Making Sure Your Plant Has Enough Light (PAR/ppfd)

One of the best measurements to use when determining if your plants are getting the proper amount of light is PPFD or photosynthetic photon flux density. PPFD measures the amount of light in the spectrum that is actually usable by the plant that is reaching the plant's surface. That spectrum is called PAR which represents wavelengths of light between 400 and 700 nanometers.
No matter the type of light you are using (flourescent, HPS, Metal Hallide, LED or the sun), PPFD is the common measure of how much light your plant has available to perform photosynthesis. PAR (or PPFD) meters are available to take these measurements.
Typical PPFD ranges that allow for healthy growth in the vegetative stage are between 400-600 and between 600-900 in the flowering stage.