What is difference between PAR & PPF&PPFD ?

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What is difference between PAR , PPF , PPFD ?

You may likely confused by above metrics when you searching for a grow lights , the purpose of this article is to identify PAR , PPF , PPFD :

PAR:

PAR : short for Photosynthetically Active Radiation ,represents the fraction of sunlight with a spectral range from 400 to 700 nm which is plants perceive and sensitive light .


PPF

How much PAR the fixture produces (measured as Photosynthetic Photon Flux)
PPF is photosynthetic photon flux. PPF  measures the total amount of PAR that is produced by a lighting system each second. This measurement is taken using a specialized instrument called an integrating sphere that captures and measures essentially all photons emitted by a lighting system. The unit used to express PPF is micromoles per second (μmol/s). This is probably the second most important way of measuring a horticulture lighting system, but, for whatever reason, 99.9% of lighting companies don’t list this metric. It is important to note that PPF does not tell you how much of the measured light actually lands on the plants, but is an important metric if you want to calculate how efficient a lighting system is at creating PAR.

PPFD

How much instantaneous PAR from the fixture is available to plants (measured as Photosynthetic Photon Flux Density)?
PPFD is photosynthetic photon flux density. PPFD measures the amount of PAR that actually arrives at the plant, or as a scientist might say: “the number of photosynthetically active photons that fall on a given surface each second”. PPFD is a ‘spot’ measurement of a specific location on your plant canopy, and it is measured in micromoles per square meter per second (μmol/m2/s). If you want to find out the true light intensity of a lamp over a designated growing area (e.g. 4’ x 4’), it is important that the average of several PPFD measurements at a defined height are taken. Lighting companies that only publish the PPFD at the center point of a coverage area grossly overestimate the true light intensity of a fixture. A single measurement does not tell you much, since horticulture lights are generally brightest in the center, with light levels decreasing as measurements are taken towards the edges of the coverage area. (Caveat Emptor: Lighting manufacturers can easily manipulate PPFD data.

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