Background Article by Dr. Christian Lappe, Director Scientific Affairs & Technical Communication | Principal - ZEISS Expert Ladder
The eye is one of our most important sensory organs. Its photoreceptors are capable of perceiving a portion of the electromagnetic spectrum. This spectrum, visible to humans, is what we call light. Without light there can be no vision, no contrast, and no colors. But light also affects our bodies, our physical health, our well-being, and our sleep/wake cycle. Light controls a wide range of processes within the human body. A question which has been the focus of recent discussion is: What about blue light? Is it harmful for our eyes, especially in the case of modern, artificial LED light sources? And if it is harmful, how much harm does it cause?
The portion of the electromagnetic spectrum which is visible to the human visual system lies approximately between 380 nm and 780 nm. This range is also referred to as "light" or VIS (for "visible"). Short wavelengths under 400 nm, which lie close to the visible spectrum, make up the ultraviolet (UV) spectral range. Longer wavelengths above 780 nm belong to the infrared (IR) spectral range.
The boundary between the visible light spectrum and the non-visible UV spectrum, as well as the boundary between visible light and IR, overlap since there is a certain amount of variance in how individuals perceive light and also because light perception depends on the intensity of the light in question. Thus, while specifying precise boundaries between the UV, VIS and IR ranges is desirable from a technical point of view, it is not justifiable physiologically. In the short wave portion of the spectrum, this overlap runs from approximately 380 nm to 400 nm in the range in which violet-blue light can be perceived. For this reason, the blue light spectrum is also often specified as running from 380 nm in the blue-violet range to 500 nm, where the blue spectrum transitions to green.
But 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 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. Today we are exposed to this potentially hazardous blue light for longer periods of time, often until late into the night. In the past, the human eye was only exposed to the extremely intense blue light inherent in natural sunshine during the daytime. With the setting of the sun in the evening and the use of light sources such as candles and fireplaces, which emit light in the warmer visible spectrum, the blue portion of the spectrum would diminish.
The energy inherent in electromagnetic radiation interacts with biological tissue and with structures that it comes into contact with. Experts have been aware for some time that UV light can potentially cause damage to biological tissue such as our skin and our eyes. This is also called the actinic UV hazard, which primarily affects the conjunctiva, cornea and crystalline lens structures of the eye.
Several decades ago scientists already discovered that a certain action spectrum of blue light in the wavelength range between 380 nm and 510 nm with an action maximum at 440 nm may be responsible for possible damage to the retina. Scientists call this blue light hazard. Some of them even believe that the blue light hazard plays a major role in the occurrence of age-related macular degeneration (AMD).
There are generally different mechanisms at work in how radiation (or light) damages the eye. The hazards arising in daily life are of a photochemical nature, in particular photooxidation processes at the cellular level. In short, the absorption of specific wavelengths in photosensitive structures in the retina (the chromophores) by means of the generation of excited and reactive molecular structures causes damage to the surrounding tissue or to specific tissue structures. These are generally long and cumulative processes which first manifest after many years of constant micro-damage, as in the case of AMD.
The human body has protective measures which it uses against this potential and light-induced damage to the eye. Examples of these include melanin and macular pigment. However, these diminish with age. At the same time, the products of oxidative stress on proteins arise. An example of this is the age pigment lipofuscin. Lipofuscin accumulates in the retinal pigment epithelium (RPE), thus reducing the viability of the RPE. Over the long term, this effect can lead to the death of RPE cells in entire areas, as well as to vision loss and blindness.
These photochemical processes can be initiated in the human retina by the high-energy portion of blue light. However, the dose-response relationship is much less understood than the general mechanism. Furthermore, its clinical evaluation is still the subject of current research. However, despite recommendations to approach this issue with caution, ideas – in some cases wildly speculative ones – about the damage potential of different blue-light-emitting light sources, such as mobile phone displays or the LED lights in living room lamps, have emerged.
Apart from the considerations above, specific portions of the blue light spectrum do affect how glare is perceived, in particular discomfort glare. This results in reduced visual comfort. An example of this, well-known to drivers, are the unpleasant and irritating modern LED and xenon headlights on cars.
Amidst the widespread discussion on the dangers of blue light, it often goes unmentioned that light also affects our well-being in positive ways. Our internal clock (the so-called circadian system) is controlled, among other things, by the perception of blue light. Blue light has a vitalizing effect on us, it keeps us awake and suppresses the production of melatonin in the body, which, as demonstrated in recent research on blue light exposure at night among young people, affects our quality of sleep.
Due to its dual nature, represented on the one hand by potential health hazards, and on the other by its positive contributions to well-being, blue light is occasionally and strikingly described as "a curse and a blessing".
It is useful here to understand that blue light can be subdivided into different wavelength ranges, each of which can strongly impact one effect or another.
In addition to the scientific considerations of blue light, there are also limits and standards from the field of standardization which need to be taken into consideration. These include standards such as the American Conference of Governmental Industrial Hygienist (ACGIH) or European Directive 2006/25/EC, both of which recommend an exposure limit value to protect the eyes. Scientific studies have examined the emission of blue light by digital displays and its impact on the human visual system in relation to these defined standards. However, these studies show no increased risk for the human eye on the part of modern displays in relation to the recommended standards. These results are by and large explained as being due to the significantly lower light intensity of such displays as compared to the sun.
When examining the new findings, however, it must be noted that the standards forming the basis of the tests are defined only for a short period of time, that of a single working day. There are currently very few scientific studies which look at the potential consequences of long-term exposure – including those that hypothesize cell damage caused by blue light. However, the light sources used in these studies have a much higher energy level than normal lights, such as those used for interior lighting or modern displays.
The current state of scientific and clinical research suggests that there is no acute risk of retinal damage caused by interior lighting of any kind (LEDs, displays, etc.) or by the daily use of mobile devices such as smartphones and tablet PCs.
However, there is still the question as to how artificial blue light, especially during the later hours of the day, affects our circadian system, and hence our quality of sleep, well-being and health. Moreover, the possibility of long-term damage to the human visual system, which was not addressed in the given standards, as well as potential damage caused by the blue light portion of the significantly more intense light from the sun, has yet to be clarified.
Until further validated findings are made, we must deal with the dual nature of blue light in a responsible and balanced manner.
The eye and vision
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