Cannabis has been legitimized and legalized in many states. Because of its clandestine history, many apocryphal tales persist. Chief among them are lighting myths. Decades of literally hiding your light under a bushel have kept these misguided notions around.
“Old-school cannabis growers believe it’s a special crop, different than any other plant,” said Marc van Iersel, a horticulture professor at the University of Georgia. “In reality, it’s just one more photoperiodic greenhouse crop. In many ways, it’s not that different from growing a poinsettia or chrysanthemum.”
Of the many myths and old wive’s tales, three misconceptions around grow lights have hung around the longest.
MYTH: Cannabis responds best to the red and blue spectrum
FACT: “While cannabis does respond to the red and blue spectrum, full-spectrum light (from natural sunlight or full-spectrum LEDs) is the most effective for growing cannabis,” said Alex Gerard, chief technical officer at Las Vegas grow light manufacturer Fohse. “Full-spectrum LEDs are similar to natural sunlight, providing the full range of light within photosynthetically active radiation, increasing yield and harvest quality.”
MYTH: Cannabis needs to be grown under high-pressure sodium lights for flowering and metal halides for vegetative growth.
FACT: “Some growers believe the more reddish light emitted by high-pressure sodium lights supports flowering,” Irsel said. “Flowering in short-day plants (i.e. cannabis) isn’t induced by different light spectrums. It is induced by reducing the photoperiod. Switching between metal halides and HPS is labor-intensive and unneeded.”
MYTH: Cannabis grown under LEDs needs more CO2.
FACT: “The only factor that influences the need for CO2 is the amount of daily light integral (DLI) the crop receives, whether that’s from natural sunlight or electrical lighting,” said Travis Higginbotham, vice president of production at Oakland, California-based Harborside. “It isn’t the fixture that makes the difference, it’s the total amount of light the plant receives, regardless of what fixture is used.”