The Measure of Success

Looking at data can be tricky. Numbers need context. For example, given the importance of light to a plant’s growth (light, from all parts of the spectrum between 400-700 nanometers (nm), at varying degrees, drives photosynthesis, which is how a plant feeds itself), it could seem somewhat surprising that “just” 57% of cultivators said they measure light intensity (PPFD) and/or light quality (spectrum). However, without previous years’ data to compare it to, it’s difficult to determine whether or not this percentage reflects a significant growth in the number of cultivators measuring light intensity and quality.

So is measuring light truly important? David Holmes, a grower with 18 years of cultivation experience and founder of Clade9, a company that manages and operates cultivation facilities in California, Nevada and Arizona, says it is. “Measuring light intensity is extremely important for all cultivators. Without knowing how much light your plants are getting, it’s hard to make decisions regarding your environmental controls and nutrition,” he says.

Still, far more cultivators measure relative humidity (81%), ambient room temperature (79%) and nutrient solution pH (76%), and even CO2 concentration (62%) and media pH (58%).

LIGHT METERS USED: *Data was collected only from the 169 respondents who indicated that they collect data on light intensity (PPFD) and/or light quality (spectrum). **Total may exceed 100% because respondents could select all that apply.

When Things Get Intense

If you’re one of the 57% of research participants who measure light intensity and/or quality, you know whether your plants are getting too intense light or insufficient light, and can make necessary adjustments (e.g., using dimmers, shade or blackout curtains, or even turning lights off). If you’re not measuring light, however, how can you know whether you’re giving your plants too much or too little? One way is to check for visual cues. However, once visual cues are present, they may be too little too late. “Too much turns the plants yellow at tops, and too little light yields poor growth with plants stretching toward the light with wispy, weak stems and branches,” says Mel Frank, an internationally recognized author, publisher, photographer and frequent cannabis-magazine contributor with more than five decades of experience in cannabis cultivation.

Holmes agrees. “Usually the plant will get stretchy, and the stems will be much weaker [if light is not intense enough]. This can lead to smaller flowers and more disease problems,” he says.

“Too much light,” on the other hand, says Holmes, “typically causes nutrient deficiencies across the board. I’ve analyzed leaves that have been too close to an HID, and they were deficient in almost every nutrient. The amount of light a plant can take depends on many factors, including the age of the plant, variety, type of light and other environmental factors such as VPD [vapor pressure deficit].”

Aside from just too much or too little, other philosophies surround light intensity and the ability to adjust it. Some believe that in late flower stage, the light intensity should be dimmed to mimic the fall season. Others experiment by increasing and decreasing light intensity to mimic the sun’s rays over the course of a day, which may include dimming lights at night to reflect the light of a full moon.

But how many growers are actually concerned with the ability to dim lights when needed? Nearly half (48%) of the cultivators in CBT’s research rated dimming important (provided a rating of 4 or 5 on a 5-point scale) with regard to controlling light intensity and allowing for greater flexibility in their gardens. One-quarter of cultivators rated dimming as unimportant (giving it a 1 or 2 on the 5-point scale).

As cultivators and lighting companies continue to experiment with light intensity, recorded, repeatable examples of positive impact on crops will build in the form of concrete data to support or negate some of the existing beliefs. In fact, through CBT’s regular coverage, lighting seems to be among the top factors cultivators are interested in learning more about. In this respect, time will be on cultivators’ sides.

VERTICAL FARMING: * Based on research participants who grow only indoor and/or in greenhouses using supplemental lighting.