6 Side Effects of Sleeping with the Lights on

Most people find it easier to fall asleep in a dark room, but have you ever wondered why that is?

Human beings are hard-wired to follow the patterns of the sun, and our circadian rhythms depend on external light levels to regulate our sleep.

But since the birth of electricity, artificial lighting has begun to disrupt this natural balance.

Whether it’s street lights outside your window, blue light from your cell phone, or the light in your bedroom that you forget to turn off before you drift away into dreamland, all of this excess illumination could be playing havoc on your sleep cycle.

Is Sleeping With the Lights on a Bad Idea?

Is Sleeping With the Lights on a Bad Idea

In short, yes. And in this post, I’ll explain why.

First, we’ll look at how light affects sleep and some side effects you might experience if you routinely forget to flip the off-switch before bedtime.

Then, I’ll share some tips for reducing light levels so you can get the best night’s sleep possible and wake up feeling happier, healthier, and ready to face the day.

How Does Light Affect Sleep?

Plenty of external factors influence our slumber, but light is the single most important one of all. Here are some ways light plays a role in our sleep.

1. Sleep Cycles

Sleep Cycles

Most adults go through four to six sleep cycles per night, with each one lasting an average of 90 minutes at a time. Each cycle is made up of four stages, including the all-important Rapid Eye Movement (REM) phase, which is considered the most restorative stage of sleep.

But if an external source (e.g., light) wakes us up in the middle of the night, the crucial transitions between these cycles are interrupted, causing us to spend less time in those all-important later sleep stages. And as a result, our overall health and well-being take a hit.

2. Circadian Rhythms

Circadian Rhythms

Our circadian rhythm is the internal body clock that tells us when it’s time to fall asleep and when it’s time to wake up. And the primary driving force behind it is…you guessed it… light.

But when light exposure fails to match the natural patterns of the sun, from which our biology evolved, our circadian rhythms can be thrown off-kilter.

When the human eye perceives light, it sends signals to the brain that effectively reset the circadian rhythm, and this phenomenon occurs even when you’re fast asleep with your eyes closed.

And the results of these circadian resets can be profound. Not only do our bodies struggle to regulate sleep patterns, but our internal systems and mental health suffer, too.

3. Circadian Rhythm Disorders

Circadian Rhythm Disorders

Multiple circadian rhythm disorders can occur due to unnatural light exposure, including, but not limited to.

4. Jet Lag

Jet Lag

Traveling via plane across multiple time zones can seriously confuse the body’s circadian rhythms. In the space of just a few hours, the brain is faced with a completely different day-night cycle, and as a result, we wake up too early or struggle to fall asleep at a reasonable time.

Thankfully, the effect is temporary, and after a week or so in the new time zone, our circadian rhythms naturally acclimatize, and a normal sleep pattern resumes.

5. Shift Work Disorder

Shift Work Disorder

Those who work during the hours of darkness typically sleep during daylight hours, and this unnatural sleep/wake pattern can play havoc with circadian rhythms.

And it’s not just our sleep that suffers; this disruption can also lead to hormone imbalances, particularly the production of ghrelin and leptin, which stimulate and suppress the appetite.

As a result, night shift workers are much more prone to obesity and have an increased risk of developing type II diabetes.

The impact is even more significant for those who work a varying schedule of night shifts and day shifts, as the body never gets a chance to settle into a consistent sleep/wake pattern.

6. Free-Running Disorder

Free-Running Disorder

Also known as Non-24-Hour Sleep-Wake Rhythm Disorder, Free-Running Disorder is a deregulation of the circadian rhythm which renders it unable to reset every 24 hours.

Interestingly, this disorder primarily affects people who are blind, as the retinas are incapable of transmitting adequate light signals to the brain to trigger a normal circadian response. As a result, the internal body clock becomes confused, leading to insomnia and excessive tiredness during the day.



Light also plays an important role in regulating melatonin, a crucial sleep hormone produced by the pineal gland.

During the day, melatonin production is halted or slowed, and as the sun sets and darkness falls, it naturally increases, making us feel drowsy.

But exposure to light, either natural or unnatural, later in the evening suppresses melatonin and stops us from falling asleep.

This also has a knock-on effect on our circadian rhythms, leading to further problems for our night-time routines and overall health.

The most natural way to combat melatonin suppression is to limit exposure to artificial light after sunset. But if that’s not feasible: you may have to speak with your doctor about supplementing with synthetic melatonin to help regulate your sleep/wake cycle.

Different Types of Light That Affect Sleep

Different Types of Light That Affect Sleep

All types of light can affect sleep, but daylight has the most significant impact of all.

This is because daylight has a much higher measure of illuminance, known as lux, than even the brightest sources of artificial light.

