Blackout vs dimming vs opaque curtain: what's the difference?
A dimming curtain filters light, allowing 20 to 50% to pass through, ideal for living areas where a soft ambiance is desired. An opaque curtain blocks 85 to 95% of light, sufficient for a standard bedroom but not for total darkness. A blackout curtain blocks 100% of light, with zero halos at the edges, essential for baby rooms, night work, or home cinemas.
The choice depends on your room and your sensitivity to light. This guide compares the three types with real percentages, a summary table, and a room-by-room guide to help you invest in the right curtain.
Why the confusion between blackout, dimming, and opaque poses a real problem
The terms "blackout," "dimming," and "opaque" are used interchangeably by most curtain sellers. A quick look at home decor websites reveals the confusion: "blackout" curtains for 25 euros that let the morning light through, "opaque" curtains presented as blackout solutions, and "dimming" curtains whose descriptions promise near-total darkness.
The result is predictable: thousands of disappointed buyers. According to an analysis of customer reviews on major French marketplaces, phrases like "lets light through" and "not really blackout" appear in 30 to 40% of negative reviews for curtains labeled "blackout."
The core problem: the term "blackout" is not regulated in France. No standards, no mandatory certification, no controls. Any manufacturer can call their curtain blackout without anyone verifying it. This article definitively clarifies the differences between these three types of curtains and provides concrete criteria to choose the one that truly meets your needs.
Dimming curtain: gently let light in
A dimming curtain is a fabric that filters natural light without blocking it. It allows between 20 and 50% of external light to pass through, depending on the thickness and density of the weave. The effect in the room is a soft, diffused light that preserves natural illumination while eliminating direct sun glare.
Typical dimming fabrics include thick sheers, linen, light cotton, and airy woven polyester. Density: 80 to 200 g/m². Their structure deliberately allows some light rays to pass through while ensuring good visual privacy: from the outside, the interior of the room is not clearly visible during the day.
The dimming curtain is the natural choice for a living room, lounge, kitchen, or daytime office. It creates a warm atmosphere without plunging the room into darkness and allows natural light to be enjoyed. According to ANSES (French Agency for Food, Environmental and Occupational Health & Safety) recommendations, exposure to at least 1,000 lux of natural light for 30 minutes a day contributes to the regulation of circadian rhythm and sleep.
The limitation is obvious: a dimming curtain does not block light for sleeping. If your bedroom overlooks a streetlamp or if the morning sun wakes you up, a dimming curtain will not solve the problem.
Opaque curtain: block most of the light
An opaque curtain is a thick fabric that blocks between 85 and 95% of light. The room is very darkened when drawn, but not in complete darkness. In full summer sun (up to 100,000 lux outside), a residual halo of 5,000 to 15,000 lux typically remains visible, either through the fabric itself (especially if it is light-colored) or at the edges of the curtain.
Typical opaque fabrics include thick polyester, velvet, double weaves, and high-grammage cotton-polyester blends. Density: 200 to 400 g/m². Their density is sufficient to significantly darken a room, but their structure does not include a technical membrane specifically designed to block 100% of light.
The opaque curtain is perfect for a standard adult bedroom, a guest room, or any room where partial darkness is sufficient. If you are not particularly sensitive to light and the residual halo from a streetlamp or the morning sun doesn't bother you, an opaque curtain will work perfectly.
The limitation to be aware of: if you are sensitive to the slightest light source, if you work nights and sleep during the day, or if your baby wakes up at the first ray of sunshine, an opaque curtain will not be enough. The difference between 90% and 100% of blocked light is immense for a sensitive person: a study published in the Journal of Clinical Sleep Medicine (2022) shows that exposure to just 10 lux during sleep (the equivalent of a halo under the door) increases heart rate and reduces deep sleep quality.
Blackout curtain: zero light, really?
A certified blackout curtain is designed to block 100% of light. When properly installed, the room is in complete darkness, even in full summer sun at noon. This is the level of total darkening sought by light-sensitive individuals, night shift workers, and parents of young children.
To achieve this performance, technical blackout curtains use multi-layered assemblies: an outer decorative fabric, a light-blocking layer (membrane or opaque coating), and an inner technical lining. Density: 400 g/m² and above, with the most effective models exceeding 600 g/m². It is this multi-layered structure that guarantees zero light, not just the thickness of the fabric.
