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Light Measurement
Frequently Asked Questions

Q What is the difference between a PAR Sensor and Quantum Sensor?

A A PAR sensor and quantum sensor both measure photosynthetically active radiation (PAR). These terms are both used for sensors that measure light in the 400-700 nm waveband. The terms are interchangeable.

Q What is the advantage in using the LI‑191R Line Quantum Sensor vs. the LI‑190R Quantum Sensor?

A The LI‑191R gives you the integrated PAR over the 1 meter length. This is ideal for measuring light interceptance by a plant canopy. Under canopies, there are areas that are completely sunlit, completely shaded, and areas that have some transmission of partial light through the leaves. The LI‑191R gives an average PAR over all these conditions. The LI‑190R measures light at a single point.

Q How many light sensors can connect to the LI‑1500 datalogger at one time?

AYou can connect up to three LI‑COR light sensors, using the three BNC bulkhead connectors.

Q How many sensors can I connect to the LI‑250A light meter?

A One sensor can be connected to the LI‑250A light meter at a time but up to two multipliers can be saved.

Q What are the differences between the BNC, BL, and SMV sensors?

AThe "BNC" sensors terminate with BNC connectors and are most commonly used with the LI‑1500 datalogger or LI‑250A light meter. The BL sensors have bare leads that deliver a microamp current output. The SMV sensors are connected to a Standard Millivolt Adapter and have bare leads with a variable resister with a standardized 10 mV output at full scale.

Q Do LI‑COR sensors require external power?

A No. LI‑COR sensors are based on a photodiode, which generates its own current. Power must be provided to the data reader, however.

Q I need to measure how much light my experimental plants are receiving. Which type of sensor should I use?

A The quantum sensors (LI‑190R and LI‑191R) measure light in the photosynthetically active radiation waveband. These sensors should be used to determine how much PAR a set of plants or canopy is receiving.

Q I'm working on a smart building that opens and closes window shades based on the internal light levels. Which sensor would be best for this?

A The LI‑210R photometric sensor measures light as perceived by the average human eye. It should be used in any application that relies on human perceptions of light such as smart buildings or external lighting arrays.

Q I'm going to put a solar panel on my building next year and want to know how much sun it receives. Do you have a sensor that measures that?

A The LI‑200R pyranometer measures solar radiation from 400 to 1100 nm and will give you a good idea of how much sun your building receives.

Q Do these sensors need to be recalibrated?

A Yes, we recommend that all our light sensors be recalibrated every two years. Recalibration can be done year-round for all sensors except the LI‑200R. The LI‑200R can only be calibrated between March 1 and September 30 each year.

Q How do I wire these sensors to my data logger?

A This will depend on your data logger. If a microamp BNC connection is available, you can order the BNC termination option to provide this. If a two-wire connection is required, then use either the BL bare wire termination, SMV Standard Millivolt Adapter, or a millivolt adapter.

Q Which wire is which on my three-wire sensor or millivolt adapter?

A For the BL sensors, the brown wire is negative, the blue wire is positive, and the bare wire can be connected to ground to reduce signal noise. For the millivolt adapter, the green lead is positive and the blue lead is negative.

Q What if I wire my sensors incorrectly?

A The provided wiring instructions are for use with the standard negative multiplier of the sensor. If you reverse the wiring, simply reverse the sign of the multiplier.

Q I entered the wrong multiplier into my datalogger. Can I fix it so I don't lose all my data?

A Absolutely. To fix a dataset, simply divide by the incorrect multiplier and multiply by the correct value.

Q My datalogger says I can only do 4-20 mA or 0-5 V inputs. Can I still use your sensors?

A Yes, you probably can. Please call our support staff at 1-800-447-3576 and they will be happy to discuss connection options with you.


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