Previous research into ipRGC-influenced light (IIL) responses indicates that both illuminance and correlated color temperature (CCT) affect people’s well-being (15). Moreover, illuminance and CCT can also affect occupants’ satisfaction with and comfort in the environment (16, 17), improved satisfaction with environmental conditions is associated with improved daily life satisfaction.

In these studies, higher IQ levels were associated with a reduced positive impact of sunlight on happiness (Add Health study, U.S., 1994–2008).

The effect of sunlight on mood is also reflected in the fact that light can either enhance or reduce feelings of joy and sadness, depending on its timing and intensity. Denissen et al. (12) found that sunshine increases both positive and negative emotions, indicating that the relationship between sunlight and mood is complex and not purely beneficial.

The positive effect of sunlight on life satisfaction may be attributed to both its direct influence on mood and the fact that people are more likely to engage in outdoor activities when the weather is sunny, further contributing to well-being. However, studies like those by Buscha (56) have suggested that exposure to sunlight may have a negligible effect on well-being, particularly in cases where other factors, such as personal preferences or environmental stressors, influence mood more strongly.

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