What is blue light and how can I protect my eyes from it?

You’ve probably heard the term blue light a lot lately, but do you know what it really means, and should you be worried about the impact it can have on your health? ZEISS expert, Dr. Christian Lappe answers some important questions to shed more light on the topic.

We live in a digital age and we’re spending more and more time working on, and managing our lives on devices such as smartphones, tablets and computers. With the COVID-19 pandemic we’ve experienced an even bigger shift towards a digital lifestyle. In fact, research has shown that people of all ages, from all over the world have been spending significantly more time on digital devices since April 2020.¹

This lifestyle change has made people aware of blue light transmissions and the potentially harmful effect it can have on our sleep patterns, as well as our vision.

But what exactly is blue light, and is it really something we should be concerned about? Dr. Christian Lappe, Director of Scientific Affairs & Technical Communication at ZEISS Vision Care is an expert on blue light. His answers to some important questions regarding blue light will clarify a lot of concerns on the topic.

To understand what blue light is, we need a little bit of background on how the human visual system works. Only a fairly small part of the electromagnetic spectrum can be seen by the human visual system. We typically refer to this part as the “visible light spectrum” (VIS). The visible light spectrum (VIS) enables vision and the perception of visual information.

Blue light is part of this visible light spectrum, and it originates from both natural and artificial sources. It has the shortest wavelength of the visible light spectrum, but the highest light energy.

Wavelength is measured in nanometres, and the human eye can see light from approximately 380-780 nm, located in-between the adjacent spectral bands of ultraviolet radiation (UVR) up to 400 nm and infrared radiation (IR) as of 780 nm.

Yes it can. But to understand how, I need to give you a little background first.

Although highly complex, let’s think of the visual process quite simply: Light enters the eye, and illuminates the photoreceptor level of the eye’s retina. Depending on the geometry, intensity and the spectral composition of the light entering, different photoreceptors elicit specific signals. These signals are then directed along the visual path to the brain, where they are processed in the visual cortex to assist with the perception of objects in our environment.

First and foremost, light is necessary for vision. However, the impact of colours goes beyond visual processing. Colours are also connected to our biological and physiological systems which can influence and change our biorhythms, and our physiological and psychological well-being. Colours can therefore change our perception of the environment, evoke associations and emotions and influence physical rhythms and moods.

There is compelling scientific research showing that inadequate exposure of the photoreceptive retinal ganglion cells to blue light may aggravate some common age-associated ocular heath threats like macular degeneration, but can also trigger problems including sleep disorders, depression, and impaired cognitive function. Because of these findings, it has become apparent that blue light plays an important role in several very relevant elements of health and wellbeing, including circadian rhythms, that may in turn affect sleep patterns.

There is scientific evidence that high-energy visible (HEV) light in the blue and violet end of the spectrum is capable of damaging the retina via phototoxic mechanisms. The long-term effects of photo-oxidative stress can also damage the retinal cell structures.
This is true for high light intensities and spectral blue light components of natural blue light exposure e.g. from the sun.

There is also a plethora of publications concluding that typical digital displays and architectural illumination utilizing LED technology are not considered to be harmful to the human retina. The typical intensities from these sources are far below current thresholds of photobiological risks.
Therefore current scientific insights do not confirm a specific medical risk or acute hazard to the retina from digital devices and LED-type illuminations.

This being said, it is widely known that the eye should be protected from bright solar exposure including UV radiation and high-energy visible light (i.e. blue light). It’s also important to avoid staring into technical high-power sources like laser pointers (regardless of the colour of the laser beam).

Blue light is necessary for human colour and high-contrast vision, and photoentrainment of blue-light via photosensitive ganglion cells in the retina is elementary to our well-being.

Luckily evidence shows that there is no direct retinal harm from digital displays. However, there are certain opto-physical effects relating to blue light passing through the ocular media (crystalline lens and vitreous) of our eye. These effects relate to limited vision quality and perceived visual discomfort.

Because it is involved in both beneficial and harmful ocular effects, the blue light spectrum cannot be labeled as simply good or bad. ZEISS refers to this as the “dualism of blue light”. If we are to mitigate the risk of eye damage, we must do this very carefully so that we do not cause a different kind of problem.

For example, in the past some lenses contained light absorbers to reduce most or all blue light. If this approach is taken without careful thought, several problems may occur. The first is that blue-blocking lenses can make the world look intensely yellow or orange. Generally, such lenses are not tolerated very well. The second problem is the negative impact on contrast and colour vision. A third problem of removing all blue light with lenses is that it can have a negative impact on the regulation of our circadian rhythms.

So, when it comes to blue light, we are faced with a balancing act. On one hand we want to protect the retina from unnecessarily high levels of blue light that predominantly originates from the sun. We also want to moderately reduce the amount of digital blue light from digital devices in order to avoid visual discomfort and help manage so-called digital eye strain (DES). On the other hand, we don’t want to block the beneficial blue light, as it may interfere with the natural diurnal cycle of alert activity and restful sleep.

By wearing blue light glasses. However, protecting the eye, and in particular the intraocular structures from blue light, is not a straightforward process. Ocular coverage by strong colour filters and blockers are effective, but they come with severe constraints in vision, perception, and well-being.

A more complex and extremely technical challenge is to create smart blue-light filtering that attenuates the desired spectral band, but within the limitations that are acceptable for the wearer. Smart blue light filters in all-day ophthalmic lenses can be introduced via material and coating science. To get a little technical – specific substrate additives to the lens material can reduce spectra-specific light blocking or filtering through a process of absorption. The desired wavelengths are absorbed in molecules in the substrate, and the inherent photon energy is transferred in non-optical energy inside the substrate.

Another option for blue light filtering is by wearing anti blue light glasses with functional coatings of the lens surface. Such reflection coatings back-reflect the desired spectra so that reflected light does not enter the lens.
With both approaches, back-reflected light and absorbed light inside the substrate do not reach the eye and the retina.

It answers to two main needs:

1. Prevention and protection of long-term degenerative effects of high-intensity blue light exposure that comes from natural daylight. The intrinsic energy of blue light can trigger and entertain photo-oxidative stress to retinal cells. These phototoxic processes are assumed to be cumulative and can lead to ocular damage like the often mentioned Age-related Macular Degeneration (AMD).
   
   
2. The other need is related to vision comfort. Blue light may cause intraocular scatter and chromatic aberrations that are assumed to contribute to the pathology of digital eye strain. Excessive blue light is also identified as one of the culprits causing psychological glare.

Smart blue light filters in all-day ophthalmic lenses can be introduced via material and coating science. Special substrate additives to the lens material can reduce spectra-specific light blocking or filtering through a process of absorption. The desired wavelengths are absorbed in molecules in the substrate, and the inherent photon energy is transferred in non-optical energy inside the substrate.

Another way of blue light filtering is by functional coatings of the lens surface. Such reflection coatings back-reflect the desired spectra so the reflected light does not enter the lens. It should not be confused with Anti-reflection (AR) coatings that are usually applied to premium lenses to avoid unwanted reflections. A blue light protection lens coating fitted onto lenses only reflects a specific part and intensity of the desired spectrum to be blocked and therefore is a specific modification of an AR coating.