If you’ve ever worked in a commercial grow operation, a backyard high-tunnel, or even a research lab testing cannabis under supplementary lighting, you’ve probably wondered: how often should I replace my horticultural lighting? As someone who’s spent the last eight years talking daily with growers across North America and Europe, running product tests in our own 10,000 sq ft test greenhouse, and troubleshooting lighting failures at 2 a.m. during peak growing seasons, this is not a question with a one-size-fits-all answer. It’s a question that depends on what kind of light you’re using, how it’s set up, what you’re growing, and how you define “end of life.” Let’s break this down like we would with a grower calling our support line—no jargon, just real-world science and experience you can actually use. Horticultural Lighting
First, let’s get one misconception out of the way: horticultural lighting isn’t like your kitchen overhead bulb, where you replace it when it burns out. Most growers expect linear or near-linear performance from their lights, because even a 5% drop in light output over a few months can mean a 5-7% hit to your yield, per data from the University of California’s Department of Environmental Horticulture. That’s the difference between turning a profit and breaking even for a 10,000 sq ft leafy greens farm, or between harvesting a full crop and losing 20% of it for a specialty herb grower.
So let’s start with the two most common types of horticultural lighting, because their replacement timelines are night and day. High-Pressure Sodium (HPS) lights, the old workhorse that’s still used in many older facilities, have a well-documented lifespan. HPS bulbs are rated for 10,000 hours of rated life, but that’s the point at which their light output drops to 70% of their original value—the industry standard for “end of useful life” for horticultural lighting. What most growers don’t know is that HPS bulbs usually start dropping off sharply after 8,000 hours. We’ve seen that in our test greenhouse: an HPS bulb that’s been on for 8,500 hours puts out usable light, but the spectrum shifts too, leaning more red and less blue, which is bad for vegetative growth and can cause stretching in young seedlings. We recommend replacing HPS bulbs every 8,000 hours of operation. If you run your lights 18 hours a day, that works out to about 14.5 months. If you run them 24/7 for a flowering crop, that’s closer to 11 months. Simple math, right?
Now, the newer LED horticultural lights, which are what we manufacture, work very differently. LED lights have a much longer rated lifespan, usually 50,000 hours, but again, that’s a raw hour count, not useful life. The key metric here is lumen maintenance, and for quality horticultural LEDs, manufacturers test for L70 lifespan—when the light output drops to 70% of original. For our own line of commercial LEDs, we test to L80, meaning we only consider the light past 80% output as still useful for optimal growth. That changes the timeline. But here’s the catch: not all LEDs are equal. Cheaper, off-brand LEDs that you might find at a big-box home store for a grow tent might only hit L70 at 25,000 hours, because they use lower-quality diodes and heat sinks. Our LEDs, with high-efficiency Bridgelux diodes and passive cooling designed for 24/7 operation, hit L80 at 50,000 hours. That means if you run them 18 hours a day, that’s over 7.5 years of useful life. Run them 24/7, that’s a little over 5.5 years. But wait—this isn’t the end of the story for LEDs. Even before they hit that L80 mark, two other things factor in: driver lifespan and spectrum shift.
Drivers are the part of LED lights that convert wall power to power the diodes. They’re the most common point of failure, not the diodes themselves. Most quality horticultural LED drivers are rated for 50,000 hours, but we’ve seen cheap drivers burn out in as little as 15,000 hours. That’s a huge problem—because if your light’s driver fails, your whole fixture is useless, even if the diodes are still fine. So when we quote timelines to growers, we always tell them to account for driver replacement. We offer a 5-year warranty on our fixtures, which covers both diodes and drivers, but for growers who want to plan ahead, we recommend budgeting for driver replacement at around 40,000 hours, which is just before most drivers start to show wear. The other hidden factor for LEDs is spectrum shift. Even if a diode is still putting out 85% of its original light, over time, the blue diodes degrade faster than the red ones. That means your light will start leaning more red, which is great for flowering cannabis or tomatoes, but terrible for leafy greens like lettuce or basil that need balanced blue light to keep their leaves tight and prevent stretching. For growers of leafy greens, we actually recommend replacing LEDs every 6 years, even if they’re still at 82% output, because the spectrum shift is hurting crop quality. For flowering crops that thrive in red-heavy light, you can wait until you hit that L70 mark at 6.5 years.
Now, let’s talk about variables that can throw all these timelines out the window, because this is where most growers get tripped up. First is operation hours. This sounds simple, but many growers run their lights on timers that are off by 10-15%—they think they’re running 18 hours a day, but the timer is cutting it short or leaving it on longer. Over a year, that adds up to hundreds of extra hours, which shortens your light’s lifespan. Another big one is environment. If you’re growing in a hot, humid space, like a tropical greenhouse or a closed grow room without proper ventilation, your lights run hotter. Heat is the enemy of both HPS bulbs and LEDs—high temperatures speed up degradation of the filament in HPS bulbs and the diodes in LEDs. We had a grower in Florida call us last year, complaining his LEDs were burning out in 3 years instead of 5. When we walked through his space, we found he had the light fixtures mounted directly on the ceiling above his crop, with no air flow around the fixtures, so they were running 10-15 degrees hotter than their rated operating temperature. Once he adjusted his ventilation and mounted the fixtures 12 inches above the canopy, his lifespan jumped back to 5 years. That’s a huge difference—just a small adjustment to environment cuts replacement time in half.
