Summary

Contributing author

This space will hold a lower level summary on Irradiance. Irradiance is synonymous with photon flux density, the flux of photons onto a unit area. For photosynthesis, it is usually expressed for the waveband 400-700 nm (PAR, photosynthetically active radiation), equivalent to photosynthetic photon flux density (PPFD), micromol photons m^-2 s^-1.