Wednesday, January 3, 2018

sun - Why aren't 100% UV blocked sunglasses safe to view an eclipse with?


I am not planning on staring into the sun during an eclipse or any other time.



I have been reading about how no variety of regular sunglasses are safe enough to view the eclipse with. I'm not talking about being able to see things clearly, but just actual eye safety.


From what I understand it is the ultraviolet light that causes damage to the retina, but maybe it is more complicated.


How do my eyes get hurt if I am looking at the sun through so called "100% UV protection" and what makes the eclipse glasses sold in stores different?


edit: To clarify this is not about how the rays from the sun are dangerous, but about why "100% UV blocking" sunglasses fail. Do other dangerous rays get through? Is the "100%" marketing? Essentially, in what way are the best consumer sunglasses inadequate for looking at an eclipse.


Answers about pupil dilation and what makes an eclipse more dangerous for naked-eye viewers are not what I'm after.



Answer



The damage to your eyes comes from the total energy from the visible and near - infrared region even when you wear a 100% UV blocked sunglasses.


When you look at the sun in normal days, the visible light from the sun itself is enough for your eyes to trigger pupillary constriction and blink reflex in order to give you at least partial protection.


But when you look at an eclipsed sun, the light and energy from the infrared region will be more than the light from visible region. So no pupil constriction and blink reflex to save you. And the energy from IR rays will burn your eyes.


So it is unsafe to watch an eclipsed sun even with sunglasses, whether they have UV protection or not.



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