First, there are two types of blue light: the natural blue light of the sun and the artificial blue light emitted by LED lamps, energy-saving lights as well as smartphone and computer displays. There is an ongoing scientific discussion as to whether, and how, blue light causes damage to the eyes. In this short article, we'll tell you what you need to know about blue light, the necessity for our normal vision, any potential eye damage, and even the positive effects of blue light on our circadian rhythm and well-being.
An in-depth version of this article, including explanatory illustrations, is available here.
Some portion of the electromagnetic (EM) spectrum is generating signals and perception in the human visual system. This part is called “light”, the non-visible bands of the EM spectrum are often referred to as “radiation”, e.g. UV radiation or IR radiation. The visible spectrum encompasses the band of approx. 380nm (blue - violet) to approx. 780nm (red). The blue light is the part of the light spectrum with the shortest wavelengths between 380nm and 500nm. The blue light is adjacent, and partly overlapping with the UV radiation spectrum, that is characterized by even shorter wavelength (100nm – 400nm).
Blue light is of paramount importance for a normal and rich color vision and high contrast vision. The human retina consists of three color receptors for the colors blue, red and green, and only the full functionality of all three cone-type receptors ensures normal color vision. Another kind of photoreceptors in the eye are allowing for vision at low light conditions in dark environments. These rod-type receptors are dominantly sensitive also in the blue and blue-green spectrum. Since the rod-type receptors are also dominant in the retinal periphery they therefore allow for peripheral vision and motion perception.
Research in life-science disciplines has created an undisputable body of evidence of health hazards and biological cell damage from UV exposure. This is true for skin and also for ocular tissues. Wavelength of EM 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. Since the blue light is next to the UV spectrum, and the blue light holds the highest photon energy of all visible light spectrum, a legitimate question addresses the potential of cells being damaged from blue light exposure. In contrast to UV-related research – for blue light there is still substantial research ongoing, and conclusive evidence to be delivered.
While scientific studies show that blue light can trigger metabolic processes that can, through photo-oxidative stress to cells, lead to long-term degradation of cell integrity and eventually support premature cell death. However – the observed damage cues for the ocular, namely the retinal structures are multiparametric hazards. And because the consequences are of long-term time scale / decades than years – a proper discrimination of the causality is hard to show.
The most popular assumed blue light hazard of excessive blue light exposure of the eye, and hence the retina, is a supportive effect on patients developing AMD, the age-related macular degeneration.
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. However, scientists are currently unable to say what dose and what light sources have significant damage-causing potential. So far available scientific results only imply that artificial blue light from typical architectural LED lighting, or displays is far below any known thresholds to create health damages in human ocular system.
We are surrounded by natural blue light throughout the day, since it makes up a big portion of the light spectrum emitted by the sun. Prior to the invention of the light bulb, the human eye ceased to be exposed to the extremely intense blue light of the sun after dusk. Today this is no longer the case, as we are surrounded by increasing amounts of artificial blue light. This is because popular modern sources of light, such as LED lamps, energy-saving lights and (smartphone) displays, emit a relatively larger portion of blue light than, say, traditional light bulbs. By consequence we are exposed to potentially hazardous blue light for much longer periods of time, often into the night. Concerned people see in this extended exposure to blue light an additional risk to our eyes. On the other side we have to consider that the typical lighting or displays only emit irradiance levels of a fraction of the irradiance of our sun.
The human retina can synchronize the local circadian rhythm to light - dark cycles. The so called photoentrainment seem to specifically benefit from existence (day) or absence (night) of blue light to impact the metabolic process of segregation of melanopsin, also known as the sleeping hormone. As long as blue light is detected on the retina the melanopsin segregation is suppressed and the human stay rather alert and awake. Once the intensity of blue light is being reduced and dropping, the segregation is not suppressed anymore and the sleeping hormone is flushing through the body. Fatigue is an effect. Science has shown that a strong difference in suppression and release of it has a positive impact on sleep quality. The fatal effects of disturbed sleep quality had also been scientifically shown. So our biological rhythm benefits from a blue-light rich day.
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 (SAD) during the "darker" months of the year.
A specific band of the blue light affects how glare is perceived, in particular discomfort glare. Modern LED and HID (xenon) headlights on oncoming vehicles are experienced by many motorists as unpleasant and irritating. They reduce vision comfort and make it difficult to see with ease. Scientists refer to the notion of psychological glare to describe the effect. Special glasses for motorist, such as the ZEISS DriveSafe, can sometimes help with this discomfort glare. These headlights, however, only impair vision comfort for short periods of time, and potential health-related damage caused by blue light is not relevant in this case.1
Excessively intensive blue light exposure during the evening and night can lead to sleep disturbances. Observations suggest a link between the existence of smartphones, tablets and mobile devices and their excessive utilization by children and teenagers with symptoms linked to sleep disorders. Studies have started to investigate the effect of so-called ALAN (artificial light at night) to sleep disorders and its consequences to the patients.
This question is an ongoing subject of research as well. Due to the lack of definitive evidence, there is plenty of room for hypotheses and speculation in this regard. Most scientific studies which investigate the potentially hazardous effect of blue light radiation from digital displays to the human visual system, rely on animal or in vitro cell testing. The relevance of these results and its extrapolation to the human eye needs to be considered with caution and skepticism. Many of these studies also work with light intensities which are not found in daily life and /or normal use of such devices. None of these studies so far has been able to show an increased risk for the human eye from modern displays. The primary explanation proposed for this conclusion up to date is that displays have a significantly lower light intensity as compared to the sun.
For blue light, as for many other negative environmental factors, a simplified medieval wisdom originating from Paracelsus can be quoted: the dose makes the poison. Without question, spending time in the sun requires protecting the eyes against the intense blue light of the sun. As much as it is absolutely necessary to protect eye (and skin) from excessive exposure with UV radiation. Quality sunglasses and photochromic glasses that cohere to international standards and the recommendations from health organizations can provide the necessary protection.
By contrast, current research does not suggest that there is any acute risk of retinal damage from interior lighting of any kind. LEDs, energy-saving lights and even intensive use of digital displays are so far not known to pose any risk for eye health. However, exposure to artificial blue light, especially late in the day, may have a disturbing effect on the circadian rhythm and in consequence on sleep cycles and well-being in general. For wearers of eyeglasses, protecting yourself against blue light is an easy choice. Blue-filtering properties of clear all-day spectacle lenses can be ordered as a lens upgrade when you purchase your glasses.
DriveSafe is a registered trademark of Carl Zeiss Vision GmbH.