Why does light still come in around blockout curtains and blinds?

Where the light gets in

• The sides. A roller blind's fabric is narrower than its brackets, and a curtain stops at the end of its track. Either leaves a gap.
• The top. A face fixed track or the roll of a blind leaves a space above it.
• The bottom. A curtain that clears the floor and a blind that stops at the sill both let light under.
• The middle. Where two curtains meet, a gap opens unless they overlap.
• Seams and hems. On a coated blockout curtain, each stitch is a pinhole in the coating.

What reduces it on curtains

• A track that runs wider than the window and, where possible, is fixed to the ceiling.
• Returns, where the track position allows them, so the curtain turns back to the wall at its fixed end.
• An overlap where two curtains meet in the middle.
• A separate blockout lining, which covers stitch holes.

What reduces it on roller blinds

• Fitting the blind outside the frame, with an overlap past the opening on every side.
• Back roll, so the fabric sits close to the window.
• A curtain in front of the blind, which covers the side gaps.

What to expect

A well fitted blockout curtain or blind makes a room much darker, not pitch black. If full darkness matters, say so before you order, because the choices above are made at the measure and are hard to add later.

Tell your curtain or blind retailer how dark you need the room. They can plan the fixing, the overlaps and the layers at the measure and quote them. Speedy Blinds makes for retailers and does not measure or quote for homeowners.