Lighting Measure: PAR, PPF, PPFD and DLI

Before choosing a Grow Light for our horticultural growing, we need to know what's the metrics of horticulture lighting, how to choose and measure a great grow light.

There are some essential metrics, such as watt, lumen, lux, PAR, PPF and PPFD, DLI, helpful for measuing a light, and promoting plant growing, production. Today we will talk about PAR, PPF, PPFD and DLI.

PAR is the photosynthetically active radiation. PAR is measured by the amount of micro moles of light per square meter per second.

PPFD is that how many PAR photons on a surface, is expressed in micro moles per second per ㎡. It allows quantifying on a given surface, at a given distance from the lighting, the number of photons PAR incidents per second. PPFD is a vital measure because it indicates the amount of light available to the plant for its photosynthesis,

Different plants need different PPFD level, such as Tomato need 150-600, Cucumber need 150-600, but cannabis need 200-600+

PPE is the radiometric efficiency, showing how much PAR photons are delivered per watt consumed. PPF shows how much photons are delivered from electrical energy supplied. PPF = PPE * Watt.

DLI, the daily light integral, is the number of photosynthetically active photons accumulated in a square meter over a day, that mean how many PAR photons per day are demanded by plants. As plants' need of PPFD, each plants also have it's favor DLI, which has a significant impact on the plants root, growth, height, flower, etc.

Many ferns grow well at a DLI of 4-6, cyclament at 6-8, fuchsias at 10-12, chrysanthemums at 10-14, petunias at 16-18 and cut-flower rose plants at 18-22 mol/m-2/day.

Shading-loveing plants need relatively low DLI, large, warm-season plants need higher DLI. Following i list some for your reference.