Sunshine duration or sunshine hours is a climatological indicator, measuring duration of sunshine in given period (usually, a day or a year) for a given location on Earth, typically expressed as an averaged value over several years. It is a general indicator of cloudiness of a location, and thus differs from insolation, which measures the total energy delivered by sunlight over a given period.
Sunshine duration is usually expressed in hours per year, or in (average) hours per day. The first measure indicates the general sunniness of a location compared with other places, while the latter allows for comparison of sunshine in various seasons in the same location.[1] Another often-used measure is percentage ratio of recorded bright sunshine duration and daylight duration in the observed period.
An important use of sunshine duration data is to characterize the climate of sites, especially of health resorts. This also takes into account the psychological effect of strong solar light on human well-being. It is often used to promote tourist destinations.[1]