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.

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.

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.

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.

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.

Here are some frequently asked questions and answers regarding blue light and its impact on vision.