Environmental
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LI-191 Line Quantum SensorMeasure Photosynthetically Active Radiation in Plant Canopies
The LI-191 Line Quantum Sensor spatially averages PPFD over its one-meter length. During photosynthesis, plants use energy in the region of the electromagnetic spectrum from 400-700 nm (1, 2). The radiation in this range, referred to as Photosynthetically Active Radiation (PAR), can be measured in energy units (watts m-2) or as Photosynthetic Photon Flux Density (PPFD), which has units of quanta (photons) per unit time per unit surface area. The scaled units most commonly used are micromoles of quanta per second per square meter (µmol s-1 m-2). 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.
Absolute Calibration: ± 10% traceable to NIST. The LI-191 is calibrated via transfer calibration from a LI-COR reference Quantum Sensor. Sensitivity: Typically 7 µA per 1000 µmol s-1 m-2. Linearity: Maximum deviation of 1% up to 10,000 µmol s-1 m-2. Stability: < ± 2% change over a 1 year period. Response Time: 10 µs. Temperature Dependence: ± 0.15% per °C maximum. Cosine Correction: Acrylic diffuser. Azimuth: < ± 2% error over 360° at 45° elevation. Sensitivity Variation over Length: ± 7% maximum using a 1” wide beam from an incandescent light source. Sensing Area: 1 meter L x 12.7 mm W (39.4” x 0.50”). Detector: High stability silicon photovoltaic detector (blue enhanced). Sensor Housing: Weatherproof anodized aluminum case with acrylic diffuser and stainless steel hardware. Size: 116 L x 2.54 W x 2.54 cm D (45.5” x 1.0” x 1.0”). Weight: 1.8 kg (4.0 lbs.). Cable Length: 3.1 m (10.0 ft.). The LI-191 Line Quantum Sensor comes with a bubble level, detachable 10 ft. (approximately 3 m) cable and hardsided carrying case. Depending on the readout device used to connect the LI-191 Line Quantum Sensor, you may choose one of three configurations: The LI-191SA cable terminates with a BNC connector and can be directly connected to a readout device such as the LI-250A Light Meter or LI-1400 DataLogger. The LI-191SA and the 2290 Millivolt Adapter can be used to connect the LI-191 to a data acquisition device or datalogger requiring a millivolt signal. The LI-191SL is an LI-191SA and a standardized output millivolt adapter. The LI-190SL produces a standardized 10 mv/2000µmol s-1 m-2 output that eliminates the need to change calibration constants or multipliers when type SL sensors are exchanged in the field. 50 ft (15 m) and 100 ft (30 m) extensions cables are also available. Other accessories are described on the Accessories Page. LI-191SA Quantum Sensor (with BNC connector) LI-191SL Quantum Sensor (LI-191SA and standardized millivolt adapter) 2290 Millivolt Adapter for the LI-191SA 2222SB-50 Extension Cable (50 ft) for the LI-191SA and LI-191SL 2222SB-100 Extension Cable (100 ft) for the LI-191SA and LI-191SL
Additional literature related to the LI-191 is also available:
If you have any questions about the LI-191 please feel free to contact us and discuss with our Applications Analysts and Scientists (or your local LI-COR Distributor) how the LI-191 can help you with your research. Search for LI-191 PublicationsSelected Links
Please submit your published papers or links to your websites to be featured here by contacting the Product Manager, Mr. Brent Claassen. Journal ReferencesUse the academic search engines below to find references to the LI-191 in many peer reviewed scientific publications. For best results, start with the search terms provided below or use the forms to customize a search. Results open in a new window. References from HighWire Press - Internet Imprint of the Stanford University Libraries
References from Google Scholar™Common Internet searches can be performed with Google, and many articles can be found with Google Scholar: The LI-191 includes a printed copy of the Instruction Manual. You can download future updates of the LI-191 manual on this page.
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