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The Hidden Dangers of Blue Light

Before artificial lights were invented, people mainly lived by the light of the sun. Evenings were spent in darkness, with perhaps some candles for a modicum of light. Today, the evenings are as bright as the day, and we don’t even think about the fact that this light is quite unusual. Unfortunately, it seems that we might be paying an expensive price for this. Research has demonstrated that if we are exposed to light during the night, our circadian rhythm, or biological clock, becomes disrupted. As a result, the quality of our sleep is affected. Perhaps more worrying, however, is that recent research has demonstrated that this could lead to serious health conditions, including obesity, heart disease, diabetes, and cancer.

Because of those concerns, further research is taking place. One of the most interesting outcomes of this is that different types of light affect us in different ways. Blue light, for instance, is beneficial during the day as it helps us pay more attention, react more quickly, and have a better mood. However, it is this very type of light that is the most problematic at night. And because we now use so much time staring at screens and using energy efficient light, we are exposed to far too much blue light, particularly once it is dark.

Understanding Blue Light

Blue light is visible light that is high in energy and is close to the ultraviolet rays in frequency, which is potentially harmful. Normally, blue light goes through the eye to the retina as it is a visible type of light, meaning our eyes are designed to be able to see it. When light is visible, it triggers biological responses that allow us to see.

There has been a significant amount of research over the past three decades that have shown that UV light can actually harm the eye, as well as having been linked to conditions such as growths on the eye, pterygia, and cataracts. There is also some suggestion that it may lead to age-related macular degeneration (AMD). Because of this research, the majority of sunglasses, eyeglasses, and even contact lenses, have been made so that they block UV light.

LED lights, high-intensity headlights, and compact fluorescent bulbs all emit higher levels of blue light than the old fashioned incandescent bulbs. This has caused people to be overexposed to blue lights. Additionally, this type of light is found in tablets, cellphones, computer monitors, and TV screens. When people are exposed to too much blue light, the focusing system of the eye is placed under far more strain.

The Harvard Study

In a recent Harvard study, researchers first looked at how circadian rhythms were influence by light. They found that the rhythm is different for everybody, but an average length of 24 1/4 hours is normal. If people stay up late, they have a slightly longer length, and vice versa. In 1981, Dr. Charles Czeisler showed that daylight ensures that the circadian rhythm remains aligned with the natural environment.

Many studies have shown that when people are exposed to light during the night, for instance, when they work night shifts, they are more likely to develop certain types of cancer, including prostate and breast cancer. Other associated health concerns include obesity, heart disease, and diabetes. Researchers do not yet know why this happens, other than that melatonin is suppressed when exposed to light. Melatonin is an essential hormone in the regulation of the circadian rhythm.

During the Harvard study, some information was released about the connection between melatonin and obesity and diabetes. Ten people were placed on a schedule to change their circadian rhythm. During the course of the study, they entered a prediabetic state due to increases in blood sugar levels. Their leptin levels decreased, and this hormone is needed to ensure that people feel full after a meal.

The study also showed that dim light can have an effect on melatonin and circadian rhythms. Just eight lux, lux being a level of brightness, can disrupt sleep rhythms, according to one piece of research. It is now believed that one of the reasons why so many people get insufficient sleep is because of light exposure. This lack of sleep, in turn, can lead to an increased risk of cardiovascular problems, diabetes, and depression.

All light has the potential to suppress melatonin, but it seems that night time exposure to blue light is the worst of all. In the Harvard study, researchers looked at the difference between exposure to green light and blue light over a period of six and a half hours. The results demonstrated that blue light shifted circadian rhythm by three hours, whereas green light only shifted it for one and a half hours.

The University of Toronto also performed a similar study. They studied the difference between people who did not wear goggles and would be exposed to dim light, and those who were exposed to bright light but wore blue-light blocking goggles. It was found that the two groups had similar levels of melatonin. This does suggest that blue light could suppress melatonin very strongly. Additionally, it suggests that those who struggle to sleep at night, be that due to work or due to disrupted rhythms, could protect themselves by wearing goggles. Unfortunately, most commercially available goggles also block other types of lights, meaning they are not suitable for indoor use. Those that only block out blue light are very expensive.

Blue light, clearly, has a negative impact on health. While we all strive to become more energy efficient, this actually has a detrimental effect on overall health. One suggestion, therefore, is that the coating inside LED lights be changed. This could ensure that they remain energy efficient, but that they emit less blue light.

What Individuals Can Do

As a result of the Harvard study, a number of recommendations have been made:

  • Use red nightlights instead, as these have the least power.
  • Do not use any screens between two and three hours before going to bed.
  • Wear blue light blocking goggles if you work nightshifts or otherwise must use screens at night.
  • Make sure you get plenty of bright natural light in daytime, so that your biological clock is ready for sleep at night.

The National Taiwan University’s College of Medicine Study

The National Taiwan University’s College of Medicine completed a similar study as the Harvard study in a response to the Canadian government changing the standards for energy efficient light bulbs in 2014. While they looked to a certain degree at the impact of this type of light on melatonin and sleep, they also looked at how this type of light could damage the retinal cells.

This particular study was performed on rats, in which they were exposed to conditions mimicking the lighting used in the average domestic property. What this study showed was that, after just nine days of exposure, the retinal cells in rats were damaged, both in those exposed to cool white and blue LED lighting. Rats who were not exposed to any type of artificial lighting showed much less retinal damage. They did show some damage, however, and this is believed to be due to the fact that all the rats in the study were all albino rats. However, the researchers felt that their study showed the lights not only damaged retinal cells, but that they damaged them irreparably as well.

At the same time, the researchers, professors of ophthalmology and epidemiology, did want to ensure that people understood the benefits of blue light as well. If exposure happens during the day, it has the potential to protect people against myopia. This is even after natural light exposure, which has far greater levels of blue light.

The Benefits of Blue Light

Visual light has a number of physiological benefits. Blue light, specifically, relates strongly to our biological rhythm, also known as the sleep/wake cycle. When exposed to blue light at the right time, it helps us to stay awake and it ensures our brain can tell us when we start to get tired. However, by using electronic equipment in the dark, in close proximity to our eyes, we are disrupting this significantly. Choosing to switch off two to three hours before sleep will ensure we do not experience blue light damage, but only use its benefits to our overall health instead.

Resources and References:

Harvard Health Publications – Blue Light Has a Dark Side (

Environmental Health Perspectives – White Light-Emitting Diodes (LEDs) at Domestic Lighting Levels and Retinal Injury in a Rat Model (

Points De Vue – The Benefits and Dangers of Blue Light (