Are Blackout Blinds Actually Blackout?
The blackout blinds have been fitted, but the room is still not dark. Light creeps in at the sides, glows above the headrail, or seeps underneath the hem. The blind itself looks fine. The room does not behave as expected.
This is a genuinely widespread problem, and it comes from a misunderstanding about what the word blackout actually means when it appears on a blind label. This guide explains the difference between blackout fabric and a blackout installation, which blind types actually deliver darkness, and what to do if your current blinds are not performing as you expected.
What Does Blackout Actually Mean on a Blind?
When a blind is described as blackout, the term refers to the fabric or material used to make it, not to the overall performance of the installation. A blackout fabric is one that prevents light from passing through the material itself. In testing, true blackout fabrics allow less than one percent of light transmission through the cloth when measured in controlled conditions.
What the blackout label does not account for is the gap between the blind and the window frame. A perfectly blackout-rated fabric fitted inside a window recess will still show light at the sides, at the top and sometimes at the base, because light travels around the blind rather than through it. A 5mm gap at the edge of a roller blind in a sunlit room is enough to produce a visible stripe of light across a wall. The fabric is doing its job. The installation is where the darkness is lost.
This distinction matters enormously when choosing a blind for a bedroom, nursery, shift worker's room or any space where genuine darkness is the goal.
The Most Common Reason Blackout Blinds Do Not Work
The single most common cause of a disappointing blackout blind is choosing the wrong blind type for the job. Vertical blinds, Venetian blinds and slatted blinds of any kind cannot provide true blackout, regardless of the material they are made from. Light passes through the gaps between the slats, around the edges of each louvre, through the holes where the operating cords run, and around the entire perimeter of the blind.
A true blackout installation requires a single continuous piece of fabric covering the window with no gaps at the sides, top or base. Roller blinds, Roman blinds and pleated blinds are the blind types capable of delivering this, provided they are the right size, fitted correctly, and ideally finished with a cassette or frame system that addresses edge gaps.
If you have been sold vertical blinds or slatted blinds as blackout window treatments, the material may well be blackout rated, but the product is fundamentally unsuited to delivering a dark room. No amount of adjustment will change this.
The Four Places Light Gets Through a Blackout Blind
Understanding where light enters around a blackout blind helps in choosing the right solution. There are four common points of entry.
The sides
This is the most visible and most frequently complained about source of light bleed. A standard roller blind fitted inside a window recess must be slightly narrower than the recess itself to operate without catching on the sides. This clearance gap, even a few millimetres, creates a channel for light to enter. In a room with strong morning sun or a bright street light outside, this gap is immediately noticeable.
The top
The headrail of a roller blind sits above the fabric and does not cover the full width of the window at ceiling or lintel height. Light enters above the roller tube in a stripe across the top of the window. A cassette roller blind addresses this by enclosing the roller mechanism in a housing that sits flush against the top of the recess, eliminating the gap above the fabric.
The base
At the bottom of a lowered roller blind, the fabric hem bar rests against the windowsill or hangs in the air if the sill is lower than the base of the blind. Neither creates a seal. Light enters beneath the fabric, particularly in rooms where the window sill is not perfectly level or where the blind is mounted above sill height.
Through the fabric itself
In cheaper blackout fabrics, the coating applied to the back of the material can thin or develop small imperfections over time. When held up to strong light, pinholes or thin patches become visible. This is less common with quality fabrics but is worth checking when assessing why a blind is not performing as expected.
Which Blind Types Actually Deliver a Dark Room?
Perfect fit blackout roller blinds
A perfect fit blind clips directly into the inner bead of the window frame using a bracket system that requires no drilling and leaves no clearance gap at the sides. Because the frame is part of the fitting, the fabric sits flush against all four edges of the window. There is no side bleed, no top gap and no space for light to travel around the blind. For uPVC and aluminium framed windows, this is the most effective solution for achieving genuine darkness. Redwood Blinds supplies and fits perfect fit blackout roller blinds across Bournemouth, Poole, Dorset and Hampshire.
Cassette roller blackout blinds
A cassette roller blind encloses the roller mechanism in a housing that sits flush against the top of the window recess, eliminating the gap above the fabric that standard rollers leave. Combined with a fabric that reaches the full width of the recess with minimal side clearance, a cassette roller significantly reduces the light entry points that cause most blackout failures. For timber framed windows where perfect fit brackets cannot be used, a cassette roller blind is often the most effective alternative.
Blackout Roman blinds
Roman blinds with a blackout lining sit close to the wall or window frame and have a narrower headrail than roller blinds, which reduces the top gap. When fitted inside a well-proportioned recess, a blackout-lined Roman blind performs well. The soft fold of the fabric when raised is also contained within the recess rather than bunching outward. Roman blinds are a particularly good choice in rooms where aesthetics matter as well as light control.
Blackout pleated blinds
Blackout honeycomb or pleated blinds in a perfect fit frame offer the best overall performance of any blind type. The cellular structure of the fabric adds insulation in addition to light exclusion, and the perfect fit frame eliminates edge gaps entirely. For nurseries and bedrooms where both darkness and thermal comfort matter, a perfect fit blackout pleated blind is the most complete solution available.
What to Do If Your Current Blackout Blinds Are Not Working
If the blinds currently fitted are vertical, slatted or Venetian, replacing them with a roller or pleated blind in blackout fabric is the most straightforward solution. The existing fittings may need to come down entirely depending on the window type.
