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

MQS-B Cosine Corrected Mini Quantum Sensor

The Cosine Corrected Mini Quantum Sensor MQS-B is designed for light measurements in units relevant for plant leaves.

Light has been defined with regard to properties of the human eye; for photosynthesis research, sensors with spectral and directional sensitivity relevant for plants are required.

Design: Mini quantum sensor for selective PAR (photosynthetically active radiation) measurement, cosine corrected for PPFD (photosynthetic photon flux density) measurement.
Sensor housing: Black anodised aluminium
Diffuser material: Perspex
Signal detection: High stability silicon photovoltaic detector with filter set for PAR correction. Signal output typically -2 μA / (1000 μmol m-2 s-1)
Temperature coefficient of photodiode: 0.01 %/K
Absolute calibration: ± 5%
Angular dependence: error < 4% between -80° to +80° from normal axis
Immersion coefficient: Typically 1.32
Operating temperature: – 5°C to + 45°C
Cable length: 3 m
Connector: BNC
Power supply: Not required
Dimensions: Height: 16 mm; diameter: 14 mm; Diffuser diameter: 5.5 mm
Weight: 32 g

The MQS-B sensor detects photosynthetically active radiation (PAR), which is the electromagnetic radiation between 400 and 700 nm.

More specifically, it measures photosynthetic photon flux density (PPFD), which is the amount of PAR hitting a surface from one side, whereby beams not perpendicular to the surface only contribute with the cosine of their angle of incidence measured to the surface-normal. The unit for PPFD is μmol m-2 s-1.

Spectral Response

MQS-B Figure 1

Fig. 1 Typical response between 350 nm and 750 nm of a MQS-B sensor. The solid line shows the ideal response of a photon flux sensor for photosynthetically active radiation.


MQS-B Figure 2

For comparison Fig. 2, shows the response to energy fluence rate from 350 – 750 nm.

Angular Response

The MQS-B sensor uses a plastic diffuser to obtain an angular response error of less than ± 4% (-80° to 80° angle).

MQS-B Figure 3

Fig. 3 shows a typical angular response curve of the MQS-B sensor compared to the ideal characteristic.


MQS-B Figure 4

Fig. 4: Typical error of angular response of the MQS-B sensor