Another variable: crop type. This is something I learned when working with a small craft cannabis grower in Oregon a few years back. He was replacing his HPS bulbs every 10,000 hours, but when he switched to our LEDs for flowering, he noticed his yield actually dropped in the third year of operation. We tested the light, and found that the blue light content had dropped by 12% after 4.5 years of use, even though the diodes were still at 83% output. For cannabis in flowering, that blue light drop meant his plants were stretching more, producing less bud. So for high-value crops that require consistent spectrum—cannabis, specialty herbs, microgreens, even ornamental flowers like roses—you need to lean towards the lower end of the lifespan range. For lower-value, high-volume crops like leafy greens that tolerate minor spectrum shifts, you can stretch that timeline out a bit more.
Wait, what about old bulbs vs. new technologies? I get asked this all the time. A few growers still swear by their 15-year-old HPS systems, and honestly, if you’re growing tomatoes in a high-tunnel where light quality is less critical, and you’re watching for the output drop, they can work. But HPS uses 2-3 times more energy than LEDs, so even if the bulb only lasts 11 months, the energy savings from LEDs will make up for the higher upfront cost in 1-2 growing cycles. We had a lettuce grower in Michigan switch from HPS to our LEDs 4 years ago, and he’s told us he’s only replaced one set of drivers so far, and his electricity bill is down by $12,000 a year. That’s a huge payoff.
Now, let’s talk about what the industry research says, to back up what I’ve seen in the field. A 2022 study from the International Society for Horticultural Science (ISHS) tested 12 different LED horticultural fixtures from 8 manufacturers, and found that for fixtures used 24/7 in commercial grow operations, average useful lifespan was 4.8 years for high-quality LEDs, compared to 0.9 years for HPS bulbs. The study also found that growers who replaced their lights at the L70 mark had a 6-8% higher yield than those who waited until the light burned out completely. Another 2021 study from Penn State Extension looked at cannabis growth under aging LEDs, and confirmed that spectrum shift after 4 years led to a 10% reduction in bud weight, even when light output was still at 85% of original. That’s not a small number—for a 1,000 sq ft grow, that’s thousands of dollars in lost revenue.
So how do you actually track this? We don’t just recommend guessing, or counting days. We recommend investing in a light meter that measures photosynthetically active radiation (PAR) over time. A good PAR meter will let you track your light’s output, so you can see when it drops to 80% or 70%, depending on your crop, and plan your replacement around that, not just arbitrary timeframes. For HPS lights, it’s even simpler: a quick check of the light’s color. If it’s looking more yellow than bright white or warm orange, that’s a sign the spectrum is shifting, and it’s time to replace it.
Now, let’s get to the part that matters most to you as a grower: what should you do right now? If you’re running HPS lights, start tracking your operation hours, and plan to replace bulbs every 8,000 hours, or immediately if you notice a drop in yield or spectrum. If you’re running LEDs, calculate your operation hours, account for your crop type and environment, and plan for full fixture or driver replacement around the 4-6 year mark, depending on your setup. But here’s the thing: every grow is different. If you have a 5,000 sq ft herb grow in a controlled environment, your timeline will be different from a 50,000 sq ft leafy greens farm in a greenhouse. That’s why we don’t just give generic advice at our company—we work with each grower to analyze their specific setup, crop, and operation, so we can give a timeline that fits their needs.
At the end of the day, the goal of replacing your horticultural lighting isn’t just to avoid a bulb burning out—it’s to maintain consistent, optimal light for your plants, which means consistent yield, consistent quality, and consistent profit. I’ve seen growers save thousands by replacing their lights too early, and lose tens of thousands by waiting too long. The sweet spot is finding that balance between avoiding unnecessary costs and not leaving money on the table because of aging lights.
If you’re not sure where your lights stand, or you want to upgrade to a more reliable system that’s tailored to your operation, our team of horticultural lighting specialists is here to help. We can walk you through testing your current lights, checking your environment, and putting together a replacement plan that works for your budget and your crops. No sales pitches, no generic advice—just real solutions from people who’ve been in the grow space with you.
References
Static Water/ Water Flow Module University of California Department of Environmental Horticulture, 2019. Lumen Maintenance and Crop Yield in Horticultural Lighting.
International Society for Horticultural Science, 2022. Comparative Lifespan Analysis of Commercial Horticultural Lighting Fixtures.
Penn State Extension, 2021. Spectrum Degradation and Crop Performance Under Aging LEDs for Cannabis Cultivation.
Horticultural Research Institute, 2020. Best Practices for Horticultural Lighting Operation and Maintenance.
UVLEDTEK Group
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