In winter, supplemental lighting isn’t just about meeting a crop’s DLI target — it’s also about managing the ripple effects on heat, humidity, and airflow.
For growers who treat lighting as an isolated decision, environmental swings can stress plants and overload equipment.
“Lights produce heat,” said Justin Morse, Design Consultant at LLK. “Traditionally, one of the benefits of using HPSs in the winter was that they were a source of heat. And so maybe you would use less natural gas during that time… or propane. The one challenge, though, is when the lights turn off, you have a sudden lack of that heating supply. And plants are transpiring still.”
That mismatch — heat disappearing while moisture remains — can trigger condensation, microclimates, and disease pressure.
Right-sizing HVACD equipment is an important part of the solution, in addition to designing lighting, heating, cooling, and airflow as a coordinated system.
Why Rapid Swings Are Risky
Plants don’t like sudden environmental changes. Justin sees this when the lights are turned on or off abruptly.
“Generally, plants do not enjoy quick, rapid changes to their environment,” he said. “[Ramping lights] lessens the impact on HVAC, as it won’t have to react as suddenly to environmental changes.”
That’s why LLK often recommends dimming LEDs up or down over 30–60 minutes, giving both plants and equipment time to adjust.
Without strategies like these, operators risk the classic winter problem: warm, humid air hitting cooler surfaces as lights cut off, leading to condensation across benches or blackout curtains.
Shade, Dimming, and Deadbands
Lighting integration would be easier if it were just about heat. But throw in shading systems, dimmable LEDs, and variable sunlight, and the feedback can get messy fast.
Justin stressed the importance of anticipating these shifts rather than reacting to them after the fact.
“Outlining all the different periods on a daily basis and planning that when you’re doing the initial HVACD infrastructure build out [is] critical,” he said.
“[Lighting] is going to interact with the systems that change and affect the environment. That can be plants themselves. That can be the HVAC equipment, dehumidification. And so zooming out and taking a look at that is an important part of planning it out. Sometimes folks look at peaks and valleys, but not necessarily how things are changing during the middle,” he explained.
In design, this means mapping conditions and system inputs across pre-dawn, ramp-up, midday, ramp-down, and dark periods, then designing controls to anticipate rather than chase those shifts.
It also means engineering airflow paths that continue working even during blackout curtain closure, often by using light traps to allow ventilation without leaks. Consider: Is a blackout curtain effectively reducing overall air volume while plants continue to transpire?
Deadbands — small tolerance zones where lights and shade don’t react instantly to every fluctuation — also help stabilize the environment.
Integrating deadbands corresponds to fewer sudden swings in PPFD and fewer temperature and humidity jolts for HVACD to handle.
The Biosecurity Angle
Lighting can introduce unexpected biosecurity risks if it isn’t considered alongside other systems.
Justin recalled one traditional approach growers sometimes used to sanitize: closing the greenhouse tight and letting solar gain spike temperatures to “cook” pathogens or insect eggs.
That may have been popular in the HPS era, but it’s more risky with LEDs.
“LEDs are high tech, with sensitive electronics on board. Understanding the risks, I don’t advise to cook your greenhouse using some of the older methods, particularly if you have LEDs.”
Maintenance practices matter too. Aerosolized oils or foliar sprays can deposit residues on LED lenses, slowly lowering light output if fixtures aren’t cleaned.
This is just one example of how lighting systems are intertwined with every other aspect of production.
Shade, Space, and System Priorities
The biggest consideration in integrating lighting is how those fixtures coexist with the systems already in place. Shade systems, for example, often dictate what’s possible.
“Lighting infrastructure is generally dispersed throughout the entire cropping area,” Justin explained. “Moving shade systems generally have the right of way, and you need to work around them.”
In addition to being mindful of existing infrastructure, “Is there a crop growing in there that you need to either schedule around or be careful with? Thinking about that up front, and then rebates, too.”
That means installation planning has to account for how crop production, lights, shades, and HVAC equipment interact in real time.
If controls aren’t sequenced properly — or if fixtures are mounted without considering curtain movement — it can result in conflicts that create both operational inefficiencies and crop stress.
By treating shading and lighting as complementary systems rather than competing ones, operators can avoid constant adjustments and facilitate a steadier environment for HVACD equipment.
The Takeaway
Greenhouse lighting doesn’t exist in a vacuum. Every decision about fixtures, scheduling, and controls has consequences for heat balance, humidity, and airflow.
Treating lighting as a standalone add-on is a recipe for winter stress, both for crops and for infrastructure.
“Lighting… it is tied with everything,” Justin said.
By planning lighting and HVACD as a single system — ramping rather than flipping, setting deadbands to avoid feedback loops, maintaining airflow through dark periods, and building biosecurity into cleaning and maintenance — greenhouse operators can avoid the pitfalls of shorter days.
