Definitions

Photosynthetically Active Radiation (PAR)

This is NOT a measurement or “metric” like feet, inches or kilos. PAR defines the type of light which is needed to support photosynthesis in plant life.

Photosynthetic Photon Flux (PPF) A measurement of the total light (photons) emitted by a light source each second. PPF tells us how much PAR is emitted by a light source. Measured in “micromoles per second” and expressed as: μmoles/second

Photosynthetic Photon Flux Density (PPFD) A measurement of the light (photons) that reach the target each second. PPFD is measured over a one meter square area in “micromoles per square meter per second” and expressed as μmol/m2/s.

Day Light Integral (DLI) A cumulative measurement of the total amount of light (photons) that reach the target during the photoperiod. DLI is measured over a one meter square area in “moles per square meter per day” and expressed as mol/m2/d.

• Mole A mole is a term used in science and is equal to something called “Avogadro’s number”, which is 602,214,150,000,000,000,000,000.
• Micromole One millionth of a mole or 602 quadrillion.
• Photons The name physicists give to light particles. Photoperiod The period of time during which natural or artificial light is available to promote photosynthesis in plant life each day.