You bought a blockout blind, and the room still isn't dark. A bright line glows down each side, the top of the curtain lights up at sunrise, or the venetians send thin stripes of light across the bed. It is a common frustration, and it matters most for shift workers, parents of babies and toddlers, and anyone setting up a home cinema.

A truly dark room usually comes down to fit and layering as much as fabric. Here is where light gets in, and how to stop it.

Where the light actually comes from

When a "blockout" room isn't dark, light is almost always getting in one of four ways:

• Through the fabric. Sheer, light-filtering and dimout fabrics let light through by design.
• Around the edges. Gaps down the sides, across the top and under the bottom of a blind or curtain.
• Between slats. Venetian and vertical blinds leave small gaps between slats and around the cord holes, even when closed.
• Over the top. Light spills over a curtain track that sits low on the wall and bounces off the ceiling.

Fix them in that order. There is no point perfecting the fit of a fabric that lets light through.

Step 1: Start with a true blockout fabric

"Blockout" and "blackout" mean the same thing: a fabric designed to stop light passing through. In Australia it is usually called blockout. It is different from light-filtering and dimout fabrics, which soften light rather than stop it.

Not sure what you have? Hold the fabric up to a bright window. If you can see a glow through the fabric itself, it is not blockout. Our guide to blockout vs light-filtering blinds covers the choice in more detail.

Everything below assumes a blockout fabric, such as a blockout roller blind or a blockout curtain.

Step 2: Choose the right fit for roller blinds

A roller blind cannot touch the sides of the window frame. The fabric has to roll freely between the brackets, so there is always a small gap at each edge. How you mount the blind decides how much of that gap you see.

• Recess fit (inside mount) sits inside the window frame. It looks neat and built-in, but light can show down both sides.
• Face fit (outside mount) is fixed to the wall or the frame above the window, so the fabric covers the whole opening and overlaps it. This hides the side gaps, which makes it the better choice for bedrooms where darkness matters most.

Our made-to-measure roller blinds are available in both. For a face fit, measure wider than the window opening so the blind overlaps the frame on both sides. If you are not sure how much, our free measure and quote service can take care of it.

Step 3: Hang curtains wider, higher and longer

Curtains are easier to make dark than blinds, because they can overlap the window on every side.

• Wider: extend the track past the frame. Our curtain measuring guide suggests adding 100–200mm on each side when framing a window. More overlap means less glow at the sides.
• Higher: a ceiling-fixed track, or a wall-fixed track set well above the frame, cuts the light that spills over the top.
• Longer: take the curtain to the floor, or just above it, rather than stopping at the sill.
• In the middle: on a centre-opening track, the two overlap arms should meet so the curtains cross over instead of leaving a slit. Our curtain installation guide shows how.

Step 4: Layer for total darkness

The darkest rooms almost always have two layers. The blind closes off the glass, and the curtain covers the gaps around the blind.

• Blockout roller blind plus blockout curtain: a strong combination for bedrooms, nurseries and media rooms.
• Double curtains: a sheer and a blockout curtain on a dual track, so you get soft light by day and darkness at night. You choose whether the sheer sits at the front or the back.
• Double roller blinds: a light-filtering layer and a blackout layer in one blind, so you can switch from day to night without a second product.

How to black out venetian blinds

This is a common question, and the straight answer is that venetian blinds cannot be made fully dark. Light passes through the small gaps where the slats meet and through the holes for the lift cords. If you love your venetians, you have two good options:

• Keep them and add a blockout curtain over the top. The venetians handle daytime light and privacy; the curtain handles darkness.
• Use different products in different rooms. Keep venetians in living areas, and choose a face-fit blockout roller blind for the bedroom.

Quick fixes if you are renting

If you cannot drill into walls, temporary options include suction-cup blackout blinds, static-cling blackout film on the glass, and a blockout curtain on a tension rod. None will look as tidy as a made-to-measure blind, so check your lease or strata rules before you fix anything permanent.

Checklist for a dark room

• The fabric is blockout, with no glow when you hold it to the light.
• Roller blinds in bedrooms are face fit, overlapping the frame.
• The curtain track runs 100–200mm past the frame on each side.
• The track sits high, on the ceiling or well above the frame.
• Curtains reach the floor and overlap in the middle.
• Bedrooms and media rooms have two layers: a blind plus a curtain.

Frequently asked questions

Is blockout the same as blackout?

Yes. Both describe a fabric designed to stop light passing through. Blockout is the more common term in Australia.

Can a roller blind make a room completely dark?

The fabric can stop light, but a roller blind always has small gaps at the edges. A face fit hides most of them, and adding a blockout curtain over the blind gets you closest to total darkness.

What is the darkest option for a nursery?

A face-fit blockout roller blind with a floor-length blockout curtain on a track that runs past the frame. If you prefer one product, double curtains with a blockout layer are a good alternative.

Do blockout blinds also keep a room cool?

They help, especially when they fit closely and are closed before the room heats up. Our summer guide to keeping your home cool explains what works best.

Need help getting it right?

Getting a room fully dark often comes down to a few millimetres in the measurements. Book a free measure and quote anywhere in Greater Sydney and we will recommend the right fit for each window, or browse our blockout curtains and double curtains online.