RV8JD
Well Known Member
From the American Astronomical Society:
eclipse.aas.org
How to View a Solar Eclipse Safely
How to Use Solar Viewers | Indirect Viewing Methods | Do Solar Viewers Expire? | Cleaning Instructions | Welding Filters
"Are Welding Filters Safe for Solar Viewing?
The ISO 12312-2 standard was based, in part, on decades of experience using welding filters for observing the Sun. A welding filter with a shade number of 12 or higher transmits a safely tiny percentage of the Sun's light across the spectrum, whether made of tempered glass or metal-coated polycarbonate. Most observers find the view through a shade 12 welding filter uncomfortably bright and the view through a shade 15 or higher-numbered welding filter unattractively dark. The "sweet spot" is shade 13 or 14, which best matches the view in purpose-made eclipse glasses and handheld solar viewers, except that the image is green rather than yellow-orange or white. Shade 13 and 14 welding filters are rarely stocked in welders' supply stores, though, so you'll probably have better luck finding them by shopping online. Two good sources of shade 14 welding filters are safesolarviewing.com and Phillips Safety Products.
You should not use adjustable and/or auto-darkening welding helmets or similar products to view the Sun. Many don't go as dark as shade 13 or 14, and even those that do post a grave risk to your eyesight, either because you accidentally adjust them to an unsafe setting or because they don't auto-darken fast enough when you look at the Sun with them."
