How light behaves around a window treatment — and what to expect before you order
The short version. “Blackout” describes the fabric — it means the material itself does not pass light. It does not mean the finished window will be completely dark. Light still travels around the edges of almost every window treatment. If total darkness is your goal, read the section on side channel systems below, or just ask us — we will tell you honestly what a given product will and will not do in your room.
Every fabric we sell falls somewhere on a scale of how much light it lets through. The name describes the weave and coating of the material, measured on its own — not the performance of the installed window treatment.
The distinction that matters: blackout fabric is about the material. A blackout room is about the whole assembly — fabric, hardware, mount, and how it meets the window opening.
A shade is a flat panel that has to move, which means it must be slightly narrower than the space it travels in. That clearance is where light gets in.
An inside mount shade is manufactured roughly a quarter to a half inch narrower than the window opening so it can raise and lower without binding. That leaves a light gap of about ⅛″ to ¼″ down each side. In a dark room facing a bright morning, those two thin lines are clearly visible. This is normal, it is how the product is engineered, and it is not grounds for a warranty claim.
An outside mount — where the shade is mounted on the wall above the window and overlaps the opening on all sides — reduces side light substantially. If darkness matters more to you than the built-in look, ask us about outside mount. It is usually the single most effective change you can make.
If you genuinely need a dark room — a nursery, a shift worker's bedroom, a media room, a migraine sufferer — the fabric alone will not get you there. A side channel system will get you close.
Channels are aluminum tracks mounted down both sides of the window. The edges of the shade ride inside them, so the side gaps are physically covered rather than merely narrow. Paired with a sealed cassette at the top, this is the only configuration we sell that approaches true darkness. On Norman roller shades we offer this as Full Blackout Side Channels.
What to expect from a side channel system. A dramatic improvement — most people describe it as the difference between “dim” and “dark.” You may still see a faint outline at the very top or bottom, and channels are visible hardware on the window frame, which changes the look. They also require adequate mounting depth and a blackout fabric to work; pairing channels with a light filtering fabric defeats the purpose.
Blackout lining makes a real difference to a drapery panel, but fabric panels darken a room differently from a shade, and they have their own light paths.
A layered treatment — a blackout shade at the glass with drapery over it — consistently outperforms either one on its own, and it is what we recommend when a room needs to be genuinely dark and still look finished.
Identical shades perform very differently in different rooms. Before deciding, consider:
We do not guarantee complete darkness from any product we sell, including those described as blackout or fitted with full blackout side channels. We are telling you this before you order rather than after.
What we do stand behind: the fabric will be the light-blocking material it is sold as, the product will be built to the manufacturer's specification, and it will be free from defects in materials and workmanship under the warranty described in our Terms of Agreement.
What is not a defect: edge light gaps at the sides, top or bottom of a correctly manufactured treatment; light at seams, stitching or needle holes in sewn goods; light between slats or vanes; and light visible after your eyes have adjusted to a dark room. These are characteristics of window treatments, not faults, and they are not covered by warranty or grounds for return of a custom made-to-order product.
Talk to us first. If a room needs to be dark, say so before you order — tell us the room, the direction it faces and what is outside the window. We will tell you plainly what will work, what will not, and what it costs. That conversation is free, and it is a great deal cheaper than a custom shade that does not do what you hoped.