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

PQ-500 Package: microCache and Full-spectrum Quantum

The PQ-500 package includes an SQ-500 Full-spectrum Quantum sensor with a 30cm cable and microCache Bluetooth micro-logger. Alternatively, the PQ-510 package has 2 metres of cable. When paired, the micrologger and the quantum devices are a powerful tool for monitoring photosynthetically active radiation with research-grade accuracy for optimal plant growth.

The SQ-500 sensor is a trusted industry standard for making accurate PPFD measurements.

The new AT-100 microCache (µCache) micro-logger is a rugged, standalone, battery-powered device that can collect over 400,000 data points and connects your sensor to your iOS or Android device via Bluetooth using our ApogeeConnect app.

The app allows you to make real-time measurements, set custom datalogging intervals, monitor and graph daily lights integrals, measure photoperiods, download datasets, and more.

Alternatively, the PQ-510 package is supplied with a 2 metre length of connection cabling.


AT-100 microCache Bluetooth Micro-Logger



Measuring PAR with the Apogee µCache Logger



SQ-500 Full Spectrum Quantum PAR Sensor

The SQ-500 is a self-powered, analog full-spectrum quantum sensor with a 0 to 40 mV output. 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 density (PPFD): 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).

Sensors that measure PPFD are often called quantum sensors due to the quantized nature of radiation. A quantum referes 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. Apogee Instruments SQ series quantum sensors consist of a cast acrylic diffuser (filter), photodiode, and signal processing circuitry mounted in an anodized aluminum housing, and a cable to connect the sensor to a measurement device. Sensors are potted solid with no internal air space. The range of SQ-500 series quantum sensors are designed for continuous PPFD measurement in indoor and outdoor environments:

  • Rugged Design: The head is submersible and suitable for use in all climate conditions. 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 anodised aluminium body and electronics are fully potted.
  • Excellent Cosine Response: Sensors measure PPFD with a cosine response accurate within ±5% at 75° zenith angle.
  • Refined Spectral Response: The improved spectral response of the SQ-500 increases the accuracy of LED measurements, making it ideal for use with both natural and electric light sources.
  • Accurate, Stable Measurements: Calibration in controlled laboratory conditions is traceable to a NIST lamp. Long-term non-stability, determined from multiple replicate quantum sensors in accelerated aging tests and field conditions, is less than 2% per year.
  • Typical Applications: 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 PPFD in aquatic environments, including salt water aquariums where corals are grown.


How to Choose a Quantum Sensor


Apogee microcache with Quantum Sensor Quickstart Guide


µCache (AT-100)
Communication Protocol Bluetooth® Low Energy (Bluetooth 4.0+)
Bluetooth Range approx. 45 m (line-of-sight)
Data Logging Capability Averaging Interval: 1-60 minutes
Sampling Interval: ≥ 1 second
Data Log Capacity Over 400,000 Entries (approx. 9 months at a 1-minute logging interval)
Time Accuracy ± 30 seconds per month at 0° C – 70° C
Battery Type 2/3 AA 3.6 Volt Lithium Battery
Battery Life
(impacted by sampling interval
and amount of time connected to a mobile app)
approx. 1 year w/ 10-second sampling interval and an average of 5 minutes daily connected time
approx. 2 years w/ 60-second sampling interval and an average of 5 minutes daily connected time
Operating Environment -40 to 85 C
Dimensions 66 mm length, 55 mm width, 18 mm height
Weight 52 g
IP Rating IP67
Connector Type M8
ADC Resolution 24 bits


Power Supply Self-powered
Current Draw
Output (Sensitivity) 0.01 mV per µmol m-2 s-1
Output Type 0 to 40 mV
Calibration Factor (reciprocal of sensitivity) 100 µmol m-2 s-1 per mV
Calibration Uncertainty ± 5 %
Measurement Repeatability Less than 0.5 %
Long-term Drift per Year Less than 2 % per year
Non-linearity Less than 1 % (up to 4000 µmol m-2 s-1)
Response Time Less than 1 ms