Blockout curtains still letting light in?

It is one of the most common disappointments with new curtains. The fabric sample was held up to a lamp in the showroom and nothing came through. The curtains arrive, go up, and at dawn the room has a bright frame of light around the window, a stripe down the middle and a glow on the ceiling. The curtains are blockout. The bedroom is not dark.

The explanation is simple. A blockout rating describes the cloth. It says nothing about the edges, and light is very good at finding edges. A curtain hung from a rod above the frame, stopping at the frame on each side and meeting its partner in the middle without overlap, can leak enough light to wake a light sleeper even though the fabric itself stops almost everything. The good news is that most of the leaks can be closed with fitting, and some can be closed on curtains you already own.

Fabric versus fit

There are two separate questions. Does light pass through the fabric? And does light pass around it? Buyers tend to focus on the first, and most of the light in a disappointing bedroom comes from the second.

For light through the fabric, the choice is between a face fabric with a blockout lining sewn behind it, a triple weave fabric that has a dense black thread woven into its middle layer, and a coated blockout that has a foam or acrylic backing. Light blocking varies by the exact product, colour and construction. Ask for its stated performance and test the proposed sample against bright daylight. The differences, covered in the sheer versus blockout guide and on the blockout curtains page, are mostly about how they drape, how they age and how they clean.

For light around the fabric, what matters is the hardware, the heading, the width and the length. That is where the rest of this guide spends its time, because it is where the fix usually is.

Do the dawn test before you change anything

Guessing where light gets in wastes money. The reliable method is to sit in the room with the curtains closed and the lights off at the time of day that bothers you, usually early morning in summer. Give your eyes a minute to adjust, then look at each edge in turn: the top, both sides, the middle join and the bottom. Then look at the face of the curtain for glow or pinpoints.

Note what you see, and how bright it is. A thin line down one side is a different fix from a broad bright band across the top. Take a photo on your phone, which exaggerates light leaks and makes them easier to compare. The gap finder below uses exactly these observations.

The five paths light takes

1. Over the top. The biggest leak on most rod-hung and wall-fixed curtains. Light shines up onto the ceiling through the gap between the heading and the wall, and the whole room glows. A ceiling-fixed track may reduce it, but check the actual clearance above and behind the heading. Where the ceiling is not usable, a pelmet with closed ends does the same. Eyelet and tab top curtains often leave a top light path around the rod and heading. A suitable pelmet may cover that path if its depth clears the fabric.

2. Down the sides. A curtain that stops at the frame, or that stands off the wall on rod brackets, leaves a bright line each side. The fix is to extend the track well past the frame so the curtain covers the wall, and to add returns so the side edge turns back to meet the wall. Extending the track also lets the curtain stack off the glass in the day.

3. The centre join. Two curtains meeting in the middle leave a slot unless they overlap. Overlapping master carriers or an overlap arm on a track let one curtain pass in front of the other. On a rod the two leading rings can be crossed, but it is less effective. For a single window that only one person opens, a one-way draw with a single curtain removes the centre join altogether.

4. Under the hem. A curtain that stops well above the floor, or at the sill of a window that has a wall below it, lets light spill down and across. Floor length with a small clearance removes most of it. On a sill-length curtain, extending the track and making the curtain drop below the sill helps.

5. Through the fabric. Covered in the next section, because the causes are different.

When light comes through the fabric itself

If the whole curtain glows, the fabric is not blocking enough light. Light coloured coated blockouts and some lighter triple weaves can glow in direct sun even when they are sold as blockout, because the face fabric and coating are thin. A face fabric with a separate blockout lining behind it usually performs better, because there are two layers and the lining is made for the job. Hold a sample up to a window in full sun before ordering, not to an indoor lamp.

Pinpoints usually mean holes. In a coated fabric they can be cracks in an aged coating, where the backing has been folded or washed and has started to break up. Lines of dots often follow stitching, where the needle has pierced the lining, typically at side seams, hems or where a heading tape is sewn on. Good workroom practice keeps visible stitching away from the light path, or adds a strip of lining behind it. Pinpoints along the top can also come from the holes in some heading tapes. A fabric that has cracked will not recover, and the cleaning guide explains how to avoid cracking a coated back in the first place.

Colour matters in another way. A pale face fabric with a white blockout lining looks light and fresh in the room, but in a bedroom that needs to be very dark, a mid or dark tone lining side shows less glow at the edges. The side of the lining facing the glass also reflects heat in summer, so a pale window side and a mid tone room side is a common compromise.

How dark is dark enough?

Not every bedroom needs the same level of darkness, and the fix list gets more involved as you go darker. It helps to decide which of three levels you need before spending money.

Comfortable. A dim room where early light does not wake most people. A good blockout on a wall-fixed track with the track extended past the frame is usually enough. This suits most main bedrooms.

Dark. A room where a light sleeper or a young child can sleep past sunrise in summer. This calls for careful top-gap control using a suitable heading position or pelmet, returns on the sides, an overlap in the middle and floor length. It is the setup we would suggest for most nurseries and for anyone who has already been disappointed by standard blockout curtains.

Very dark. A room for day sleep after night shifts. The dark setup plus the best performing fabric construction, attention to stitching lines, and in some cases a second layer. At this level, anything around the window also counts: light under the bedroom door, standby lights and gaps around an air conditioner.

Layering for day and night

A dark bedroom can feel gloomy in the day. The usual answer is a double track: a sheer on the room side for daytime privacy and softened light, and a blockout behind it on the window side for night. The blockout stays open all day, the sheer stays closed, and at night the blockout is drawn. Two layers also trap more air, which helps with warmth, as the thermal curtains guide explains.

The trade-off is stack space. Two curtains stacked at each side of the window take more wall than one, so the track needs to extend further past the frame. On a window close to a corner, that can limit the option. We check stack space at the measure before recommending a double track.

We make curtains only. If you already have a blind in the window recess, a curtain on a ceiling track in front of it can cover the blind's edge gaps, which many recess-fitted blinds have. That can be a simpler route than replacing the blind. The curtains or blinds guide covers where each suits.

Fixing curtains you already have

Before replacing curtains, check whether the fabric and width are adequate. If the curtains are wide enough to cover the window and some wall, and the blockout layer is intact, most of the leaks can be closed with hardware alone: a ceiling-fixed track, extended past the frame, with returns and overlapping carriers. The curtains may need rehooking or a small adjustment to the drop to suit the new height, which is a straightforward alteration. Unlined curtains in good condition can have a blockout lining added.

Replacement makes more sense when the curtains are too narrow to overlap and reach past the frame, when the coating has cracked, or when the heading is eyelet or tab top and the room needs to be dark. Adding width may leave a visible join, and rod headings may need a suitably sized pelmet to reduce the top gap.

Mistakes and how to fix them

Blockout questions