How to Choose Horticultural Lighting for Wholesale (7-Step Checklist)

For the last four years, I've handled purchasing for a commercial greenhouse operation—ornamental annuals and vegetable starts, about 65,000 square feet of covered bench space across two sites. My title says office manager. The actual job is internal buyer: I chase quotes, collect certificates, and translate between what the head grower wants and what the finance team will approve.

This article is the checklist I wish someone had handed me in 2022, when we started replacing high-pressure sodium fixtures with LED. It applies whether you're a large grower placing a bulk order or a grow light distributor deciding which horticultural lighting manufacturer to carry. I used it when evaluating Heliospectra, and I would use it for any brand. There are seven steps, and the order matters more than people think.

Step 1: Start with a DLI target, not a wattage

Nearly every RFQ I received in that first year started the same way: “we need 600-watt fixtures.” Watts are easy to compare. They just do not tell you whether the crop gets enough photons on the shortest day of the year.

The number that matters is DLI, or daily light integral, measured in mol/m²/day. Think of it as how much useful light the crop receives over a full day. DLI comes from sunlight through the greenhouse glazing plus supplemental lighting. If you know your target DLI, your winter sunlight, and roughly how much light the roof blocks, you can work backwards to the number of photons you need to add.

Before I talk to any sales rep, I ask our grower:

• What DLI does the crop need in the rooms we plan to light?
• What is the greenhouse transmission in the worst months?
• How many hours per day can we run supplemental light?
• Does the target change at a certain growth stage?

“I don’t care how many watts the fixture pulls,” our head grower likes to say. “I care how many photons arrive at the bench over 12 hours.”

That sentence changed how I compare products. Your first deliverable is therefore a written DLI target, not a fixture count. If that number is blank, every later comparison is guesswork.

Step 2: Demand photometric files, not a single PPF number

PPF (photosynthetic photon flux) tells you the total photons the fixture emits every second. It is useful. It is not enough. Two fixtures with identical PPF can light a greenhouse completely differently, depending on optics and board layout.

Ask each manufacturer for an IES or LDT photometric file. Load those files into a lighting tool, or ask their sales engineer to show you a PPFD map at your actual mounting height and spacing. If they cannot produce it, treat that as a red flag. When you are a distributor, the question will eventually come from your own customer: “Why are the edges darker in this bay?”

Here is a quick culture test. Search for “Heliospectra grow light” or any other brand you are evaluating, and count how many clicks it takes to go from the product page to a photometric file. Three clicks is a good sign. Forty-five minutes of clicking through PDFs is also information, and it is information you can collect before you order.

Step 3: Compare photon efficacy at the wall

Once I have a short list, I compare efficiency: PPF divided by input power at the wall, expressed in μmol/J. The phrase “at the wall” matters because it includes driver losses, not just the LED board.

It is tempting to think you can sort by PPF per dollar. That approach ignores the cost of electricity for the next ten years. Here is an example of what I mean. Two fixtures, each producing 2,100 μmol/s. At 3.0 μmol/J, one draws 700 W. At 3.6 μmol/J, the other draws 583 W. Over 4,000 running hours per year, that is roughly 470 kWh per fixture per year. Multiply by 400 fixtures and $0.12/kWh, and you are looking at about $22,500 per year before maintenance.

That is why I always look for the exact input wattage on the spec sheet. If a datasheet lists PPF but hides the wattage, e-mail the manufacturer and watch how long it takes to get a straight answer. The response time will tell you what your own customers would experience later.

A second caution: ask whether the published efficiency is measured at 25°C or at an operating temperature closer to a real greenhouse in July. Values can drop when driver compartments get hot. I do not mean the marketing number is a lie; I mean it is measured in the best possible conditions.

Step 4: Decide how much spectrum flexibility you actually need

I am a purchasing person, not a plant scientist, and I will not tell you exactly which spectrum to run. That decision belongs to the grower. What I can tell you is that “full-spectrum” means different things on different datasheets.

Compare the spectral power distribution charts, not the label. Check the far-red part of the graph if your crops are photoperiod-sensitive. And ask what happens to the spectrum when the fixture is dimmed to 30 or 50 percent; some designs shift noticeably, while others hold the same balance.

Then ask a business question: how many crop types and growth stages will this fixture need to serve? In a multi-crop greenhouse, adjustable spectrum lets one SKU cover more situations. Heliospectra horticultural lighting, for example, includes products built around adjustable intensity and spectrum, which is useful for an operation that grows a mix of crops. If you run one crop in one house, a fixed-spectrum fixture with a good efficacy number and a lower price may serve you better.