That’s why night shift workers are so susceptible to circadian rhythm disorders, as they fight against millions of years’ worth of evolution to get some shut-eye during the day.

Another hugely influential type of light is the blue light emitted by devices such as cell phones, laptops, and tablets. Blue light has a much shorter wavelength than most other forms of artificial light, leading to a bigger impact on our sleep cycles, circadian rhythms, and melatonin production than longer-wavelength light.

So, you’ve probably heard it before, but if you want to get a good night’s sleep, avoid using your electronic devices for at least a couple of hours before bedtime.

The Side Effects of Sleeping with the Lights On

The Side Effects of Sleeping with the Lights On

If we routinely fall asleep with the lights on or stare at our screens late into the evening, it can have some pretty serious and unwanted side effects, such as…

1. Insomnia

It’s an obvious one, but insomnia is the most common side effect of too much light exposure, and unfortunately, a lack of sleep can lead to many more serious health consequences.

2. Depression and Anxiety

According to recent studies, excess light exposure at night can cause depression and anxiety.

It doesn’t even have to be light from a lightbulb; even the soft glow of the TV while sleeping can have a big impact on your mental health.

But those of us who work nights are at even greater risk. Research shows that shift workers are significantly more likely to develop depression and other psychiatric problems than those who work a regular 9-5.

3. Obesity

Again, night shift workers are much more likely to develop weight problems than daytime workers, thanks to dysregulation of hunger hormones caused by over-exposure to light.

But anyone who routinely sleeps with the lights on is susceptible to weight gain. One study published by the  National Institutes of Health showed that women who slept with a television or a light on in their bedroom were 17% more likely to gain 5 kilos or more within a 12-month period.

4. Long-Term Chronic Illness

The circadian rhythm disruption caused by over-exposure to light has a direct negative effect on our body’s psychological, cardiovascular and metabolic functions.

Over time, this can lead to multiple chronic diseases, including insulin resistance, type II diabetes, hypertension, and heart disease.

5. An Increased Risk of Cancer

New research shows that sleeping with the lights on, or even sleeping in an area with heavy light pollution that penetrates inside your bedroom, can increase cancer risk.

Scientists think the reason for this comes down to that all-important sleep hormone, melatonin, which strengthens the body’s ability to suppress tumors. Conversely, a lack of melatonin due to over-exposure to light weakens the body’s natural defenses against cancer cells.

6 Tips for Reducing Light Exposure for a Good Night’s Sleep and Better Health

Here are six simple ways to reduce light exposure that can make a big difference.

1. Use Blackout Curtains or Blinds

Use Blackout Curtains or Blinds

If you live in an area with a lot of light pollution, blackout curtains or blinds can help make your bedroom as dark as possible.

2. Red Light Therapy

Red Light Therapy

If you can’t avoid using light in your bedroom before or during sleep, try switching your regular lightbulb to a red-light therapy lamp. Red spectrum light mitigates the harmful effects of blue light and aids the production of melatonin, helping you drift off quicker and stay asleep for longer.

3. Dim the Lights a Couple of Hours Before Bedtime

Dim the Lights a Couple of Hours Before Bedtime

Use a dimmer switch to lower the light levels in your home a few hours before bedtime, particularly if the sun has already set.

4. Try Eye Shades

Try Eye Shades

If keeping your bedroom dark is impossible, eye shades are a cheap and simple solution to blindfold your retinas from unwanted natural and artificial light effectively.

5. Set a Sleep Routine

Set a Sleep Routine

Erratic sleep patterns will throw your circadian rhythms out of whack. So, try to stick to the same bedtime every night and set your alarm for the same time each morning to help your body clock stay regulated.

6. Avoid Blue Light-Emitting Gadgets in the Evening

Avoid Blue Light-Emitting Gadgets in the Evening

Switching off screens before bed is one of the single biggest things you can do to lessen the impact of artificial light on your sleep. If avoiding your cell phone really isn’t an option, consider investing in a pair of blue-light-blocking glasses to lessen the harmful effects.


Overexposure to natural and artificial light comes with some pretty serious side effects that impact not only our sleep but our overall health and wellbeing, too.

But if you’ve been regularly sleeping with the lights on, or staring at your phone into the wee small hours, don’t panic. The good news is that these negative effects can be quickly reversed by returning to the standard light/dark cycles that our bodies evolved to follow.

So, if you’re struggling to drift off at night, try following the tips above and make your sleep environment as dark as possible, and see what a difference it can make for you.

Sarah Wagner

I'm Sarah Wagner, and I founded Sweet Island Dreams in 2022. It's a blog dedicated to helping people mental vacation virtually anytime they want. By providing information about the best sleep of your life, I help people drift away to paradise without ever having to leave their bed!

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