One of the most commonly used terms when referring to the power of a given grow light is the word lumens. For years, it has been the standard measurement of the growing capability of metal halide and high pressure sodium grow lights. The problem is that this term has been used incorrectly for over 30 years. In this article, we will explore the real meaning and correct use of lumens and further describe what you should be looking for when it comes to choosing LED grow lights that pack the most growing-power for your dollar.
What are Lumens and Lux
Lumens and lux are both measurements popular with grow light manufacturers – both HID and LED – to give potential customer a reference point for the relative brightness of various lights. In some jurisdictions, a lamp’s lumen output rating must be on the label as required by law. What we are told (and have been for years) is that the higher the lumen rating of a given light, the better, faster, bigger, etc. your plants will grow.
But there is one MAJOR problem with using Lumens as a reference point for growing plants.
By definition, a lumen is a measurement of how bright (the power) a light is perceived by the human eye. The term lux is very similar to lumen in that it measures the intensity of light, however, it also takes into account the total area covered by a given number of lumens. For now, don’t get bogged down by the technical side, just know that lux and lumen both measure the intensity of light to the human eye.
So what’s the big deal? A bright light is good, right? The sun does a pretty good job at growing things and it’s really bright. Don’t we want to mimic the sun?
Well, yes and no . . .
Lumen & Lux Are Irrelevant To Plant Growth
Unless the plants under your grow lights have eyes, lumens & lux make zero difference in how well your plants grow. Plants respond most efficiently to light that is beyond what humans can perceive so it does not necessarily matter how bright your light is. As a matter of fact, 80% or more of the light emitted by either the sun or from HID lights, goes unused by plants for photosynthesis. It is that portion of light that we humans see with our eyes and can register as being bright.