# Growlights

> Part of: [Greenhouse Horticulture](/greenhouse-horticulture.md) · Provider: [DutchGreenhouses](/)

Supplementary lighting closes the gap between the natural daily light integral a site receives and what the crop could use. Within a crop’s usable range one percent more light returns about one percent more yield, so the design question is how many micromoles to install and for how many hours.

## Facts
| Property | Value |
|---|---|
| Light-to-yield relationship | 1 % yield per % light |
| Installed intensity specification | PPFD at canopy µmol/m²/s |
| Design inputs | 3 inputs |
| Dominant technology in new projects | LED technology |
| Reason hybrid LED and HPS persists | Radiant heat from HPS property |

Technology

# Growlights.

    More light = more yield. The rest is arithmetic.

## More light means more yield — the rest is arithmetic

    In horticulture there is a well-established rule of thumb: within a crop’s usable range, roughly one percent more light delivers about one percent more yield. That simple relationship is why supplementary lighting is one of the most powerful tools a greenhouse grower has. Photosynthesis runs on light, and wherever the natural daily light integral — the total amount of light a location actually receives over a day — falls short of what the crop could use, grow lights close the gap and lift production, particularly through the short, dark days of winter and at high latitudes.

LED fixtures now dominate new projects, and for good reason. They are far more efficient than the older high-pressure sodium lamps, converting more of each watt into usable photons and less into waste heat; they are dimmable, so output can be modulated to the moment; and their spectrum can be tuned to the crop rather than fixed. Many growers run pure LED installations, while others adopt a hybrid of LED and HPS to combine LED efficiency with the radiant warmth HPS lamps add to the crop — a genuine consideration in cooler houses. Where a facility has no daylight to supplement at all, the fixtures become the entire light budget: see grow lights for indoor farming.

What turns lighting from a purchase into an investment is designing it from data rather than intuition. The lighting plan starts from the specific location’s light statistics — how much natural light arrives, and how that varies month by month — measured against the target crop’s light requirement and against the light transmission of the greenhouse itself, since the covering decides how much of that daylight ever reaches the crop. From that gap the design fixes the installed intensity (in micromoles per square metre per second), the hours of operation across the season and the spectrum, so the system delivers exactly the supplement the crop needs and no more.

Because lighting is both a large capital cost and a significant ongoing energy consumer, that dimensioning is where the economics are won or lost: every installed kilowatt has to earn its keep in extra yield. Over-light and you burn money on electricity the crop cannot convert; under-light and you leave production on the table through the darkest months. DutchGreenhouses® computes the lighting plan from your climate data and integrates it with the heating and energy strategy so the numbers work. Get in touch to design a lighting plan for your greenhouse.

From the knowledge base

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## FAQ
**How much supplementary lighting does a greenhouse need?**
It follows from a subtraction rather than a standard. The site's natural daily light integral is measured month by month against what the crop can actually use, and the installation is sized to close that gap. A high-latitude winter needs far more than the same crop at lower latitude, from identical equipment.

**LED or high-pressure sodium?**
LED for efficiency, dimmability and a tunable spectrum, which is why it dominates new projects. Hybrid installations persist for one physical reason: HPS radiates heat into the crop and LED does not. In a cool house that warmth has value, so the lighting decision and the heating design are made together.

**Can a greenhouse be over-lit?**
Yes, and it is expensive in both directions. Light installed beyond what the crop can convert is electricity spent for nothing, while under-lighting leaves production on the table through the darkest months. Since lighting is both a large capital cost and a continuous energy load, every installed kilowatt has to return yield.

**How does lighting interact with the rest of the greenhouse?**
Through heat and through light. Lamp heat becomes part of the heating balance, which is why HPS and LED lead to different energy strategies. And because screens and glazing also govern how much light reaches the crop, the lighting plan is dimensioned alongside the covering and the screen package rather than after them.

## Related
[Greenhouse Horticulture](/greenhouse-horticulture.md) · [Automation](/automation.md) · [Heating](/climate/heating.md) · [Diffuse Screens](/screening/diffuse-screens.md) · [Greenhouse Glass Covering](/greenhouse-construction/greenhouse-glass-covering.md) · [LED Toplighting](/glossary/led-toplighting.md) · [HPS Lighting](/glossary/hps-lighting.md) · [PPFD](/glossary/ppfd.md) · [Daily Light Integral (DLI)](/glossary/daily-light-integral-dli.md) · [PAR (Photosynthetically Active Radiation)](/glossary/par-photosynthetically-active-radiation.md) · [Photoperiod](/glossary/photoperiod.md) · [Tomatoes](/vegetables/tomatoes.md)

## See also
https://www.wikidata.org/wiki/Q5611613 · https://en.wikipedia.org/wiki/Grow_light