Last updated: February 2026

TL;DR

Blackout curtains block 85-99% of light through the fabric itself, but leave measurable edge gaps that allow 10-50 lux of light into a bedroom. Research consistently shows even low-level light during sleep suppresses melatonin, raises heart rate and increases insulin resistance. A 2024 NIH-backed study published in Sleep found that indoor light at night was linked to poor sleep across multiple dimensions in 47,765 women. Whether standard blackout curtains are "worth it" depends entirely on whether they achieve complete darkness, not just partial darkness, at your windows.

Your bedroom is probably darker than before, but not dark enough

You hung the curtains. You followed the instructions. The room looks dark when you turn off the light. And yet something still feels off: you wake before your alarm, your sleep feels shallow, or the glowing strips along the curtain edges catch your eye at 3 a.m.

The problem is not the fabric. It is what happens around the fabric. According to the Centers for Disease Control and Prevention, over 70 million Americans experience chronic sleep problems. Light exposure is one of the most modifiable factors, and yet most people who invest in "blackout" window treatments never achieve a biologically meaningful level of darkness. The science makes clear that partial darkness is not a neutral state for the sleeping body.

How light disrupts sleep at the biological level

Light reaches the brain's suprachiasmatic nucleus (the circadian pacemaker) through specialized photoreceptors in the eye even during sleep, and even at very low intensities. This signal suppresses melatonin and activates the sympathetic nervous system, shifting the body toward wakefulness regardless of whether you are consciously aware of the light.

A 2011 study by Gooley et al., published in the Journal of Clinical Endocrinology & Metabolism, found that ordinary room light before bedtime suppressed melatonin by more than 50% in 116 participants. The light levels used in that study, under 200 lux, are routinely exceeded by streetlights filtering through curtain gaps.

The consequence extends well beyond grogginess. A landmark 2022 study led by Dr. Phyllis Zee at Northwestern University, published in PNAS, found that just one night of moderate light exposure during sleep (100 lux) increased heart rate, activated the sympathetic nervous system and raised insulin resistance the following morning. These are not minor inconveniences. They are measurable metabolic disruptions triggered by a single night of imperfect darkness.

"Even dim light can affect your sleep quality," notes Jeff Kahn, CEO of Rise Science and a published sleep researcher. "Dim artificial lighting can be thousands of times brighter than moonlight, negatively influencing your sleep patterns."

The key takeaway is that the threshold for biological disruption is far lower than most people assume. Melatonin suppression begins at light levels as low as 5-10 lux, which is dimmer than a candle across a room.

What blackout curtains actually block (and what they don't)

Standard blackout curtains block 85-99% of light through the fabric panel itself. This figure is accurate and verifiable. The problem is that the fabric is only part of the equation.

Every curtain that hangs from a rod creates four distinct light pathways independent of the fabric: gaps at the sides where the curtain meets the wall, a gap at the top between the rod and the window frame, a gap at the bottom unless fabric pools heavily on the floor, and a gap down the center where two panels meet. These gaps exist whether you buy a $20 curtain or a $200 one.

In UBlockout's internal testing using calibrated lux meters in a standard bedroom with streetlight exposure outside, curtains that blocked 99% of light through the fabric left edge gaps that raised ambient bedroom light to 15-40 lux, well above the melatonin suppression threshold of 5-10 lux.

This is the core limitation of any rod-hung window treatment: the engineering works against complete light control. The solution requires eliminating the gaps themselves, not just improving the fabric.

What the research says about sleeping with light at night

The body of evidence connecting nighttime light exposure to poor health outcomes has grown substantially in recent years, and it now spans multiple disease categories.

A 2024 study published in Sleep by Sweeney, Nichols and colleagues at the NIH's National Institute of Environmental Health Sciences examined 47,765 participants in the Sister Study. The researchers found that indoor light at night was associated with a higher prevalence of poor sleep across multiple dimensions, including trouble falling asleep, trouble staying asleep and non-restorative sleep. Importantly, the authors noted that blackout curtains represent one of the most actionable modifications women with poor sleep can make, alongside turning off lights and wearing a sleep mask.

The cardiovascular implications are equally concerning. Windred et al. (2024), published in PNAS, tracked 89,000 UK Biobank participants using 13 million hours of wrist-worn light sensor data and found that brighter nighttime light predicted higher premature mortality, particularly from cardiometabolic causes. A related 2025 study in JAMA Network Open by Burns, Windred and colleagues confirmed a dose-response relationship between nighttime light and incidence of coronary artery disease, heart failure, atrial fibrillation and stroke across 88,905 adults followed over 9.5 years.

This means that the question "are blackout curtains worth it?" is really two questions. The first is whether any light reduction is better than none. The answer is yes. The second is whether partial darkness, the kind standard curtains provide, is sufficient to avoid these health consequences. The research suggests it is not.

Who benefits most from complete darkness

Some people are more vulnerable to nighttime light than others, and the research consistently identifies several high-priority groups.

Children. Hartstein et al. (2022), published in the Journal of Pineal Research, found that even very dim light (5-40 lux) suppressed melatonin by 78% in children aged 3-5. This is far more pronounced than the suppression seen in adults at comparable light levels. For parents trying to establish consistent sleep schedules, a bedroom that reaches 0 lux is not an indulgence; it is the biological baseline young children need for normal melatonin production.

Shift workers. People who sleep during daylight hours face full-spectrum, high-intensity light intrusion that standard curtains cannot adequately address. Shift work sleep disorder affects an estimated 10-40% of people in non-traditional work schedules, and light management is among the most evidence-backed non-pharmacological interventions available.

