Industry Application
Greenhouse LED lighting should be designed around the difference between available natural daylight and the crop’s target daily light integral, rather than fixture wattage alone. The design question is how many moles per square metre per day the structure delivers in the weakest month, how much the crop needs, and how the gap is closed with the fewest installed watts.
Illustrative image of a typical greenhouse environment — not a customer installation photograph.
Technical focus on this page
Seasonal DLI deficit, top versus intercanopy, structure and humidity
How this application works
A greenhouse is a hybrid system: daylight supplies the base load, and supplemental lighting fills a seasonal deficit. That single difference changes the entire planning method compared with an indoor room. Fixture count is not derived from area alone, because the same structure can be light-limited in December and self-sufficient in June.
Transmission is the first number to establish. Glazing type, age, dirt, structural shading, gutters, trusses and thermal screens all reduce what reaches the crop, and the reduction is not uniform across the floor. Extension guidance for commercial houses puts typical transmission at 60–70 %, so a third of the outdoor resource can be lost before the crop sees it, and the figure should be measured in the actual house rather than taken from a glazing datasheet (Runkle, How much supplemental lighting do you need?).
The second number is the crop’s target DLI by growth stage. For most ornamental crops a common minimum target is 10–12 mol/m²/day, while vegetable crops are usually higher (Runkle, Maximizing the benefits of supplemental lighting). Once the monthly natural DLI and the target are both known, the deficit is arithmetic — and it tells you whether you need supplemental lighting at all, which months it must run, and how many hours per day it is worth operating.
Application challenges
These are the constraints that decide whether a lighting plan survives contact with an operating facility.
A lighting system sized for December is idle in July; one sized for the annual average leaves the crop short in the weakest months. Most commercial greenhouse designs are therefore sized for a defined target month, and the control system handles the rest of the year by dimming or switching zones.
Glazing haze, condensation films, hanging baskets, irrigation booms and thermal screens all intercept light before it reaches the canopy. Measure transmission in the actual house rather than trusting a catalogue figure, and re-measure after screen installation.
In tall fruiting crops, the upper canopy intercepts most of the light. Intercanopy fixtures raise the light level in the middle and lower layers where fruit set and quality are determined; relying on top light alone means over-lighting the top to satisfy the bottom.
Greenhouse interiors combine high humidity, condensation on cold surfaces, sulfur vaporisation and routine chemical application. Fixtures and drivers need corrosion-resistant housings and an IP rating that matches the actual washdown and fogging regime, not a dry-room rating.
Retrofitting HPS to LED changes point loads, hanger positions and circuit design. LED fixtures are usually lighter, but the distribution and control architecture differ, and existing contactor switching may not support dimming or DLI-based control.
Some jurisdictions restrict upward light emission, overnight operation or light spill beyond the property line. Screening, shielding and scheduling may be required, and they affect both fixture choice and the achievable photoperiod.
Lighting requirements
Each metric below has to be set from the crop, structure and operating practice — not from a generic watts-per-square-metre rule.
| Parameter | Planning target | Why it matters |
|---|---|---|
| Natural DLI by month | Measured or modelled for the specific site, corrected for glazing transmission | The deficit, not the crop target alone, sets the installed capacity. |
| Crop target DLI | Stage-specific; fruiting crops commonly 20–30 mol/m²/day, leafy crops 12–17 | Defines how much of the deficit is worth closing in each production phase. Published greenhouse guidance suggests a 12–14 mol/m²/day minimum for lettuce and at least 15 — preferably more than 20 — for vine crops (Runkle, Lighting greenhouse vegetables). |
| Supplemental PPFD | Sized from the deficit and the planned operating hours: PPFD = deficit ÷ (hours × 0.0036) | Converts a daily photon gap into an intensity the fixtures must add to the natural level. For high-light vegetable crops, 125–175 µmol/m²/s is a typical supplemental intensity, rising to around 200 µmol/m²/s in northern-European tomato houses (Runkle, Lighting greenhouse vegetables). |
| Operating hours | Usually coordinated with the natural photoperiod; long summer days need less supplement | Running supplemental light when daylight already meets the target is pure waste: extension guidance is to light at night and in cloudy weather and to switch off once the daily light integral passes roughly 10–12 mol/m²/day (Runkle, Maximizing the benefits of supplemental lighting). |
| Uniformity across the floor | Minimum-to-average around 0.8 in the lit zone; accept lower values only outside the crop area | Greenhouse floors are uneven; structural shadows create permanent low-light zones. |
| IP rating and corrosion resistance | IP65 or better for humid houses with fogging or washdown | Condensation and chemicals shorten the life of dry-rated fixtures dramatically. |
| Control integration | DLI-based dimming linked to the climate computer where available | Supplemental lighting should respond to measured light, not to a fixed clock. |
Reference data
Planning references compiled from horticultural lighting literature and standards. They are starting points for your own trials, not guarantees of performance.
