Do blackout blinds actually block 100% of light?

The short answer is that the fabric used for blackout blinds can block over 99% of incoming light, but like with curtains, it’s the gaps around the edges that can prove problematic.

This is why we offer zipped-edge blackout systems, made to complement our roller blinds. The zips, found on the edge of the fabric, lock directly into aluminium side channels, installed to the side of your windows, whether they’re on walls or your roof.

We really recommend this if your number one priority is to block as much light as possible, whether that’s to achieve better sleep, for watching movies, theatre installation, etc.

In this blog, we expand on blackout blinds in more detail and explain how they can be used to their full potential.

Introducing blackout blinds

Blackout blinds are window treatments fitted with a specialist fabric engineered to prevent light passing through the material, achieved through dense weaving, foam backing or multi-layer coatings.

At Saxon Blinds, we supply and install the KuroLok blackout system, a premium zipped-edge solution widely regarded as one of the most effective blackout blind systems available. Blackout fabrics can be used across vertical blinds, pleated blinds and motorised systems, but blackout roller blinds are the most common format:

• Single piece of fabric: No gaps between slats, unlike venetian blinds for example, which are better suited to more communal spaces
• Clean, minimal profile: They sit flush to the window
• Easy to operate: Open with chain, crank handle or motors
• Scalable: Suitable for a small office window or a large glazed facade
• Compatible with recessed headboxes: Ideal for built-in architectural installations
• Suitable for vertical windows and rooflights

A reliable choice for schools, homes, offices, hotel rooms, nurseries, home cinemas and healthcare environments.

Do blackout blinds block 100% of the light?

Yes the fabric does, or at least over 99% of it. The problem is installation. A standard roller blind sits in front of the window but does not seal against the window frame or into the window recess. Light travels around the blind, not through it, producing a halo of light around the edges regardless of how good the fabric is.

If you sleep adjacent to a window, this can quite easily mean several early mornings due to the influx of sunrise.

How to make your blackout blinds block 100% of incoming light

The solution is sealing the edges with a zipped-edge retention system (like the KuroLok option we supply & install for you):

1. A zip profile is fitted to both vertical edges of the blackout fabric
2. The zip locks into a plastic insert inside slim aluminium side channels fixed to the wall or window recess
3. When the blind is closed, there is no gap for unwelcome light to enter the space.
4. The enclosed aluminium headbox seals the blind at the top
5. The result is a fully sealed barrier with no light bleed at the sides, top or bottom

Side channels are typically between 24mm and 35mm wide, discreet enough for most settings, including fully recessed installations.

What about dim-out blinds?

Not every space needs total darkness. Dim-out fabrics reduce light significantly without blocking it entirely, useful when full blackout would be too dark, some natural light is still desirable, or the priority is to reduce heat transfer rather than complete light exclusion.

This has made them especially popular recently given the number of heatwaves we’ve been having!

The KuroLok system is compatible with dim-out and sunscreen fabrics, so the same zipped-edge hardware works wherever precise light control is the goal.

When you need genuine total darkness: the KuroLok system

For bedrooms, theatres, media rooms, laboratories, schools and hospitality venues where complete light exclusion is non-negotiable, a standard roller blind will not suffice regardless of the fabric.

The KuroLok system, supplied and installed by Saxon Blinds, delivers total blackout through zipped-edge fabric retention, robust aluminium side channels and discreet installation options.

Key specifications:

• Full blackout performance, zero light leakage
• Up to 24m² per blind (4m width x 6m drop)
• Operates up to 30° off vertical, suitable for sloping glazing
• Manual or full Somfy motorisation with BMS integration
• Recessed headbox and side channel options
• Powder-coated aluminium in any RAL finish
• Sustainable, PVC-free fabric options available

Suitable for: bedrooms, education, corporate, hospitality, laboratories, healthcare, theatres and high-end residential.

Frequently asked questions

Can KuroLok blinds be used on a roof light or skylight?

Yes. The system operates up to 30° off vertical. For fully horizontal rooflights, a sister system using constant-tension springs is available.

What is the difference between blackout blinds and blackout curtains?

Blackout curtains hang away from the window, allowing light in at the sides and top. A zipped-edge blackout roller blind sits within the window recess and seals the edges, delivering genuine complete darkness.

Can the KuroLok system be motorised?

Yes. It integrates with Somfy motorised controls and is compatible with BMS platforms including Control4, Lutron, Crestron and KNX.

Are blackout blinds good for improving sleep quality?

Absolutely. Blocking early morning sunlight supports melatonin production, improving sleep quality. We regularly install these blinds to rooms occupied by shift workers and young children, especially those who need rest during daylight hours.

Do blackout blinds help with energy bills?

Yes. Blackout blind fabric adds insulation at the window, reducing heat loss in the winter and gain in the summer, helping maintain room temperature, a practical benefit for homeowners and commercial spaces alike.

Are blackout blinds the perfect solution for home theatres?

Yes. They create a true dark environment by blocking outside light completely, making them ideal for home theatres and any space where glare and ambient light need to be eliminated.

Who are Saxon Blinds?

Saxon Blinds is one of the UK’s leading independent blind manufacturers, with over 25 years of in-house manufacturing and installation experience. Based in Northampton, we work nationwide but predominantly across London and the Home Counties, the Midlands and surrounding regions, serving clients across education, healthcare, hospitality, corporate and public sector environments, alongside smart home and high-end residential projects.

Our range covers commercial roller blinds, motorised systems, vertical blinds, venetian blinds and complete blackout solutions including KuroLok. Accreditations include BBSA, CSCS, PASMA and Enhanced DBS checks.

Call us on 01604 603111, email sales@saxonblinds.co.uk or book a free design consultation.