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.
LED grow lights, or Light-Emitting Diode lamps, are an increasingly popular choice for indoor plant growing principally because they can deliver more intense light output with less energy and heat production, and they have a much longer useful life than that of high pressure sodium, fluorescent, high-intensity discharge or incandescent lamps. Most grow lamps are used commercially and industrially, but some residential use occurs. LEDs are made in several colors to mimic the ranges of natural sunlight that drive maximum photosynthesis and plant performance. LED grow lights are also popular because they can be used in standard bulb fittings and do not require special ballasts or non-standard electrical fixtures. LEDs come in 2-watt to 15-watt equivalents and in a range of sizes and colors.
Determine the optimal lighting requirements for your particular plant or plants to thrive if they were living outdoors. Figure out the intensity of light and for how many hours a day it is needed. Often this information is on the plant tag or little plastic pick stuck in the soil of your plant. Online garden resources can help you make the determination if your plant is unmarked. This is what you need to mimic indoors with LEDs. If your plants grow outdoors in shade they need less light indoors. If they are vegetables and grow in full sun for 14 hours per day outdoors then that is the bar you must meet in order for the plant to thrive indoors.
Provide a mix of red spectrum and blue spectrum LEDs. Plant photosynthesis is most responsive to these two spectrums. According to research conducted by NASA, mixing at least 80 percent red LEDs and roughly 20 percent blue LEDs is a successful ratio for growing plants indoors. You can easily switch out a few of the blue LEDs for white without harming the plant growth. This will allow you to see what’s happening with your plants much more readily because white LEDs have a spectrum of green, yellow and orange, which is more easily visible to the human eye.
Adjust your LEDs to hang above your plant tops by anywhere from 5 inches to 20 inches, according to the plant’s size and light intensity requirements. Your goal is to have the plant greens showered in light to their edges but not have the light spill or be wasted on surrounding areas where there are no plants. Height adjustment of lighting helps achieve this economy as plants grow, changing in both shape and size.
Determine if your plants require light and dark periods. If so, connect your LED lights to a timer to regulate their on and off cycles to save you time, worry and labor. If your plants prefer long daylight periods and short night periods, program the automatic timer for that length of light cycle.