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Enabling better global research outcomes in soil, plant & environmental monitoring.

Apogee S2-400 Series PAR-FAR Sensor

The sensor features a rugged, aluminum housing that is fully-submersible and built to withstand harsh conditions, and high-quality cable terminating in pre-tinned pigtail leads for easy connection to dataloggers and controllers. The sensor cable includes an IP68 marine-grade stainless-steel cable connector to simplify sensor removal and replacement from permanent installations for maintenance and calibration. Typical applications of PAR-FAR sensors include measuring both the traditional PPFD photosynthetic photon flux and separately quantifying the photon flux of far-red photons (700-760 nm). The outputs include the traditional quantum flux, the far-red photon flux, and the far-red fraction (far-red photon flux density / sum of PPFD and far-red photon flux density). This sensor quantifies far-red photons, and for many applications it reduces the need for a more complex measurement with a spectroradiometer.

Further applications include:

  • Monitoring plant light environments
  • Researching plant morphogenic activity
  • Photobiology studies.

The S2-441 PAR-FAR sensor is a unique two-channel digital sensor for measuring both the PAR (PPFD) and Far-red outputs of electric grow lights with SDI-12 communication protocol.

The S2-442 PAR-FAR sensor is a unique two-channel digital sensor for measuring both the PAR (PPFD) and Far-red outputs of electric grow lights with Modbus communication protocol.


You can use the S2-441 Sensor in a Sensor-Node IoT (Internet of Things) Package

The SNiP-PFR is a ‘Sensor Node Integrated Package’ for LoRaWAN or CAT-M1 communication of real-time measurements for continuous plant, light and environmental monitoring.

The base SNiP-PFR integrates 1x S-NODE and 1x S2-441 PAR-FAR Sensor (from the Apogee SI-400 Series) to a site’s unique network, communication and power requirements. The S-NODE can support an additional 3 sensors.


Available Videos:

Spectral response of PAR detector (blue) and Far Red detector (red) compared to defined response of plants to radiation (dashed).

Calibration Uncertainty ±5%
Measurement Repeatability less than 1%
Long-term Drift less than 2% per year
Non-linearity Less than 1 % (up to 4000 µmol m⁻² s⁻¹) (PAR); Less than 1 % (up to 1000 µmol m⁻² s⁻¹) (Far-Red)
Response Time less than 0.6 s
Field of View 180°
Spectral Range 389 to 692 nm ± 5 nm (PAR); 702 to 761 nm ± 5 (Far-Red)
Directional (Cosine) Response ± 2 % at 45˚; ± 5 % at 75˚ zenith angle
Temperature Response Less than 0.1 % per C
Operating Environment -40 to 70 C; 0 to 100 % relative humidity
Dimensions 30.5 mm diameter, 36.6 mm height
Mass 51 g
Cable 5 m of shielded, twisted-pair wire; TPR jacket (high water resistance, high UV stability, flexibility in cold conditions); pigtail lead wires; stainless steel (316), M8 connector
4 years against defects in materials and workmanship