PAR (Photosynthetically Active Radiation)

Photosynthetically active radiation (PAR) is the light in the band that plants and algae use for photosynthesis, reported in µmol/s/m². On this platform it is an underwater light reading from a multiparameter water-quality sonde, and it has one source: the YSI 6-Series sondes, which can carry a PAR sensor among their channels.

The 6-Series covers YSI's large and mid-size sondes (the 6600, 6600EDS, 6920, and 6820) and the compact 600-series. All are now discontinued by YSI (the 6600 is succeeded by the EXO2 and the 6920 by the EXO3), so on the platform PAR mostly serves existing deployments.

A 6-Series sonde connects to a Thiamis gateway over SDI-12. Its response is an ordered list of values with no labels, so the sensor order configured in YSI's software when the sonde is prepared determines which value is PAR. A deployment reports PAR only when it was set up with that sensor.

Another sonde family in the sensor catalog, the Eureka Manta, also offers a PAR sensor, but the platform's Manta driver cannot read it, so PAR from a Manta does not reach the platform.