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Photosynthetically Active Radiation (PAR)

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PAR measures irradiance -- the amount of sunlight or ambient light that diffuses through water compared to surface light, PAR focuses on the dynamics of the photic zone, typically 1 - 5 meters below the surface and leads to an understanding of photosynthesis, toxic algae blooms and eutrophication (nutrient loading)


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Specification Sheets

Photosynthetically Active Radiation (PAR)

Catalogs & Brochures

European Service Centre

Scientists studying phytoplankton and photosynthesis and measuring chlorophyll need to measure PAR in order to resolve the absorption rate. High levels of PAR can indicate photoinhibition (limiting photosynthesis in shallow water) which affects the submerged aquatic vegetation and certain aquatic species.

YSI measures PAR using single or dual Li-Cor sensors attached to a YSI 6600V2 sonde for continous field monitoring.

Optional wiped PAR is available for long term monitoring in high fouling conditions.


  • 200m (non wiped) maximum operating depth
  • Compatible with YSI 6600, 6600EDS or 6600EDS sondes
  • Measurements averaged over a 60 second time period, filter time user adjustable
  • Units are millivolts or umoles/sec/m2
  • Absolute calibration +/- 5%
  • Sensitivity typically  3uA per 1000 umol s-1 m-2 in water
  • Stability < +/- 2% change over one year period
  • Response time 10uS


Asymmetrical Mounting System (unattended)

  • 200680 Dual LI-COR 2π PAR on one-sided mounting bar
  • 200690 Single LI-COR 2π PAR with wiping system on one-sided mounting bar
  • 200700 DUal LI-COR 2π PAR with wiping system on one-sided mounting bar

Symmetrical Mounting System (profiling)

  • 131041510 Single LI-COR 2π PAR with mounting and counterbalance bar
  • 131041530 Single LI-COR 4π PAR with mounting and counterbalance bar
  • 131041520 Dual LI-COR 2π PAR (up/down) with opposing mounting bars




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