Do not pay for flexibility you will not use. Do not buy a fixed spectrum when your internal grower is already telling you they need separate far-red channels next year. Either mistake gets expensive halfway through a wholesale order.

Step 5: Check the hardware against your actual greenhouse

An LED fixture may be designed for a dry warehouse. A greenhouse is the opposite: condensation drips from the glazing, irrigation water gets sprayed around, and the air can be full of fertilizer dust or sulfur vapor.

• IP rating. For wet or damp locations, I look for IP65 or IP66. If the fixture is rated IP20 and the vendor says it will be fine “as long as you mount it correctly,” get that promise in writing.
• Corrosion resistance. Check the housing and fasteners. In a greenhouse with sulfur vaporizers, unprotected electronics and hardware do not age well.
• Serviceability. LEDs themselves rarely fail first. Drivers and connectors do. Ask where the driver sits, whether it can be replaced without cutting cables, and what a spare driver costs.

The question I forgot in an early quote was simpler: when something breaks, do we repair the fixture or replace the whole unit? If you have 600 fixtures, a sealed unit that cannot be repaired becomes a recurring capital expense, not a one-time purchase. For a grow light distributor, spare driver stock should be part of the margin plan, not an afterthought.

Step 6: Verify the controls story before installation day

A great fixture with poor controls will make your head grower unhappy for years. The controls conversation should happen before the purchase order, not on the day the electrician arrives.

Ask what control signal the fixture supports: 0–10 V, PWM, DALI, or a proprietary system. Then ask which greenhouse climate computers the manufacturer has tested with. If the only answer is “we have an API,” and you do not have an integrator on staff, count that as extra cost, not a feature.

Ask how low the fixture actually dims. Some lights dim smoothly to 1 percent; others cut off at 10 percent. If you use sunrise and sunset ramping to avoid shocking plants, that low-end behavior matters. If the light is supposed to follow a DLI setpoint, make sure the sensor and algorithm are part of the delivered package, not a separate project.

We rejected one otherwise strong fixture because it only worked with a proprietary app. The app worked fine, but it did not talk to our climate computer, which meant 400 fixtures on a separate manual schedule. No thanks.

Step 7: Audit the business behind the brand

At wholesale scale, you are choosing a greenhouse lighting manufacturer that will be on the other end of a warranty claim, a spare part request, or an OEM conversation. So audit the business, not just the beam spread.

Ask for the warranty document and read what it covers. Does it include the driver? Who pays shipping on a failed unit? Is the claim process replace-first or inspect-first? Also ask how long after a model is discontinued the manufacturer commits to providing spares. Those answers matter more than the difference between two PPF charts.

If you are a grow light distributor or an OEM/private label buyer, add the channel questions: minimum order quantities, lead times for 50 units vs 1,000 units, packaging options, and whether the manufacturer will supply dedicated SKUs with your brand. Get the answers in writing.

Compliance deserves its own line. Do not accept “we are certified” as a statement. Ask for a listing number, check it against the official database, and confirm that the model number matches the fixture you intend to buy. A product can be UL listed for one market and not listed for another. A DLC listing has requirements that change, so verify current qualifications rather than relying on a sales PDF.

This is where Heliospectra earned our attention more than on any single output number. When we evaluated Heliospectra grow light products, the specs were competitive, but the real difference was that the compliance documents and OEM/private label answers were easy to verify. For a wholesale buyer, verifiability is a feature.

Three expensive mistakes I still see

If you only read the steps, read this section too. These are patterns that show up after people sign wholesale orders.

• Comparing fixture price instead of cost per photon delivered. A cheap fixture can cost more in electricity in year two than the price difference in year one. Put the energy cost into the comparison, plus spares and expected service life.
• Skipping the pilot run. Photometric files are necessary, but they are not proof of how a fixture behaves on a bench in July. Run a full crop cycle in one bay before committing to hundreds of units. It slows the process by a few weeks and saves a lot of rework.
• Assuming similar specs mean similar performance. I made that mistake in 2023. Two fixtures looked almost identical on paper, so I ordered based on price and availability. The installed results were different enough that we re-tested the second bay. Lesson learned: verify the product that actually arrives, not the product in the brochure.

One final note: regulations and incentive lists change. Verify current certification requirements in your market before you order, and ask the manufacturer to confirm that the fixtures you are buying match the documentation on the day they ship.

If you take one thing from this checklist, take this: compare photons per day at the canopy, then verify every claim until it is boring. The brands that make that easy are the ones worth calling back when you need a second greenhouse.