How Blocking 400nm to 550nm Light Improves Sleep

Blue light glasses are a great option to fall asleep faster and improve the quality of your sleep. Glasses which block blue and green light between 400nm and 550nm have been shown to impede the capacity of bright light to suppress melatonin production. This is the key to how blue light glasses can help you take control of sleep issues.

In a world filled with screens, bulbs, and other sources of light, its easy to throw off your body's natural ability to wind down at night. In this article, we'll explain why 400-550nm light is a great option to improve your sleep.

What is 400-550nm Light?

The visible light spectrum consists of a small segment of wavelengths that make up the electromagnetic radiation spectrum - it ranges from 380-780 nanometers (nm). Blue light is between 400 nm and 490 nm, which is why blue wavelengths of light are often called short wavelengths of visible light.

Blue light is emitted all around us, every day — both indoors and outdoors, from the screens on our digital device to the sun. Extended exposure to certain wavelengths of light may cause eye fatigue and discomfort, but don’t worry! Our blue light filtering glasses and computer screen glasses can reduce your exposure to potentially harmful blue light.

The Sleep-Disrupting Effects of 400-550nm Light

Light, especially light with a wavelength of 400-550nm, substantially interacts with your biological clock which in turn impacts your sleep-wake cycle. Light exposure too close to your bedtime impedes your body's ability to fall asleep quickly and to have restful sleep once you do fall asleep.

Contrary to popular belief, your biological clock isn’t a single internal clock. It's actually a network of peripheral clocks distributed across organ systems and cells. The master circadian clock is called the suprachiasmatic nucleus (SCN) - it runs these peripheral clocks on a tight ship. The SCN receives internal and external circadian cues to kick off a series of biological processes pivotal to your day-to-day functioning.

Among these circadian cues, light exposure is thought to be the most potent one for humans. Light starts and stops your circadian rhythm, which in turn, influences your wake and sleep times. In that sense, light (especially blue light) acts as a double-edged sword that can keep your body clock on track or throw it off course.

When it comes to keeping your body clock on track, it’s very important to get light first thing in the morning. This is the cue to your body to suppress melatonin now that it’s morning, but it also tells your body to start producing melatonin again 14 to 16 hours later.

However, as we mentioned, light can also throw your body clock off course and cause circadian misalignment. To understand how circadian misalignment holds you back from the sleep you need, let’s take a look at the interaction between nighttime blue light exposure and your body’s melatonin production.

Two to three hours before your bedtime, your body starts producing melatonin. This is called the dim light melatonin onset (DLMO) and marks the start of your daily Melatonin window. This is the window of time that your body generates peak levels of melatonin to give you the best chance of falling asleep and sleeping through the night. To take advantage of this window, you need to go to bed during it.

Unfortunately, blue light exposure foils your body's attempts to synthesize melatonin. This is due to a special group of neurons in your retina called the intrinsically photosensitive retinal ganglion cells (ipRGCs). The ipRGCs send light signals to the SCN to run interference with your sleep-wake cycle.

Although the primary function of ipRGCs is to promote circadian alignment, untimely blue light exposure can lead to the opposite. That's because ipRGCs express the photopigment melanopsin. In the presence of blue light, melanopsin suppresses your natural melatonin production. This will delay your Melatonin window, and you will naturally find it harder to drift off to sleep at your normal bedtime.

The reason being, ipRGCs' response to light exposure does not immediately turn off in the absence of light. It will take some time for your body's melatonin production to start working again after you've extinguished all light sources. Predictably, your target bedtime is pushed back further. This cuts into your sleep duration.

Research also indicates blue light exposure disrupts normal sleep patterns as it:

  • Significantly reduces REM (rapid eye movement) sleep
  • Suppresses deep sleep in the first few hours before its rebound in the early morning

All of these blue-light-induced biological changes prevent you from getting naturalistic sleep — meaning you wake up not feeling and functioning at your best.

How do 400-550nm Blocking Glasses Work?

Blue light glasses improve sleep by inducing dim-light melatonin onset by reducing activation of intrinsically photosensitive retinal ganglion cells (ipRGCs).

ipRGCs are the cells in your retina that are most sensitive to blue light and are a major input for circadian regulation, which is your body's 24-hour hour cycle to regulate physical, mental, and behavioral changes over the course of your day. Researchers have also linked ipRGCs to mood regulation.

Here’s what happens when you put on blue-light blocking glasses:

  • The glasses block out all blue wavelengths, preventing blue light from entering your eyes.
  • In the absence of blue light, the ipRGCs in your retina aren't activated to produce melanopsin.
  • Your body then produces sufficient melatonin as per normal to help you get enough sleep.

What Does Research Say About 400-550nm Blocking Glasses for Sleep?

This is one of those rare questions that virtually all researchers, clinicians, and those interested in sleep can agree on. Blue light glasses are affective for improving sleep. 

Researchers at the University of Oklahoma College of Medicine's Department of Psychiatry and Behavioral Sciences conducted a meta-analysis of 29 experimental publications involving evening wear of blue light blocking glasses for sleep or mood disorders. Of those 29 studies, 24 were specifically focused on blue light glasses for sleep.

Here are excerpts from a few of the studies:

  • A recent systematic review published in the Journal of Chronobiology International shows "substantial evidence for blue-blocking glasses" in inducing sleep in people with insomnia, jet lag, and shift work. More significantly, these eyeglasses helped participants fall asleep more quickly. 
  • The Journal of Ophthalmic and Physiological Optics reports blue-light filtering glasses "decreased night-time stimulation of ipRGCs." This led to a 58% increase in nighttime melatonin levels and regulated sleep patterns among test subjects.
  • The Journal of Lighting Research and Technology found that wearing blue-light blocking glasses while using light-emitting devices helped avoid melatonin suppression in teenagers.

Out of the 24 publications focusing on sleep that were reviewed in the meta-analysis above, there was substantial evidence for blue light blocking glasses being a successful intervention for reducing sleep onset latency in patients with sleep disorders, jet lag, or variable shift work schedules.

Ultimately, the researchers stated that Blue Light Glasses are effective to:

  • Help you meet your sleep goals: Wearing blue light glasses at the right time ensures your body produces optimal melatonin levels nearer to your desired bedtime so you can fall asleep more quickly and stay asleep throughout the night
  • Give you the energy you need for the day: Achieving healthy levels of sleep by consistently meeting your sleep need helps ensure that your energy levels are sufficient to keep you functioning optimally throughout the day

Given that the biological mechanism for blue light glasses is well-established and that clinical research has shown that blue-blocking glasses are effective for inducing sleep, it's safe to say that blue light glasses are a viable intervention to recommend to people with insomnia or a delayed sleep phase, particularly for people who have high screen-usage time at night.

When Should I Wear Blue Light Glasses for Sleep?

Because ipRGCs are capable of "very long-lasting light responses," exposing yourself to blue light for an hour will often sustain melanopsin production longer than that. To maximize the sleep-inducing benefit of blue light blocking glasses, we recommend wearing them 60 minutes before you plan to go to sleep.

The rationale is to give your body sufficient time to wane melanopsin levels and start your melatonin production. By the time you're ready for bed, your body will be more likely to have optimal melatonin levels. Predictably, you fall asleep easily and stay asleep throughout the night.

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