What instrument measures sunshine duration in meteorology?

A sunshine recorder measures the duration of bright sunshine in meteorology.

The classic Campbell–Stokes recorder uses a glass sphere to focus sunlight onto a specially prepared card. As the Sun moves across the sky, the focused light burns a trace in the card. The length of the trace indicates how long sunshine was strong enough to meet the instrument’s threshold.

Sunshine duration does not mean every minute between sunrise and sunset. It records periods when direct solar radiation is sufficiently intense, so clouds, haze, and low solar elevation can interrupt the measurement. Modern electronic instruments use photodiodes or other sensors and record the result digitally.

A sunshine recorder is different from a pyranometer. A pyranometer measures total incoming solar radiation, including diffuse light scattered by the atmosphere, while sunshine duration focuses on direct bright sunshine. Weather services use both measurements for climate records, agriculture, solar-energy planning, and public weather information.