Can you view a solar eclipse with a welding mask?
The short answer here is “yes, you can,” but that doesn’t necessarily mean it’s a good idea. The longer answer here is that this depends on the shading of the lens. We are often asked if it’s OK to look at the sun or watch a solar eclipse through a welding mask lens. I’m taking the chance that every mom in America will want to slap me, but yes, you can use a welding helmet to view an eclipse IF you have the correct shading and that means a Shade 14 welding helmet.
Welding helmet lens shading for viewing an eclipse
Shading 12 – most likely too bright
Shading 13 – should be just right, but it can be hard to find
Shading 14 – may be too dark.
Note that I didn’t make those up or say what felt right to me – these are the shading parameters set for by NASA to look at a solar eclipse. They also caution against just pulling any old welding mask and trying it – this is not something you want to try. Ensure the lens has at least a Shade 12 filter as an alternative to eclipse glasses. That may even be too bright.
Ok, so let’s explore some of the information – or perhaps misinformation – you may see littered around the internet.
How bright is a welding arc compared to the sun?
I’ve seen some sites proclaim that the sun is “brighter than a welding arc” because the luminosity of an item does not change due to distance. This takes into account the definition of Luminosity, but not “Apparent brightness”, which is what should actually be considered.
All those stars you see out there? Many are every bit as luminous as our sun, and yet it doesn’t hurt a bit to look at them.
Because of the distance.
Ever look at the headlight of a car up close? Compare that to what it looks like a mile down the road. The headlight doesn’t put out less light when it’s a mile away. The distance makes it less bright to you – the apparent brightness is less due to the distance (and atmosphere, water vapor, etc.).
Luminosity is the intrinsic brightness of an object, while “apparent brightness” is the brightness’s perceived luminosity, diminished by distance. That’s an astronomical definition I pulled from a NASA site, and it makes perfect sense.
So what we should be comparing is the apparent brightness, not the luminosity. Comparing an arc weld to the sun in terms of luminosity, the sun wins. But it’s not the luminosity we should be comparing, it’s the apparent brightness, and for that, the humble arc weld wins out over the noble Sun.
Aside from all the formulae and technical gobbledegook, we’ve all already done the acid test more than once.
Ever squint at the sun? Sure, you did.
Did it blind you momentarily? Maybe a bit.
You probably had a black dot in your vision for a bit, and then it went away. Maybe a bit of pain, but it also went away.
Now – ever squint at a welding arc? Not even remotely the same thing. Intense pain, huge black spots in your vision for a while, perhaps a lingering headache to boot. Your eyes may feel itchy for a while. Do this for too long or one too many times, and you can end up with “arc eye”, which feels every bit as terrible as it sounds like it should. How bright is a welding arc compared to the sun? Too dang bright to look at!
So, concerning “apparent brightness”, I have to say that the arc weld wins over the sun and just about anything else you will encounter on any given day. I’d steer clear of looking directly into lasers, directly at nuclear blasts, or putting your eye up too close to a halogen bulb. Any of these will ruin your day and give you a whole new appreciation for the importance of “apparent brightness”.
Luminosity vs. apparent brightness – the geeky details
Let’s break out the Astronomy dictionary:
Luminosity: the intrinsic brightness of a celestial object (as distinct from its apparent brightness diminished by distance).
Apparent brightness: How bright the star appears to a detector here on earth
The image below does a great job of explaining this (thank you, Penn State). The blue circle with the “S” is our Sun. R, 2R, and 3R are different distances from the sun. You can see that the light is more dispersed, and therefore less concentrated, the further you get away from the source. What we’re seeing is that if you double the distance (2r), you effectively halve the apparent brightness (indicated by the red lines coming through each quadrant. If you triple the distance (3r), you reduce the apparent brightness by a factor of nine.
Light scatters and becomes less focused – less bright – over distance. Also, keep in mind that sunlight is also being filtered by our atmosphere, which includes a lot of dust, smog, and water vapor.
So, my point is that the distance does matter, despite what you may read elsewhere. It matters to this discussion regarding if you can wear your welding helmet to look at an eclipse. Because an eclipse is “pretty bright”, and your welding helmet is designed to protect your eyes against “pretty bright” things.
Back to the original point of whether or not using a welding helmet to view the eclipse is a good idea, I’d say it’s not a terrible one. There are worse ways to go about it. Using your welding mask with an appropriate shade means you use a tool that exists expressly to look at very bright things. It makes sense to me that your welding helmet is a pretty good answer here.