Photosynthetic Active Radiation (PAR): PAR represents a range of light wavelength from 400 to 700 nanometers (roughly the range visible to human eye) which is the optimal wave length for photosynthesis. Light particles of lower wavelentgths carry too much energy and can be damaging to plant cells and tissue while those of wavelengths exceeding 700 do not have enough energy to trigger photosynthesis.
Photosynthetic Photon Flux Density (PPFD): PPFD represents the quantity of PAR (measured in micromoles) that illuminates the surface of 1 square meter over the course of 1 second.
Lumen: lumen is a measurement unit that represents the quantity of light emitted by a single source
Lux: Lux is a measurement unit that is used to measure the quantity of light (measured in lumen) illuminating the surface of 1 square meter.
Spectrum: Spectrum is a collective term that encompasses all the know frequencies of electromagnetic radiation and their respective wave lengths. (Note: Light is a type electromagnetic radiation)
Photosynthesis: Photosynthesis is a process conducted by plants and microorganisms which have chlorophyll that transforms water and carbon -dioxide molecules into sugar molecules and oxygen. The process requires a certain wave length (400 to 700 nanometers) to shine on the plants, which then uses the energy from the light particles to start the process.