You know the feeling — you stay up working in front of your laptop until the early hours, or you scroll through your Instagram feed on your phone before turning off the lights, and then… you just can't fall asleep. You know you're tired - you yawned just a minute ago. So what's going on? Blame the blue light emanating from your electronic devices like your computer, tablet, and phone.
What is Blue Light?
Go outside and get a good dose of sunshine. However, blue light is not only in sunlight; it's everywhere, including the screen you're reading this on right now. In fact, TVs, computers and mobile phones mostly use blue light for their screens. Due to its efficiency and low cost, blue light has also become the dominant wavelength for everyday lighting for both home and commercial use. Blue light also comes from light-emitting diodes (LEDs), used in energy-efficient light bulbs and to illuminate TV, computer, tablet and smartphone screens. Blue light has a short wavelength, so it produces more energy than bulbs with longer wavelengths, such as red light, do.
Fun fact: 95% of the energy of blue wavelengths is converted into light, leaving only 5% wasted as heat. 
Like red light, blue light is part of the visible light spectrum, where it varies between about 380 nm and 500 nm, making it one of the shortest wavelengths with the highest energy. In natural sunlight, blue light is always present with red light, leading to numerous therapeutic effects.
Blue light can have good properties. Being exposed during the day will wake you up and make you more alert and can even improve your mood. Blue light-emitting glasses and panels are used to treat a number of problems, such as seasonal affective disorder (SAD), jet lag, and premenstrual syndrome.
Blue light doesn't just enter the body through the eyes - your skin absorbs it too. Hospitals use blue light to treat babies with jaundice - it helps to get rid of the yellow pigment bilirubin in the blood.
Blue light isn't all good news, though. Progressive LED technology has enabled us to remove the red and short-wave infrared (NIR) wavelengths from many of our primary light sources. This increases efficiency due to a higher concentration of blue wavelengths. For energy consumption and savings, this is a classic win-win scenario. But our bodies and our sleep may be the unexpected losers.
In natural sunlight, blue wavelengths always go hand in hand with red wavelengths, so our bodies, long ago, evolved to metabolize the two together. But when blue is present without red, as in most of our modern environments, there are potential negative consequences. Below we will address both the potential positive and negative health effects of excess blue light.
Not all light is created equal. Blue light is one of the highest energy and most efficient wavelengths within the light spectrum. Using it for everyday lighting was such a big advance that Shuji Nakamura won the 2014 Nobel Physics Prize for pioneering it. Blue light can have many benefits for human health, but in this case too much of a good thing becomes a bad thing.
This article will give you a brief overview of blue light: what it is, how it works, pros and cons, and the best ways to mitigate the dark side of modern blue light advancements.
Blue light, the benefits for your health
If you're trying to make the most efficient lamp or computer monitor, you want as much blue light as possible. But when it comes to your health, remember that blue always goes better with red. The blue light you get from natural sunlight can be good for you because it comes with the full spectrum of light, including therapeutic red and shortwave infrared light. Natural blue light is especially important for regulating your vital circadian rhythm, the term for your body's sleep-wake cycle.
To explain, let's go to your brain. The suprachiasmatic nucleus (SCN) is a small part of your hypothalamus and acts as the body's bio-alarm clock.  The SCN regulates your sleep cycle and if it gets a healthy dose of blue and red light during the day, you sleep better. You are also more alert and have better hormone levels, body temperature, immune function and digestion.  If you stay indoors too much and don't get enough daylight during the day, chances are your sleep isn't as well regulated and you're more tired than you should be.
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Blue light and sleep
The problem is that newer artificial lighting such as LEDS and energy-saving light bulbs (CFLs) do not contain the infrared, violet, and red light found in sunlight, and instead increase the intensity of the blue light to a level where we have not evolved. This is known as "junk light."
You're inundated with this messy light all day and most of the night — whether you're on your phone, working on your computer, or watching TV — and all this exposure to blue light is ruining your sleep. 
Too much blue light is bad for your health. It's great during the day when your body expects it, helping your brain communicate effectively with the rest of your body. But now we live in a blue-lit world where our electronics and lighting hit us with blue light at all times. Our bodies just weren't designed for blue light 24 hours a day.
