If you’ve ever had trouble sleeping, you may have been advised to keep off your phone — and any other electronic screen for that matter — at least an hour before bed. This is because the blue light that your screen emits interferes with your body’s inner biological clock, your circadian rhythm, and confuses it with the daytime when it is bright outside and you’re wide awake. Blue light on its own is not necessarily harmful; it actually benefits us in situations where attention, memory and alertness are required — during the daytime, when most of us are awake. However, exposure to blue light at times other than when required to be awake (such as the nighttime) can be potentially harmful; blue light and sleep don't go well together, and can encourage a host of subsequent health concerns — including depression, diabetes, obesity and cardiovascular diseases. Fortunately, most of these harmful effects of blue light can be avoided by implementing good sleep hygiene, which ensures you get enough quality sleep for regular body functioning.

What is blue light and how does it work?

All the light and different colors that we see are actually electromagnetic radiation (EM radiation) traveling through waves of varied frequencies. Blue light belongs to a range of colors on the visible light spectrum — a fraction of the greater electromagnetic spectrum, seated between ultraviolet rays and infrared rays — and is the only type of EM radiation that is detectable by the human eye. Blue light has the second-highest frequency range of 620-670Hz, right in line after violet (670-790Hz). It also has the second shortest wavelength on the color spectrum, which ranges from violet to red. The short wavelength and high frequency of blue light results in light with significantly higher energy than colors on the opposite end of the spectrum (red). This explains why blue light has been linked to greater alertness and improved attention span, among other beneficial effects of blue light. 

What are common sources of blue light?

When talking about blue light, most people automatically think of cell phones, TVs and other electronic devices with digital screens. While these are, indeed, familiar sources of blue light, there is another more common source of blue light that we don’t typically think about: the sun.

The sun emits rays of all colors on the rainbow: red, orange, yellow, green, blue, indigo and violet (or ROYGBIV). This concept is better demonstrated by Newton and his glass prism experiment in 1665. Newton was curious about light and color, and particularly about sunlight, which appeared to him as a white color. To figure out the true color of sunlight, Newton’s experiment played with color refraction off of a glass prism. Newton darkened his room to allow only one sliver of sunlight to come through the window. He placed the glass prism in the line of sunlight and was met with an astounding display of colors (ROYGBIV). The glass prism was able to separate all the colors found in white sunlight based on the refraction of light at an angle. His prism experiment found that sunlight, although it appears white, contains all colors of light — including blue.

Aside from sunlight, most artificial lighting we find indoors, such as fluorescent and LED lights, are also huge culprits of blue light emittance. Some of these bulbs emit a brighter, white light made from red, green and blue. You can notice this in the blue-white tint of the light when you turn your light on. Although they are energy-saving, LED lights are not ideal lighting sources for when you are about to head to bed. Bulbs with a warmer light are more suitable for the bedroom and for before bedtime, helping to avoid the blue light and sleep issues that can arise.

Last but not least, most electronics with digital screens are potent sources of blue light. This could be your e-reader, your bedroom TV, your laptop, your Carplay system or any other common device you use. These devices and digital screens emit high-energy blue light that may disrupt your inner biological clock when it comes time to sleep. 

What are the benefits of blue light?

Our bodies are designed to rise with the sun and sleep in the dark.

Blue light, whether it be from sunlight or artificial sources, is a subtle nudge to your body to stay awake. Blue light happens to be one of the more potent sources of high-energy light, which explains its associations with improved memory and greater attention and alertness. When exposed to blue light, your body suppresses the production of melatonin, the hormone associated with the regulation of your circadian rhythm (hence blue light and sleep don't mesh). Research finds that 6.5 hours of exposure to blue light compared to the same time of exposure to green light (lower energy) results in twice the amount of melatonin suppression as for the latter. In addition, blue light exposure activates the melanopsin photosensitive retinal ganglion cells (mRGCs), neurons found in your eye, which project to and activate the locus coeuleus — the part of your brain associated with releasing norepinephrine through the cerebral cortex. Norepinephrine, a hormone and neurotransmitter, helps increase alertness and attention and influences your mood, memory and sleep. With all these cues, the body recognizes that it is not yet time to sleep so it does its best to remain alert. This helps us stay awake during the day when we need to do work and be productive.

A five-month study of different correlated color temperature (CCT) lighting and their influence on Grade 2 student behavior in a public elementary school found that higher levels of CCT lighting (blue light), as opposed to lower levels of CCT lighting (red light), were associated with more on-task student behavior in the classroom. In other words, blue light — as opposed to red light — seemed to encourage students to concentrate on their assigned tasks, thereby increasing their productivity. Interestingly enough, this same study also found that higher levels of CCT lighting (blue light) led to more physical movement around the classroom, particularly amongst the male students. This study, and many others, showed that blue light can be strategically utilized to improve working and learning environments where attention, alertness and memory are crucial. 

When blue light becomes potentially harmful

Although blue light is helpful during the daytime when we are awake, its same beneficial qualities prove detrimental during the evenings right before bed. Blue light signals our bodies to keep awake when our bodies are trying to unwind and relax before sleep. What results is an extension of the waking hours of your day into your sleep time and an inevitable disruption to your circadian rhythm. Chronic disruptions to your circadian rhythm may increase the chances of developing certain diseases and health conditions including cancer, cardiovascular disease, diabetes, obesity, depression and gastrointestinal and digestive issues. Circadian rhythm sleep disorders (CRSD), including delayed sleep-wake phase disorder (DSPD) — where your sleep pattern is disrupted by a delay of two or more hours and resulting in a later wake time, may also develop. 

The negative relationship between blue light and sleep relates to the fact that when sleep quality or duration are disrupted, a host of subsequent health issues follow suit. Inferior sleep patterns are harmful to everyone’s health, but prove to be even more challenging to those with existing metabolic health conditions, such as diabetes. Sleep helps you better regulate levels of blood sugar throughout the day, which is why sleep is a critical factor in diabetes management. Furthermore, sleep quality and duration directly impact how well your muscles recover from exercise, which in turn can impact your ability to optimally manage your weight and keep your immune system healthy, among other physiological impacts. (Learn more: Why Is Sleep Important For Muscle Recovery?)

How long before bed should I avoid blue light?

If blue light at night impacts your ability to get quality sleep at night, you may wonder: “How long before bed should I avoid blue light?” Sleep experts recommend cutting off screen time 1-3 hours before bed. However, it’s not so much the preciseness of time that counts, but the habit of staying away from screens right before bed. 

Avoiding the harmful effects of blue light

Some of us are night owls and our best work is done at night. Others of us work the graveyard shift and don’t have a choice in the matter. Regardless of your preference or situation, your exposure to light at night (LAN) — and especially its impact on your sleep — can be harmful to your overall health. Fortunately, there are tiny changes you can adopt to minimize the potentially harmful effects of blue light:

• For digital screens on your cell phone, laptop, or computer, you can adjust your device settings or install an app to filter out blue light. Most Apple products have the Night Shift setting, which adjusts the display colors on your screen to a warmer hue and reduces the amount of blue light your screen emits. Many Android and Windows operating systems have similar features you can take advantage of. There are also many free blue light filter software programs, such as Iris Mini, f.lux or Redshift, that you can download on your laptop or computer to minimize blue light exposure at night. 

• For a more up close and personal blue light filter, consider investing in blue light filter glasses. They may look like your average pair of glasses, but their lenses are crafted with special filtering technology to block out some of the blue light that digital screens emit. Some blue light filter lenses may even have a warm tint to them, such as an amber color. A 2018 randomized trial of 14 participants with insomnia attempted to measure the efficacy of such amber-lensed blue light filtering glasses by comparing them to clear placebo lenses and observing their impact on the participants’ sleep. The results of this seven-day study found that wearing amber-lensed blue light filtering glasses two hours before bed, compared to wearing clear-lense glasses two hours before bed, improved sleep for the participants who suffered from insomnia. Blue light filtering glasses may not block all the blue light emittance from your devices and screens, but at the very least they can help mitigate the effects of blue light.

While these apps, settings and blue-light filtering products do help to decrease blue light emittance from your screens, don’t count on them to shield you from the inevitable effect of LAN: interference with your inner biological clock and disruptions to your sleep.

Key takeaways

The culture of instant gratification and the increasing demands of work have caused an inevitable addiction to our phones, laptops and TVs. If you’ve ever caught yourself quitting one screen only to hop onto another, you know exactly what we mean. Aside from affecting our ability to concentrate and be productive, these devices and digital screens emit potent blue light that affects our bodies. During the right time of the day, blue light can actually be beneficial to us; it suppresses melatonin production in the body and encourages the release of norepinephrine, the hormone and neurotransmitter associated with increased alertness and attention. However, during the nighttime — when most of us are getting ready for bed — these same qualities of blue light make it harder for us to fall asleep, leading to poor and disrupted sleep. Sleep, so crucial to maintaining optimal health (particularly for those with diabetes and other chronic disorders), can be compromised by evening exposure to blue light. Therefore, making a concerted effort to minimize blue light exposure at night — and practicing other habits of good sleep hygiene — can truly improve your health.