I found a lense online that sais it blocks 90% of uv light. I intend to look at the sun, is that last 10% (lets say, no clouds, hot day, mid summer as a worst case) gonna hurt my eyes? Hurt as in any pain, not just damage.
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You should absolutely not use a filter that blocks only 90% of the UV.
The normal recommendation for looking at the sun is to use a #14 welding filter. The specs for welding filters are given here:
http://www.aoa.org/x5364.xml
In the near UV, a #14 filter passes no more than 0.000027%. (See table 1 in above link.) That means it blocks 99.999973%, while your filter blocks only 90%. Don't even think about risking your eyes with a 90% filter.
Welding filters are inexpensive, and you can find them at stores with welding supplies. Sometimes it's hard to find a #14. In that case, you can buy two filters that add up to 15 (that's correct -- 15, not 14) and put them together (e.g., a #6 filter plus a #9 filter). You can put tape around the edges to make sure they stay together.
You can also buy safe solar filters from companies like Thousand Oaks Optical and Rainbow Symphony.
As for the pain caused by an inadequate filter, I can't say; but you have only two eyes, and you want them to last a lifetime.
The normal recommendation for looking at the sun is to use a #14 welding filter. The specs for welding filters are given here:
http://www.aoa.org/x5364.xml
In the near UV, a #14 filter passes no more than 0.000027%. (See table 1 in above link.) That means it blocks 99.999973%, while your filter blocks only 90%. Don't even think about risking your eyes with a 90% filter.
Welding filters are inexpensive, and you can find them at stores with welding supplies. Sometimes it's hard to find a #14. In that case, you can buy two filters that add up to 15 (that's correct -- 15, not 14) and put them together (e.g., a #6 filter plus a #9 filter). You can put tape around the edges to make sure they stay together.
You can also buy safe solar filters from companies like Thousand Oaks Optical and Rainbow Symphony.
As for the pain caused by an inadequate filter, I can't say; but you have only two eyes, and you want them to last a lifetime.
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No good, not even close (and it's not just the UV, but also the visible light which can do damage if it isn't reduced significantly).
Your best bet is to use a filter designed specifically for looking at the sun, eclipse sunglasses if you can get them are probably the best bet for naked eye viewing though sufficiently dark arc welding glasses (number 14 or darker) could also be used (recent ones would be better).
A full aperture solar filter that goes over the front of a telescope could also be used for naked eye viewing by holding it up in front of your eyes (I've done it, was even able to see a transit of Venus naked eye) and can also go on a telescope for a bit more resolution/magnification (just stay as far as you can away from eyepiece solar filters, those things are dangerous, illegal to sell in many places as well).
You could also try solar projection using binoculars or a small telescope whereby you just project the image onto a white sheet of cardboard or whatever without looking at the sun directly.
Your best bet is to use a filter designed specifically for looking at the sun, eclipse sunglasses if you can get them are probably the best bet for naked eye viewing though sufficiently dark arc welding glasses (number 14 or darker) could also be used (recent ones would be better).
A full aperture solar filter that goes over the front of a telescope could also be used for naked eye viewing by holding it up in front of your eyes (I've done it, was even able to see a transit of Venus naked eye) and can also go on a telescope for a bit more resolution/magnification (just stay as far as you can away from eyepiece solar filters, those things are dangerous, illegal to sell in many places as well).
You could also try solar projection using binoculars or a small telescope whereby you just project the image onto a white sheet of cardboard or whatever without looking at the sun directly.
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Will 10% of the Sun's ultraviolet light hurt your eyes while looking directly at the Sun through a lens?
Well... yes. However, it's really nothing to worry about.
The reason I say that is that the light in the visible range of the electromagnetic spectrum will fry your eyes long before the ultraviolet light has a chance to do anything to you. If you're daft enough to look directly at the Sun through anything less than a high-shade welding filter, the ultraviolet damage you receive will be the *least* of your problems.
Well... yes. However, it's really nothing to worry about.
The reason I say that is that the light in the visible range of the electromagnetic spectrum will fry your eyes long before the ultraviolet light has a chance to do anything to you. If you're daft enough to look directly at the Sun through anything less than a high-shade welding filter, the ultraviolet damage you receive will be the *least* of your problems.
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10% is still a lot...I recommend you don't look at the sun...