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

SQ-120 Electric Calibrated PAR Sensor

The SQ-120 is a self-powered quantum sensor that measures photosynthetically active radiation and is calibrated for use with electric lights. The SQ-120 is ideally suited for aquatic tanks, glasshouse or indoor use where electric or artificial lights are the main source of radiation for plant growth.

The sensor housing design features a fully potted, domed-shaped head making the sensor fully weatherproof and self-cleaning. Photosynthetically active radiation (PAR), or photosynthetic photon flux (PPF), is the wavelength range from 400 to 700 nanometers and is strongly correlated with plant growth. Gardeners, greenhouse managers, growth chamber users and salt-water aquarists measure PAR to insure optimal specimen health.

The SQ-120 is ideally supported by the LSM1 Light Sensor Meter for PAR Sensors for a complete data logging and long-term monitoring solution. For spot measurements or a portable, handheld device, refer to the MQ-100 Instrument or the MQ-200 Instrument.

Sensitivity: 0.2 mV per µmol m-2 s-1
Calibration Factor: 5.0 µmol m-2 s-1 per mV (reciprocal of sensitivity)
Calibration Uncertainty: ± 5%
Measurement Repeatability: <1%
Non-stability (Long-term Drift): < 2% per year
Non-linearity: < 1% (up to 4000 µmol m-2 s-1 )
Response Time: < 1 ms
Field of View: 180°
Spectral Range: 410 nm to 655 nm (wavelengths where response is greater than 50 % of maximum)
Directional (Cosine) Response: ± 5% at 75° zenith angle
Temperature Response: -0.06 ± 0.06% per °C
Operating Environment: -40 to 70°C, 0 to 100% relative humidity, can be submerged in water up to depths of 30m
Dimensions: 2.4 cm diameter and 2.8 cm height
Mass: 90g (with 5m of lead wire)
Cable: 5m of shielded, twisted-pair wire. Santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions). Pigtail lead wires
Warranty: 4 years

Radiation that drives photosynthesis is called photosynthetically active radiation (PAR) and is typically defined as total radiation across a range of 400 to 700 nm. PAR is often expressed as photosynthetic photon flux (PPF): photon flux in units of micromoles per square meter per second (µmol m-2 s-1, equal to microEinsteins per square meter per second) summed from 400 to 700 nm (total number of photons from 400 to 700 nm). While Einsteins and micromoles are equal (one Einstein = one mole of photons), the Einstein is not an SI unit, so expressing PPF as µmol m-2 s-1 is preferred.

Sensors that measure PPF are often called quantum sensors due to the quantised nature of radiation. A quantum refers to the minimum quantity of radiation, one photon, involved in physical interactions (e.g. absorption by photosynthetic pigments). In other words, one photon is a single quantum of radiation. Typical applications of quantum sensors include incoming PPF measurement over plant canopies in outdoor environments or in greenhouses and growth chambers, and reflected or under – canopy (transmitted) PPF measurement in the same environments.

Apogee Instruments SQ series quantum sensors consist of a cast acrylic diffuser (filter), photodiode, and signal processing circuitry mounted in an anodised aluminium housing, and a cable to connect the sensor to a measurement device. Sensors are potted solid with no internal air space, and are designed for continuous PPF measurement in indoor or outdoor environments. SQ series sensors output an analogue voltage that is directly proportional to PPF under sunlight (e.g. model SQ-110) or electric lights (e.g. model SQ-120). The voltage signal from the sensor is directly proportional to radiation incident on a planar surface (does not have to be horizontal), where the radiation emanates from all angles of a hemisphere.