Solar Light’s Model 501 Series Radiometers are rugged meteorological-grade instruments which measure solar radiation outdoors and underwater (up to 16.4 feet / 5 meters maximum depth.) World Class manufacturing practices and NIST traceable calibrations ensure a high degree of reproducibility and comparability from unit to unit. Large networks of these precision devices are relied upon by many of the world’s most prestigious meteorological observatories, weather stations, and research agencies worldwide, such as the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and the Natural Resource Ecology Laboratory (NREL.) Digital versions are available with Sensor Recorders, and analog versions are available with output voltage which is proportional to the measured UV solar radiation. In addition, all 501s feature controlled internal temperature to ensure the highest levels of accuracy.