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The SQ-500 is a self-powered, analog full-spectrum quantum sensor with a 0 to 40 mV output. The sensor incorporates a blue-enhanced silicon photodiode and custom optical filters with a rugged, self-cleaning sensor housing design, anodized aluminum body with acrylic diffuser, and high-quality cable terminating in pre-tinned pigtail leads for easy connection to dataloggers and controllers. Typical applications include PPFD measurement over plant canopies in outdoor environments, greenhouses, and growth chambers, and reflected or under-canopy (transmitted) PPFD measurements in the same environments. Quantum sensors are also used to measure PAR/PPFD in aquatic environments, including salt water aquariums where corals are grown. Sensor includes IP68 marine-grade stainless-steel cable connector 30 cm from head to simplify sensor removal and replacement for maintenance and recalibration.


The analog version of this sensor (SQ-500) comes with the inline cable connector placed 30 cm from the sensor head for either standard use as a long-cable pigtail sensor, or for use with our microCache Bluetooth Micro Logger by unscrewing the connector, discarding the long section of cable and then screwing the sensor to the mating connector on the microCache.


Apogee Instruments SQ-500-SS: Full-Spectrum Quantum Sensor

  • Power Supply



    Output (Sensitivity)

    0.01 mV per µmol mˉ² sˉ¹


    Calibration Factor (Reciprocal of Sensitivty)

    100 µmol mˉ² sˉ¹ per mV


    Calibration Uncertainty

    ± 5 %


    Calibrated Output Range

    0 to 40 mV


    Measurement Range

    0 to 4000 µmol mˉ² sˉ¹


    Measurement Repeatability

    Less than 0.5 %


    Long-term Drift

    Less than 2 % per year



    Less than 1 % (up to 4000 µmol mˉ² sˉ¹)


    Response Time

    Less than 1 ms


    Field of View



    Spectral Range

    389 to 692 nm ± 5 nm (wavelegths where response is greater than 50 % of maximum)


    Spectral Selectivity

    Less than 10 % from 412 to 682 nm ± 5 nm


    Directional (Cosine) Response

    ± 5 % at 75˚ zenith angle


    Azimuth Error

    Less than 0.5 %


    Tilt Error

    Less than 0.5 %


    Temperature Response

    -0.11 ± 0.04 % per C


    Uncertainty in Daily Total

    Less than 5 %



    Blue-enhanced silicon photodiode



    Anodized aluminum body with acrylic diffuser


    IP Rating



    Operating Environment

    -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m



    24 mm diameter, 37 mm height



    100 g (with 5 m of lead wire)



    5 m of shielded, twisted-pair wire with TPR jacket (high water resistance, high UV stability, flexibility in cold conditions)

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