Sunshine duration
Radiation & sun sunshine hours bright sunshine duration
Sunshine duration counts time with sufficiently strong direct sunlight. Daylight alone does not count: a day with twelve hours of daylight can still have no sunshine hours.
The sun has to get through
Comparable measurements use a threshold: direct solar radiation must exceed 120 watts per square metre, measured perpendicular to the sun’s rays. Qualifying intervals are added up, usually as hours per day.
Three hours need not come all at once
Twelve sunny breaks lasting fifteen minutes each add up to three sunshine hours. A daily total therefore says little about when you can catch the sun. The changing cloud cover or an hourly forecast is more useful for timing.
Sunshine through the year
Day length and cloud cover affect the number of sunshine hours. Monthly and annual averages belong to a particular station and reference period. They cannot be read as a guarantee for a holiday or weekend.
Sunny does not automatically mean warm
A clear winter day can have plenty of sunshine while remaining cold. Solar elevation and the air mass matter. Sunshine duration also cannot tell you the UV index. The sun can look welcoming while its radiation is still strong.