| Crop | Target DLI (mol/m²/day) | Typical supplemental PPFD | Strategy note |
|---|---|---|---|
| Tomato (vine) | 20 – 30 | 125 – 200 µmol/m²/s | Top light plus intercanopy in tall crops; coordinate with CO₂ and humidity control |
| Cucumber | 20 – 30 | 125 – 200 µmol/m²/s | Fast canopy development; check upper-canopy temperature under high PPFD |
| Pepper | 18 – 25 | 100 – 175 µmol/m²/s | More tolerant of moderate light; avoid over-sizing for the weakest month only |
| Strawberry | 15 – 25 | 75 – 150 µmol/m²/s | Photoperiod and cultivar interactions; day-extension is often more valuable than peak intensity |
| Leafy greens / lettuce | 12 – 17 | 80 – 150 µmol/m²/s | Short cycles; supplemental light is often used to stabilise supply rather than maximise growth |
| Herbs and transplants | 12 – 20 | 75 – 150 µmol/m²/s | Uniform trays matter more than peak PPFD; watch edge rows near sidewalls |
Supplemental intensities follow published guidance for high-light vegetable crops — 125–175 µmol/m²/s typical, around 200 µmol/m²/s in northern-European tomato production (Runkle, Lighting greenhouse vegetables); DLI targets follow the same extension guidance and the national DLI maps of Faust & Logan (2018). Winter deficits depend on latitude, glazing and screens — calculate for your own site before sizing fixtures.
| Factor | Top lighting | Intercanopy lighting | Planning consequence |
|---|---|---|---|
| Primary job | Raises overall DLI across the floor | Raises light inside the canopy profile | Top light sets the dose; intercanopy sets the distribution |
| Best fit | Low crops, young plants, uniform benches | Tall fruiting crops, dense canopies, multi-layer gutters | Match to crop architecture, not to habit |
| Installation | Hangers from trusses, high mounting | Suspended between rows at crop height | Row spacing and trolley access constrain the layout |
| Maintenance | Accessible from the aisle or catwalk | More exposed to crop contact and spray | Higher IP rating and mechanical protection needed |
| Control | Zone dimming with the climate computer | Often a separate zone, lower hours | Plan separate circuits and channels |
| Risk | Over-lighting the top to reach the bottom | Shadowing if rows are too narrow | Verify with a vertical PPFD profile, not a single point |
Neither strategy replaces the other in tall crops. The right split depends on canopy height, crop architecture and how much of the lower profile must stay productive.
Lighting system design
The order matters: geometry and targets first, fixture count second, verification and control last.
Measure light inside and outside the structure on a clear day, at canopy height, at several positions. Correct for the screens and structure that will be in place during the production period, not for an empty house. This is the same method extension guidance recommends: read the sensor outside, read it immediately inside, and take the ratio as the transmission figure.
Combine site irradiance data with measured transmission to get natural DLI for each month. Compare against the crop target to see which months have a deficit and how large it is.
Decide which month the system must satisfy — often the weakest month of the main crop cycle — and how much of the deficit is economic to close. A partial deficit is a legitimate commercial choice if it is a deliberate one.
Divide the deficit by operating hours and by 0.0036 to get the additional PPFD required. Longer hours reduce the intensity needed but overlap more with natural daylight, so the two must be optimised together.
