish light increases alertness, while warm yellow-reddish light calms and relaxes.

Bright light improves mood and decreases depression, and dimmer light decreases energy and alertness.

It is estimated that Americans spend over 90 percent of their days indoors. Therefore, when thinking about easily modifiable interventions to improve mood, we should consider the features of indoor environments. The most important of these is light.

Research shows that lighting brightness, "color temperature," timing, rhythm, and locations of indoor lighting can all improve mood.

The first four—brightness, "color temperature," timing, rhythm—all affect mood through the brain’s non-visual (non-image forming) pathways, starting when light hits special receptors at the back of the eye, which send signals directly to the brain’s clock center. The fifth (location) affects mood through the brain’s visual pathways.

Brightness and Color Temperature

Color temperatures of light, measured in Kelvin (K), are not actually blue or red, but are at the blue and red ends of the color spectrum. Think of the bright blue sky in the early morning, shifting to a reddish sky in the evening at sunset. At the lowest end, 2200K lighting is equivalent to candlelight, while the high end, 4000K, is equivalent to bright full-spectrum morning sunlight. You can find examples on the web of rooms lit with different temperatures of light to see the difference.

Many studies have shown that bright white (bluish) light, either delivered through full-spectrum light boxes or sun exposure, can help prevent and reduce depressive symptoms in people with seasonal affect disorder (SAD). Recent studies also indicate that it reduces depressive symptoms and enhances positive emotions and alertness in people without depression.

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