Why Blackout Curtains Let Light In: Gaps, Fit and Practical Fixes

A blackout curtain can block light through its material while daylight still enters around the edges. Before replacing the fabric, work out whether the brightness is passing through the curtain or through an uncovered part of the window.

This guide helps you describe the problem clearly and prepare for a fitting assessment. Start with the blackout curtain collection if you are comparing new options, but check the existing installation before buying a replacement.

Identify where the light enters

Close the curtains as you normally would when the window is bright. Look at the centre join, both sides, the top and the bottom. Note whether you see a narrow line of light, a broad uncovered area or a glow through the material itself.

A photograph of the whole window and a close view of each gap can help explain the issue. Camera exposure changes how bright a room appears, so use photographs to show the location rather than prove a light-blocking percentage.

If the material itself seems too translucent, compare blackout and room-darkening curtains before planning hardware changes.

Check side coverage and the centre join

Curtains that only cover the glass width may leave the edges exposed when viewed from an angle. Ask a fitter whether the rod or track position, side returns or curtain width could improve coverage. The available wall space and nearby furniture affect what is possible.

At the centre, make sure both panels travel freely and meet as intended. A bracket, restricted runner or tightly stretched heading may prevent proper closure. Do not force a panel past its hardware.

Use our blackout curtain measuring guide to record the window and hardware separately. Our curtain fabric quantity guide explains why finished coverage and fabric quantity are different measurements.

Review the heading and top gap

The distance between the curtain and the wall, together with the heading and mounting height, affects the path light can take above the fabric. A change of heading or hardware may help, but it should be planned around the complete installation.

Read the eyelet and pinch pleat comparison and the curtain rails versus rods guide before discussing alternatives. Neither heading alone guarantees a completely dark room.

Check the finished drop and obstructions

A short curtain may leave an uncovered strip below the window. A longer curtain can also sit awkwardly if it catches on furniture or another obstruction. Check that the fabric hangs freely and closes without being pushed away from the window.

Measure the current hanging position to the intended hem level. Do not assume that extending the curtain onto the floor is the only solution. Discuss clearance, cleaning and the way the window opens when agreeing the final length.

Separate fabric performance from colour

Changing from cream to dark grey does not fix an uncovered edge. A suitable light-coloured fabric or lining can provide blackout performance; the exact construction matters. Our guide to light-coloured blackout curtains explains what to ask about samples.

If you need new dimensions or a different lining arrangement, use the custom blackout curtain guide to prepare your specifications. For a sleeping space, the bedroom blackout guide brings the fabric and room layout decisions together.

Prepare for a fitting assessment

1. Photograph the curtains open and closed.

2. Mark where light enters and when it bothers you.

3. Record the window size, rod or track width and current curtain drop.

4. Note any restricted movement, loose fittings or obstructions.

5. Ask which adjustment is proposed and what it includes.

See what to expect from curtain installation in Nairobi before arranging work. Contact Curtains Kenya for a fitting assessment with your photos and measurements so the team can discuss suitable next steps.