For tall crops, allocate part of the installed capacity to intercanopy fixtures at crop height. Verify with a vertical PPFD profile so that the lower canopy is not relying on light that never arrives.
Confirm hanger points and point loads, circuit capacity, and whether the climate computer can dim by DLI or only switch by time. Control capability determines whether the design can actually follow the weather.
Worked example
Illustrative example — assumptions stated below, not client data
| Step | Calculation | Result |
|---|---|---|
| Consistency check on the natural-light figure | 8 ÷ 0.70 and 8 ÷ 0.60 | Inside 8 mol/m²/day implies roughly 11–13 mol/m²/day outside at the 60–70% transmission typical of commercial houses. If a measured outdoor value is far from that band, one of the two readings is wrong |
| Deficit to close | 22 − 8 | 14 mol/m²/day |
| Required supplemental PPFD | 14 ÷ (16 × 0.0036) | ≈ 243 µmol/m²/s at canopy level |
| Installed PPFD including distribution allowance | 243 ÷ 0.85 | ≈ 286 µmol/m²/s of fixture output |
| Fixture count for 1,000 m² | 286 × 1,000 ÷ 1,000 µmol/s | 286 fixtures, then re-checked against rafter spacing and structural shadows |
| Installed load and power density | 286 × 400 W ÷ 1,000 m² | 114.4 kW installed, i.e. 114 W/m² of lit area |
| Energy per winter day | 114.4 kW × 16 h | ≈ 1,830 kWh/day at full output — the figure the payback calculation has to start from |
Two assumptions dominate the result: the natural DLI and the operating window. Closing the same 14 mol/m²/day over 12 hours instead of 16 raises the required PPFD to about 324 µmol/m²/s and the fixture count with it, while the daily energy stays in the same range but the load profile changes. Recalculate with your own measured transmission, target month and fixture PPF — and note that this is a photon budget for one deficit month, not a lighting layout.
Three different kinds of number
The worked example above is an initial estimate. It is not a lighting layout, and it is not a verified PPFD. Keeping the three apart is what stops a photon budget from being quoted as delivered performance.
Monthly DLI deficit ÷ operating hours ÷ distribution allowance, converted into fixture count and installed load.
Arithmetic on two assumed inputs (natural DLI and hours). Valid for budgeting and for comparing supplier proposals — invalid as a claim about how the crop will perform.
Rafter and truss positions, hanger points, screen and gutter obstructions, then a predicted PPFD grid at canopy height plus a vertical profile through the crop.
A design deliverable stating the mounting height, the grid resolution and the minimum-to-average ratio, including the effect of structural shadows.
Inside-versus-outside transmission measured on a clear day, PPFD measured on a canopy grid under the installed layout, and the DLI logger trend across a full production month.
Measurement data only. A single point reading at head height is not verification of a greenhouse lighting system.
Fixture selection
Selected from the six fixture categories we manufacture; the right mix depends on ceiling height, canopy structure and control requirements.
Base DLI supplementation across the floor
High-mount fixtures with greenhouse-grade ingress protection and corrosion-resistant housings, sized to the monthly deficit rather than to the peak.
Raising light inside tall crop profiles
Slim bars hung between rows add light where the top canopy has already absorbed most of the incident radiation, improving lower-fruit development.
Flexible zoning over benches, gutters and propagation areas
Movable or reconfigurable fixtures suit multi-crop greenhouses where the lit area changes between seasons.
Real products
Specifications shown are the confirmed values from each product record. Where a parameter is not confirmed by the source material, it is not displayed here.
400W / 800W / 1200W top light, one to three heads, PLC control, 3960 µmol/s at 1200W.
View product details
250W / 320W top light, 1200 mm die-cast body, 218 diodes, IP65, CE.
View product details
150W three-sided intercanopy bar, 1156 mm, 18,000 lm, IP65, rope or bracket mount.
View product detailsOEM & ODM
We build fixtures to a specification, document what was built, and support the certification and packaging work that a private-label programme needs.
