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What is a Lumen?

  A lumen is a measurement of the amount of light that falls on one square foot of surface located one foot from the light source. It is, essentially, a measurement of light output.  

What is the Ideal Lumen Output of an LED Grow Light?

  When selecting an LED grow light for cultivation purposes, lumen output is not a relevant factor. This is because lumens measure brightness as it is perceived by the human eye. Because the human eye is most sensitive to green, orange, and yellow light—the wavelengths plants use least for photosynthesis—lumens do not tell you what you need to know about the quality of an LED grow light as it relates to your plants. Instead, note the metrics for PAR, PPF, and PPFD.