The real market problem. The term "blackout" is not regulated in France. No standard defines how much light a curtain must block to bear this label. A manufacturer can sell a curtain that blocks 80% of light and call it "blackout" without any consequences. This is the main source of negative reviews like "my blackout curtain lets light through."
The problem of side halos. Even with a truly 100% blackout fabric, if the curtain does not completely cover the window, light infiltrates through the edges: at the top, bottom, and sides. These light halos are the #1 source of disappointment, and no standard-sized curtain can completely eliminate them, as the dimensions never exactly match those of your window.
The solution to these two problems: a custom-made blackout curtain with 100% blackout*. Kurtens curtains offer exactly that: total darkness, zero halos at the edges thanks to manufacturing to the exact dimensions of each window. And because every curtain is a thermal and soundproof blackout curtain, you also benefit from a thermal gain of up to 7 °C* and sound attenuation of 22 dB*.
The blackout curtain is essential for: adult bedrooms sensitive to light, baby rooms, home cinemas and projection rooms, night work, and naps in mid-summer.
Comparative table: dimming vs. opaque vs. blackout
| Criterion | Dimming | Opaque | Certified Blackout |
|---|---|---|---|
| Light blocked | 50 to 80% | 85 to 95% | 100% |
| Remaining light | 20 to 50% | 5 to 15% | 0% |
| Typical density | 80 to 200 g/m² | 200 to 400 g/m² | 400 to 620+ g/m² |
| Layers | 1 (single fabric) | 1-2 (thick or double fabric) | 3+ (technical multi-layer) |
| Daytime privacy | Good | Very good | Total |
| Ideal for | Living room, kitchen, office | Standard bedroom | Baby room, night, home cinema |
| Main limitation | Does not block for sleeping | Possible residual halo | Requires custom-made for zero halo |
| Indicative price | 15 to 60 euros | 30 to 100 euros | 80 to 350 euros |
This table highlights a simple reality: each type of curtain has its legitimate use. The dimming curtain is not a bad product; it is a product designed for a different need. The problem arises when one buys a dimming or opaque curtain believing they are getting a blackout one.
How to choose according to your room
Living room: dimming is often the best choice
In a living space, natural light is an asset to preserve. A dimming curtain filters direct glare while maintaining 300 to 500 lux in the room (recommended level for daytime activities). Privacy is ensured during the day without sacrificing brightness. A blackout curtain in a living room is rarely necessary, unless you have a video projector.
Adult bedroom: opaque or blackout depending on your sensitivity
If streetlamp or morning light doesn't prevent you from sleeping, a quality opaque curtain sufficiently darkens the room (5 to 50 lux residual). But if you are sensitive to the slightest light source, if you wake up as soon as it gets light, or if you work nights, only a true 100% blackout curtain guarantees the darkness you need (less than 1 lux). The WHO recommends less than 5 lux in the sleeping environment for optimal rest.
Baby room: blackout is essential
Infants and young children are extremely sensitive to light variations. A light halo at 6 am in summer, however discreet (10-20 lux is enough), can be enough to wake a baby and shift their entire sleep rhythm. In a baby's room, a 100% custom-made blackout curtain is not a luxury; it's a practical necessity. The curtain must completely cover the window to eliminate any side halos.
Office and remote work: dimming during the day, blackout for video calls
For comfortable work, a dimming curtain prevents screen glare while maintaining 300 to 500 lux of natural light, the level recommended by standard NF EN 12464-1 for screen work. If you regularly conduct video conferences, a blackout curtain allows you to perfectly control backlighting and your face's illumination on screen.
Home cinema and projection room: blackout mandatory
No compromise is possible in a projection room. The slightest stray light degrades image quality, reduces contrast, and makes dark scenes unreadable. Only a 100% blackout curtain, custom-made to completely cover the windows, guarantees the complete darkness (less than 1 lux) necessary for a cinema experience. It is also a good complement to window thermal insulation to maintain a stable room temperature.
The trap to avoid: the "blackout" that isn't one
Since the term "blackout" is not regulated by any standard in France, you cannot rely on the word alone. Here are 4 checks to make before buying:
- Ask for the blackout percentage. A true blackout will show 100%. If the seller cannot answer or remains vague ("very blackout," "nearly blackout"), it's probably an opaque curtain.
- Check if the fabric is tested or self-declared. A serious manufacturer provides test data. A manufacturer who merely writes "blackout" in the product title without proof does not deserve your trust.
