Apogee SQ-640-SS Quantum Light Pollution Sensor


Many plants are affected by interruptions in dark periods even by extremely dim light. Apogee’s new Quantum Light Pollution Sensor is designed to detect photons from 340-1040 nm that are below the sensitivity level of a typical quantum sensor. Detecting stray photons that disrupt the night is critical in preventing negative effects in plants such as hermaphrodism and stunted growth.


The SQ-640 Quantum Light Pollution sensor is a self-powered sensor. The sensor features a rugged, aluminum housing that is fully-submersible and built to withstand harsh conditions. 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 Quantum Light Pollution sensors include incoming PFD measurements over plant canopies in indoor greenhouses or in growth chambers, and reflected or under-canopy (transmitted) PFD measurements in the same environments. Since the detector on this particular Quantum Light Pollution sensor is sensitive to radiation with wavelengths up to 1100 nm, beyond the range of wavelengths that influence plants, we recommend only using the SQ-640 sensors in indoor grow environments utilizing LED lights.

The analog version of this sensor (SQ-640) 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.


Power Supply: Self-powered

Sensitivity: 1 mV per µmol mˉ² sˉ¹

Calibration Factor: 1 µmol mˉ² sˉ¹ per mV

Calibration Uncertainty: ± 5 %

Measurement Range: 0 to 200 µmol mˉ² sˉ¹

Measurement Repeatability: Less than 0.5 %

Calibrated Output Range: 0 to 200 mV

Long-term Drift (Non-stability): Less than 2 % per year

Non-linearity: Less than 1 % (up to 4000 µmol mˉ² sˉ¹)

Response Time: Less than 1 ms

Field of View: 180°

Spectral Range: 340 to 1040 nm ± 5 nm (wavelengths where response is greater than 50 %)

Directional (Cosine) Response: ± 2 % at 45° zenith angle, ± 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 %

Housing: Anodized aluminum body with acrylic diffuser

IP Rating: IP68

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

Dimensions: 30.5 mm diameter, 37 mm height

Mass: 51 g

Cable: 5 m of two conductor, shielded, twisted-pair wire; TPR jacket; pigtail lead wires; stainless steel (316), M8 connector located 25 cm from sensor headWarranty4 years against defects in materials and workmanship