How to Light a Commercial Greenhouse: LED Horticulture Lighting Basics

LED has changed commercial greenhouse lighting more than any other technology in the past decade. Lower energy use, longer lifespan, full spectrum control, and the ability to tune light output to the crop. But only when the system is designed correctly. 

This LED horticulture lighting guide covers spectrum, PPFD, DLI, space sizing, and the HPS conversion pitfalls that cost growers the most. Beyond LED Technology is a US-based commercial LED brand working with greenhouse operators and commercial growers across the US.

Full Spectrum vs Targeted Spectrum LEDs

The spectrum a fixture produces determines how plants grow under it. This is the most fundamental decision in any LED horticulture lighting guide and it starts with understanding what plants actually use.

What Is a Full Spectrum Grow Light?

A full spectrum grow light produces the range of light wavelengths that plants need to grow. This mainly includes blue light (400 to 500 nm), red light (600 to 700 nm), and the wavelengths in between. Some fixtures also include far red and UV light, which can help with flowering and stem growth.

For most commercial greenhouse crops, a full spectrum grow light is the best choice. It supports every stage of growth, works for many crop types, and eliminates the need to switch fixtures between the vegetative and flowering stages.

When Does Targeted Spectrum Make Sense?

Targeted spectrum LEDs focus on specific light wavelengths, usually a higher ratio of red and blue light. They are designed for specific tasks, such as propagation or a single stage of plant growth, and can be more efficient in those settings.

If you're growing different crops or moving plants through multiple growth stages in the same facility, a full spectrum grow light offers greater flexibility and works well throughout the entire growing cycle.

PPFD and DLI Explained Simply

These two measurements are the foundation of any well-designed greenhouse lighting system. They appear in every serious LED horticulture lighting guide for good reason. They are the numbers that actually determine whether plants receive enough light.

What Is PPFD?

PPFD stands for Photosynthetic Photon Flux Density. It measures the number of photons in the PAR (photosynthetically active radiation) range landing on a square metre per second. The unit is μmol/m²/s. Think of it as the intensity of light at the plant canopy at any given moment.

What Is DLI?

DLI stands for Daily Light Integral. It measures the total amount of PAR light a plant receives over an entire day — the cumulative dose, not the instantaneous intensity. DLI is calculated from PPFD and photoperiod: DLI = PPFD × hours of light × 0.0036. The unit is mol/m²/day.

Understanding both PPFD and DLI matters because you can hit a target PPFD and still under-deliver on DLI if the photoperiod is too short. Both numbers need to be planned together.

 

According to Michigan State University Extension, DLI is one of the most important environmental variables affecting plant growth, quality, and development in greenhouse production — and most growers significantly underestimate how much artificial light is required to hit target DLI levels during low-light seasons.

Sizing Lighting for Your Grow Space

Getting the fixture count and placement right is as important as choosing the correct spectrum and PPFD target. An under-lit canopy limits yield. An over-lit one wastes energy and can cause heat stress. Sizing correctly is where this LED horticulture lighting guide gets practical.

Step 1 — Define Your Target PPFD and DLI

Use the reference chart above to establish the PPFD and DLI targets for your crop and growth stage. These targets drive every calculation that follows.

Step 2 — Calculate Coverage Area per Fixture

Every fixture has a rated PPFD output at a specified mounting height. Beyond LED Technology's STEEL LED Grow Light 480W delivers 1,200 μmol/s across its coverage footprint. The 720W version delivers 1,760 μmol/s. Divide the target PPFD by the fixture's output per square metre at your mounting height to determine how many fixtures are needed per zone.

Step 3 — Account for Uniformity

Hotspots and dark zones both reduce yield quality. Fixture overlap, typically 20 to 30%, ensures even PPFD distribution across the canopy. Request a photometric layout from your lighting provider before finalising fixture placement. It is the only accurate way to confirm uniformity before installation.

The US Department of Energy reports that LED horticultural lighting systems can reduce energy consumption by 40 to 75% compared to legacy HPS systems in commercial greenhouse applications, while delivering equivalent or improved photon delivery to the canopy.

Common Mistakes When Switching From HPS

HPS to LED conversion is where most commercial greenhouse lighting projects go wrong. The physics are different enough that a direct swap without recalculation almost always produces suboptimal results.

1. Matching wattage instead of PPFD

A 600W HPS and a 600W LED do not produce light the same way. LEDs are much more efficient, typically delivering 2 to 2.5 μmol/J compared to 1 to 1.4 μmol/J for HPS. This means you usually need fewer LED watts to achieve the same PPFD. Matching wattage instead of PPFD can lead to overspending and overlighting your crop. 

2. Not adjusting mounting height

HPS fixtures are usually mounted higher because their light spreads more widely. LEDs produce a more focused beam. If you keep the same mounting height after switching to LED, your crop may receive less PPFD than expected. Always calculate PPFD based on your actual mounting height. 

3. Ignoring heat changes

HPS fixtures produce much more radiant heat than LEDs. Switching to LED reduces cooling costs, but it can also affect your growing environment. In some cases, especially during winter, your HVAC system may need adjustment to maintain the right temperature. 

4. Skipping the transition period

Plants grown under HPS can become stressed when moved directly to full spectrum LED lighting. Start at 70 to 80% of your target light intensity and gradually increase it over two to four weeks. This gives plants time to adjust to the new light quality. 

For broader reading on how LED technology is transforming commercial facility operations beyond horticulture, Beyond LED Technology's article on how smart LED lighting is transforming warehouses and industrial facilities covers similar efficiency principles applied to industrial contexts. And for facilities exploring hybrid energy approaches, the article on Solar and LED hybrid lighting systems is worth reading alongside this guide.

FAQ

What is the difference between PPFD and DLI in greenhouse lighting?

PPFD measures the light reaching the plant canopy at a specific moment. DLI measures the total light the plant receives over an entire day. PPFD shows light intensity, while DLI shows the total daily light. Both are important for effective greenhouse lighting. 

Can I replace HPS fixtures with LED directly without redesigning the layout?

Usually not. HPS to LED conversion changes light distribution, heat output, and PPFD at the canopy. You may need to adjust fixture spacing, mounting height, and the lighting schedule to get the best results. 

What PPFD do most commercial vegetable crops need?

Most leafy vegetables grow well at 150 to 400 PPFD. Fruiting crops like tomatoes, peppers, and cucumbers typically need 400 to 900 μmol/m²/s, depending on the growth stage. Always match PPFD with your DLI target. 

Is a full spectrum grow light necessary for all crops?

Not always, but a full spectrum grow light is the most practical option for commercial greenhouses. It supports multiple crop types and all growth stages without changing fixtures. 

How do I know if my greenhouse is under-lit or over-lit?

Under lit plants often become pale, stretched, or slow growing. Over lit plants may show bleaching, tip burn, or heat stress. The best way to check light levels is with a PAR meter or quantum sensor that measures PPFD at the canopy. 

Conclusion

Commercial greenhouse lighting requires careful planning. Choose the right spectrum for your crop, meet the correct PPFD and DLI for each growth stage, and design the layout for even light coverage. If you're replacing HPS fixtures, calculate your lighting needs again instead of matching wattage.

Every greenhouse is different. Ceiling height, crop type, climate control, and available sunlight all affect the final lighting design. Planning these factors early helps you avoid costly mistakes later.

Beyond LED Technology is a US based commercial LED brand offering LED horticulture lights for commercial greenhouses. Every fixture includes full specifications, photometric data, and product support. Visit beyondledtechnology.com to find the right lighting solution for your grow space.