Light density of computer screens
When talking about the harmful potential of blue light in the light of computer screens, one argument for the harmlessness of this radiation is often the low light density of these screens. Alexander Wunsch, a well-known photobiologist and physician is dealing with some of the most common misunderstandings in this text:
Up to now photo retinitis (a damage of the retina) is described by optometrists only in people without an eye lens and through the impact of daylight.
In the future, one may have to differentiate between acute and chronic photo retinitis. While the symptoms of an acute photo retinitis become apparent within a few hours, it takes years, sometimes decades before the damage of a chronic photo retinitis can be diagnosed. A study by the French health authority ANESES assumes that the sum of blue light that the retina is exposed to over a lifetime correlates with the occurrence of AMD (age-related macular degeneration). It is therefore recommended not to use white or blue light LED lights in the presence of children, because they have very transparent eye lenses. Scientists speak about an accumulative effect of blue light shares with the understanding that limiting the amount shortwave blue light that the eye is exposed to, is potentially a preventative measure against the development of age-related macular degeneration.
No damage to the retina through daylight are described whether a person had natural or artificial eye lenses.
This statement is not true; as an example there is the observation that ofter implanting a completely transparent artificial eye lenses, the occurrence of AMD increased. Again, we talk about a chronic and not an acute process.
The light density (luminance) of TFT monitors is about the power of ten below the light density of daylight.
The light density of monitors is indeed much lower than that of daylight. But there are indications that not only the absolute light intensity has to be regarded, but also the spectral distribution of the light, which plays a vital part. Furthermore, a pure consideration of intensities neglects the fact that the concentration of visual pigment in the retina depends on the brightness of the surrounding. The extreme adaption ability of the eye to different light densities isn´t limited to the activity of the pupil (max. factor 16!), but is primarily done by chemical adaption. When it´s dark, a much higher concentration of visual pigments can be found in the photoreceptors. This enlarges the “target-area” for photochemical damage. Under natural conditions only bright daylight contains blue wavelengths, which therefore meet low concentration of photo-pigments. When artificial light, with a much lower intensity, has a high portion of blue light, this meets higher concentration of photo-pigments. Because these exposed photopigments can act as photochemical sensitizers, a photochemical damage from low intensity light is also possible.
Although millions of TFT monitors are used, no damage through the light of the TFT monitors has been reported.
Chronic damage of the retina does not develop within a few years. TFT monitors have not been in use long enough to assume harmlessness, especially as the occurrence of the age-related macular degeneration continuously increases since non-thermic light sources (e.g. fluorescent lamps, energy saving light-bulbs and TFT monitors) have been introduced.
The increasing age of the population cannot explain this fact, especially not when the age at the occurrence of ADM lessens. For a risk evaluation the increased use of non-thermic light sources has to be taken into account. The current practice of risk assessment for light sources, e.g. through ICNIRP* or CIE**, is based on an eight-hour-day and must be amended, because many people are not only looking into a monitor for eight hours during work, but are also exposed to blue light at home, when sitting front of the television, or through room lighting. It should be noted, that artificial light sources such as energy saving lamps or white-light-LEDs, are especially active in that spectral area which is mainly responsible for the so-called blue light-hazard and photo retinitis.
*ICNIRP = International Commission of Non-Ionizing Radiation Protection
**CIE = International Commission of Illumination
Contact:
Alexander Wunsch, physician and light biologist, Heidelberg, GERMANY wunschart@mac.com