Blue light messes with your circadian rhythm by suppressing melatonin - the hormone that tells your brain when it's time to sleep. Blue light tells your body that it is daytime.
That's why watching TV or scrolling on your phone right before bed can make it harder to sleep. Your body is getting all that blue light, and the color is actually telling your brain that it's the middle of the day, right before you try to fall asleep. Your SCN doesn't know or care that you have to go to work early tomorrow, it acts like it's noon when you stare at a bright screen in the dark before bed. 
Normally, the pineal gland -- an organ in the center of the brain -- releases melatonin a few hours before you go to bed. But blue light can mess up this process, making you less sleepy. Blue light does this by stimulating a type of light sensor — called intrinsically light-sensitive retinal ganglion cells (ipRGCs) — in the retina of the eye. These sensors send light information to the circadian clock and tell when it is time for the body to sleep and wake up.
Blue light directly inhibits our body's melatonin flow, impairing our ability to fall asleep, in addition to negatively impacting the quality of sleep we get. [6+7] Poor sleep over time can become a chronic condition, and exhaustion can make it much more difficult to overcome other health challenges. There are so many people who don't get enough sleep and experience the negative consequences every day. Most of these people have no idea that the artificial blue light they are surrounded by all the time is one of the biggest obstacles to a good night's sleep.
A 2014 study found that people who read before bed with a light-emitting device took longer to fall asleep, slept less deeply, and were more attentive than people who read a printed book.
More health risks from blue light
Too much blue light at night is linked to serious health problems. Your mitochondria - the power generators in your cells - have to produce a lot more energy to process blue light. If the mitochondria in your eyes are overloaded, the rest of your mitochondria can become stressed as well. This causes inflammation throughout the body, increasing your risk of serious and chronic disease. These include:
- Cancer: A recent study found a direct link between blue light exposure and an increased risk of breast and prostate cancer. People who were exposed to a lot of blue outdoor light, such as streetlights, at night had a higher risk of developing breast and prostate cancer, compared to people who were less exposed. Other studies have shown that a disrupted circadian rhythm increases your risk of cancer.
- Diabetes and weight gain: A 2016 study found that adults exposed to blue light at dinner had higher glucose levels, a slower metabolism and more insulin resistance compared to adults who ate in low-light conditions.
- Heart disease: Too much blue light disrupts your sleep, and too little sleep increases your risk of developing heart disease. Blue light is also linked to obesity and metabolic disorders, both of which are significant risk factors for cardiovascular disease.
- Vision impairment: Blue light can lead to macular degeneration - damage to the retina that often leads to vision loss. More than 11 million people over the age of 60 have some form of macular degeneration, so it's a problem close to home.
What can you do about harmful blue light exposure?
Feeling down from poor sleep and lack of energy? Here are some practical ways to reduce your artificial exposure to blue light and improve your body's natural rhythms.
- Block blue in the eyes: Look for some blue light blocking glasses and software for your devices that limit your blue exposure.
- Disconnect unnecessary electrical appliances in your bedroom: go around your room and unplug the LED to blacken your sleeping area.
- Add red: lower color temperature lighting, such as orange and red wavelengths are good choices in the dark.
- Darker environment at night: Keep the environment darker so that your body can relax after the sun goes down. Reading real books is better than a screen. Blackout window treatments and sleep masks work for many people because they block out unwanted light at night.
- Switch to night mode on your phone, tablet and PC: It's best to put all your devices away before going to sleep, but that's not always possible in this technology-driven world.
- Catch the sunrise: Romantic sunsets get all the love, but a great way to reset your circadian rhythm is to get up early and watch the sun come up.
Conclusion: red vs blue when it comes to health
Blue light has done amazing things for our lighting and electronics, but our bodies and sleep cycles pay the price when we're overloaded with artificial blue wavelengths at the wrong times. While natural blue and red light from the sun have different health benefits when taken together, blue light on its own keeps us awake at night and causes bags under our eyes in the morning. The good news is that you can easily reduce artificial blue light and add more healthy red light to your life, especially with our glasses and lamps.
Scientific sources and medical references: