Article first published: May 2022
Last update: August 2023
This article will provide important information about blue light, including its role in normal vision, the ongoing scientific debate regarding its potential for causing eye damage, as well as the positive effects it can have on our eyes.
The human visual system is sensitive to a specific portion of the electromagnetic spectrum, known as "light." Other parts of the electromagnetic spectrum, which cannot be seen by humans, are referred to as "radiation," such as ultraviolet (UV) radiation. The visible spectrum includes wavelengths that range from approximately 380 nanometers to 780 nanometers. Blue light is a type of light with wavelengths between 380 and 500 nanometers, which is the shortest wavelength in the visible spectrum.
Transcription of the video
Question: What is blue light?
Answer: We are surrounded by radiation of different wavelengths, the so-called electromagnetic spectrum. Only a very small part of the spectrum is perceptible to us humans as visible light. This ranges from short wave blue light to longer wave red light. Blue light represents the part of the visible spectrum with the shortest wavelength between 380 and 500 nanometers and is a major component of our daylight. So, the natural source of blue light is the sun, but we are increasingly exposed to artificial light sources used indoors such as LED technology or all the displays, screens and smartphones that surround us. All these devices emit a lot of blue light. In short: blue light is part of the visible spectrum and is present in artificial and natural light sources.
In this video, ZEISS expert Dr. Christian Lappe explains blue light in more detail.
Natural blue light surrounds us all day long, as it is part of the light spectrum emitted by the sun. Before the invention of the light bulb, the human eye was only exposed to this very intense blue light from sunrise to the evening hours. Things are different nowadays, as we are surrounded by more and more artificial blue light. And the modern light sources that are in widespread use, such as LED lamps, energy-saving light bulbs, or (smartphone) displays, emit a relatively higher proportion of blue light than the "classic light bulb". So overall, we are exposed to blue light for a much longer period of time than in the past – often into the night.
Research in life-science disciplines has created an indisputable body of evidence of health hazards and biological cell damage from UV exposure. This is true for the skin as well as the eyes. The wavelength of electromagnetic radiation is connected to its photon energy by physical laws. The shorter the wavelength the higher the inherent energy. The photon energy is the culprit of possible damage to cells and molecules. It is a valid concern whether blue light can harm cells, considering that it has the highest photon energy among visible light and is next to the UV spectrum. Unlike UV research which has already resulted in findings, research on the effects of blue light is ongoing and there is currently no conclusive evidence available.
Transcription of the video
Question: Is blue light harmful to the eyes?
Answer: Blue and especially blue-violet light has very high energy due to the short wavelength and thus the potential to cause eye damage. This is especially true for the retina where the light is bundled and interacts. We must of course distinguish between long-term and acute short-term damage. A typical example of short-term effects occurs when looking into a glaring very bright light source. In this case the wavelength is almost irrelevant. We should not do that anyway because it is definitely hazardous for the eye. Long-term effects on the other hand are a separate issue. That is the continuous exposure of the retina to a specific lighting source which can lead to metabolic processes and changes in the retina. One example related to blue light is the so-called photooxidative stress. This could lead to metabolic changes associated with AMD – age-related macula degeneration. This long-term effect needs to be addressed. But the intensities of artificial blue light from LEDs and screens are far below any currently defined thresholds related to blue light hazards. The photobiological risk assessment specifies certain thresholds at which we must classify sources of light. Standard electronic lighting falls below these thresholds by a factor of 40 to 200. This doesn’t apply to outdoor activities when we spend time in daylight and are exposed to the sun outside protection from uv radiation and intense blue light is definitely a good idea. But indoor electronic devices don’t play a role in the risk assessment. Another aspect that we have to consider is the impact blue light has on health and well-being. This is a different type of effect that blue light has on humans.
ZEISS expert Dr. Christian Lappe: Is blue light harmful to the eyes?
The relatively high levels of energy inherent in the comparatively short wavelengths of blue light have been shown to impact metabolic processes in retinal cells. It is entirely plausible that excessive exposure to blue light can cause damage to the retina. Although it is true that the intensity of artificial blue light from architectural LED lighting or displays is typically within safe thresholds for human ocular systems, eye care professionals worldwide report common patient complaints of reduced visual comfort and symptoms like headaches or burning eyes.
How do modern technical lights such as LED lamps, xenon lamps, and energy-saving lights, as well as radiation from electronic displays, affect our vision? All of these "new light sources" that are designed to make our lives better and easier contain a higher proportion of blue light than traditional light bulbs. In addition, we are often exposed to this blue light for long periods of time, often until late at night at short visual distances. This combination strains the eye muscles and can contribute to visual discomfort and symptoms associated with digital eye strain.
Apart from the considerations above, specific portions of the blue light spectrum do affect how glare is perceived. An example of this, well-known to drivers, is the unpleasant and irritating modern LED and xenon headlights on cars.
Transcript of the video
Question: Does blue light reduce visual comfort?
Answer: Blue light has an influence on human vision. I’d like to use two examples to illustrate it. One of them is the color of the sky. So, why is the sky blue rather than a different color? The other example is the effect of light splitting in a prism. Everyone is familiar with this one too. When I direct white light into a prism the spectral colors appear at the back. These are two physical optical effects that depend on the wavelength. And the shorter the wavelength the stronger is that effect. And for blue-violet light the wavelength is shorter than for other spectral colors.