Common mistakes
Each of these shows up after installation, when the layout is already fixed and the circuits are already run.
| Mistake | What to do instead |
|---|---|
| Copying indoor fixture-count maths into a greenhouse | Start from the monthly natural DLI and the resulting deficit; the greenhouse already receives light for free, and the deficit changes month by month. |
| Assuming catalogue transmission equals installed transmission | Measure inside and outside on a clear day with screens and structure in place, then apply the measured figure. |
| Running supplemental light when daylight already meets the target | Use DLI-based control or at minimum a light sensor; fixed-clock operation wastes energy in bright weeks. |
| Sizing only for top light in a tall fruiting crop | Check a vertical PPFD profile and allocate capacity to intercanopy fixtures where the lower canopy is light-starved. |
| Specifying dry-room IP ratings in a fogged house | Match the IP rating and housing material to the actual humidity, condensation and washdown regime, and check the driver enclosure separately. |
Related technical guides
Published articles that explain the measurement and selection logic used on this page.
Greenhouse Guide
Plan supplemental LED lighting for a commercial greenhouse — calculate the DLI gap, choose top-lighting vs intercanopy, size fixtures by PPFD and PPE, and integrate dimming with your climate computer.
Read the guideTechnology
PPF is total photon output (µmol/s), PPFD is canopy intensity (µmol/m²/s), and PPE is efficacy (µmol/J). Learn the exact units, formulas and how to use each when specifying LED grow lights.
Read the guideTechnology
Full-spectrum fixtures are the default choice for most growers. Multi-channel systems cost more but add spectral control. Which one fits your operation?
Read the guideRelated articles
In-depth guides written for this application — planning, spectrum, DLI and layout.
Greenhouse
When greenhouse supplemental LED lighting pays off, how to size the addition to natural light, and how to avoid the two classic mistakes — too little or too much.
Read Article
Greenhouse
Top lighting and intercanopy (interlighting) solve different greenhouse problems for vine crops. Compare where each fits, with a layout and energy view for tomatoes and cucumbers.
Read Article
Greenhouse
Plan a Daily Light Integral for greenhouse vegetables and flowers: crop bands, seasonal targeting, and how to convert DLI to the supplemental PPFD your LEDs must add.
Read ArticleEvery technical figure on this page is traceable to one of the sources below. Each entry gives the publication, its author or issuing body and year, a resolvable link, and the specific claim on this page that it supports — an institution name on its own is not evidence, and no manufacturer marketing material is used here as independent research. All links were checked and resolved on 19 October 2026.
Runkle E., Michigan State University Extension / Greenhouse Product News
Supports on this page: The 60–70% transmission range for commercial greenhouses, the inside-versus-outside measurement method, and the step-by-step conversion from a DLI deficit plus operating hours into a required supplemental intensity.
Runkle E., Greenhouse Product News, January 2018 (Michigan State University Extension)
Supports on this page: The 10–12 mol/m²/day minimum DLI target for ornamental crops, the rule to light at night and in cloudy weather, and the switch-off threshold once the daily light integral passes that band.
Runkle E., Michigan State University Extension Floriculture Team
Supports on this page: The crop targets in the table: 12–14 mol/m²/day minimum for lettuce, at least 15 and preferably over 20 for vine crops, and 125–175 µmol/m²/s of supplemental intensity rising to about 200 µmol/m²/s in northern-European tomato production.
Faust J.E. & Logan J., HortScience 53(9): 1250–1257 (2018)
Supports on this page: The monthly natural-DLI profile used to identify which months carry a deficit, and the regional variation behind the statement that winter deficits depend on latitude.
American Society of Agricultural and Biological Engineers, standard S640 JUL2017 (reaffirmed 2022)
Supports on this page: The units used for the deficit conversion: DLI in mol/m²/day, PPFD in µmol/m²/s, and the 0.0036 factor that links the two over a stated number of hours.
Where a source could not be confirmed as publicly accessible, the claim it would have supported has been written as a lower-certainty statement rather than given a citation. Planning ranges remain starting points for your own trials — they are not guarantees of performance, and no figure on this page is a quotation.
Industry FAQ
Specific follow-up questions about this application, answered directly and then explained.
Send the growing area, crop and stage, target PPFD or DLI, ceiling or layer height and your market requirements. We will come back with a fixture proposal, a layout suggestion and the documentation you need to evaluate it.
