Every fall, as daylight hours shorten, greenhouse operators find themselves at a crossroads. The sun is fading, yields are at risk, and the most obvious solution — turning on the lights — can quickly drive up operating costs.
Justin Morse, Design Consultant at LLK, sees this tension play out every season. When asked about the main lighting challenges greenhouse operators should plan for in the fall and winter, he said:
“Mainly increased operational costs due to using more electricity. That’s the big one. Light pollution can be a concern, too, depending on where you are, what you’re growing, and what kind of photoperiod you need to supplement. But I think the big one is just month over month: the operational costs of running supplemental lighting and balancing that with the yield.”
That balancing act — how much light a crop truly needs versus what it costs to deliver — defines whether a grower survives the winter profitably or starts eroding their margins.
When Plants Don’t Get Enough Light
Experienced growers know the risks of under-lighting. Seasonal drops in DLI, if not managed, show up quickly in plant quality.
“If you’re not meeting the requirements of the crop, a lot of things can go wrong,” Justin explained.
For example, “You can have defects in the crop, like slowing growth. Plants get leggy or have longer internodal growth. You can have flower development that’s delayed or just flower abortion. You can have nutrient disorders because there’s just overall less photosynthesis… sometimes you can even confuse some of these crop defects with a virus.”
But light isn’t only for photosynthesis — the effects of lighting ripple into nutrition, morphology, and pest resilience. Weaker leaves, for example, can be more susceptible to insect damage.
Many operators will turn to supplemental light as a hedge against production losses in the face of seasonal sunlight reduction.
So, if light can be considered insurance during the fall and the winter, and there’s a cost to that, how do you know when you’re investing too much?
The Problem of Overestimation
Justin sometimes finds that growers overstate their lighting needs when requesting a light layout. “I’ve seen it that they estimate more than they need,” he said.
“If they say, ‘I need 800 micromoles,’ sometimes they might not subtract the pie slice that they would get naturally, even in winter. Even if it’s low — five to ten DLI on an overcast winter day. If you can subtract that with your photoperiod, then [it’s] ‘Oh, I actually only need 600 micromoles.’”
That “pie slice” of natural winter light might not be enough to grow a crop on its own, but it still counts toward the DLI bucket.
Forgetting to include it can lead to oversizing a lighting system, wasting capital on fixtures, and overspending on electricity every month.
The ROI Equation
So how do you decide whether supplemental light is truly worth it? Justin boils it down to one phrase: “The juice has to be worth the squeeze.”
The equation includes more than just fixture efficiency. Electricity rates — especially time-of-use tariffs — can turn profitable hours into financial losses.
Crop value is another factor: extra DLIs might matter greatly for vine crops where fruit quality is at stake, but might not pay back for leafy greens.
Labor schedules, shading strategies, and even local ordinances around light pollution can all tilt the calculation.
Smarter Use of Controls
Even once a system is in place, operating strategy matters. Justin pointed to dimming and shade integration as examples where growers sometimes overlap their tactics unfavorably.
“Particularly when you have LED with dimming and shade control… sometimes you might have too much [light], but then it covers. And then now you might be dipping below [the threshold]. And so you have a feedback that you need to tune out, and it really requires monitoring — maybe tuning the system, and allowing somewhat of a deadband gap as well, so that things aren’t just constantly bouncing back and forth between not enough light [and] too much light.”
Other strategies, like ramping lights on and off gradually, help stabilize the environment and avoid stressing HVAC systems.
Some operators experiment with light banking — extending photoperiods in the morning or evening to avoid mid-afternoon solar gain and peak electricity rates.
The right approach depends on the crop and the facility’s infrastructure, but in each case, controls provide levers to reduce costs without sacrificing production.
The Hidden Costs
Fixtures and electricity aren’t the only things to consider when calculating lighting ROI.
Justin highlighted several risks that can trip up operators who don’t plan ahead.
Dirty power, for example, can cause major problems for sensitive LED drivers. Particularly in rural areas, it can help to investigate service with a power monitor ahead of major renovations.
Newer electrical codes requiring GFCI breakers for horticultural lighting have introduced additional complexity in new builds.
And something as simple as lens cleaning can impact delivered light.
“Investigate if you can clean the lenses on the optics of your LEDs,” he said. “You can get total overall output dropping with the accumulation of — say, fogging or a spray or something like that — and it’ll just build up and build up.”
Use a light meter to compare supplemental light output year over year.
Planning With the End in Mind
For LLK, supplemental lighting always comes with additional considerations: crop thresholds, energy economics, infrastructure realities, and long-term ROI.
The growers who come through winter profitably are the ones who do the math upfront, subtract that “pie slice” of natural light, and design with their future needs in mind.
“So many things in cultivation are interconnected… usually when you’re changing one thing, there are other things that are going to be affected by it,” Justin said.
And you have to weigh that thought with, “Does it make sense from an economic perspective? You can pour more light on, but are you getting value out of it that makes it worthwhile to do in the first place?”
In the end, fall and winter lighting isn’t a question of how much light you can give a crop, but whether that light delivers a return worth the investment.
