You bought blockout blinds to sleep in. You fitted them. And you still wake up at 5am because a stripe of light is coming in around the edge. If that sounds familiar, you are not alone — it is the single most common complaint about blockout roller blinds.
The good news: the problem is almost never the fabric. It is the gaps. This guide explains exactly where the light gets in and how to stop it, so your blockout blinds actually do their job.
Quick answer: Blockout fabric blocks light through the material — but light still enters at the sides, top and bottom, and through the centre join on wide windows. The two most effective fixes are side channels (aluminium profiles the blind slides into) and outside-reveal mounting (fitting the blind over the frame instead of inside it).
What's in this guide
Where the light actually gets in
A blockout roller blind is a single sheet of fabric on a tube. Even a perfect sheet leaves four gaps:
- Sides — between the fabric edge and the window frame. Usually the worst offender.
- Top — between the roll and the headbox or ceiling.
- Bottom — at the sill, if the blind does not sit flush.
- Centre — on wide windows with two blinds, the join between them.
Fitting the blind "inside the reveal" (within the window frame) is the usual cause of side gaps, because the blind sits behind the frame and light spills past its edges. If you want darkness, you have to close those gaps deliberately.
Fix 1: side channels
Side channels — also called side tracks — are aluminium profiles fixed to each side of the window, with a groove the blind fabric slides into. They block side light completely — it is the closest thing to a true blackout for a roller blind, and it is the fix we recommend for any bedroom where darkness matters. See how we match the channel to the blind on our blockout blinds with side tracks page.
You can see it fitted in our project gallery — a Sydney bedroom where side channels shut out street light and early morning sun.
What to know:
- Costs more than a standard blind, but far less than the frustration of a light-striped bedroom.
- Works with most blockout fabrics, though the channel and the blind should be specified together.
- Essential on west- and east-facing windows, where the low sun finds every gap.
Fix 2: outside-reveal mounting
Instead of fitting the blind inside the window frame, you mount it on the wall or architrave outside the frame, so it covers the whole window plus the edges. This alone eliminates most side light gaps.
| Inside reveal | Outside reveal | |
|---|---|---|
| Appearance | Neat, contained in frame | Sits proud of the frame |
| Side light gaps | Usually visible | Covered |
| Best for | Living areas, neat finish | Bedrooms, light control |
| Works with side channels | Sometimes | Yes, ideally |
For a bedroom, the winning combination is outside-reveal mounting plus side channels. That is what turns "blockout" into "actually dark".
Fix 3: wide windows and the centre gap
On windows wider than a single blind can cover without sagging, two blinds are used side by side — and light leaks through the join. Options:
- Linked blinds — two blinds on a shared bracket, operated together, with the join minimised.
- A wider single blind — available, but needs a larger tube and heavier hardware to avoid sagging. Ask for the maximum width the system supports.
- An overlap strip — a small vertical strip that covers the join between the two fabrics.
If you have been told "wide blinds are not available", that is not correct — wide and linked systems exist. It is a question of specifying the right tube and bracket.
Fix 4: top and bottom gaps
- Top: a headbox or pelmet encloses the roll and blocks light from above. Ceiling-mounting also helps where the ceiling is close to the window.
- Bottom: the blind should finish flush with the sill, or slightly overlapping it. A bottom channel or a small floor overlap closes the last gap.
Remember: darkness is about fit, not fabric. Two identical blockout fabrics can produce completely different results depending on how they are mounted and whether side channels are used.
What to ask before you buy
- "Will you mount it outside the reveal?" If darkness matters, the answer should be yes.
- "Do you offer side channels?" The most important upgrade for a bedroom.
- "What is the maximum width without sagging?" So you know whether you need linked blinds.
- "Is there a headbox or pelmet option?" To close the top gap.
- "Who measures?" Have the supplier measure — it transfers the risk of a wrong size to them.
Our verdict
If your blockout blinds are still leaking light, the fabric is not the problem — the gaps are. Fix them in this order: mount outside the reveal, add side channels, close the top with a headbox, and handle wide windows with linked blinds. Do that, and a blockout roller blind will finally give you the dark room you paid for.
Frequently asked questions
Why do blockout roller blinds still leak light?
Blockout fabric blocks light through the material, but light still enters through the gaps — at the sides between the blind and the window frame, at the top around the roll, and along the bottom sill. On wide windows with two blinds, light also leaks through the centre join. The fabric is not the problem; the gaps are.
What is the best way to stop light gaps on a roller blind?
The single most effective fix is side channels — aluminium profiles on each side that the blind slides into, blocking side light completely. Outside-reveal mounting (fitting the blind over the frame rather than inside it) also covers side gaps. For bedrooms, side channels plus an outside-reveal mount give the closest thing to a blackout.
Should a blockout blind be mounted inside or outside the reveal?
Outside the reveal is better for light control, because the blind covers the whole window frame and stops light leaking around the edges. Inside-reveal mounting looks neater but almost always leaves visible light gaps at the sides. If darkness matters, mount outside the reveal.
Can I get one roller blind wider than 3 metres?
Yes. Wide roller blinds are available, but beyond a certain width the fabric needs a larger tube and heavier hardware to avoid sagging, and very wide windows may be better served by two linked blinds or a linked motorised system. Ask your supplier for the maximum width their system supports without sag.
Are motorised roller blinds worth it?
Motorised roller blinds are worth it for wide or hard-to-reach windows, very tall windows, and linked blinds on large windows where you want them to move together. They add convenience and can be integrated with smart-home systems, but for a standard bedroom window a quality manual chain-operated blind is perfectly adequate.
Want a bedroom that is actually dark?
Book a free in-home measure. We'll check your window, recommend outside-reveal mounting and side channels where needed, and quote a fixed price.
Book a free measure & quoteOr call us at 0423 353 538
Sync Blinds Sydney is a family-owned window covering specialist based in Auburn, NSW. We measure, make, and install roller blinds, curtains, flyscreens, pergolas, Zipscreen, awnings, and plantation shutters across Greater Sydney. Call 0423 353 538 or view our roller blind range.