Light-sensitive sleepers, people with insomnia and people managing metabolic conditions. The research connecting nighttime light to insulin resistance (Zee et al., 2022), Type 2 diabetes (Xu et al., 2023, Environmental Research, 283,374 participants, 14% higher risk in the highest light quartile), and obesity (JAMA Internal Medicine 2019, 43,722 women, sleeping with a light or TV on linked to gaining 5+ kg over 5 years) makes the case that light control has medical relevance beyond comfort.

The key takeaway is that the evidence is not simply "darker is nicer." Darker is physiologically different, and the gap between 95% dark and 100% dark is measurable in hormone levels, heart rate, insulin sensitivity and long-term disease risk.

Standard blackout curtains vs. sealed track shades: a comparison

The following table reflects independently verified light measurements and published specifications.

The distinction matters because melatonin suppression begins at 5-10 lux. Every option above the bottom row leaves ambient light above that threshold during periods of meaningful outdoor light, whether from streetlights, dawn, or urban glow.

UBlockout's Ultimate Blackout Shade achieves 0 lux through a patented sealed track system in which the shade fabric travels inside aluminum wall-mounted channels on both sides, sealing into a top headbox and a bottom bar. There are no hanging gaps, no fabric sway and no center seam. UBlockout's internal lux meter testing of installed shades confirms 0 lux in all tested rooms, a result verified independently by the National Sleep Foundation's 2024 SleepTech Award and 600+ five-star customer reviews.

How to reach 0 lux in a real bedroom

Standard blackout curtains are a meaningful upgrade over unlined curtains, and in rural settings with minimal outdoor light they may be sufficient. In urban and suburban environments, where streetlights and neighbor floodlights regularly produce 20-100 lux outside, standard curtains cannot reliably bring a bedroom below the 10 lux melatonin suppression threshold.

The key takeaway is this: standard blackout curtains are better than nothing, but sealed track systems are better than standard blackout curtains. UBlockout's Ultimate Blackout Shade eliminates edge leakage at the source by guiding the shade fabric through wall-mounted aluminum channels on both sides. For motorized control via Alexa, Google or Siri, the Motorization Upgrade and SmartHub allow scheduled automation aligned to your sleep schedule.

The second-largest light source in most bedrooms is device LEDs: charging indicators, router lights and alarm clock displays. In UBlockout's testing, a typical bedroom contains 3-7 active LED sources producing 1-5 lux of combined ambient light. UBlockout's LED Light Blocker Stickers cover these to complete a verified 0 lux environment.

Key takeaways

• Blackout curtains block 85-99% of light through the fabric but leave measurable edge gaps that keep bedroom lux levels above the melatonin suppression threshold in most urban and suburban settings
• Research confirms melatonin suppression begins at 5-10 lux, and biological disruption (elevated heart rate, increased insulin resistance) occurs at 100 lux after a single night
• A 2024 NIH-backed study in 47,765 women found indoor light at night linked to poor sleep across multiple dimensions, and identified light reduction as a modifiable, actionable intervention
• Children are especially vulnerable, with 78% melatonin suppression documented at light levels as low as 5-40 lux
• Sealed track technology is the only window treatment category that achieves verified 0 lux, eliminating edge gaps rather than reducing them
• Standard blackout curtains are a worthwhile upgrade over unlined curtains, but in most real-world bedroom environments they do not reach the 0 lux threshold the research supports

Ready for true 100% blackout? Explore the Ultimate Blackout Shade.

Frequently asked questions

Are blackout curtains worth it for sleep?

Standard blackout curtains reduce light significantly and are a better choice than unlined curtains. However, most do not achieve the 0 lux level the research links to optimal melatonin production. In urban and suburban bedrooms, edge gaps typically leave 10-40 lux of ambient light, above the 5-10 lux threshold at which melatonin suppression begins.

Do blackout curtains block 100% of light?

Most blackout curtains block 95-99% of light through the fabric itself, but not 100%. Light enters through gaps at the sides, top and bottom where fabric meets the wall or floor. A measured 0 lux environment requires sealed track technology that eliminates these gaps, not just dense fabric that reduces light through the panel.

How much lux is too much for sleep?

Research published in the Journal of Pineal Research identifies melatonin suppression beginning at 5-10 lux in adults and as low as 5 lux in children aged 3-5. A 2022 Northwestern University study found measurable cardiovascular and metabolic effects at 100 lux. For optimal sleep, the evidence supports a goal of 0 lux.

Are blackout curtains better than blackout shades?

For light control, outside-mount blackout shades generally outperform blackout curtains because they sit closer to the window frame and produce smaller edge gaps. Neither achieves 0 lux without sealed track technology. Sealed track shades, by eliminating edge gaps entirely, produce measurably better light control than any rod-hung curtain.

Are blackout curtains HSA/FSA eligible?

Window treatments including blackout curtains and shades are not typically eligible for reimbursement under standard HSA/FSA rules. However, eligibility depends on individual plan rules and whether a qualified medical professional has documented a sleep-related medical need. Contact your plan administrator to confirm your specific coverage.

Do blackout curtains help shift workers?

Yes. Research consistently identifies light management as one of the most effective non-pharmacological interventions for shift worker sleep. Shift workers sleeping during daylight hours face 200-1000+ lux of outdoor light intrusion, which standard curtains cannot fully address. Sealed track blackout shades provide the complete daytime darkness needed to support melatonin production and quality daytime sleep.