To choose LED grow lights for a commercial greenhouse, begin with two facts — what your crop needs and what your sunlight already delivers — and then judge every supplier proposal against the same yardstick: the fixture family that physically fits your roof height and canopy, the PPFD uniformity those fixtures actually deliver at your installed height, the cost per useful photon rather than per watt, and the after-sales and spare-parts support a multi-year installation depends on. The right choice is almost never the fixture with the biggest headline number; it is the proposal that best matches your crop, your structure and your budget, with figures you can independently verify.
Start from the crop and the sunlight — not from a fixture
A greenhouse is not a blank room. It already receives daylight, and your crop already has a known light appetite. Those two numbers — the daily light integral (DLI) your crop wants and the DLI your location and glazing actually deliver — set the entire supplementing job, long before you look at a single fixture. University extension work ties crop quality directly to DLI: Michigan State University Extension reports that plants grown under a DLI below 10 mol·m⁻²·d⁻¹ develop fewer roots and less shoot growth and can take up to twice as long to reach transplant size, while the e-GRO transplant guide (Owen, Ohio State University, 2025) places the optimal vegetable-transplant DLI at 10–15 mol·m⁻²·d⁻¹, with heavier feeders such as eggplant at 15–20. At the same time, a greenhouse transmits only a fraction of outdoor light — MSU greenhouse energy guidance notes structures can lose 60 percent or more of incoming radiation through glazing, framing and condensation. So the real question is not how many lights but how much of the crop DLI the sun fails to provide here, in this season, and that gap is what your LED top lighting must close. Our greenhouse applications page maps crop-specific starting points, and the Complete Planning Guide works through the DLI-gap calculation in full.
Match the fixture family to your greenhouse structure
Once you know the gap, the structure decides the fixture family — not the other way around. A tall, high-wire tomato or cucumber house needs high-output Greenhouse Top Lighting mounted near the gutter or truss, throwing light down into the canopy from above. A dense leafy-green or herb bench, or a double row where upper leaves shade the lower ones, may benefit from intercanopy lighting placed between or below the canopy to lift lower-leaf photosynthesis. And where you are fine-tuning spectrum or adding a specific wavelength, supplemental spectrum fixtures — far red, UV or other targeted bands — add a narrow job on top of the broad white canopy light. The trap is choosing the family from a catalogue photo: a fixture that is perfect for a 3-metre rack aisle is wrong for a 7-metre vine house, and vice versa. Measure your clear mounting height (fixture to the highest obstruction or canopy) and your row spacing first; the fixture that fits those two numbers is the one to evaluate.
Judge proposals by PPFD uniformity, not by watts or headline PPF
Two fixtures can share an identical wattage and an identical total output (PPF) yet deliver completely different light to your plants, because optics, spacing and mounting height change how that output lands on the canopy. What you actually grow under is PPFD — the photons arriving per square metre per second — and, more importantly, how evenly they arrive across the whole bench. Commercial layout guidance cited by LED Grow Lights Depot reports roughly 20–30 percent PPFD change per 5 cm of mounting-height error at close rack distances, and the same sensitivity applies at greenhouse scale: a photometric map drawn at the wrong height flatters the proposal. When you compare supplier offers, ask for a PPFD map at your real installed height and canopy, not at the factory test bench, and read the uniformity (the coefficient of variation or min/max ratio) as carefully as the average. A 10 percent lower average with 5 percent uniformity beats a 15 percent higher average with 30 percent variation, because uneven light makes uneven crops and uneven grades. The fixture-requirements article shows how the count follows from that target PPFD and your area.
Compare the real costs, not just the sticker price
The purchase price is the smallest and least interesting number on the page. A buying decision that ignores installation, running and maintenance can flip the ranking completely. The table below separates the four cost buckets and the trap in each, so you can ask every supplier for the same line items and compare like with like.
| Cost bucket | What to compare | The trap if you skip it |
|---|---|---|
| Purchase (fixtures and drivers) | Quoted price per fixture including drivers and mounts; volume tier at your quantity | Low fixture price with expensive proprietary drivers or mounts that lock you in |
| Installation | Brackets, cabling, labour, rigging access, electrical work per zone | Hidden rigging or rewiring cost that exceeds the fixtures on a tall house |
| Running | Input watts per fixture × hours per day × days per year × local $/kWh | A 10 percent efficacy gap compounds into five-figure energy cost over the install life |
| Maintenance and spares | Driver or module replacement cost, spare-part lead time, labour to swap | An integrated fixture that needs full replacement when one driver fails |
Running cost is where efficacy quietly decides the winner. Two fixtures that hit the same canopy PPFD but differ by 10 percent in efficacy will diverge in energy bills every hour they run, and a greenhouse lighting system runs for years. Ask each supplier for the real input watts at your target output, not the marketing wattage, and drop both into the formula above before you rank the bids.
Score the supplier, not just the product
A greenhouse install runs for years, so the company behind the fixture matters as much as the fixture itself. Score each bidder on the same short list: do they supply a photometric report at your height (not just a datasheet), the certifications your target market requires (ETL and DLC for North America, CE for the EU, and so on — never assume one certificate covers every market), a realistic lead time with batch-to-batch consistency, named spare parts with lead times, and an after-sales channel that answers in your timezone. The supplier-inquiry article lists exactly what to send so the quote already contains these items; the scorecard below turns the replies into a comparable score.
| Criterion | What good looks like | Red flag |
|---|---|---|
| Verified light data | PPFD map at your real mount height and canopy, with uniformity | Only a lab PPF number, no installed-height map |
| Market certifications | Correct marks for your country (ETL and DLC, CE, etc.) | One generic CE mark claimed for every market |
| Lead time and batches | Stated build slot, consistent batches across phases | Vague in stock, no batch-consistency plan |
| Spare parts | Named spares with lead times and a swap procedure | No spare strategy; full fixture replacement only |
| After-sales | Responsive technical channel, warranty terms in writing | No local support, verbal-only warranty |
A greenhouse selection and RFQ checklist
Before you ask for quotes, write down the few numbers that decide the recommendation. The checklist below is the same one our team uses to turn a vague request for greenhouse lights into a comparable set of proposals; send it to each supplier and you will receive offers you can actually rank.
Greenhouse LED selection checklist
- Crop and stage: what you grow and at which phase (sets the DLI and PPFD target)
- Location and glazing: country or region, covering material, any existing lights (sets the sunlight baseline)
- Greenhouse dimensions: ridge height, eave height, bay and row spacing, bench or gutter layout
- Clear mounting height: fixture-to-canopy or fixture-to-obstruction distance
- Supplemental target: the DLI gap you need closed, or recommend if unknown
- Photoperiod: hours of supplemental light per day in the target season
- Electrical supply: voltage, phase, watts per circuit, breaker rating
- Controls: dimming, scheduling, integration with your climate computer
- Quantity and phasing: fixtures now plus any planned expansion zones
- Target market: country or region of use (drives certifications and labels)
- Budget frame: not a hard number, but the cost buckets you care about most
- After-sales: required spare-part lead time and warranty expectation
With that checklist in hand, you can evaluate every proposal on equal terms — fixture family fit, verified uniformity, total cost of ownership and supplier support — instead of being pulled toward whichever bid opens with the largest PPF. When you are ready, send the checklist through our contact form and we will return a per-zone recommendation with the photometric map and assumptions stated up front.
Frequently asked questions
Should I choose top lighting, intercanopy lighting, or both for my greenhouse?+
It follows from crop structure and how much light the upper canopy steals from the lower leaves. Tall high-wire vine crops such as tomato and cucumber usually start with top lighting from the truss or gutter; dense low crops or double rows where lower leaves are shaded often add intercanopy fixtures between or below the canopy. Many houses use both, with intercanopy lifting the lower third that top light cannot reach. The right mix depends on your row spacing and canopy height, which is why the mounting-height and row-spacing numbers in the checklist matter.
Is it better to buy on watts, PPF, or efficacy?+
None of those three alone. Watts is just energy in, not light out. PPF is total light out, but says nothing about how evenly it reaches your plants. Efficacy (PPF per watt) tells you how efficiently a fixture converts energy to photons, which drives running cost — but only at your installed height and uniformity. Buy on the total cost of useful, evenly delivered light: required PPFD × your area, divided by the dollars, including running cost over the install life.
How much does greenhouse mounting height actually change the choice?+
A lot. Mounting height sets beam spread and overlap, which set uniformity. At close rack distances, commercial layout guidance reports roughly 20–30 percent PPFD change per 5 cm of height error, so a fixture specified at one height can underperform at another. Always ask for the PPFD map at your real clear height, not the catalogue height, and treat a proposal without that map as unverified.
Which certifications matter for a commercial greenhouse install?+
It depends entirely on the market. North America commonly expects ETL and DLC listings; the EU expects CE; other regions have their own marks. Certifications are not interchangeable, and a fixture lacking the right mark for your country can be refused at import or fail an inspection. State your target market in the RFQ so the supplier quotes the correct certification set rather than assuming one global mark.
Two quotes look similar — how do I pick between them?+
Score them on the supplier checklist, not the headline price: verified PPFD uniformity at your height, correct market certifications, stated lead time with batch consistency, named spare parts and after-sales. A lower sticker price with no installed-height map, vague certifications or no spare strategy is usually the more expensive choice once installation, energy and downtime are counted.
Can I light one zone first and expand later?+
Yes, and it is often the sensible path. A pilot zone lets you verify uniformity and crop response before committing the full house, and it de-risks the purchase. The trade-off is batch consistency: agree up front that later batches match the first in spectrum and output, and confirm the supplier can hold that across your phases. State the planned expansion in the RFQ so the quote covers continuity, not just the first zone.
Sources
- e-GRO / Ohio State University — Managing Daily Light Integral to Improve Vegetable Transplant Quality (Owen, 2025) — optimal transplant DLI 10–15 mol·m⁻²·d⁻¹, crop-specific ranges (eggplant 15–20).
- MSU Extension — How Low Can You Go? Low DLI Impacts Young Plant Quality (Wollaeger and Runkle, 2014) — DLI below 10 mol·m⁻²·d⁻¹ reduces roots and shoot growth and can double production time.
- MSU Extension — Greenhouse Energy Conservation Strategies (Runkle et al.) — DLI concept and greenhouse transmission loss of 60 percent or more.
- Purdue Extension — Measuring and Interpreting Daily Light Integral (Torres and Lopez, HO-238) — the standard extension reference for DLI measurement and the PPFD-to-DLI relationship.
- LED Grow Lights Depot — Commercial Grow Room Lighting Layout — 30 cm measurement grid, 10–20 percent overlap, mounting-height sensitivity.
About this article
Written by the LUMAGROW Technical Team from publicly available extension and research references (e-GRO/Ohio State 2025, MSU Wollaeger and Runkle 2014, MSU Greenhouse Energy Conservation, Purdue HO-238, and LED Grow Lights Depot). LUMAGROW product references reflect our actual Greenhouse Top Lighting, Intercanopy and Supplemental Spectrum ranges. The DLI and transmission-loss figures are cited as published study and extension results, not LUMAGROW performance claims, and this article describes a purchasing-decision framework rather than quoting specific prices, MOQs or lead times, which vary by project. It is deliberately distinct from our Complete Planning Guide (DLI-gap maths) and fixture-requirements article (count estimation).
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