By Brandon Peters, MD

In a world increasingly dependent on technology, bright screens are more commonly part of our everyday life. These screens range broadly in size and purpose: televisions, computers, tablets, smartphones, e-books, and even wearable tech. How does this artificial light, especially when viewed at night, potentially impact our sleep? Learn how light at night affects our body’s circadian rhythm and whether it might contribute to insomnia and difficulty awakening. In addition, consider ways to reduce light exposure and counteract its effects.

Before Thomas Edison and His Light Bulb

It is hard to imagine a time before artificial light existed. It is such an integral part of our lives that we consider ourselves deeply inconvenienced when we lose power in a storm. Think back to what life was like before modern technology like computers and televisions, before light bulbs, and even before electricity.

Primitive societies and people were highly dependent on the natural availability of light. The sun ruled life. It is no surprise that it was worshiped in ancient Egypt. When artificial light became possible, things dramatically changed.

The Influence of Light on the Body’s Functions

All life on Earth has developed patterns of activity dependent on the timing of day and night. When isolated from the natural environment, innate circadian patterns will be revealed. As an example, most humans have an internal clock that runs just over 24 hours in length. However, light profoundly affects the timing of sleep and wakefulness, metabolism, and hormone release.

Morning sunlight has a key influence on life’s functions. It promotes wakefulness and ends sleep. It can help shift the desire for sleep slightly earlier. In the winter, when sunlight comes later, we may want to sleep in or suffer from symptoms called winter depression.

Due to the length of our internal clock, our bodies have a natural tendency towards delay in the timing of our sleep. This means that we always find it easier to go to bed and wake later. Have you ever noticed how easy it is to stay up another 15 minutes but how difficult it is to wake just 15 minutes earlier? Morning sunlight can profoundly reset this internal clock.

How Artificial Light at Night Impacts Sleep

Unfortunately, artificial light at night can negatively affect the timing of our sleep. Light shifts sleep timing, and light at night can shift our desire for sleep later. This can result in difficult falling asleep, as occurs with insomnia. Night owls, or those with delayed sleep phase syndrome, may be especially susceptible.

Not everyone is sensitive to these effects. If you are especially sleepy, perhaps due to inadequate total sleep time or poor sleep quality, you are unlikely to be impacted.

There are several important factors to consider:

The Source of Light

Artificial light can come from light bulbs and many other sources, including televisions, computers, tablets, smartphones, e-books, and even wearable tech. Each of these can generate a different intensity of light. Near screens may have more impact that those across a room.

The Amount of Light

Most overhead lights generate a light intensity that varies from about 500 to several thousand lux. For comparison, full sunlight at midday may be 100,000 lux in intensity. Commercially available lightboxes often generate about 10,000 lux. The screen of your smartphone may create hundreds of lux of light, depending on the settings you use. Even smaller amounts of light, such as from a tablet screen, may have an impact in some people.

The Color of Light

Much is made of the fact that blue light is responsible for shifting circadian rhythms. Full spectrum light – what you might consider as “white light” or “natural light” – contains the blue wavelengths. Blue-blocker sunglasses (with an amber or orange lens) and screen filters are sold to block this light wavelength.

The Timing of Light

One of the most important variables is when you are exposed to light, including from artificial sources. There is evidence that light at night could shift your desire for sleep by about 1 hour. This delays your ability to fall asleep and may impact your desire to wake in the morning.

Therefore, it is very important to turn down the lights at night, especially preceding your bedtime. Some people may need to avoid excessive artificial light exposure for the 1-2 hours before going to bed. This means turning off the phone, powering down the computer, and avoiding light from tablets, e-books, and other sources.

Instead, try to stick to low-tech options: listen to some music, read a book printed on old-fashioned paper, or page through a magazine. By reducing and eliminating your exposure to light at night, you may find that you are able to sleep better. If you continue to struggle, speak with a sleep doctor about additional treatment options.

The Science of Sleep

When considering how optimal sleep occurs, it is important to understand the two primary contributors: homeostatic sleep drive and circadian rhythm. Sleep drive is the fact that the longer you stay awake, the sleepier you will become. This is due to a chemical that gradually builds in the brain with prolonged wakefulness. This chemical is called adenosine. High levels of adenosine contribute to the onset of sleep. Sleep, at least in part, is a process of clearing this chemical away until consciousness is restored. Interestingly, caffeine blocks this signal and alcohol enhances it.

The circadian rhythm is the complement to this system. It is predominately an alerting signal that strengthens during the daytime and is largely absent overnight. It becomes strongest in the late evening hours, when we would expect to feel fairly sleepy. There is a lull in the mid-afternoon, which can contribute to a desire to take a nap then. The circadian rhythm is based in our genetics, persisting without external influences. It contributes to sleep-wake propensity, hormone release, and metabolism. These processes are linked to the day-night cycle of light and darkness via the eyes.

How Light Changes Sleep

A simple anatomy lesson reveals the importance of light exposure to sleep. The eyes perceive light via the retina and pass this information along the optic nerves, extensions of the brain itself. These optic nerves receive input from each eye and cross at a location called the optic chiasm. Just above this is an area of the brain called the hypothalamus, a functional area that is integral to the control of the processes described above.

Within the hypothalamus lies the suprachiasmatic nucleus. This is the control center of the body’s circadian rhythm. It is the central pacemaker, coordinating the activities of all the body’s organs, tissues, and cells. Therefore, light input can be directly linked to the influence of many of the body’s processes.

In particular, light exposure can suppress the desire for sleep. Morning sunlight exposure may help to wake us, initiating the circadian alerting signal. In the same way, artificial light at night may affect the timing of sleep. It may contribute to insomnia in susceptible individuals, especially among those with a tendency towards being a night owl (called delayed sleep phase syndrome).

Preserving Darkness in the Night

What impact did Thomas Edison have on sleep in inventing the light bulb? As society has evolved, the potential disturbances have only expanded. With electricity, our evenings are filled with activity: televisions, computers, tablets, e-books, and phones that flicker light into our eyes. Moreover, the activity itself may keep us awake, shorten our total sleep time, and interfere with a relaxing buffer zone before bedtime. There is some evidence that light at night may adversely affect sleep.

Research has demonstrated that in the spectrum that we perceive as light, the blue wavelength is the one that can change our circadian rhythms. Therefore, industries have developed to supply filters and glasses that block the blue light. It seems that even short bursts of light, especially when of higher intensity, can impact sleep’s timing.

The sun is much more powerful in intensity compared to light from bulbs or screens. Full sunlight may be 100,000 lux in intensity while overhead lights may be just 1,000 lux. Therefore, a blast of sunlight at night could profoundly impact sleep. For susceptible individuals, artificial light may also negatively impact sleep onset and contribute to insomnia.

As a result, it is recommended that people who have difficult falling asleep may benefit from reduced light exposure prior to bedtime. Preserve the last 1 hour, and perhaps longer in highly sensitive individuals, as an electronics-free zone. Power off your screens, especially those that are closer to your eyes. It is also advisable to keep your bedroom free of electronics to preserve sleep. This is especially important advice for teens and children.

Why might some people not be bothered by light at night? The complement system, characterized by sleep drive and building levels of adenosine, could counteract these effects. If you are sleepy enough, you may not be bothered by the light. If you struggle with persisting insomnia, consider speaking with a sleep specialist to help determine ways for you to improve your sleep.

How Does Screen Light Affect Sleep?