Blackout Blinds for Bedrooms That Stay Dark

Light enters around a blackout blind at four places. The sides are the worst, because the fabric must be narrower than the recess to run freely. The top glows where the roll sits clear of the head of the frame. The bottom shows a bright line where the base rail stops short of the sill. And lower-grade coated fabrics show pinholes, tiny flaws in the coating that look like stars in a dark room.

Each has its own fix. Side channels — slim aluminium profiles screwed to the reveal — capture the edges of the fabric. A cassette or pelmet closes the top. A bottom channel, a brush seal or a weighted rail that sits into a sill profile closes the base. Pinholes are prevented by choosing a properly coated or multi-pass fabric and inspecting it against a bright light before it is made up.

Inside the recess, a blackout blind looks neat and leaves the wall clear, but it only works with channels; otherwise the side gaps are unavoidable. The recess must also be reasonably square. Old laterite walls and Portuguese-era openings are often out by a centimetre or more from top to bottom, and a channel fixed to a crooked reveal will bind the fabric. We measure the diagonals and at three heights before deciding.

Outside the recess, fixed to the wall or the face of the frame, the blind overlaps the opening and the light it misses is caught by the wall. This is the usual route for Romans and for openings too irregular for channels.

A dark blackout fabric facing the glass absorbs the sun and turns into a radiator. On a west-facing bedroom in May, the back of the blind can be hot to touch by late afternoon, and that heat ends up in the room. A white, pearl or reflective-coated backing returns a share of the sunlight back through the glass before it is absorbed.

Most of our blackout rollers are specified two-faced: reflective or white to the window, the chosen colour to the bed.

A sealed blackout blind creates a narrow, still pocket of air between itself and the glass. In the rains, when the air is saturated and the glass is cooler than the room, that pocket condenses. Water beads on the pane, runs to the frame and wets the bottom of the blind.

Choose coated fabrics rather than lined cotton for bedrooms that stay closed through the monsoon, and keep the air-conditioner drying the room when it is in use. On any dry spell, raise the blinds for an hour and open the window. In a house left shut for months, leave blinds raised rather than lowered so the glass and frames can dry out between storms.

Side channels, cassettes and bottom rails are usually aluminium, which suits the coast well when it is anodised or powder-coated. The weak points are the small parts: the screws that hold the channels, the brackets inside the cassette and the chain or spring in the mechanism. Plated steel corrodes fast in salt air and leaves orange streaks down a white channel.

In sea-facing rooms we specify stainless fixings throughout, a plastic or stainless chain, and a cassette that keeps salt-laden dust off the rolled fabric.

The most complete bedroom answer is two layers. The blind seals the glass; a curtain in front adds softness, absorbs sound, covers the aluminium channels when drawn and catches any remaining glow at the top.

Because the blind is doing the hard work, the curtain can be lighter — a lined linen rather than a heavy blackout drape — which is kinder in the humidity and easier to clean. Plan the curtain track to clear the blind's cassette and channels, and keep the stack of the curtain off the glass so the blind can still be raised.