100% Blackout Curtains: How to Get Total Darkness
A genuine 100% blackout curtain blocks all light, but total darkness depends as much on the fitting as on the fabric. Most curtains sold as "blackout" block direct light without reaching complete darkness, because light leaks in at the sides, the top and the bottom.
This guide explains what sets a genuine 100% blackout apart from an ordinary blackout, how to decode the levels of light blocking, and how to achieve complete darkness in a room.
Why a "blackout" curtain often still lets light through
A curtain labelled "blackout" is not necessarily a 100% blackout. Many block direct light but leave a residual glow, for two reasons.
First the fabric: too thin, loosely woven or without a dense layer, it lets daylight filter through. Then, and this is the most common, the leaks at the edges. Light gets around the curtain at the sides, over the top above the pole, and at the bottom if the curtain stops too short. A 100% blackout fabric poorly fitted leaves a room far from complete darkness. The full diagnosis of light leaks is in our article on light coming in at the sides of the curtain.
What makes a genuine 100% blackout
A genuine 100% blackout rests on the construction of the fabric, not on the colour. Two approaches exist: a dense layer applied to the back of the fabric, or a core of tightly packed yarns set between the layers that absorbs light. The best-performing curtains combine a tight weave with a technical layer at the back.
Colour does not determine light blocking: a light fabric that is properly built blocks as much as a dark one. We set this out in our article on the white blackout curtain. For complete darkness, Kurtens offers a genuine 100% blackout, in several colours and fabrics.
Decoding the levels of light blocking
Not all curtains that "darken" are equal. Here is how to place what you are buying.
| Type | Effect on light | Use |
|---|---|---|
| Sheer / light-filtering | filters daylight, keeps brightness | daytime privacy |
| Semi-blackout | darkens strongly, residual glow | living room, day room |
| Standard blackout | blocks direct light, possible leaks at the edges | bedroom |
| 100% blackout | complete darkness if zero leaks | nursery, daytime sleep, projection |
The term "blackout" covers everything except sheers: on its own, it does not guarantee 100%. For the difference between blackout, light-filtering and opaque, see our comparison of blackout, light-filtering and opaque.
Kurtens covers these levels made-to-measure, from semi-blackout to 100% blackout, in several fabrics, colours and styles, to match the light blocking to each room.
Achieving complete darkness: the fabric is not enough
A 100% blackout fabric only delivers complete darkness with no light leaks. Three rules:
- Cover wide: the pole extends 15 to 20 cm beyond each side of the window, and the curtain drops to the floor.
- Hang high: fit the pole about 15 cm above the window, or fix from floor to ceiling to remove the glow at the top.
- Favour made-to-measure: a curtain cut to the exact dimensions of your wall removes the side gaps that standard sizes always leave.
Simple test: close the curtain in broad daylight and look for a glow around the edges. If there is one, the problem almost always comes from the fitting or the dimensions, not the fabric.
The rooms where 100% changes everything
100% blackout is not just a comfort. In some rooms, it changes quality of life.
- Bedroom: darkness helps you fall asleep and sleep deeply, especially in summer when day breaks early.
- Baby's or child's room: daytime naps and early bedtimes call for complete darkness.
- Night work: sleeping during the day demands total light blocking, impossible with a partial blackout.
- Home cinema: a dark room matters more than an expensive projector, as we explain for the home cinema curtain.
Frequently asked questions
Does a blackout curtain block 100% of light?
Not always. "Blackout" does not mean 100%. The result depends on the construction of the fabric and the fitting: an ordinary blackout blocks direct light but often leaves a glow.
Why does my blackout curtain let light through?
Most often because of leaks at the edges: sides, top above the pole, bottom too short. It is a question of dimensions and fitting before it is a question of fabric.
Does the colour of a curtain change the light blocking?
No. It is the construction of the fabric that blocks light, not the shade. A light fabric that is properly built blocks as much as a dark one.
How do you achieve complete darkness in a bedroom?
A 100% blackout fabric, fitted wide and high (15 to 20 cm of overhang, floor to ceiling if possible), ideally made-to-measure to remove the side gaps.
What is the difference between blackout and 100% blackout?
A blackout blocks direct light. A 100% blackout delivers complete darkness, provided every leak is eliminated. The difference comes down to the fabric and the fitting.
Does made-to-measure improve light blocking?
Yes. A curtain cut to the exact dimensions of your wall removes the side gaps that standard sizes always leave, the leading cause of a glow.
For the right level of light blocking at your dimensions, discover Kurtens made-to-measure blackout curtains, from semi-blackout to 100% blackout, in several fabrics and colours, made to the centimetre.
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