The light visible to the human eye (approx. 380-780nm) is also used by plants. This part of the electromagnetic radiation, which powers photosynthesis, is named PAR and is usually found in wavelengths from 400 to 700nm.
For plant growers, biologists and scientists the most important data in the light requirements for plants is PPFD (photosynthetic photon flux density). PPFD is a measurement of the amount of light that actually reaches a plant (the number of photosynthetically active photons that fall on a given surface each second).
1. PPFD or Photosynthetic Photon Flux Density and
2. YPFD or Yield Photon Flux Density
3. Illuminance - Lux
4. Spectral Irradiance
5. CRI - Color Rendering Index, R1-R15, Ra
6. CIE1931 chromaticity (x,y) coordiantes
7. CIE1976 UVS (u’,v’) coordinates