Most people assume their bedroom is dark enough. It usually isn't. Streetlight through a gap in the curtains, the first hint of dawn at 5 am, a neighbour's security light. None of it feels like much, but your body registers it long before you'd call the room "not dark." Choosing the right block-out curtain is one of the few home changes with genuine, measurable evidence behind it.
Why Darkness Actually Matters for Sleep
Light doesn't need to wake you up to disrupt your sleep — it can do that while you're still asleep. Research has found that ordinary room light exposure before bed can suppress melatonin production by more than 50%, with disruption beginning at surprisingly low levels, around 5–10 lux (roughly the brightness of a streetlamp glow through a window). A 2022 Northwestern University study went further, finding that a single night of moderate light exposure during sleep (about 100 lux) was enough to raise heart rate, activate the body's stress response, and increase insulin resistance the following morning. A large 2024 NIH-backed study tracking nearly 48,000 women linked nighttime indoor light to higher rates of difficulty falling and staying asleep — and identified blackout curtains as one of the most actionable changes for improving it.
In short: this isn't about preference. A genuinely dark room is a measurable input into how well you sleep and how your body recovers overnight.
What "100% Block Out" Actually Means
Not all curtains marketed for the bedroom do the same job, so it's worth knowing the difference before you buy:
- Light-filtering curtains soften and diffuse light but let a room stay visibly bright. Good for living spaces, not for sleep.
- Blackout-lined curtains have a separate opaque lining sewn behind a decorative face fabric; effective, but the lining and outer fabric can behave differently over time.
- 100% block-out curtains (like all four curtains in Himmel's Curtains collection) are woven or backed so the fabric itself is fully opaque, blocking light directly rather than relying on a secondary lining layer.
The fabric is only half the story, though. A curtain can be 100% opaque and still let real light into the room, which most buying guides skip.
The Part That's Usually Missed: Gaps, Not Fabric
Light behaves like water — it finds the way around, not just through. Independent testing on blackout fabrics has shown that curtains blocking 99% of light through the fabric itself can still leak 15–40 lux around the top, bottom, and sides, well above the 5–10 lux threshold that affects melatonin. A single one-inch gap at the edge of an otherwise perfectly opaque curtain does more damage to a "dark room" than most people realise.
This is entirely fixable, and it's the part worth spending five extra minutes on when you hang new curtains:
- Go wider than the window. Mount the rod so it extends at least 15–20cm beyond each side of the window frame, and choose a curtain width generous enough to fully cover that span when closed (Himmel's block-out curtains are cut with enhanced fullness for exactly this).
- Go longer than the sill. A floor-length drop (or one that just grazes the floor) closes the bottom gap that a shorter curtain leaves open.
- Overlap at the centre. Where two panels meet, a few centimetres of overlap prevents a vertical seam of light down the middle.
- Mount close to the wall. The closer the rod sits to the wall (rather than projecting outward), the less light can wrap around the sides.
None of this requires special hardware, it's how you hang a normal curtain rod, just with the gaps in mind.
What Else to Check When Choosing
- Fabric weight and weave. A double-woven construction (like the Sinclair) adds density without adding stiffness, which tends to hold its blackout performance and drape better over years of use than a single-layer weave.
- Backing colour. A contrast or grey backing (used across Himmel's range) helps the curtain hold its blackout performance and resist visible sun-fade on the outward-facing side.
- Noise and thermal insulation. A genuinely dense block-out fabric does double duty — the same weight that stops light also dampens outside noise and adds a layer of insulation against heat and cold, which is part of why 100% block-out curtains tend to feel different in the hand than lighter curtains.
- Eyelet vs other headings. Eyelet headings (used across this range) sit close to the rod with minimal gap at the top and hang in consistent, even folds. Both good for coverage and a considered look.
Himmel's Block-Out Curtains, Compared
| Brooklyn | Sinclair | Chloe | Dakota | |
|---|---|---|---|---|
| Fabric | 100% polyester, contrast backing | 100% polyester, double-woven, white backing | Premium textured weave | 100% polyester, thick fabric, grey backing |
| Texture | Lightly brushed | Tactile, distinctive weave | Irregular, textured surface | Irregular textured surface |
| Colours | Charcoal, Stone, Silver, Grey, Beige | Light Stone, Creme Grey, White | Oatmeal | Almond, Pearl Grey |
| Sizes | 225x225cm, 225x250cm | 225x225cm, 225x250cm | 225x225cm, 225x250cm | 225x225cm, 225x250cm |
| Price | R1,250 | R1,200 | R1,300 | R1,300 |
All four are cut with enhanced fullness for a proper pleated drape when closed, which, per the hanging notes above, isn't just about the look, it's part of what keeps light from escaping down the centre.
FAQ
How dark does a bedroom need to be for better sleep?
Research points to a threshold as low as 5–10 lux for melatonin suppression to begin, which is dimmer than most people assume "dark" means. The goal is as close to 0 lux as your window and room allow.
Do block-out curtains actually block 100% of light?
The fabric itself can be fully opaque and still let light in around the edges. Getting close to full darkness depends as much on how the curtain is sized and hung (width, drop length, and overlap) as on the fabric's own light-blocking rating.
What's the difference between blackout-lined and 100% block-out curtains?
Blackout-lined curtains use a separate opaque lining behind a decorative fabric. 100% block-out curtains are opaque through the fabric or backing itself, which tends to hold its performance more consistently over the curtain's life.
Do block-out curtains help with noise and temperature too?
Generally yes — the density that blocks light also reduces outside noise transfer and adds insulation, which is a common reason people choose block-out curtains for bedrooms even beyond the light benefit.
The Takeaway
A better night's sleep starts with getting closer to true darkness, and that comes down to two things: a genuinely opaque fabric and hanging it so it actually covers the window. Brooklyn and Sinclair are currently in stock and ready to solve both.
