Blue light and sleep: stop screens 1 hour before bed

Understanding sleep mechanisms

The biological clock and circadian rhythm

Our body operates on an internal rhythm of about 24 hours, the circadian rhythm. This rhythm regulates many physiological functions, including the wake-sleep cycle. It is primarily synchronized by light: exposure to bright light signals the brain that it is time to be awake and active; the decrease in light signals the approach of rest.

In both children and adults, the biological clock triggers a cascade of physiological changes in the evening preparing for sleep: a drop in body temperature, a slowing of metabolism, and especially the secretion of melatonin, the sleep hormone.

Melatonin: the key sleep hormone

Melatonin is produced by the pineal gland when ambient light decreases. Its secretion gradually increases in the evening, peaks in the middle of the night, and then decreases towards morning. This hormone induces drowsiness and facilitates falling asleep.

The problem is that melatonin production is sensitive to light, particularly blue light. Exposure to this light in the evening suppresses or delays melatonin secretion, thus disrupting the entire process of falling asleep.

Children's sleep needs

Children have sleep needs that are much higher than those of adults, and these needs are even more critical because sleep plays an essential role in their development. A child aged 3 to 5 years needs 10 to 13 hours of sleep per night. Between 6 and 12 years, the needs are 9 to 12 hours. Teenagers need 8 to 10 hours.

Insufficient or poor-quality sleep affects learning abilities, emotional regulation, the immune system, and growth. The stakes of quality sleep are therefore major, making anything that can disrupt it particularly problematic.

The problem of blue light

What is blue light?

Blue light refers to wavelengths between approximately 380 and 500 nanometers, located at the blue-violet end of the visible spectrum. Sunlight naturally contains a lot of blue light, which explains the blue of the sky and the role of this light in regulating our biological clock.

The problem is that LED screens (smartphones, tablets, computers, televisions) emit a significant amount of blue light. By exposing ourselves to this light in the evening, we send a contradictory signal to our brain: while darkness should signal the approach of sleep, the blue light from screens tells it that it is still daytime.

The effect on melatonin production

Many studies have shown that exposure to blue light from screens in the evening significantly suppresses melatonin production. This suppression can reach 50% or more depending on the intensity and duration of exposure. The direct consequence is a delay in falling asleep and a disruption of sleep architecture.

Children are particularly sensitive to this effect. Their eyes allow more blue light to pass through than those of adults because their lens is more transparent. Additionally, their sitting or lying position in front of screens often exposes them to more direct light.

The effects go beyond light

It would be reductive to consider only blue light. Using screens in the evening disrupts sleep through several additional mechanisms.

Cognitive stimulation keeps the brain awake. Watching captivating content, playing a game, browsing social media intensely engages attention and cognitive processes. The brain is not at all in the state of progressive relaxation that should precede sleep.

Emotional stimulation can also come into play. Scary, exciting, or stressful content generates emotions that are not conducive to falling asleep. Even seemingly neutral content can contain stimulating elements.

Behavioral engagement, the difficulty in stopping, the "just one more episode" or "one last game" pushes back bedtime and directly encroaches on sleep time.

The consequences of disrupted sleep

On development and health

A chronic sleep deficit in children has documented consequences on many aspects of development and health.

Growth is affected because growth hormone is primarily secreted during deep sleep. The immune system is weakened, making the child more vulnerable to infections. The risk of obesity increases because lack of sleep disrupts the hormones regulating appetite and promotes problematic eating behaviors.

On cognitive and academic abilities

Sleep plays a fundamental role in consolidating learning. It is during sleep that the brain sorts, organizes, and memorizes information acquired during the day. A child who sleeps poorly learns less effectively.

Attention capacities are also dependent on quality sleep. A tired child has difficulty concentrating, is easily distracted, may seem hyperactive or conversely apathetic. Their academic performance suffers.

On emotional regulation

Lack of sleep affects the ability to manage emotions. The tired child is more irritable, more sensitive to frustrations, more prone to tantrums or tears. Conflicts with peers and adults multiply.

This emotional dysregulation can create a vicious cycle: the stressed and agitated child has even more difficulty falling asleep, worsening the sleep deficit and thus the emotional problems.

The rule of screen-free hour

Why one hour?

The recommendation to stop screens at least one hour before bedtime is based on several considerations.

First, it takes time for the effects of blue light to fade and for melatonin production to return to its normal course. Exposure just before bedtime has an immediate and lasting impact. Then, the brain needs a period of cognitive and emotional decompression to prepare for sleep. Calm activities that replace screens play this transitional role.

One hour is a reasonable minimum. Some experts even recommend two hours for the most sensitive children or teenagers whose circadian rhythm is naturally shifted.

What this rule concretely states

If your child needs to be in bed by 8:30 PM, screens must be turned off by 7:30 PM at the latest. If bedtime is at 9 PM, screen time should end at 8 PM. This simple rule is easy to understand and apply, provided it is followed consistently.

The rule applies to all types of screens: television, tablet, smartphone, computer, gaming console. Even LED-backlit e-readers are included, unlike e-ink readers that do not emit blue light.