The first effect which is also responsible for the sky being blue involves scattering. The scattering depends on the wavelength and blue light is scattered more intensely. The eye produces a certain amount of scattered light especially if the ocular media through which light passes, called visual noise. You could also describe this as an image in the eye that isn’t seen sharply, but instead produces noise. In extreme cases this can cause a perception of glare or reduced contrast. This is one of the effects where blue light plays a role.
Similar to the prism we mentioned before, the second is the refraction of light, which depends on wavelength. One keyword that describes this is dispersion. Dispersion causes the different wavelengths in the eye to have other focal points. And light with a shorter wavelength such as blue light is refracted more intensely. The focal point is slightly in front of the retina, in other words: in front of the point of sharpest vision. While the focal points of green or red light are further back. This effect also leads to limitations for example in terms of focus and visual contrast. Some people have also experienced this at night when colors shift, and you suddenly can’t see so sharply. Dispersion and scattering are thus the two effects that depend on the wavelength and can effect visual comfort and quality of vision.
ZEISS expert Lappe talks about how blue light specifically affects visual comfort.
Another criticism against blue light is that people who surf the internet or are exposed to blue light from other sources just before going to bed have trouble falling asleep or complain about poor sleep quality. In fact, there is a strong link between blue light exposure and the regulation of our circadian rhythm that synchronizes our bio clock and impacts our wake-sleep cycle. Special photoreceptors in the retina contain the protein melanopsin which is particularly sensitive to a specific sub-spectrum of the blue light. Although the metabolic process is complex, the result can be described as follows: blue light exposure causes these retinal photoreceptors to suppress the production and secretion of the hormone melatonin (also known as the “sleep hormone”). As a consequence, we stay alert, awake, and agile. When there is no more blue light exiting these photoreceptors, the blocking process stops, and melatonin is secreted again. The consequence is relaxation, growing fatigue, and, eventually, sleep.
Although we rely on this natural process to keep us alert and awake during the day, it’s not ideal to experience the effects at late hours and at night. Some studies indicate that the quality and duration of sleep, particularly in young people, are impaired by using screens at night. It is recommended to discontinue use of blue light devices a couple of hours prior to bedtime.
Transcription of video
Question: Does blue light have an influence on our well-being?
Answer: Yes, a significant impact. In addition to blue light which our eyes perceive as blue color it’s interesting to know that there are also further receptors that aren’t responsible for vision. These pick up light intensities instead. Such photoreceptors are very sensitive to the intensity and presence of blue light and it’s for a very different process that’s important for humans.
They control our circadian rhythm, the regulation of our internal clock which creates the rhythm that wakes us up when it’s daytime. It’s a very complex process but works quite simply: When blue light reaches the retina in our eyes, a stimulus is transmitted to suppress the release of the so-called sleep hormone melatonin. This means we’re awake, stay awake and are alert. This is the case during the day when the sun is shining. So, humans are conditioned to the circadian rhythm.
When the blue light decreases or disappears this blockage of secretion is stopped, the sleep hormone melatonin can flow through our body, and we become tired and sleepy as a result. Besides this very positive effect of blue light during the day, there’s also a danger associated with interrupting this rhythm. This can happen if we let a lot of blue light into our eyes outside this normal daily rhythm at night and in the evening, typically due to artificial lighting. This effects the day-night-rhythm and the sleep-wake-rhythm. And sleep is of elementary importance for our health. So, we simply advice that if you don’t want to disturb this rhythm and want to get some rest in the evening you should consider reducing your exposure to artificial blue light via monitors and LED lighting in the evening.
Does blue light have an influence on our well-being? ZEISS expert Christian Lappe gives the answer in this video.
If blue light reaches the retina, it will inhibit the production and distribution of melatonin, keeping us awake and alert. This changes as soon as the intensity of blue light is reduced – we feel sleepy.”Christian Lappe
Amidst the widespread discussion on the dangers of blue light, it often goes unmentioned that blue light may also affect our well-being in positive ways. One of the first things to understand is that blue light plays a role in our normal, high-contrast, color vision. This is because the human retina consists of three color receptors for blue, red, and green, and only the full functioning of all three cone receptors ensures normal color vision.
Moreover, as already mentioned, our internal clock (the so-called circadian system) is controlled, among other things, by the perception of blue light. It has a vitalizing effect on us, it keeps us awake and suppresses the production of melatonin in the body. The long-wave portion of blue light, which runs up to 510 nanometers, is even considered to have a positive effect on mood, and special intensive blue light lamps are used to treat seasonal affective disorder during the "darker" months of the year.
Due to its dual nature, represented on the one hand by potentially reduced visual comfort, and on the other by its positive contributions to well-being, blue light is occasionally and strikingly described as "a curse and a blessing".
For eyeglasses wearers, it's easy to take care of their eyes and protect them from blue light. For some time now, there have been lenses that filter out parts of blue light. For example, ZEISS BlueGuard lenses are the latest innovation in blue light protection from ZEISS. These lenses are specifically designed to counteract the symptoms of visual discomfort and eye strain by absorbing part of the shorter wavelengths between 380 to 455 nanometers. The beneficial properties of blue light, which influence general well-being and are in a higher range of wavelengths of around 455 to 500 nanometers, are deliberately left unaffected. You can read more about ZEISS BlueGuard here or consult your eye care professional nearby.
Do you have any other questions about blue light and vision? Here are some Frequently Asked Questions and Answers about blue light and vision.
Find many more exciting articles and interviews on blue light topics here. For example, additional information on blue light filter glasses for gamers and an interview on new visual requirements in the home office.