LI-COR Biosciences Line Quantum Sensor LI-191

The Line Quantum Sensor spatially averages PPFD over its one-meter length. Measuring PAR within a plant canopy can be very difficult because of the non-uniformity of the light field. When PAR is measured with a small diameter quantum sensor such as the LI-190 Quantum Sensor, intensity can vary 10-fold between sunflecks and shadows, requiring a large number of readings to get an accurate average. The LI-191 Line quantum Sensor reduces the number of individual readings required because it effectively averages PPFD over its one-meter length. One person can quickly make plant canopy PPFD measurements in many plots in a short period of time. Rather than using multiple detectors linearly arranged over its one-meter length, the LI-191 uses a one-meter-long quartz rod under a diffuser to conduct light to a single, high-quality quantum sensor. Its response is shown below. There are two advantages to this design. First, the sensor has a very good quantum response, unlike sensors using inexpensive gallium arsenide detectors with only an approximation of the ideal quantum response. Second, it is much easier to maintain calibration on a single quantum sensor than on multiple (up to 80) individual gallium arsenide detectors.