Are blue light filters sufficient?

Many devices now offer "night" modes or blue light filters that reduce the emission of these wavelengths. Filtering glasses are also available. Can these solutions replace turning off screens?

The answer is no, or at least not entirely. These filters do reduce the amount of blue light but do not eliminate it completely. Moreover, they do not address other factors that disrupt sleep: cognitive and emotional stimulation, behavioral engagement that delays bedtime.

Filters can be used as a complement to reduce exposure in the early evening, but they should not serve as an excuse to keep screens on until bedtime.

Implementing the rule in daily life

Clearly communicate the rule

As with any family rule, clear communication is essential. Announce the rule to your children, explain the reasons in an age-appropriate manner ("your brain needs to gently prepare for sleep, and screens prevent it from doing so"), and apply it consistently.

Visually display the rule if necessary: a clock indicating the screen-off time, an evening schedule, a reminder in the living space.

Create an environment that facilitates adherence to the rule

Arrange your home to facilitate adherence to this rule. Ideally, screens should not be present in children's bedrooms. A centralized charging station where devices spend the night, set up in a common area, avoids the temptation of nighttime use.

Provide attractive alternatives for the hour before bedtime: books, board games, puzzles, calm creative activities, family discussion time.

Establish a calming evening routine

The screen-free hour ideally fits into a structured and calming evening routine. This routine can include: family dinner, a time for quiet play or creative activity, bath or shower, teeth brushing, and finally a time for reading or quiet exchanges before lights out.

This routine creates markers that signal to the brain that sleep is approaching. It advantageously replaces screen stimulation with activities that truly prepare for rest.

Managing resistance

Children accustomed to screens in the evening will likely resist the change. Anticipate this resistance and be prepared to stand firm.

For younger children, the transition can be gradual: first reduce to 30 minutes before bedtime, then to one hour. For older children, dialogue and explaining the stakes can help with adherence.

Stay firm and consistent. The first weeks may be difficult, but once the new habit is established, the benefits for sleep and the family atmosphere in the evening should be visible and appreciated by all.

The parental example

Apply the rule to the whole family

As with all rules regarding screens, the parental example is crucial. If you ask your children to put down their screens at 7:30 PM but spend the evening on your smartphone, your credibility is compromised.

Make the screen-free hour a family rule that applies to everyone. It's an opportunity to share moments together: playing a board game, discussing the day, each reading their book in shared calm.

The benefits for adults too

Adults also suffer from exposure to screens in the evening. Sleep disorders are epidemic in our hyperconnected society, and the blue light from screens contributes significantly to this.

By applying the rule to yourself, you are not only setting an example: you are taking care of your own sleep and health. Well-rested parents are more patient, more available, and more effective in all dimensions of their lives.

Frequently Asked Questions

My child falls asleep very well in front of the TV, isn't that a sign that it doesn't disturb him?

Falling asleep in front of the television is a false friend. The child falls asleep, indeed, but in conditions that do not promote quality sleep. The noise and light from the television in the background fragment sleep, preventing deep restorative sleep phases.

Moreover, this habit creates a dependency: the child becomes unable to fall asleep without the television. This crutch will be difficult to remove later and does not prepare for healthy and autonomous sleep hygiene.

Are e-books on e-readers acceptable?

It depends on the type of e-reader. E-ink e-readers (like the Kindle Paperwhite used without lighting) do not emit blue light and are comparable to a paper book. They are therefore acceptable in the evening.

On the other hand, tablets used as e-readers (iPad, Android tablets) or e-readers with LED backlighting pose the same problems as other screens. If your child reads on this type of device, apply the same stopping rule one hour before bedtime.

My teenager needs their phone for the alarm, what should I do?

This objection is common but easily circumvented. A classic alarm clock (there are very good ones available at low prices) perfectly replaces the alarm function of the phone. The phone can then spend the night in a different place than the bedroom, eliminating the temptation for nighttime or morning use.

If the teenager resists this solution, it is probably a sign that they are using their phone for something other than the alarm during the night. All the more reason to establish this rule.

Tools for Balanced Use

Apps that Respect Rhythms

Some apps integrate features that promote respectful use of biological rhythms. Dark modes and automatic blue light filters in the evening are a first step.

Training to Understand Better

Understanding the mechanisms of sleep and the impact of screens helps maintain motivation to apply the rules.

To raise awareness among the children themselves, DYNSEO's screen awareness workshop offers suitable educational resources. Discover the workshop

Conclusion: An Hour That Changes Everything

Stopping screens one hour before bedtime is one of the simplest and most effective rules you can implement to improve your children's sleep. It requires no financial investment, no particular technical skill, just consistency and perseverance.

The benefits will be felt quickly: easier falling asleep, more restful nights, children in a better mood in the morning, improved attention and learning abilities during the day. These benefits extend to the whole family.

Sleep is a fundamental pillar of children's health and development. By protecting it from the intrusion of screens, you are making a simple yet profoundly beneficial gesture for their present and future.