If the blinds are roller blinds that are letting in light at the sides or top, there are several practical improvements worth considering before replacing them outright. Fitting the blind outside the recess rather than inside it, so the fabric overlaps the wall rather than the reveal, can significantly reduce side bleed. A cassette upgrade that encloses the top mechanism addresses the headrail gap. Side channels, which act as a track for the fabric edge to run within, create a near-sealed edge and are available for retrofit on many roller blind systems.
For a bedroom that needs to be genuinely dark regardless of outside conditions, pairing a blackout roller blind with a lined curtain on a track positioned outside the recess is a practical and effective combination. The blind handles the majority of the light exclusion and the curtain covers the remaining edge gaps. This is a combination we fit regularly in bedrooms across Dorset and Hampshire, particularly in period properties where window reveals can be deep and irregular.
A Note on Fabric Quality
Not all blackout fabrics perform equally over time. Cheaper fabrics use a single-layer coating on the reverse of the material that can thin, crack or develop pinholes after extended exposure to sunlight. Better quality blackout fabrics use a separate backing layer bonded to the face fabric, which maintains its opacity throughout the lifespan of the blind.
When choosing a blackout blind, asking about the construction of the fabric is a reasonable question. A coated fabric and a bonded fabric may look identical on installation but behave differently after several years of daily use in a south-facing bedroom. Made-to-measure blinds from quality suppliers use fabrics that are specified for long-term performance, not just initial appearance.
Bedrooms, Nurseries and Shift Worker Rooms: Where Getting It Right Matters Most
The rooms where blackout performance matters most are bedrooms used by light-sensitive sleepers, nurseries where daytime napping is important, and rooms used by shift workers who need to sleep through daylight hours. In each of these situations, near-blackout is not adequate. A room that is slightly dim at 5am in June will still disrupt sleep in a way that a genuinely dark room will not.
For these rooms, a perfect fit blackout blind in a quality fabric is the starting specification. For windows that cannot take a perfect fit system, a cassette roller blind fitted outside the recess with the fabric overlapping the surrounding wall, combined with lined curtains, is the next most effective approach.
We carry out free home consultations across Bournemouth, Poole, Christchurch, Wimborne, Ferndown, Ringwood, Dorchester, Weymouth, Southampton and the wider Dorset, Wiltshire and Hampshire area. If you have a room that needs genuine darkness, we can assess the window, recommend the most effective solution, and bring fabric samples so you can see the quality of the material before committing to anything.
Frequently Asked Questions About Bathroom Shutters
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Light at the sides of a blackout blind is almost always caused by a gap between the edge of the fabric and the window frame. Standard roller blinds must be fitted slightly narrower than the recess to operate freely, which creates this gap. The solution is either a perfect fit blind that clips into the window frame with no clearance, a blind fitted outside the recess so the fabric overlaps the wall, or the addition of side channels that seal the fabric edge against the frame.
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No. Vertical blinds, Venetian blinds and any other slatted blind type cannot deliver true blackout regardless of the fabric or material used. Light passes through the gaps between slats, through cord holes, and around the entire perimeter of each louvre. If a room needs to be genuinely dark, a continuous fabric blind such as a roller, Roman or pleated blind is necessary.
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A perfect fit blackout roller blind or a perfect fit blackout pleated blind delivers the best results in most UK bedrooms with uPVC or aluminium frames. The frame clips into the window without drilling and eliminates the side gaps that cause most blackout failures. For timber framed windows, a cassette roller blind fitted outside the recess with lined curtains is the most effective alternative. The fabric quality matters as well as the fitting method, so choosing a made-to-measure blind from a quality supplier makes a meaningful difference to long-term performance.
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It depends on the blind type. If you have vertical or slatted blinds, replacing them with a roller or pleated blind in blackout fabric is the only effective solution. If you have roller blinds that are letting in light at the edges, you may be able to improve performance by fitting them outside the recess to overlap the surrounding wall, adding side channels, or fitting a cassette system to address the top gap. A home consultation with a professional fitter is the quickest way to assess what is possible with your specific windows.
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Yes. Pairing a blackout roller blind with a lined curtain is one of the most effective combinations for achieving genuine darkness in a bedroom. The blind handles the primary light exclusion and the curtain covers any remaining edge gaps. The curtain also adds insulation and a softer finish to the room. This layered approach is particularly useful in period properties with deep window reveals or irregular frames where a perfect fit system cannot be used.
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Yes. Redwood Blinds supplies and fits made-to-measure blackout roller blinds, blackout Roman blinds and blackout pleated blinds across Bournemouth, Poole, Christchurch, Wimborne, Ferndown, Ringwood, Dorchester, Weymouth, Southampton and the wider Dorset, Wiltshire and Hampshire area. We offer a free home consultation where we assess your windows, discuss the best solution for your specific situation and bring fabric samples for you to see in your own home.
Get a Bedroom That Is Actually Dark
If your current blinds are not performing as expected, or if you are looking for a made-to-measure blackout solution for a new room, we would be glad to help. Our free home consultation covers measuring, product recommendation and fabric samples, all with no obligation.
Browse our range of made-to-measure blinds at redwoodblinds.co.uk/products or call us on 07925 084214 to arrange a free home visit across Bournemouth, Poole, Dorset, Wiltshire and Hampshire.