Blackout Curtains vs Window Film: Which Blocks More Light?

📅 Last updated: May 20, 2026 · Reviewed by the Deconovo Editorial Team

TL;DR (30-Second Answer)

If your goal is maximum darkness, blackout curtains usually block more light than window film. Properly made blackout fabric can block up to about 99% of incoming light when coverage is correct, while most window films mainly reduce glare, UV, or heat rather than fully darkening a room.

If your room still looks bright after installing blackout curtains, the issue is usually light leaking around the edges (top, sides, bottom), not the fabric itself. In many cases, you can fix this without replacing your curtains by improving coverage, sealing gaps, or layering treatments.

Quick Problem Breakdown: Why Light Still Leaks In

Most blackout curtain doesn't work complaints come from where light enters, not whether the fabric is blackout. Even excellent curtains cannot block light that travels through gaps around the window frame.

• Side gaps: curtain panels do not extend far enough past the window frame.
• Top gaps: the rod is too close to the frame, letting light spill over the top.
• Wrong size: panels are too narrow (not enough overlap) or too short (light leaks at the bottom).
• Hardware limitations: rental restrictions or no-drill setups prevent ideal placement.
• Reflective surfaces: light bounces off glass, light walls, or nearby buildings into the room.

Fix 1: Extend the Rod Wider Than the Window

Best for: You already have curtains installed, but you see bright lines on the left and right edges.

1. Measure the window frame width.
2. Reposition the rod so it extends 8-12 inches beyond the frame on each side (as your wall space allows).
3. Close the panels so they overlap the wall area, not just the glass.

Fix 2: Raise the Rod Higher to Reduce Top Leaks

Best for: Light spilling in from the top, especially early morning or from overhead streetlights.

1. Move the rod to sit 4-8 inches above the window frame (higher if your curtain length allows).
2. Make sure the curtain top sits close to the wall when closed.
3. Confirm the curtain still reaches the floor or at least below the sill to avoid bottom leaks.

Fix 3: Use Wrap-Around Rods or Return Brackets to Seal the Sides

Best for: Rooms where light leaks from the edges near the wall, even when the curtains are wide enough.

1. Switch to a wrap-around rod or add return brackets so the fabric curves back toward the wall.
2. Close the curtains so the outer edges touch (or nearly touch) the wall.
3. Adjust the pleats so the fabric sits flatter against the wall at the sides.

Fix 4: Layer With a Shade or Blind Behind the Curtain

Best for: Extremely bright windows, daytime sleepers, nurseries, or rooms affected by streetlights.

1. Add a light-reducing shade or blind inside the window frame (roller shades and cellular shades are commonly used for layering).
2. Close the shade first, then close the curtains fully.
3. Focus on sealing the top and sides using Fix 1-3 for best results.

Fix 5: Seal Gaps Without Drilling (Rental-Friendly Options)

Best for: Renters, no-drill rules, or situations where you cannot change the rod position.

1. Use removable methods like adhesive hook-and-loop tape or removable adhesive strips to secure curtain edges closer to the wall.
2. At night, press the curtain edge into place along the side gap.
3. In the morning, remove or loosen if you want the curtains to move freely during the day.

When Window Film Makes Sense (And Its Limits)

Window film can be a good choice when you want to reduce glare, UV, or heat while keeping the window visually minimal. It is often used for offices, living rooms, or windows that need daytime privacy without curtains.

But for bedrooms where you need near-total darkness, most window films will not be enough by themselves because they cover only the glass, not the gaps around the frame.

For general energy efficiency context on how window treatments affect heat transfer and comfort, see the U.S. Department of Energy guidance on window treatments.

FAQ

Do blackout curtains block 100% of light?

Many blackout curtains can block up to about 99% of incoming light, but small gaps around the edges can still let light into the room.

Can window film make a bedroom completely dark?

Most window films reduce glare and brightness but do not fully darken a bedroom unless they are specialized blackout films, and they still will not seal frame gaps.

Why do my blackout curtains still leak light from the sides?

Side leaks usually happen because the rod is too narrow, the panels do not extend past the frame, or the curtain edge does not sit close to the wall.

I am renting and cannot drill holes. What is the best fix?

Start with no-drill sealing methods (removable tape or adhesive solutions) to close side gaps, and consider layering with an inside-mounted shade if allowed.

I do not want to return my curtains. What is the fastest improvement?

The quickest improvements are widening coverage (extend the rod if possible), sealing edge gaps, and adding a behind-layer like a shade to reduce brightness.

Which is better for daytime sleeping: blackout curtains or window film?

Blackout curtains are usually better for daytime sleeping because they block more light overall and can cover frame gaps that film cannot.

Can I combine window film and blackout curtains?

Yes. Film can reduce glare and heat during the day, while blackout curtains handle nighttime and sleep-focused darkness, especially when installed to minimize gaps.