Light Measurement FAQs
All 3 sensors measure the same range of light between 400nm & 700nm however the sensor response and units vary on sensor type. PAR Quantum Sensor – This is the typical sensor used in PAR research and has a square ‘ideal’ response to light across the waveband. It outputs in µmol m-2 s-1. PAR Energy Sensor – This sensor is calibrated to output in W m-2 and is designed to match an energy curve where light closer to 400nm would have less energy and light closer to 700nm would have more energy. Because of this the sensor needs to be less responsive to these higher energy wavelengths to have an equal response to photon numbers (µmols) over the whole range. The PAR Energy sensor is designed to have a flat square response when plotted in an energy curve. PAR Special Sensor – This sensor is also calibrated to output in µmol m-2 s-1, however it has a response more closely related to a real plant, i.e. it is more responsive in the red and blue areas of the spectrum and less responsive in the green area.