How to fix it
Work through these in order, the most common causes come first.
Start With the Basics
Panel width versus window width: Total closed panel width should be at least 2 to 2.5 times the window's actual width.
This is the single most common reason for visible light leakage, more common than any issue with the fabric's actual blocking rate.
Rod placement: A rod mounted directly above the window frame, rather than extending 4 to 6 inches past it on each side, leaves side gaps that let in light even with correctly sized panels.
Color choice: Lighter colors block meaningfully less light than darker colors in the same product line, which can be mistaken for a fabric defect when it is actually an expected performance difference by colorway.
Diagnosing Your Specific Problem
Light comes in mainly at the sides: This points to undersized panels or a rod mounted too close to the frame.
Extend the rod and confirm panel width against the sizing guidance above.
Light comes in mainly at the top: This points to a gap between the top of the curta in and the ceiling.
A ceiling-mounted rod, valance, or cornice board closes this gap.
A faint glow comes through the fabric itself, not around the edges: This points to the fabric's construction rather than sizing.
Our picks
Products we recommend
As an Amazon Associate I earn from qualifying purchases. Picks are based on manufacturer specs, independent reviews and owner reports.
Top pickEclipse
Thermaback backing is the most effective light and heat blocker in this list
- 52 x 84 inch single panel, grommet top
- Thermaback triple-weave blackout backing
- Blocks 98% to 99.9% of light
- Reduces energy loss through the window
- Machine washable
✓ Pros
- Thermaback backing is the most effective light and heat blocker in this list
- Noticeably reduces afternoon heat buildup in a west-facing room
- Available in dark colorways that maximize both light and heat blocking
✕ Cons
- Sold per panel, so a full pair costs roughly double the single-panel price
- Stiffer fabric hand-feel than a fabric-only curtain
Exclusive Home Curtains
Sheer overlay softens the look of the room during the day, useful for a nursery that doubles as a playroom
- 52 x 63 inch pair, hidden tab/rod pocket top
- Layered sheer overlay over a solid blackout lining
- Softer, more decorative look than a solid blackout panel
- Machine washable
- Available in multiple color combinations
✓ Pros
- Sheer overlay softens the look of the room during the day, useful for a nursery that doubles as a playroom
- Blackout lining still blocks most light once fully closed
- No cords, hangs from a rod pocket or hidden tabs
✕ Cons
- Layered construction blocks slightly less light than a solid single-layer blackout panel
- 63-inch length is short for taller nursery windows
Best overallEclipse
37-inch width is proportionally right for a narrow window, unlike bulkier 52-inch panels
- 37 x 84 inch single panel, rod pocket top
- Thermaback blackout backing
- Blocks over 99% of light
- Reduces noise and insulates against heat and cold
- Machine washable
✓ Pros
- 37-inch width is proportionally right for a narrow window, unlike bulkier 52-inch panels
- Blocks over 99% of light, matching the wider Eclipse Palisade panel
- Rod pocket top gives a traditional, gathered look that suits a small decorative window
✕ Cons
- Rod pocket top is slower to open and close than a grommet panel
- 84-inch length needs hemming for a shorter small window
FAQ
Common questions
Why does light still come through the sides of my blackout curtain?
This is the single most common cause of light leakage, and it comes from the panel being narrower than the window rather than the fabric letting light through. If the curta in rod is mounted at the same width as the window frame, closing the panels leaves a gap on each side w here light passes straight through. Extending the rod 4 to 6 inches beyond the frame on each side, along with using wider panels, closes most of this gap.
Is a small light gap at the top of the curta in normal?
Some gap at the top is common, particularly with rod pocket or grommet curtains that sit an inch or more below the top of the rod. A ceiling-mounted rod, or a valance or cornice board installed above the curtain, closes this gap for rooms w here a truly dark ceiling-to-floor result matters.
Does the color of the curta in affect how much light gets through the fabric itself?
Darker colors block more light than lighter colors in the same fabric construction, typically by 3 to 10 percentage points. A light gray or pastel blackout curta in will show more of a faint glow through the fabric itself, even when properly sized and mounted, compared to the same product in black or navy.
Will adding a blackout liner fix a curta in that isn't dark enough?
Often, yes, for a curta in that is properly sized but still lets in more light than wanted through the fabric itself. A separate blackout liner clipped or sewn behind an existing curta in adds another light-blocking layer without replacing the curta in entirely, and is a lower-cost fix than buying an entirely new set of curtains.
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