Since its creation, the PAR has created much discussion. The latest developments in specific spectrum lighting create a clear-cut necessity for some explanations.
The PAR (or PPFD) is a system of measurement of energy available to plants, in the form of light.
The creators, at the time, decreed that a chlorophyllous green plant has a need for light of frequencies between 400 nm and 700nm (nanometre). Simply explained: from a light blue through to a deep red. Green, yellow and orange are found between the two.