A debate is raging over the beneficial and the damaging effects of blue light. On the one hand, blue light can be a helpful tool in combating winter depression and insomnia. On the other hand, blue light can permanently damage the human eye. So what's the deal with blue light? And what has changed about the artificial light we experience every day? Why do our bodies need the biological effects of this wavelength? And how and when should we protect ourselves from the potentially damaging effects of blue light? Read on to find out more about the good and the bad of blue light.
The light that reaches and enters the human eye is divided into visible light, comprising wavelengths from about 390 to 780 nm, and the non-visible spectrum, which includes light in the ultraviolet range (UV light) and the infrared range (IR light).
Experts have been aware for some time that UV light can potentially cause damage to biological tissue such as our skin and eyes, and people typically use suitable means of sun protection to address this issue. However, blue-violet light also has the potential to cause damage, especially to our eyes. Blue-violet light may have less energy than ultraviolet light, but in contrast to UV light – most of which is absorbed by the front part of the eye – blue light reaches as far as the retina.
The component of light in the blue-violet band between 390 and 500 nm is known as high-energy visible (HEV) light. Wavelengths between 390 and 440 nm are seen as particularly critical and have been implicated as one of the possible causes of photoretinitis, which involves damage to the retina caused by high-energy incident light.
Scientific studies have shown that light has a biological effect on our body, among other things helping to regulate our hormone balance. The hormone melatonin plays a significant role in regulating our sleep/wake cycle, and the light energy that we require for this process is largely absorbed through our eyes. Another key factor in this process is a light-absorbing pigment in the eye called melanopsin, which has been shown to be most active in the short-wavelength portion of the visible spectrum. That means that the blue light which reaches our retina also plays a part in ensuring our psychological well-being, which is why light therapy is successfully employed to treat winter depression and insomnia.
UV light is also involved in the production of vitamins, which means that light stimulation also has an important effect on our metabolism. In summary, our bodies need blue light.
To take one concrete example, many people are familiar with the concept of age-related insomnia, which refers to the fact that elderly people seem to require less sleep. The light that reaches the human eye seems to play an important role in this phenomenon. The cataracts that older people typically suffer from, prevent some of the blue light from reaching the retina – and the intraocular lenses used to treat patients with cataracts also have the effect of blocking blue light. This might causes perturbations in the day-night rhythm of these mostly elderly individuals and alters the amount of sleep they need.
But as in so many other cases, the rule that applies here is "everything in moderation."
Too much light in the ultraviolet and blue-violet bands can damage the human eye. As well as leading to painful inflammation of the conjunctiva and cornea, it can also cause damage to the eye's crystalline lens (e.g. cataracts) and especially to the retina (macular degeneration).
That's why it is so important to wear sunglasses with 100% UV protection in strong sunshine, especially in situations where there is a lot of glare such as on water or snowy mountain slopes.
From light-emitting diodes (LEDs) and xenon light to energy-saving bulbs and electromagnetic radiation from screens, all the "new light sources" that are designed to make our lives better and easier contain a higher proportion of blue light than the old traditional light bulbs. The different spectral composition of the light means that we are exposed to significantly more blue light than before. Could this be having a detrimental effect on our eyesight?
So far no studies have been carried out to answer questions such as whether using computer displays or staring at these new sources of light for long periods of time could damage the retina. But it is important to remember that spending one hour outside on a normal overcast day exposes our eyes to 30 times more blue light than spending one hour inside sitting in front of a screen.
It makes sense that clear spectacle lenses do not require UV protection if we mainly wear them indoors. However, it is possible to get clear lenses with a blue light filter, such as DuraVision® Blue Protect. But why?
Blue light radiation from light sources or screens can be irritating or tiring for some people's eyes. A blue filter can provide people with sharper vision: the different wavelengths of visible light are refracted in slightly different ways by the cornea and crystalline lens, so not all of them strike the same focal point on the retina. Some people will be familiar with these kind of phenomena – for example the fact that it's easier to clearly see red at a distance and blue close up, or the way in which infographics with red, green and blue lines are more tiring to keep in focus than lines which are all shaded in the same or similar colours.
Some people find that light sources with a high proportion of blue light can make them feel more restless at night. When we find ourselves in a dark room or outside at dusk or at night-time, our eyes switch to a different mode of vision. In low light the human eye shifts from green sensitivity to the high-energy blue spectrum. That means we perceive blue light more intensely, which can give the sensation of increased glare. This effect will be familiar to drivers who have been blinded by the glaring headlights of oncoming vehicles, especially those with modern xenon or LED headlights. Spectacle lenses with a blue light filter can create more comfortable vision in these situations.
DuraVision® BlueProtect is a lens coating for clear lenses which can be applied as an additional layer. It offers all the benefits of a traditional DuraVision® Premium coating by ZEISS, including optimized hardness in an easy-clean design. BlueProtect also includes a blue filter which attenuates blue light in the 390 to 440 nm band. That means improved visual comfort for anyone who wants protection against blue light during indoor activities without losing the beneficial effects of blue light in the 450 to 500 nm band! Spectacles with DuraVision® BlueProtect can be worn all day long, unless you choose to wear your sunglasses for outdoor activities or use PhotoFusion® lenses, which also offer 100% UV protection.
Tablets, smart phones and other digital displays are not only changing the light spectrum we are exposed to – they are also changing our visual behaviour. It's important to recognize that we are spending far more time looking at things "close up" than we did before. That's often because the background brightness is too low. This is even a problem among children: "school myopia" refers to the increasing propensity of children to suffer from shortsightedness once they start school.
If we fail to spend enough time looking into the distance, then our eyes don't get as much opportunity to relax, and we essentially "unlearn" the ability to focus quickly for various distances. That causes digital eye strain. In addition, we naturally blink less when we're staring at digital displays, so our cornea is moistened less frequently by tear fluid. This can lead to tired, strained eyes. And in the worst case it can even impair our vision.
Our tip: We recommend giving your eyes more frequent breaks by looking into the distance much more often – even when you are in the middle of working on your laptop, tablet or smartphone. And make sure your eyes are exposed to enough brightness while ensuring they are adequately protected against excessive UV and and blue-violet light.