CIRAS-3 Operation Manual V. 1.09 56 support@ppsystems.com
PAR Measurement
The PLC3 leaf cuvettes also features two ways of measuring light in the 400-700 nm wavelengths. All
PLC3s include a cosine-corrected external PAR sensor (PARe) for measurement of ambient PAR
(Photosynthetically Active Radiation). This reading will be most reliable with the cuvette held on a
horizontal plane relative to the ground.
PLC3 Universal - includes two mini-silicon photodiode sensors beneath the cuvette window (PARi). The
silicon photodiode sensors are close to the leaf plane and used to average the irradiance beneath the
cuvette window. Irradiance is somewhat attenuated (approx. 10% attenuation) by the window. This
affects the amount of light reaching the leaf if the light source is ambient sunlight, but not if our LED light
unit is the source. This is because the internal PAR sensors are on an electronic feedback loop with the
light unit, so the desired light intensity entered by the user is always achieved.
PLC3 Conifer and Narrow – includes a single, cosine corrected PAR sensor beneath the cuvette window
(PARi). It is used to give an indication of the PAR inside the leaf cuvette and as an electronic feedback
loop to control light intensity when our light unit is used.
PLC3 Universal Leaf Cuvette
PLC3 Conifer and Narrow Leaf Cuvette
TIP
The PARi sensor will normally read about 10% lower than the PARe sensor due to attenuation of the
cuvette window.
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