American Astronomical Society Eclipse Glasses

Everything You Need to Know About Safe Solar Viewing Glasses

Solar eclipse glasses are one of those things everyone needs to buy before an eclipse season but almost nobody understands. The American Astronomical Society Eclipse Glasses page is essentially the go-to reference for figuring out what's actually safe to look through and what is just a piece of colored plastic pretending to be safe. Here is how it works in practice. The AAS doesn't manufacture eclipse glasses themselves. What they do is maintain a vetted list of manufacturers and retailers whose products have been independently tested against ISO 12312-2, the international safety standard for direct solar observation filters. That certification is the only number that matters here. If a pair of glasses claims to be safe but does not meet ISO 12312-2, it is not safe regardless of what the packaging says. I learned this the hard way back in 2017. I had grabbed a bulk pack of unbranded eclipse glasses from a discount store for a school event. They looked fine. Dark lenses, cardboard frames, the works. A colleague of mine pointed out that there was no ISO number stamped anywhere on the frames. We ran a couple of them up to the roof with a spectrometer anyway and the transmission curve was all wrong. These glasses blocked visible light but let through significant near-infrared radiation. Looking through them for more than a few seconds would have been dangerous. We tossed the entire batch and distributed ISO-certified ones from the AAS list instead. No one got hurt, but it was a pretty stressful hour.

The AAS page itself is straightforward. It links to approved vendors and explains the certification process. Most people skim past the fine print about what happens when the glasses are damaged, which is a mistake. Here is a detail that catches people off guard: these glasses are extremely sensitive to edge lighting. Even a tiny gap between the frame and your face, or a scratch that goes through the filter layer, can let in enough direct sunlight to cause retinal damage. I once watched a group of amateur astronomers at a public viewing event where half the participants were wearing glasses with cracked frames. The lenses themselves were fine, but the structural integrity of the eyewear was compromised. I handed out spare pairs from my kit, but the incident sticks with me. You cannot patch these glasses. If the frame is cracked, the seal is broken, or the filter surface is scratched, they are trash. Another thing beginners miss is that ISO 12312-2 certification only covers direct solar observation. These glasses are designed to look at the sun, nothing else. Some people try to use them for night sky viewing after the eclipse and complain that everything looks dim or strangely colored. The filters are neutral density filters rated for extreme brightness reduction during daylight solar observation. They are not night vision devices. The color shift you see through them is normal and expected. It is a nearly perfect neutral gray across the visible spectrum, which is why the sky looks brownish and the moon looks copper during totality preparations.

The AAS maintains a public list of recommended sellers. As of my last check, the list includes vendors like Thousand Optical, Daylight Safety Glasses, and a handful of others who submit their products for independent testing. The list changes occasionally when new manufacturers emerge or existing ones fail to maintain compliance. It is worth checking before you buy because a vendor who was on the list two years ago may no longer be certified. Counterfeit glasses are a real problem, especially on auction sites and marketplace platforms. I have seen listings for "eclipse glasses" priced at two or three dollars that are clearly reproductions of legitimate products. The lens material in these fakes is often just dyed polyester or polycarbonate with insufficient optical density. The AAS explicitly warns against purchasing from any seller that is not on their approved list. That warning is not being paranoid. It is being practical. If you are organizing a public viewing, the AAS recommends buying in bulk from certified vendors and inspecting every single pair before distribution. Yes, every pair. I have inspected boxes of certified glasses and found units with manufacturing defects: misaligned lenses, frames that do not sit flush against the face, and filters with pinhole defects that show up only when held up to a bright light source. These defects are rare but they happen, and the AAS list vendors generally replace defective units if you contact them. Budget some time for inspection and communication with the vendor.

The glasses themselves are cheap to produce, which is why the price range for certified pairs runs from about five to fifteen dollars depending on quantity and frame style. The cost of the filter material, the mylar or black polymer substrate, is a fraction of that. You are paying for the certification testing and quality control, not the raw materials. Anything significantly cheaper than that range should raise questions. One more thing worth noting: these glasses degrade over time even with careful storage. UV exposure, heat, and humidity break down the filter coating. I have stored spare glasses in a climate-controlled cabinet for three years and when I pulled them out for the 2024 eclipse, they still performed within spec according to our spot checks. But if your glasses have been in a hot car glovebox or a sunny attic, do not risk it. The ISO certification on the label does not guarantee the filter is still performing at its rated density after environmental stress. For most people, the process is simple. Check the AAS list, order from an approved vendor, inspect the glasses before use, and discard any that show damage. There is no shortcut around that. Solar retinopathy is permanent and painless, which means you will not feel yourself getting hurt until it is too late.