cracking the code between light, genetics, and climate

When growers talk about “dynamic lighting,” they often mean spectrum. But before you even get there, there’s the other side of the coin: dynamic DLI targeting. “Plants are photon counters,” says Theo Tekstra from Fluence. “It’s not only about the light intensity at a given moment, but about the total photons a plant receives over the day and the cycle – and how you get there.”

That might sound straightforward, but in practice it’s anything but.

© Fluence BioengineeringA high PPFD (up to 1200 µmol m-2 s-1 ) research compartment at Vertify in The Netherlands, where the Cultivating for Compounds consortium does research on crop responses in various lighting, substrate, nutrient and watering regimes on various varieties

PPFD, DLI, and genetics
The first question is: how much light can your genetics handle? Some cultivars protest loudly at 800 µmol·m⁻²·s⁻¹, while others, like Blue Dream, can happily push past 1,500. “It’s like Formula 1 racing,” Theo says. “At 1,500 µmol, everything has to be on point – air distribution, dehumidification, substrate management, temperature. If you get it wrong, you don’t just lose speed. You lose the crop.”

That’s why starting at high PPFD is rarely the best move, especially for new facilities. “Most companies don’t fire up at 1,200 right away. They need to learn their rooms and their cultivars first, then push the limits gradually.”

And in mixed rooms – common in large facilities – light zoning becomes critical. If your cultivars have very different PPFD tolerances, you’ll need to decide which varieties belong together. “Those decisions need to happen before you even talk about light strategy,” Theo notes.

Substrate, water, and climate pushback
Light isn’t an island. Choosing too small substrate volume, for example, plus high light intensities mean rapid dry-back cycles that can be difficult to manage. More photons also mean more transpiration – and that shifts the whole climate equation.

“At 1,500 µmol, plants evaporate so much they can actually cool the room. You may find yourself needing to heat at the same time you’re dehumidifying,” Theo explains. “That’s a tough balance, and some installations simply can’t handle it. Let’s not forget that 20% of evaporation happens during the night at lower temperatures, and that there are peak moments in evaporation. Be sure to define your climate envelope correctly since low temperatures and dehumidification don’t always agree with each other.”

It’s a reminder that the limiting factor isn’t always the fixture – it can also be the climate system behind it.

The greenhouse case: supplementing the sun
Dynamic DLI targeting takes on a different shape in greenhouses. The job here is balancing sunlight with LED supplementation. Winter in northern Europe makes the point painfully clear: “In the Netherlands, I can get only 2–3 moles per day, but the DLI crop target is 43 moles per day. LED becomes my main light source,” Theo says.

Even in southern Europe, the gap isn’t trivial. In Lisbon in July, peak summer, Theo still sees the need to add 20-25% supplemental light to reach crop targets. “People assume the summer sun is enough, but in reality you still need to fill in.”

And the farther north you go, the steeper the challenge. Ukraine and Portugal for example receive quite a different light sum in in winter, so growers in Ukraine need to supplement at 800 µmol, compared to 650 in Lisbon, just to hit the same target DLIs. The difference shows up in electricity bills and CapEx.

Photon acclimation: not too much, not too fast
Photon delivery aside, there’s also the pace of change. Shifting from veg to flower means a shorter photoperiod – so unless you raise PPFD, your plants will be starved of photons right when they need them most. But you can’t jump from 700 to 1,200 overnight. “You need to step it up gradually,” Theo says. “That’s photo acclimation.”

Ramp-up and ramp-down also matter within the daily cycle. Sudden lights-on spikes humidity in the room; sudden lights-off is even worse. “A soft ramp at the start and especially at the end can save you mold and mildew headaches in flowering,” he adds.

Efficiency vs. practicality
At the end of the day, every photon results in photosynthesis – but not all photons are equal. Blue photons cost 1.6 times more energy to generate than red ones. Broad-spectrum solutions exist because facilities rarely grow just one cultivar, and there’s still plenty of debate around far-red, UV, and under-canopy lighting.

That, however, is where Part Two of this article comes in, when we dive into dynamic spectrum management. For now, the lesson is simpler: DLI is not just a number, it’s a balancing act between many limiting factors, and grower skill.

“Driving at 1,500 µmol is like F1,” Theo says. “If you’re not experienced, it’s better to not put your Tesla in ludicrous mode for the first ride. You’ll still get to your destination – but without crashing the crop on the way.”

Stay tuned for part 2!

If you can’t wait for part 2, we invite you to join the upcoming Fluence webinar “Dynamic lighting in cannabis cultivation: strategies that work” on Tuesday 16th September, 14.00 CEST. Dr. David Hawley, Research & Development Lead, and Dr. Sabrina Carvalho, Research Manager EMEA, will connect cutting-edge science with practical grower applications. You’ll learn how to make dynamic lighting work in your facility with clear guidance on infrastructure, controls, and ROI.

For more information:
Fluence
fluence-led.com

cracking the code between light, genetics, and climate – pt. 1

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