On Thursday, July 27, 2017 at 10:21:07 PM UTC-4, wrote:
On Thursday, May 17, 2012 at 11:53:14 AM UTC-6, mike wrote:
I want to look at the eclipse this weekend.
Everybody says a #14 welding shade is good.
I don't have one.
So, how do the numbers stack up when you use 2?
I'm guessing it's not linear, so 7+7 doesn't = 14???
What's the math for stacking welding shades?
Thanks, mike
Relevant all over again for August 21, 2017.
So based on A Norton's formula:
4 5 6 7 8 9 10 11
4 7 8 9 10 11 12 13 14
5 8 9 10 11 12 13 14 15
6 9 10 11 12 13 14 15 16
7 10 11 12 13 14 15 16 17
8 11 12 13 14 15 16 17 18
9 12 13 14 15 16 17 18 19
10 13 14 15 16 17 18 19 20
11 14 15 16 17 18 19 20 21
So the first column and row are the shades you are adding. Follow 14 on the diagonal to combine your shades. So a #10 + a #5 is #14.
If you want to check the formula the spread sheet link is:
https://docs.google.com/spreadsheets...it?usp=sharing
Let's cite sources, and stop speculating re losing eyesight.
By the way, anorton, was your source for the formula SN = 1 + (7/3) OD (stacking welding lenses) this article?
http://www.astronexus.com/node/3 Just curious.
NASA & the NSF's AAS: welding shade 12 protects eyesight from the sun.
Aside from relying on stacking welding filter lenses according to a formula to reach Shade #14, notice that the American Astronomical Society features this article (link below) €śSolar Eclipse Eye Safety€ť by Professor B. Ralph Chou, an optometry professor with a degree in astronomy; he's also lead author of the solar viewing standard ISO 12312-2.
On special ISO eclipse glasses vs. welding lens shade 12-14, Chou's article states, "the transmittance requirements specified for welding filters in the standards for occupational eye protection are more stringent than the [solar viewing] ISO 12312-2 standard.€ť
Chou on shade 12 vs. 14: €śThe selection of the welding filter shade number is a matter of personal preference in comfort and will depend on atmospheric conditions and personal glare sensitivity. Filters with shade number 12 should be adequate to protect the eyes, but the solar image may be uncomfortably bright. Some observers may find that the solar image viewed through a shade 14 filter is too dim.€ť
The one welding shop I asked said they did sell shade 13 replacement lenses for welding helmets, but they'd sold out.
But don't believe me until you've read Prof. Chou's €śSolar Eclipse Eye Safety€ť yourself at:
https://eclipse.aas.org/sites/eclips...Eye-Safety.pdf
AAS approves shade 12 to 14 he
https://eclipse.aas.org/eye-safety/iso-certification
NASA approves shade 12 to 14 he
https://eclipse2017.nasa.gov/safety
They both mention that some people will find shade 14 too dim for viewing the eclipse. And shade 12 too bright, but safe for eyesight.