Acute and cumulative light exposure differentially influence mood in healthy adults

The study investigated how exposure to light affects mood in healthy adults living their daily lives under natural conditions. Researchers utilized wearable light sensors to track light exposure and conducted repeated assessments of various aspects of mood, such as self-reported mood ratings, cognitive measures of affective bias, and physiological monitoring.

Brighter light was found to consistently correlate with more positive self-reported mood. This association manifested over shorter timeframes, with higher levels of melanopic irradiance (light perceived by the eye's melanopsin photoreceptors) during the preceding 30 minutes being linked to increased feelings of energy. This connection remained significant even when adjusting for alertness, physical activity, and sleep-related factors, indicating that the stimulating effect of light is not solely due to its alerting properties.

On the other hand, certain positive mood dimensions, including happiness, feeling accompanied, enjoyment, motivation, and relaxation, were associated with light exposure accumulated over longer periods, specifically between 60 to 240 minutes. Moreover, happiness, feeling accompanied, enjoyment, and relaxation were further linked to daily light exposure exceeding 250 lux of melanopic equivalent daylight illuminance (EDI), a level deemed favorable for maintaining healthy daytime light exposure.

However, behavioral measures of affective bias, which assess how individuals perceive and respond to emotional stimuli, did not exhibit a robust connection with light exposure. Overall, the findings indicate that everyday light exposure has a complex relationship with mood in daily life, influencing various mood dimensions across different timeframes.