5 questions about an eclipse and eclipse blindness
Watching an eclipse unprotected can cause serious damage to the eyes. How do you properly protect your eyes? Can you also watch the solar eclipse through a CD? Five questions about eye protection during a solar eclipse.
1. Why is it dangerous to look toward the sun during an eclipse?
Looking directly at the sun during an eclipse can irreparably damage the retina, resulting in permanent blindness or visual impairment. The insidious thing is that you don’t feel it: the retina has no pain-sensitive nerves. You only notice it after a few hours, but by then it is of course already too late.
Eclipse blindness is caused by radiation on the retina that damages the cones and rods in the eye. Not because of too high a temperature, but because the radiation produces dangerous substances in the retina. This process is irreversible. You will therefore be irrevocably wholly or partially blind.
2. How do you properly protect your eyes during a solar eclipse?
Tjeerd de Faber, pediatric ophthalmologist at Het Oogziekenhuis Rotterdam: “The human eye is vulnerable to various types of radiation from the sun. Ordinary sunglasses do not protect the eyes enough when watching the solar eclipse. It is important that both children and adults are aware of the dangers and that they use eclipse glasses. Exposing the eyes unprotected to radiation from the sunlight damages the eyes and can even cause eye problems later in life. Children’s eyes are especially sensitive to sunlight: the eyes are not yet fully developed and contain fewer pigments. But beware: even with eclipse glasses you can watch the solar eclipse for a maximum of 30 seconds. If you don’t have eclipse glasses, share one with someone else and take turns. After all, they are your eyes.”
3. What is so special about eclipse glasses?
Such eclipse glasses are cardboard glasses, in which a special sun filter film has been applied. It is important to only use glasses that have been specially developed for the sun. Other types of glasses can transmit invisible, harmful radiation (UV and infrared). Do not use eclipse glasses to look at the sun through binoculars or telescopes. The concentrated sunlight immediately burns a hole in the foil and damages your eyes.
Many opticians and observatories sell eclipse glasses. They can also be found online. They usually cost a few euros and if you store them well, you can enjoy them for many solar eclipses. Before viewing the eclipse, check that the film of the glasses is not damaged. Welding glass with a darkening factor of 12 to 14 is also suitable for viewing an eclipse.
4. You also saw people watching the eclipse through a CD during previous solar eclipses, is that safe?
Peter Stalmans, an ophthalmologist at the Catholic University in Leuven, conducted a study during the previous solar eclipse in collaboration with the Faculty of Agricultural and Applied Biological Sciences of that university into the safety of those homemade sun filters and ‘real’ eclipse glasses. This showed that only the eclipse glasses and the so-called mylar foil distributed by the observatory could guarantee good protection for the eyes.
Homemade protectors such as sooty glass or a black piece of photo negative were found to transmit a large amount of infrared radiation and most CDs had too low an absorbing capacity.
5. Watch indirectly
Another way to safely view or photograph the solar eclipse is indirect observation. The easiest is with a piece of cardboard with a small, round opening in it. Hold the cardboard about three feet above the ground or in front of a wall. Optionally, you can stretch a white sheet in front of the wall or lay it on the floor. The sunlight falls through the hole in the cardboard on the floor or on the wall. Then you see the solar eclipse. You should observe indirectly indoors, because there is so much ambient light outside that the image of the sun remains round.
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