# Blackout Screens

> Part of: [Screening](/screening.md) · Provider: [DutchGreenhouses](/)

Blackout screens seal the greenhouse into darkness on a schedule, driving bud formation in crops whose flowering answers to day length. A reflective upper surface turns incoming light away while a black underside absorbs what passes, and the installation seals at gutter and gable so the darkness holds across the whole house.

## Facts
| Property | Value |
|---|---|
| Darkness achieved | up to 99.9 % |
| Energy saving in favourable conditions | 40–80 % |
| Realistic annual energy saving | 20–30 % |
| U-value of a conventional blackout screen | 3 W/m²K |
| U-value with a cavity and a transparent energy screen | 1.67 W/m²K |

Screening

# Blackout screens.

    Total darkness on demand.

## Full photoperiod control — and dark-sky compliance

    Optimal yield is not only a question of nutrients, water and climate; it is also about controlling the light your plants receive. Blackout, or light-deprivation, screens let growers manipulate day length and drive bud formation on demand, year-round, even when the natural photoperiod works against the crop. For light-sensitive plants such as cannabis and chrysanthemum, that control over flowering is the difference between hitting a market window and missing it.

Effective blacking out means eliminating outside light almost entirely. A wide range of screen fabrics is available for different light-control requirements, typically engineered with a reflective white, black or aluminised top surface to deflect incoming light and a black underside to absorb any that gets through. For the most demanding applications, dedicated double blackout fabrics achieve up to 99.9% darkness — particularly valuable for cannabis and chrysanthemum between February and October, when you want to shorten the perceived day length without letting greenhouse temperatures climb.

The same screens deliver a second benefit: energy saving. Used intelligently, blackout cloths can cut energy use significantly — as much as 40–80% in favourable conditions, and a realistic 20–30% annually from a single, well-sealed portable screen. Because the screen closes the greenhouse volume at night, it retains heat that would otherwise radiate away, so the photoperiod system and the energy strategy reinforce each other.

Blackout screens also address light emission. When artificial grow lights run before sunrise or after sunset, the glow can disturb neighbours and surrounding nature, especially where greenhouses are clustered together. Countries such as the Netherlands and Canada now impose specific regulatory limits on this light pollution, and a properly specified blackout installation is often what makes a lit greenhouse compliant. Selecting the right fabric and installation for your crop, climate and local regulations is exactly where our screening specialists can help — get in touch to discuss light-deprivation screens for your project.

From the knowledge base

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## FAQ
**What is a greenhouse blackout system?**
A blackout system is a screen installation with a light-tight cloth and sealed edges that puts the crop into darkness on a fixed schedule. It lets a grower set day length independently of the season, and it holds heat in the greenhouse while closed.

**Which crops need blackout screens?**
Crops whose flowering responds to day length, chrysanthemum and cannabis foremost among them. Shortening the perceived day brings a crop into flower on a chosen date, which is what makes a market window reachable rather than a matter of season.

**How dark does a blackout greenhouse get?**
Dedicated double blackout fabrics reach up to 99.9 percent darkness. Reaching that in practice depends on the installation sealing at the gutters and gables as well as on the cloth, because light entering at an edge undoes an otherwise light-tight cloth.

**Do blackout screens also save energy?**
Yes. Closing the greenhouse volume at night retains heat that would otherwise radiate away, and a well-sealed screen returns a realistic twenty to thirty percent annually. Combining a blackout screen with a cavity and a transparent energy screen lowers its heat transfer considerably further.

## Related
[Screening](/screening.md) · [Energy Screens](/screening/energy-screens.md) · [Diffuse Screens](/screening/diffuse-screens.md) · [Humidity Control](/climate/humidity-control.md) · [Photoperiod](/glossary/photoperiod.md) · [Screen Installation](/glossary/screen-installation.md) · [Tomatoes](/vegetables/tomatoes.md)