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Blue Light and Sleep

The jury is not out on the biological effects of light — they’re pretty well-understood. As it turns out, most of us are about as good at reducing our exposure to blue light as we are at flossing. We’re terrible at it.

The thing about blue light, is that it tends to increase our physiological arousal, promote alertness, and disturb sleep. This kind of stimulation is great first thing in the morning when we’re trying to wake up but it’s pretty lousy in the lead up to bed when our goal is to fall asleep.

Blue light isn’t exactly a new thing. Since the advent of electricity, humans have been able to control their light exposure with the flip of a switch, and now smartphones mean that many of us are taking the stimulating effect of the sun to bed with us at night.[4]

The link between our screens and sleep is complicated. Before smartphones, most of us would turn the TV off and get ready for bed. Some people would fall asleep while watching television. So doctors began recommending that people sleep with the television off or at low volume levels so as not to interfere with sleep — a practice that doctors still recommend for the best sleep.[1

Now, we use devices everywhere, even in bed, which has posed a similar set problems as the TV once did but now on a much larger scale — effectively most people are bringing their TVs to bed with them every night.

The primary problem with these screens is that they emit blue light which tricks our brains and restricts our brain’s melatonin production. Melatonin is the hormone that makes you feel tired. If you don’t feel tired, it can be difficult to quiet your mind and fall asleep.

There’s no shortage of evidence linking cell phones and other screened devices to sleep problems ranging from not getting enough sleep to hormone imbalances triggering insomnia. 

The problem

Cell phone screens and back lights are made of electrical components called light-emitting diodes, or LED lights, which emit a bright type of light known as blue light. This light is of a similar spectrum as the light you interact with during the day. 

If you’re not getting enough sleep at night, one reason may be too much late-night smartphone use. If you’re having trouble falling asleep because you don’t feel tired at bedtime, this blue light may be the culprit. 

While it may be second nature to you to read your smartphone in bed at the end of the day, this habit actually interferes with your ability to obtain good quality sleep. This is because of the properties of blue light that promote alertness.  

Luckily there are steps you can take to reduce your blue light exposure at night and allow your brain to produce the natural melatonin it needs. We’ll get to that later.

What is blue light?

Light is made up of electromagnetic particles that travel in waves. The bright white light emitted from the sun is actually a combination of several different wavelengths of light.

Sunlight appears to our eyes as white light, though it contains red, orange, yellow, green, blue, indigo, and violet light.[2]  This is because sunlight represents the sum of the frequencies of these different forms of light in the visible portion of the electromagnetic spectrum.[3]

Blue light, refers to a subtype of light in the visible portion of the electromagnetic spectrum. Blue wavelengths are the shortest and contain the most energy in the visible spectrum. Light that appears white can often have a large blue component, as is the case with LED-based devices such as smartphones and tablets.

While the sun is the largest known source of blue light, you can also obtain blue light from fluorescent lights, LED lights, flat-screen LED televisions, and the screens of computer monitors, smart phones, and tablets.[2]

Smartphones are a major source of blue light

While the blue light you obtain from screens is small compared to that obtained from the sun, the timing of when you are exposed to blue light can be instrumental in determining when you sleep.  

That’s because your brain uses blue light to set your sleep schedule, a process known as entrainment. [4] Your circadian rhythms rely on light input to determine when you should be asleep and when you should be awake.  

Typically, our bodies rely on zeitgebers, which are environmental cues that set our natural sleep-wake cycles. These cues can include the different sunlight hues during the day and evening, atmospheric conditions, temperature, exercise, eating and drinking patterns and even social interactions.

As screens play an ever-growing role in our everyday experience from a computer at work to our smartphones, watches and tablets, scientists and doctors are becoming increasingly concerned about the long-term effects of screen exposure from blue light emitting devices.

With people on average spending three hours and 15 minutes on their phones daily, That’s a lot of blue light exposure.

What are the advantages and disadvantages of blue light?

The main advantage of blue light is that it is bright and illuminating and helps you see your smartphone screen clearly.  Blue light, such as that obtained from the sun, can also help set your sleeping patterns and make sure they match up with the sun’s light-dark cycles.

However, if you are trying to sleep more or get better quality sleep, too much blue light can create or exacerbate sleep problems. The eye is not good at blocking blue light, and as a result, all visible blue light passes through the structures of the eye, reaching the retina, a layer of sensory cells at the back of the eyeball that are sensitive to light. 

In fact, studies have shown that overexposure to blue light can even damage the cells of the retina and contribute to macular degeneration.[5]

Besides causing visual problems and affecting sleep, blue light from computer screens and smartphones can also decrease visual contrast and cause eye strain, which is characterized by eye irritation and difficulty focusing.  

Blue light, melatonin, and cortisol

The science has also shown that blue light can suppress the secretion of the sleep-promoting compound melatonin, which can reduce your ability to fall asleep and stay asleep at night. 

