How is the PAR sensor calibrated?

FAQ - Li-Cor Ambient Light

1. What is PAR? Is this the same as Ambient Light?
2. Why would I want to measure PAR?
3. Under what circumstances would I use the Flat-PAR sensor instead of the Spherical-PAR sensor?
4. Q: How is the PAR sensor calibrated? A: Hydrolab recommends factory calibration of the PAR sensor every two years. This can be arranged by contacting either Technical Support or Service group in Loveland, Colorado.
   
   
5. Under what circumstances would I use the Dual-PAR sensor instead of the Single-PAR sensor?