Can You Sleep With the Light On? (UK Sleep Guide)

Sleeping with the light on may seem harmless—perhaps even comforting to some—but growing evidence suggests that it could be doing more harm than good. From disrupted circadian rhythms to impaired melatonin production, this article dives deep into the question: Can you sleep with the light on? 

And more importantly, should you?

In this comprehensive UK-focused guide, we explore how various types of light affect sleep quality, what science has to say, and practical steps to minimise light exposure for optimal rest.

What Happens When You Sleep With the Light On?

Sleeping with the light on—whether it's a bedside lamp, hallway light, or TV screen—can:

• Reduce the amount of melatonin your body produces

• Lead to fragmented, less restorative sleep

• Interfere with your internal body clock

• Increase nighttime awakenings

• Raise overnight heart rate and sympathetic nervous system activity

It doesn’t mean you can’t fall asleep. Many people do, especially those used to background light or sound. However, the quality of that sleep is often compromised, leading to lower sleep efficiency and next-day fatigue. In some cases, people don’t even realise how poorly they’re sleeping until they remove the light source.

The effect can be subtle but cumulative. Over time, small disruptions to deep sleep and REM cycles caused by light can affect memory consolidation, emotional regulation, and physical recovery.

The Science of Light and Sleep

Our sleep-wake cycle, also known as the circadian rhythm, is controlled by the suprachiasmatic nucleus (SCN) in the brain. This biological clock is highly sensitive to light, which it interprets as a signal for wakefulness.

According to the NHS and the Sleep Foundation, exposure to light in the evening suppresses melatonin production—the hormone that signals to the body that it’s time to sleep. Melatonin naturally begins to rise in the evening as darkness falls and peaks overnight. Light exposure, particularly blue light from LED bulbs and screens, can delay or blunt this rise, causing difficulty falling asleep or waking up feeling unrefreshed.

Research shows that even a modest amount of light (as low as 5 lux, equivalent to a nightlight or dim phone screen) can interfere with this process. This has serious implications for sleep quality and long-term health.

How Different Light Sources Affect Sleep

Not all light has the same impact on sleep. The wavelength (colour), intensity, and duration of exposure all play key roles. Here’s how different common sources of light stack up:

Light Source	Effect on Sleep	Mitigation Tips
LED lamps	Emit blue light which suppresses melatonin the most	Use dim red bulbs or amber-tinted shades
TV and screens	Strong blue light, stimulates alertness	Use screen filters or night mode
Streetlights	Can leak into bedrooms, particularly orange sodium lights	Blackout curtains or eye masks
Candles/incandescent	Less blue light, more sleep-friendly	Safer and more conducive to sleep
Natural daylight	Good for alertness during the day, bad at night if trying to nap	Nap in dark rooms if needed

Blue light (450-495 nm), such as that from modern screens and LEDs, is particularly disruptive. It activates melanopsin-containing cells in the retina, which suppress melatonin and stimulate alertness. In contrast, red or amber light (600+ nm) is much less stimulating and has minimal effect on melatonin.

Impact on Melatonin and Circadian Rhythms

One of the most critical consequences of nighttime light exposure is its impact on melatonin secretion and circadian phase shifts.

A landmark 2022 study in PNAS demonstrated that sleeping in a moderately lit room (100 lux, roughly equivalent to a bright indoor room) caused noticeable physiological changes. Participants had higher heart rates, lower heart rate variability, and reduced insulin sensitivity the following morning. These findings suggest that the body is kept in a more alert, stressed state even during sleep.

This kind of disruption doesn’t just affect sleep. Circadian misalignment has been linked with increased risk for:

• Metabolic syndrome

• Cardiovascular disease

• Certain cancers (especially breast and prostate)

• Depression and anxiety

Health Risks of Sleeping With Lights On

Over the long term, sleeping with lights on has been associated with several adverse health outcomes. Some of the most concerning include:

Weight gain and obesity: A 2019 study in JAMA Internal Medicine found that women exposed to artificial light at night were significantly more likely to become overweight or obese over a five-year period. Even the presence of a television in the bedroom was associated with a higher risk.

Mood disorders: Light exposure during sleep has been shown to reduce REM sleep, which plays a crucial role in emotional regulation. Disruption to REM may increase vulnerability to anxiety and depressive episodes.

Cardiometabolic dysfunction: Chronic suppression of melatonin may lead to elevated cortisol levels at night and reduced glucose tolerance, raising the risk for type 2 diabetes and high blood pressure.

Does Light Affect Children Differently?

Yes. Children are more susceptible to the effects of light at night for a few reasons:

• Their pupils are larger and clearer, allowing more light to enter

• Their circadian systems are more responsive to light

• They have not yet established strong circadian habits

While a soft nightlight may help ease anxiety or support safe bathroom visits, it's crucial to choose warm-toned, dim lighting. Avoid blue or white LEDs, and place nightlights low to the ground and away from the bed.

There is also emerging evidence that excessive light at night during childhood could affect puberty timing and increase the risk of sleep disorders later in life.

Is It Bad to Nap in Daylight?

Napping during the day isn’t inherently bad—in fact, it can be highly restorative. But the presence of daylight can reduce the depth and efficiency of those naps.

For people working night shifts or catching up on lost sleep, a dark, quiet room is ideal. Blocking out natural light using blackout blinds or eye masks helps signal the brain that it's time to rest. Without that darkness, the body may not fully engage in deeper stages of sleep.

If blackout blinds aren't available, try pairing a contoured eye mask with white noise or earplugs to maximise sleep depth.

Night Lights: Helpful or Harmful?

Night lights are a common sleep aid, especially for children, the elderly, or those prone to waking for bathroom trips. The key lies in selecting the right kind of night light.

Red or amber night lights are the best options. Unlike blue or white lights, they do not suppress melatonin significantly. Ideally, night lights should be dim, positioned low, and directed away from the bed.

For added benefit, motion-activated night lights ensure light is only present when needed, helping minimise unnecessary exposure.

How to Sleep Better in a Bright Environment

If total darkness isn’t possible, there are several effective ways to improve sleep quality even when some light is present:

• Blackout curtains or blinds: Essential for blocking both streetlights and early morning sun. Many UK homes now face increased light pollution due to modern outdoor lighting.

• Eye masks: Affordable, travel-friendly, and highly effective—especially if blackout curtains aren’t an option.

• Dimmable lighting: Switch to low-wattage amber or red-toned bulbs in bedrooms and living areas.

• No screens 1 hour before bed: Or enable blue light filters/night mode on phones and tablets.

• Smart home integration: Use programmable lights that gradually dim in the evening and slowly brighten in the morning to simulate natural sunrise and sunset.

• Wear blue-light-blocking glasses in the evening: These help limit retinal exposure from screens and artificial indoor lighting.

Final Verdict: Can You Sleep With the Light On?

Technically, yes. You can fall asleep with the light on. But the deeper question is whether you should.

Science strongly suggests that even small amounts of light exposure at night reduce sleep quality, delay melatonin production, and affect overall health. Sleeping in darkness helps synchronise your internal clock, improves hormonal balance, and protects against long-term health risks.

In modern UK households where light pollution is rising, making a conscious effort to darken the sleep environment is one of the simplest and most effective ways to boost physical and mental well-being.

Key Takeaway

Sleeping in darkness is not just a preference—it’s a biological necessity. Whether through blackout blinds, warm-toned lighting, or screen management, reducing light at night can dramatically improve how deeply and restoratively you sleep.

This blog is for informational purposes only and does not constitute medical advice. If persistent sleep problems occur, consult with a GP or sleep specialist.