Measures solar radiation and is required (along with an anemometer and a
temperature/humidity sensor) if you wish to monitor evapotranspiration.

Diffuser element and housing are carefully designed for accurate cosine
response. Silicon photo diode provides good match to solar spectrum.
Two-piece housing minimizes radiation heating, allows convection cooling
of the sensor, and prevents the trapping of water or dust. Includes built-in
level and 3' (0.9 m) cable.

Compatible with both original Vantage Pro and Vantage Pro2.

You may also need a UV Sensor and Sensor Mounting Shelf.