Digital Output Full-spectrum Quantum Sensor SDI-12

In stock (can be backordered)


In stock (can be backordered)

SKU: SN-SQ-521-SS Categories: , , , Tags: , , , ,


The SN-SQ-521-SS is a digital sensor with SDI-12 communication protocol. The sensor incorporates 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.

Spectral Response

Apogee’s full-spectrum quantum PAR sensors and PAR meters have a highly optimized photo detector that accurately measures the photosynthetic radiation spectral range of 400 to 700 nm. These are our top of the line models that measure accurately under all light sources including narrow-band LEDs. The exact spectral response of our full-spectrum models can be seen in the graph below.

SN-SQ-521-SS Full-spectrum Response

SN-SQ-521-SS Full-spectrum Sensor Spectral Response

Rugged, Self-cleaning Housing

Apogee’s Patented domed shaped sensor head (diffuser and body) facilitate runoff of dew and rain to keep the sensor clean and minimize errors caused by dust blocking the radiation path. Sensors are housed in a rugged anodized aluminum body and electronics are fully potted.

Accurate, Stable Measurements

Sensors are cosine-corrected to maintain their accuracy when radiation comes from low zenith angles. The sensors measure PPFD with a cosine response accurate within ± 5 % at 75° zenith angle. Long-term non-stability determined from multiple replicate quantum sensors in accelerated aging test and field conditions is less than 2 % per year.

Ideal for Measurements in both Air and Water

Apogee quantum sensor are calibrated to make absolute PPFD measurements in air. The waterproof sensors can be used to make absolute PPFD measurements underwater by applying an immersion effect correction factor, the SQ-420X, SQ-520, MQ-210X, and MQ-510 already apply the correction factor. For details on making underwater measurements, please refer to Underwater PAR Measurements.


To ensure accuracy each sensor is carefully calibrated in controlled conditions and traceable to NIST reference standards. The Original sensors are pre-calibrated for either sunlight or electric light sources.

Choosing a Quantum Sensor

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