On this page
Light is one of the most powerful signals your circadian rhythm responds to. Even small amounts of light during sleep — a streetlight through thin curtains, an LED standby light — suppress melatonin and reduce sleep quality. This is well-established in the research.
The problem is that most curtains marketed as "blackout" aren't. They block a significant amount of light, but not all of it. Here's how to tell the difference, and which options actually work.
Why light during sleep matters
Melatonin production is suppressed by light, particularly blue-spectrum light. Your body expects near-total darkness during sleep — the kind of darkness that existed for most of human evolution, before electric lighting.
Research consistently shows that even low-level light exposure during sleep (around 10 lux — comparable to a dim lamp in another room) increases light sleep, reduces slow-wave sleep, and elevates overnight heart rate. The effects are measurable on a tracker and felt the next day.
The two main culprits are:
- ✓External light through windows (streetlights, neighbours, early morning sun)
- ✓Indoor light sources (alarm clocks, chargers, router LEDs, standby lights)
This post focuses on windows. For indoor light, the fix is simple: cover or remove any LED that emits light at night.
The difference between "blackout" and actual blackout
Next best read
Curtains sold as "blackout" are classified by how much light they block. Three layers of tightly woven fabric blocks more light than one. But the seams, gaps at the edges, and the gap at the top above the curtain rod are where light still enters.
A curtain can be rated "blackout" and still allow significant light in around the edges. The fabric itself may block 99% of direct light — but the gaps around it let in enough to affect sleep.
This is why the installation matters as much as the curtain itself.
What to look for
Fabric density: Triple-weave or foam-backed fabrics block the most light. Look for curtains described as triple-pass blackout or with a foam backing. Avoid single-layer "blackout" fabrics — they typically block 85–90% of light, which looks dark to the eye but isn't sufficient for sleep optimisation.
Width: Curtains should extend at least 4–6 inches beyond the window frame on each side to prevent light from coming in around the edges. Most people hang curtains that are the same width as the window, which guarantees a light gap.
Height: Floor-to-ceiling is better than window-length. Hang the rod as close to the ceiling as possible to minimise the gap at the top.
Curtain rod type: A wrap-around rod (also called a return rod) curves back to the wall at each end, eliminating the side gaps entirely. This is one of the most effective and underused improvements.
The best options
NICETOWN Blackout Curtains
The most consistently recommended budget option. Triple-weave fabric, available in dozens of sizes and colours, good noise reduction as a secondary benefit. They block the fabric portion of the window effectively. At $25–40 per panel, they're the starting point most people should try first.
Shop NICETOWN Blackout Curtains →
Deconovo Blackout Curtains
Similar price point to NICETOWN, slightly different weave. Better rated for colour durability after washing. A good alternative if NICETOWN's sizing doesn't work for your windows.
Shop Deconovo Blackout Curtains →
Redi Shade Original Blackout Pleated Paper Shade
For windows where hanging curtains isn't possible — rental properties, awkward windows, temporary solutions — these adhesive paper shades cut to size are cheap and surprisingly effective. Not aesthetically pleasing but functionally useful. Good as a stopgap.
Sleep Mask (as an alternative)
If your curtain situation is complex — multiple windows, unusual shapes, a partner who needs light — a well-fitting sleep mask is sometimes the more practical solution. The key is fit: it needs to sit against your face without letting light in around the nose bridge.
The Manta Sleep Mask has a contoured design that doesn't press on the eyes and blocks light effectively without the "gap under the nose" problem most cheap masks have.
The complete darkness setup
For the most light-controlled sleep environment:
- ✓Blackout curtains with a wrap-around rod, extended 4–6 inches beyond the frame
- ✓Door gap: If light comes under the bedroom door, a door draft stopper solves it
- ✓Standby LEDs: Cover with black electrical tape or remove devices from the room
- ✓Phone: Face down, or better, out of the room entirely
- ✓Alarm clock: Use one with a dimmable or red-light display — this one has a 0-lux sleep mode
The combination of complete darkness plus the right room temperature (65–67°F) addresses two of the biggest environmental sleep disruptors simultaneously.
Common questions
Does darkness affect how quickly I fall asleep, or just sleep quality?
Both. Darkness accelerates melatonin release, which shortens sleep onset time. It also protects sleep architecture throughout the night — particularly in the second half, when sleep is lighter and more easily disrupted by light.
What about morning light for waking up?
Morning bright light is genuinely useful for anchoring your circadian rhythm. One option is a sunrise alarm clock that gradually brightens in the 30 minutes before your alarm time — this replicates natural dawn and tends to produce a gentler, more alert wake. [Lumie makes the most well-regarded version.](https://www.lumie.com/collections/wake-up-to-daylight-lamps)
Is red light okay at night?
Red-spectrum light has minimal effect on melatonin production compared to blue and white light. Using red-spectrum bulbs in the bedroom or bathroom in the evening is a reasonable approach if you need some light. Standard warm-white bulbs are significantly better than daylight or cool-white, even if not optimal.
Find the right stack for your sleep pattern
5 questions. Personalized recommendations. Free guide sent to your inbox.
Take the free sleep quiz →5 questions • 60 seconds • unsubscribe any time