- Read customer reviews. Specifically look for mentions of "halo," "light passing through the sides," or "not completely dark." These feedbacks reveal the product's reality better than any technical sheet.
- Prefer custom-made. Even an excellent blackout fabric loses its effectiveness if the curtain lets light through at the edges. Custom-made eliminates this problem by exactly covering your window.
To further delve into choosing a technical curtain with the right criteria, consult our guide for choosing your thermal curtain, which details density criteria, multi-layer structure, and measured performance.
Frequently Asked Questions
What is the difference between a blackout curtain and a dimming curtain?
A dimming curtain lets 20 to 50% of light pass through (density 80-200 g/m²) to create a soft ambiance while preserving privacy. A certified blackout curtain blocks 100% of light (density 400+ g/m², multi-layer structure) to achieve total darkness. The dimming curtain is designed for living areas (living room, kitchen), the blackout for demanding bedrooms, home cinemas, or night work.
Does an opaque curtain block all light?
No. An opaque curtain blocks between 85 and 95% of light (density 200-400 g/m²), which significantly darkens the room but does not guarantee total darkness. In full summer sun (100,000 lux outside), a residual halo of 5,000 to 15,000 lux remains visible through the fabric or at the edges of the curtain. For complete darkness (less than 1 lux), a certified 100% blackout curtain is needed.
Which curtain to choose for a baby's room?
A certified 100% blackout curtain, ideally custom-made. Babies are extremely sensitive to light variations: 10 to 20 lux is enough to wake them, especially in summer when the sun rises early. An opaque curtain that lets 5 to 10% of light filter through can disturb a baby's sleep. Custom-made eliminates side halos that standard sizes cannot address.
Why does my blackout curtain let light through at the edges?
Two possible causes. Either the curtain is not actually blackout (the term is not regulated in France, and some manufacturers use it abusively for curtains with 80-90% blackout). Or the curtain is too small for your window, and light infiltrates through uncovered spaces at the top, bottom, and sides. The solution is a custom-made blackout curtain, manufactured to the exact dimensions of your window, with 15 to 20 cm of side overlap.
Can you have a blackout curtain that is also thermal and soundproof?
Yes. The most advanced multi-layered technical curtains combine total blackout, thermal insulation, and sound attenuation in a single product. Kurtens blackout curtains offer 100% blackout*, up to 7 °C thermal gain*, and 22 dB sound attenuation*, with a density of 620 g/m². To understand the benefit of the soundproof function compared to acoustic, consult our dedicated guide.
Do I need a custom-made blackout curtain or a standard size?
Custom-made is highly recommended for a blackout curtain. The goal is to block 100% of light, and every uncovered centimeter lets through a light halo. A standard-sized curtain never exactly matches your dimensions and systematically leaves gaps at the edges. Custom-made eliminates these leaks and guarantees total darkening. This is particularly critical for baby rooms and night work.
Does a dimming curtain protect against heat in summer?
Very little. A dimming curtain (80-200 g/m²) filters direct light, but its low density does not create a significant thermal barrier. For real protection against summer heat, a high-density multi-layered thermal curtain (500+ g/m²) that creates an insulating air gap between the window and the room is needed. Kurtens thermal blackout curtains (620 g/m²) offer this dual function: total darkness and up to 7 °C thermal gain*, summer and winter.
Is the term "blackout" regulated in France?
No. No French or European standard defines the percentage of light a curtain must block to bear the mention "blackout." Any manufacturer can use this term without verification or certification. This is why you should always ask for the exact blackout percentage and check if the figure is based on actual tests or a simple self-declaration from the manufacturer.
What to remember before choosing
Each type of curtain has its legitimate use. Dimming (20-50% light filtered) is perfect for living areas. Opaque (85-95%) suits standard bedrooms. 100% blackout is essential whenever total darkness is a priority.
The trap to avoid: relying on the word "blackout" without verifying the product's actual certification or ensuring that the dimensions fully cover the window. It is the combination of a 100% certified fabric and custom manufacturing that guarantees an uncompromising result.
Discover our custom-made blackout curtains with 100% blackout* and zero halos at the edges. For a complete solution combining blackout, thermal insulation, and sound attenuation, consult our custom-made thermal and soundproof blackout curtains. Or explore all our custom-made curtains.
*Data from tests conducted under optimal conditions.
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