Do Blackout and Blockout Curtains Block the Same Amount of Light?

Not necessarily, but the name is not the reason. Blackout and blockout curtains are the same product category, so there is no built-in difference in light-blocking ability. What varies is the construction of each individual curtain: the weave, coating, lining, and fit. Two curtains with the same name can perform very differently, and two curtains with different names can perform identically.

How Light Blocking Is Measured

Light blocking is usually described as a percentage of light that does not pass through the fabric. A curtain rated at 99% blocks nearly all light, while one rated at 90% lets through about one-tenth.

Manufacturers may measure this in a lab by shining a controlled light at the fabric and recording what passes through. Because there is no single mandatory standard, test methods and claims vary between brands. A percentage on a label is useful, but it should be treated as a guide rather than a guarantee.

Typical Light-Blocking Ranges

Curtain type	Approximate light blocked
Sheer	0-20%
Light filtering	20-50%
Room darkening	70-95%
Blockout / blackout (basic)	90-99%
Blockout / blackout (triple-weave or well-lined)	99-100%

These ranges are general estimates. Individual products may fall outside them.

What Determines How Much Light a Curtain Blocks

1. Fabric Construction

The most important factor. Triple-weave fabrics use a dark middle layer to absorb and block light. Foam-coated fabrics use an opaque back layer. Lined curtains add a dedicated blockout lining. A single-layer, thin fabric is unlikely to perform at the same level.

2. Fabric Colour

Dark colours absorb more light, while pale colours reflect and scatter it. A white blackout curtain with a proper opaque layer can still block 99%, but a cheap pale curtain may glow when sunlight hits it. Dark curtains also reduce light bounce inside a room, which is helpful in home theatres.

3. Fabric Weight and Density

Heavier fabrics generally have tighter weaves with fewer microscopic gaps. However, weight alone is not proof of opacity.

4. Seams and Stitching

Needle holes in seams can create tiny pinpoints of light. Higher-quality curtains use construction techniques that minimise this effect.

5. Fullness and Pleating

A curtain gathered with generous fullness hangs in deeper folds, which reduces the chance of light passing through a stretched, flat area of fabric.

The Big Factor: Edge Leakage

In real homes, most light does not pass through the curtain fabric. It slips around the edges. Even a 100% opaque fabric will let light in if there are gaps.

Common leakage points:

• Above the rod: The gap between the top of the curtain and the ceiling or wall.
• Sides: Where the curtain edge meets the window frame or wall.
• Bottom: The space between the hem and the floor or window sill.
• Centre overlap: Where two panels meet in the middle.

How to reduce leakage:

• Mount the rod or track 10-15 cm above the window frame.
• Extend the rod 15-20 cm past each side of the window.
• Choose curtains wide enough to overlap in the centre.
• Use a wraparound or return rod so the curtain wraps toward the wall.
• Add a pelmet or valance to cover the top gap.
• Consider magnetic or Velcro side seals for extreme darkness.

Is 100% Darkness Achievable?

Rarely. Even excellent curtains may allow a faint glow in some conditions, especially in bright daylight or near streetlights. Light can also enter through other sources: door gaps, electronics with LEDs, or bright walls reflecting light. If you need total darkness, treat the curtain as one part of a system rather than the only solution.

Do Blackout and Blockout Linings Perform Differently?

Blockout lining and blackout lining are again the same product with different regional names. Performance depends on the lining’s coating and weave. A quality blockout lining sewn behind a decorative fabric can match a dedicated blackout curtain in darkness while giving the front fabric a better appearance.

How to Test Light Blocking at Home

You can compare curtains before committing:

1. Daylight test. Close the curtain on a sunny day and check from inside. Look for glowing patches.
2. Phone flashlight test. Hold a torch behind the fabric in a dark room and see whether light shines through.
3. Edge check. Stand in the room and look for light lines along the sides, top and bottom.
4. Seam inspection. Hold the seam up to a bright light to spot pinholes.

How to Read Product Descriptions

When shopping, look past the headline term. Useful phrases include:

• “99% light blocking” or “100% blockout”
• “Triple-weave”
• “Foam-backed” or “acrylic-coated”
• “Fully lined with blockout lining”

Be cautious with vague terms such as “light reducing,” “room darkening” or “dimming,” which usually signal lower performance than true blockout.

When Different Light Blocking Levels Matter

• Nurseries and children’s rooms: Daytime naps benefit from high darkness.
• Night shift workers: Sleeping during the day requires 99%+ performance and tight fit.
• Media rooms: Reduced glare improves screen contrast.
• Bedrooms facing street lights: Strong edge control is as important as fabric rating.
• Living rooms: Slightly lower blocking may be acceptable if you want soft light.

Frequently Asked Questions

Do blackout curtains block 100% of light?
The fabric may, but the full installation rarely does because light enters around the edges.

Is blockout better than blackout?
No. They describe the same type of curtain. Compare specifications instead.

Do darker curtains block more light?
Dark colours absorb more light and reduce glow, but construction matters more than colour.

Why can I still see light with my curtains closed?
Most likely edge leakage, a thin fabric, or seam pinholes.

Final Takeaway

Blackout and blockout curtains do not inherently block different amounts of light. The difference comes from fabric layers, colour, stitching and especially fit. For best results, choose a 99%+ rated, triple-weave or well-lined curtain and install it wide and high enough to minimise edge gaps.