LumiGrow releases Horticultural Lighting Terms Guide

LumiGrow releases Horticultural Lighting Terms Guide

The guide provides information on Photosynthetically Active Radiation, Photosynthetic Photon Flux and more.


As a continuation from the Lumens, Lux and PAR explanation, LumiGrow dives deeper into the light measurements that are important for plant growth to make the best lighting choice for production.

Photosynthetically Active Radiation (PAR)

PAR is the waveband of the light spectrum that plants use for photosynthesis. PAR is not a measurement of light, but rather represents the waveband in the light spectrum which is used by plants for photosynthesis. That’s why it is said, “PAR is for plants.”

Lumens are a measurement of the amount of light that’s visible to the human eye. Lux is the measurement of the intensity of lumens, thus 1 lux equals 1 lumen per square meter. These measurements shouldn’t be used in horticultural applications since they don’t measure the light that plants use for photosynthesis, hence the saying, “Lumens are for humans.”

Photosynthetic Photon Flux (PPF)

PPF is the amount of PAR a light source produces. PPF is measured in microles per second or μmol·s-1. PPF tells you how much light your fixture will produce that plants can use for photosynthesis.

Photosynthetic Photon Flux Density (PPFD)

PPFD is the amount, or intensity, of PAR light that lands on a square meter each second. PPFD is measured in micromoles per square meter per second, or μmol·m-2·s-1. In other words, PPFD is how much PPF is hitting each square meter of your crop at any given second. It is important to look at PPFD when planning grow light installation. Adjusting your fixtures’ height and density will affect the PPFD at crop canopy.

Daily Light Integral (DLI)

DLI is the amount of PAR that lands on a square meter surface over a 24-hour period. DLI is measured in moles of light per square meter per day, or mol·m-2·d-1. This can be thought of as the accumulation of PPFD over a full day. In other words, the DLI is a plant’s daily caloric intake of light.

Photosynthetic Photon Efficacy (PPE)

PPE measures a light fixture’s efficiency for converting electrical energy into PAR light. This is expressed as micromoles per Joule, or μmol·J-1. PPE is an important measure for comparing the efficiency of different manufacturers’ fixtures.

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