Used to measure sunlight under a plant canopy where the light field is non-uniform, the LI-191R Line Quantum Sensor measures PAR with a single detector integrating measurements over its 1-meter length. The LI-191R makes it easy to measure under-canopy light in many plots quickly and consistently. It measures light in units of Photosynthetic Photon Flux Density (PPFD), which is expressed as μmol s-1 m-2.

Why choose the LI-191R PAR Light Sensor?

• Improved water resistance for long-term outdoor deployment
• Integrated measurements using a single detector prevents variance found in sensors that use multiple detectors
• Selected by the National Ecological Observatory Network (NEON®) for integrated PAR measurements
• Compatible with the HOBOnet Analog Mote that transmits data automatically to cellular RX stations and LI-COR Cloud remote monitoring platform.

 

 

Absolute Calibration	± 10% traceable to National Institute of Science and Technology (NIST). The LI-191 is calibrated via transfer calibration using a reference LI-190R Quantum Sensor. Transfer error is ± 5% (included in the ± 10%)
Sensitivity	Typically 7 μA per 1,000 μmol s-1 m-2
Linearity	Maximum deviation of 1% up to 10,000 μmol s-1 m-2
Response Time	10 μs
Temperature Dependence	± 0.15% per °C maximum
Cosine Correction	Acrylic diffuser
Azimuth	< ± 2% error over 360° at 45° elevation
Operating Temperature Range	−40 °C to 65 °C
Relative Humidity Range	0% to 95% RH, Non-Condensing
Sensitivity Variation over Length	± 7% maximum using a 2.54 cm (1”) wide beam from an incandescent light source.
Sensing Area	1 m × 12.7 mm (39.4” × 0.50”)
Detector	High stability silicon photovoltaic detector (blue enhanced)
Sensor Housing	Weatherproof anodized aluminum housing with acrylic diffuser and stainless steel hardware.
Size (L x W x D)	121.3 × 2.54 × 2.54 cm (47.7” × 1.0” × 1.0”)
Weight	1.4 kg (3.0 lbs.)
Cable Length	3.1m (10.0 ft.)

 

How does the line quantum sensor work?

The LI-191R uses a 1-meter long quartz rod under a diffuser to direct light to a single filtered silicon photodiode. The entire LI-191R diffuser is sensitive to light over its 1-meter length. Since the diffuser is one continuous piece, the LI-191R essentially integrates an infinite number of points over its surface into a single value that represents light from the entire 1-meter length. Optical filters block radiation with wavelengths beyond 700 nm, which is critical for under-canopy measurements, where the ratio of infrared to visible light may be high. The unique design of the LI-191R provides an excellent quantum response that is close to the ideal quantum response.

 

Learn More About the Science Behind the Design