Skylight availability under typical nebulosity conditions

A thorough study of skylight availabilities under arbitrary atmospheric and cloudiness conditions has suggested that the exterior illuminance levels are dependent on the cloud types and their sky cover with regard to whether the presence or absence of sunshine characterises the local daylight climate. Recent Japanese measurements seem to confirm independently the Czechoslovak and Russian data. Thus the more systematic and radiation-based empirical relations for skylight illuminances under main sky and cloudiness types are justified.