As it turns out, light in general, whether in the blue or red spectrum, elevates levels of the stress hormone cortisol which can further derail sleep efforts.[7]

How to reduce exposure to smartphone blue light

You’ve learned about the effects of blue light on sleep, vision, and even your body’s neurochemistry. So, you may be wondering how to reduce your exposure to this type of light, both at night so you can sleep better, and in general.

Here are a few ways to reduce exposure to blue light from digital devices:

  • Limit screen time on your personal electronic devices. Take breaks from smartphone use to give your eyes a rest.
  • Reduce the brightness of your electronic devices at night. While this does not eliminate blue light, it does reduce the overall amount of blue light to which you are exposed.
  • Use ‘night mode’ on your smartphone or laptop. Many smartphone and laptop manufacturers offer a ‘night mode’ for your screen. In night mode, warmer colors in the device’s display, such as reds and oranges, are enhanced, while cooler colors such as blues and purples are toned down, leading to reduced blue light radiation, which can help you sleep better. Check out Night Shift [8] for Apple devices, and “Blue Light Filter” from Samsung.[9]  Microsoft’s Windows operating system also offers a night mode.[10]
  • Invest in a blue light filter app.  If your smartphone does not offer a ‘night mode’ setting, look for blue light filter apps such as the apps recommended here.[11]
  • Consider the use of a screen filter. Screen blue light filters are available for smartphones, computers, and tablets. Screen filters work to reduce the blue light emitted from your screen so that less blue light reaches the retina.
  • Consider blue light blocking glasses.[12] Look for computer glasses with a yellow tint, as these can block out blue light to ease eye strain and reduce blue light radiation.

Keep in mind that at night, you should seek to minimize blue light. Look for alternative light sources such as red light, which has a longer wavelength and the least power to suppress melatonin secretion at night. Avoid looking at bright screens, whether on a smartphone, television, or computer, two to three hours before your bedtime.  

Finally, make sure you get exposure to lots of bright light during the daytime, which will help align your brain’s circadian rhythm with the natural light-dark cycles of the Earth.[13]


In summary, while blue light radiation is a normal part of the visible light spectrum, and is also found in sunlight, there are times of the day which you should seek to minimize your exposure to blue light in order to sleep better. 

There are a variety of tools, such as apps, computer and smartphone settings, and light-blocking filters and glasses to reduce your exposure to blue light at night. Reducing blue light at night boosts melatonin and reduces nighttime cortisol levels, promoting healthier, better-quality sleep.


Blue light: A type of visible light emitted by smartphone screens and backlights that can interfere with one’s sleeping patterns.

Entrainment: The body’s natural process of using sensory and other stimuli, such as sunlight, to set the body’s circadian rhythm, or sleep-wake cycle.  While the purpose of entrainment is to ensure that the body is in tune with the light-dark cycles of the Earth, artificial light sources such as smartphone blue light can also interrupt and interfere with entrainment, leading to sleep problems.

Retina: A layer of sensory cells at the back of the eyeball that are sensitive to light. 

Sleep-maintenance insomnia: A type of insomnia characterized by difficulty staying asleep, and more specifically, by waking up too early and being unable to go back to sleep.

Sleep-onset insomnia: A type of insomnia in which sleepers are unable to fall asleep in the beginning of the night.


  1. “Too early to get up, too late to get back to sleep.”  Harvard Medical School. Available at
  2. “Blue Light and Your Eyes.”  Prevent Blindness. Available at
  3. “What Color is the Sun?” Stanford University.  Available at
  4. Wright KP et al.  2014. “Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle.”  Curr Biol. Available at
  5. Ratnayake, K., Payton, J. L., Lakmal, O. H., & Karunarathne, A. (2018). Blue Light Excited Retinal Intercepts Cellular Signaling. Scientific Reports, 8(1), 10207. Available at:
  6. Glatter, R. 2018. “Is Blue Light From Your Smart Phone Harmful To Your Eyes?” Forbes. Available at
  7. Figueiro M and Rea M. 2010.  “The Effects of Red and Blue Lights on Circadian Variations in Cortisol, Alpha Amylase, and Melatonin.”  International Journal of Endocrinology. Available at
  8. “Use Night Shift on your iPhone, iPad, and iPod touch.”  Apple. Available at
  9. “Turn on Blue Light Filter on Your Galaxy phone.” Samsung.  Available at
  10. “Set your display for night time in Windows 10.”  Microsoft. Available at
  11. “6 Blue Light Filter Applications to Reduce Digital Eye Strain.” Lifewire. Available at
  12. Tomaine, G. 2018.  “I Wore Blue Light Blocking Glasses Every Day for a Week — Here’s What I Learned.”  Good Housekeeping. Available at
  13. “Blue light has a dark side.”  Harvard Medical School. Available at

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