Under what circumstances would I use the Dual-PAR sensor instead of the Single-PAR sensor?

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. How is the PAR sensor calibrated?
5. Q: Under what circumstances would I use the Dual-PAR sensor instead of the Single-PAR sensor? A: A Dual-PAR sensor is used when ambient light needs to be analyzed in a differential mode, where sunlight intensity is measured both at the surface of the water and in the water column. In this way, light attenuation can be monitored, providing an integrated indicator of water clarity over the entire vertical water column.