Light for Plants

PPF & PPFD Guide to compare GROW-LEDS

Essential information to compare horticultural lights

In the following we would like to introduce you to the PPF and PPFD measures. They are of great importance and can give you essential information on the performance of a light source, which is used to promote plant growth. Furthermore, the PPF value allows you to compare different light sources and select the appropriate substitute for standard light sources, which are used in horticulture.


PPF is the abbreviation for “photosynthetic photon flux“. It gives the information on the number of photons, which are emitted by a light source. Only photons in the wavelength range from 400nm to 700nm are considered. This is the so-called PAR (photosynthetic active region) and photons within these wavelengths contribute to photosynthesis.

The unit of the PPF value is µmol/s (quantity of light particles emitted per second). Knowing the PPF value from different light sources allows an easy and objective comparison on the total light output which can in theory contribute to photosynthesis. Please note that the PPF does not consider the direction in which the light is emitted. It does not give the information on the amount of light which actually arrives at the plants.



Whilst the PPF value gives information on the total photon flux within the PAR region, the PPFD value determines the photosynthetic photon flux density. It refers to the photon flux in a certain area. The unit is given in µmol/(m2s). In other words, it tells you how many photons which contribute to photosynthesis impinge on the plant per second. Other than the PPF you now know how much light really can be absorbed by the plant.

Attention: Please note that the PPFD value is measured with a detector which has a small measuring area. The measured value is only valid at the exact point of measurement. It is wrong to only do one measurement and deduce the PPFD value for the whole cultivation area based only on this single measurement. Most light sources use reflectors or lenses which steer the light and distribute it across the cultivation area – often extremely inhomogeneous. The intensity variation in the cultivation area can be determined by doing multiple PPFD measurements across the area. Visualizing these measurements results in a so-called PPFD plot. This is a very useful graph which shows the effective light distribution on plant level.

 Attention: PPFD measurements are prone to errors and should be carried out by experts with high quality measurement instruments (preferably with spectrometers not integrating sensors).