Measure Photosynthetically Active Radiation
During photosynthesis, plants use energy in the region of the electromagnetic spectrum from 400-700nm. The radiation in this range, referred to as Photosynthetically Active Radiation (PAR), can be measured in energy units (watts/m²) or as Photosynthetic Photon Flux Density (PPFD), which has units of quanta (photons) per unit time per unit surface area. The units most commonly used are micromoles of quanta per second per square meter (mmol/sec/m²). Plant scientists, horticulturists, ecologists, and other environmental scientists use the LI-190 Quantum Sensor to accurately measure this variable.
Accurate measurements are obtained under all natural and artificial lighting conditions because of the computer-tailored spectral response of the LI-190. Colored glass filters are used to tailor the silicon photodiode response to the desired quantum response. An interference filter provides a sharp cutoff at 700 nm, which is critical for measurements under vegetation where the ratio of infrared to visible light may be high. A small response in the infrared region can cause an appreciable measurement error. This sensor, developed from earlier work (1), was pioneered by LI-COR and has become the standard for PPFD measurement in most photosynthesis-related studies.
The LI-190 is also used in oceanography, limnology, and marine science as a reference sensor for comparison to underwater PAR measured by the LI-192 Underwater Quantum Sensor and LI-193 Spherical Underwater Quantum Sensor.
1. Biggs, W.W., A.R. Edison, J.D. Easton, K.W. Brown, J.W. Maranville and M.D. Clegg. 1971. Photosynthesis light sensor and meter. Ecology 52:125-131.
2. Federer, C.A. and C.B. Tanner. 1966. Sensors for measuring light available for photosynthesis. Ecology 47:654-657.
3. McCree, K.J. 1972. Test of current definitions of photosynthetically active radiation against leaf photosynthesis data. Agric. Meteorol. 10:443-453.
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Sensor lead terminates with bare wires for use with a non-LI-COR metering device/data logger. Sensor delivers a microamp current output. If required, a shunt resistor can be used across the terminals of the metering device to generate a millivolt output.Click the picture for a closer look