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Lighting Terminology

terminology of light

There are a number of key acronyms and phrases used when discussing or describing grow lights. The terminology of light for grow lights has similarities, but is different, to normal home or commercial lights. The key acronyms are below with more detailed ones at the bottom of the page (click button below).

  • µmol = micromole is a unit of measure that is one millionth of a mole
  • DLI = Daily Light Integral is the total number of moles of PAR light delivered to a plant in a day (unit is mol/m2/day)
  • Power factor = the measurement of how effectively electrical power is being used in the light
  • PAR = Photosynthetically Active Radiation which is the measured range of spectra from 400nm to 700nm that trigger photosynthetic response in plants (spectra outside of this range also influence photosynthesis and should not be forgotten
Terminology of Light
  •  PPE = Photosyntehtic Photon Efficacy (µmol/s/w or µmol/J) is the measurement of how effectively the light emits photons of light energy in the PAR range
  • PPF = Photosyntehtic Photon Flux (µmol/s) is the total amount of PAR light produced by the fixture = actual power x PPE
  • Actual power = the actual or real power draw of the fixture
  • PPFD = Photosynthetic Photon Flux Density (µmol/m²/s) is the amount of PAR light on a 1 square meter surface area at a specified distance from the fixture.
  • Lighting fixture = the whole light including housing (or heat sink), driver (or ballast) and bulb or LED chip
  • CCT = Correlated Colour temperature (measured in Kelvin [K]) refers to the effective warmness or coolness of visible white light : 2000K is very warm (yellowish white) ; 6000K is very cool (bluish white)
  • CRI = Colour Rendering Index which is a measure of how well humans can perceive true colours under a light source. For example, sunlight is 100 and anything in the 50 region or below starts to lose true colour definition.
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