is the spectral composition of daylight an aetiological element in winter depression?
OBJECTIVES: Surveys on winter depression in Iceland indicate a significantly lower prevalence rate of winter SAD than expected according to Iceland’s latitude. Research into daylight availability in Iceland failed to reveal factors contributing to higher average daylight availability than predicted by latitude. In view of the well-known healing effects of bright light treatment, we propose that properties of daylight other than daylight availability may ease the symptoms of winter depression. METHOD: We analysed the spectral composition of daylight in Iceland as expressed by its chromaticity and assessed its seasonal and diurnal variations. The colorimetric properties of daylight during the year 1998 are dealt with in detail. Perception of daylight is modelled, applying the chromaticity model of MacLeod and Boynton along with environmental data on spectral irradiance recorded on location at 64 degrees 8.8′ N and 21 degrees 55.8′ W in Reykjavik, Iceland, and recently published data on c
