Application
The SQ-420 is used to measure incoming and reflected PPFD around plants and other organisms in outdoor environments, greenhouses, growth chambers, and underwater.

Internal Data Storage
The sensor has internal data storage capability with the ability to hold up to 10,000 measurements. This allows the sensor to collect data while connected to a stand-alone 5 V DC power supply such as an independent battery pack or USB wall adapter.

No Datalogger Required
The sensor can be connected to a desktop, laptop, or tablet computer via USB 2.0 type A plug to be used with the Apogee software. The included Apogee software gives the user control of data logging and calibration settings, provides a real time output display and graph of PPFD measurements and allows the data set to be saved as a csv file.

Independent Calibration
The SQ-420 is calibrated independently for sunlight and electric light to improve measurement accuracy. The light source calibration can be selected in the settings menu of the Apogee software.

The versatile SQ-420 can be used two ways – it can be connected directly to a computer for real-time measurements and data logging using the provided software, or it can be connected to a standard USB power source and act as a stand-alone datalogger capable of storing 10,000 periodic measurements internally that can be downloaded to a computer later for analysis.

Resolution: 0.1 µmol m^-2 s^-1 Calibration Factor: custom for each sensor and stored in the firmware
Calibration Uncertainty: ± 5 % (see Calibration Traceability below)
Measurement Repeatability: less than 1 %
Non-stability (Long-term Drift): less than 2 % per year
Non-linearity: less than 1% (up to 3000 µmol m^-2 s^-1)
Response Time: software updates every second
Field of View: 180°
Spectral Range: 410 nm to 655 nm (wavelengths where response is greater than 50% of maximum; see Spectral Response below)
Directional (Cosine) Response: ± 5 % at 75° zenith angle (see Cosine Response below)
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 30 m
Dimensions: 2.4 cm diameter and 2.8 cm height
Mass: sensor head weighs 90 g USB Cable: 4.6 m (15 ft)
Current Draw (when Logging): 0.35 mA
Warranty: 4 years