It’s no secret that higher light intensities equate to higher yields. But for many indoor growers, bud-boosting light intensity and unwelcome photobleaching go hand in hand.

David Hawley, Ph.D., principal scientist for Fluence, explains that doesn’t have to be the case. By understanding the mechanism behind photobleaching and how light intensity and light quality relate, you can avoid photobleaching—even under high-intensity lighting.

What Is Photobleaching?

Hawley explains that photobleaching is simply what it seems: the literal bleaching of floral bud.

“When you look at the top of the cannabis canopy, you'll see that all of the upper inflorescences or colas or floral bud—whatever you like to call it—will be bleached white. They won't look green like you might expect them to,” he says.

The cause of that superficial bleaching lies underneath, where chlorophyll and other plant pigments have broken down. Hawley compares it to cell-damaging reactive oxygen species in humans—the reason behind urgings to consume antioxidants for health.

“It's actually a very similar mechanism as to what's happening with these chlorophylls in the plants,” he says.

With photobleaching, through several very specific steps, reactive oxygen species generated in the cannabis plant pull electrons off chlorophyll. “When that happens, chlorophyll no longer has the means to hold itself together, so it basically disintegrates.” Hawley says. “Chlorophyll is what makes plants look green, so if it goes away, you're just left with white floral bud tissue.”

What Clues Reveal Photobleaching Has Started?

Hawley explains that photobleaching doesn’t announce itself with early morphological cues in the leaves. Instead, you may go into your grow and notice the upper inflorescences look a bit pale, or you may discover the very tips of plants are totally white. “Those are signs of things to come,” he says.

Although an inexperienced grower could possibly misdiagnose photobleaching as a nutrient deficiency, Hawley says the two look noticeably different.

And, while chlorosis is still a breakdown of chlorophyll, it works through a different means.

“[Chlorosis] is basically chlorophyll being scavenged and reallocated in the plant,” he explains. “You'd probably see that more in the leafy tissue and it would be a little bit more gradual. You wouldn't see such a stark, bleached floral bud.”

What Light Intensities Trigger Photobleaching?

With the right light quality, Hawley explains that you can avoid photobleaching even at light intensities reaching 2,500 PPFD (photosynthetic photon flux density, measured in micromoles per meter squared, per second). “We haven't tested higher than that just because the sheer commercial practicality of putting any more light on the canopy than that becomes pretty unreasonable,” he says. “Economically, it stops making sense.”

However, the Fluence team has seen photobleaching occur at 800 micromoles or lower with lighting rich in red light.

Courtesy of Fluence

“We’ve even had the very rare cannabis cultivar that would bleach around 800 micromoles with white light, but that's the exception. Most cannabis cultivars do appear to tolerate white light without problem,” he adds.

Hawley says most growers run around 1,300 to 1,500 micromoles without problems. But higher intensities bring higher yields.

“The sweet spot, if you have the infrastructure to support it, that we see is around 1,850 to 1,900,” he says.

But be mindful of the cultivar caveat, he stresses. Certain cultivars may bleach much, much lower.

Fluence research has shown that light quality near 60% to 65% red is enough to induce bleaching, even at conventional intensities such as 1,300 PPFD. “Honestly, it's pretty surprising to me, because when we pull [red light] down to the 40-something percent range, it’s a non-issue,” Hawley says.

He explains that the relative fraction of red light—not the absolute quantity of red light—seems to make the difference.

With light quality in the 40% red range, as with Fluence’s broad spectrum R4 lighting, photobleaching doesn’t seem to occur even at light intensities hitting 2,500 PPFD. “It does seem to be something about the ratio and balance of red amongst everything else,” Hawley says.

The most important point to understand is that photobleaching doesn’t occur with a more balanced broad spectrum. “I theorize that that's because we're balancing the energy across the entire range of PAR or photosynthetically active radiation. We not focusing that energy into a narrow peak,” he adds.

How Does Photobleaching Impact Crop Yield and Quality?

For growers struggling with photobleaching, impacts on yield and quality, particularly secondary metabolites, are primary concerns. “Honestly, photobleaching shouldn't have an enormous impact on either of these things,” Hawley says.

Yield is similar to a tomato, he explains. Cannabis flower, like the tomato fruit, doesn’t rely on high levels of local photosynthesis to put on mass.

“The buds do so little of that, that it doesn't really impact the yield all that much,” he says.

With quality, separating correlation and causation complicates things. Hawley has seen cases where there is a correlation between photobleaching and lower concentrations of cannabinoids and terpenes. But he’s also seen photobleached plants with cannabinoid and terpene concentrations equal to plants grown with no photobleaching under white light.

“It's really tough to say that photobleaching causes a decrease in cannabinoid and terpene concentration, but there may be a correlation. But it's also probably fair to say, photobleaching aside, a more red light quality induces a lower potency—and disentangling those two things is pretty tough,” Hawley says.

How Can Growers Avoid Photobleaching Altogether?

If photobleaching hits your grow in the middle of a flower cycle, Hawley says reducing light intensity is the only way to stop what’s underway. But a better approach is to use light quality that avoids photobleaching even at high light intensities.

“The biggest thing is to use the right light quality. If you're using the right light quality, you can go basically to the highest intensity you can achieve in your facility with very, very little risk of photobleaching. So that's the very best thing you can do,” Hawley says.

