Sky quality meter

The SQM is equipped with a silicon photodiode functioning as detector which is partially covered by a rejection filter for the near-infrared wavelength.

Beyond amateur astronomers, the SQM photometers have become very popular among researchers from different fields of study, including associations involved in fighting light pollution.

Typically, the data provided by SQMs are recorded in magnitudes, denoted as m or mag, specifically in mSQM (or magSQM), where the subscript SQM indicates that the measured radiance is calculated by weighting the electromagnetic radiation according to the spectral responsivity of these instruments.

In urban environments, SQMs frequently record large variations in radiance due to the presence or absence of clouds.

Radiance measurements taken by SQM-LU devices are stable within the temperature range of −15 °C to 35 °C, with variations smaller than the 10% systematic uncertainty stated by the manufacturer.