He adds that proper light quality enables growers to push to higher intensities, while light quality more rich in red demands reduced intensity instead. “But when you reduce intensity, you're also reducing yield. Most cannabis producers are in the business of making money. They would like yield to be high,” Hawley says. “And to get the highest yields, they have to use a more balanced, more white spectrum with less red.”

When Jake Van Wingerden launched SunMed Growers’ first cannabis greenhouse in 2017, he brought a lifetime of horticultural experience to the table. A third-generation grower from one of ornamental horticulture’s most-celebrated families, Van Wingerden equipped the 70,000-square-foot Dutch-style greenhouse with supplemental high-pressure sodium (HPS) lighting.

Looking back on what’s now known as Phase One, Van Wingerden says budget drove the choice of HPS over light-emitting diode (LED) technology. With a finite amount of cash and a tight schedule, he was focused on meeting the project’s deadline. He recalls, “I honestly didn’t put too much thought into it—HPS or LED—because I wasn’t up to speed on the LED light world.” But his base of lighting knowledge soon changed.

Running Unintentional Lighting Trials

Coming from ornamental bedding plants, Van Wingerden wasn’t accustomed to running a 52-week-a-year crop under supplemental lights. As he puts it, “Maryland has many cloudy days, and wintertime light stinks most of the time.”

When SunMed cultivation launched and electric bills rolled in, lighting got his attention. But utility expenses weren’t the biggest eye opener as months progressed.

“That first year, we saw dramatic differences between our summertime crops and our wintertime crops as far as potencies and yields. So, it was very evident within the first year or year and a half that we needed to put more lights in here,” he recalls. “Go a week with no sun in the wintertime, you’re losing money.”

Van Wingerden soon started analyzing the benefits of LED lighting versus HPS. “It was a clear distinction, specifically in electrical usage,” he says. “Making the decision to go with LED was fairly easy.” Once he decided to supplement SunMed’s existing HPS lighting with LEDs, his vendor search led him to Fluence and a relationship that, like his cultivation facilities, has grown.

As SunMed prospered, Van Wingerden began designing Phase Two to bring his cannabis cultivation facilities up to 250,000 square feet, with 190,000 square feet in canopy. After experiencing the benefits of Fluence LEDs versus HPS lighting firsthand, he chose to go with Fluence again for the expansion.

Completed in 2021, Phase Two of SunMed Growers launched with Fluence LED supplemental top light, the VYPR Series. But more changes were ahead.

Analyzing the Math of Payback

Courtesy of Fluence

Shortly after Phase Two launched, Van Wingerden’s advisory team suggested doubling the new greenhouse’s supplemental lighting. Led by his long-time consultant Royal Heins, and including Bruce Bugbee and Mitch Westmoreland from Utah State University’s Crop Physiology Laboratory, the team has been conducting on-site cannabis research with SunMed for about one year.

Van Wingerden recalls when the team shared research showing a linear increase in yield related to increased light intensity. “It was a 45-degree angle. The more light you give, the more yield this plant gets,” he says. Then he saw it on a spreadsheet—the cost of the fixture, the cost of the electricity, and the price per gram he could get. “It was a complete no-brainer decision to increase the light,” he says.

“When you rely on the sun for your primary light source, that sun doesn’t shine its brightest every single day. But the plant itself can absorb the brightest sunlight you can give it every single day,” he says. “When we spreadsheeted it out, I saw what we were losing based on the number of days we’re not getting that ideal light. It was millions of dollars of potential sales we were losing by not having it.”

Van Wingerden stuck with the Fluence horticulture team for the additional lighting. “They’re very customer-oriented and -focused. And that speaks to me because that’s how I try to run my companies,” he says.

The additional lighting gives SunMed the ability to provide plants with enough supplemental light to keep Daily Light Integrals (DLI) at 40 to 50 moles of light per square meter per day, 365 days per year. “It was a multi-million-dollar investment to do that, but we think it pays back within a year with the additional yield that the greenhouse will give us,” Van Wingerden says.

Finding Efficiencies and Balance

SunMed’s newly doubled Phase Two lighting is now installed and functional. But the team is turning it on in phases, taking time to finesse growing practices and other factors to accommodate the effects of increased light intensity in the grow.

“Cannabis is a plant that can absorb a tremendous amount of light. When you first get into this industry, how much it can absorb takes you by surprise. And when you get up to this type of light level, everything else has to accommodate,” Van Wingerden says.

“All of a sudden it’s a different greenhouse and everything else has to catch up,” he explains. “More light means more water, more water is more feed, and you have to make sure everything stays in balance. That’s our work in progress.”

When growing at SunMed’s scale, Van Wingerden says it’s all about that balance between light, irrigation, CO₂, feed and plant growth. “It’s all very synergistic. You can’t just turn one on,” he says. “It’s like a lever. You push one lever up, all the others have to adjust as well. And so that takes a little bit to dial in, but we’re getting there.”

Van Wingerden says actual energy savings in the switch to LEDs are hard to quantify: “Since 2017, we’ve been in continuous construction growth mode. I keep adding and building and adding and building.” As the grow expands, so do SunMed’s electrical bills, but Van Wingerden points out that the data on energy savings per watt with LEDs (to the tune of 40% greater efficiency, he says) is clear. And so are the potential gains being turned into profits.

With plans for SunMed’s Phase Three in motion, including a bump to 380,000 square feet of canopy, Van Wingerden is sold on high light intensity, LEDs and the Fluence team. “Really what has kept me a loyal customer is just their level of customer service and the ease to doing business with them,” he says. “They treat us right.”