11 March 2024

American Astronomical Society Offers Warnings & Reassurances on Eclipse Glasses

With just four weeks to go until the April 8th North American total solar eclipse, consumer interest in eclipse glasses and other solar viewers is beginning to spike. Some sellers are making misleading claims about their products and posting questionable documentation of their safety. Nevertheless, the American Astronomical Society (AAS) Solar Eclipse Task Force wishes to reassure the public that it has seen no evidence that any of the eclipse glasses or other solar viewers being sold for use on April 8th are unsafe.

Safety First

On April 8th, totality –– the few minutes when the Moon completely obscures the Sun’s bright face –– will occur only within a narrow path that crosses Mexico, sweeps from Texas to Maine, and traverses parts of eastern Canada. Outside this path, most of North America will have a partial solar eclipse, which is nothing like a total one. The totally eclipsed Sun is about as bright as a full Moon in the sky and is just as safe to look at directly without eye protection. But during the partial phases before and after totality (within the path) and throughout the entirety of the partial eclipse (outside the path), the Sun is dangerously bright and must be viewed only through special-purpose safe solar filters.

Solar Eclipse Viewers
Safe solar viewers come in a variety of styles, including (from left to right) eclipse glasses with cardboard frames, handheld viewers, and eclipse glasses with plastic frames. Courtesy Rainbow Symphony and American Paper Optics.

Safe solar viewers are those that block all but a minuscule fraction of the Sun’s ultraviolet, visible, and infrared light. Overexposure to sunlight in these parts of the spectrum can cause severe eye injury, ranging from temporarily impaired vision to permanent blindness. “Solar filters that provide safe, comfortable, unmagnified views of the Sun generally transmit between 1 part in 100,000 (0.001%) and 1 part in 2,000,000 (0.00005%) of its visible light,” says Rick Fienberg, Project Manager of the AAS Solar Eclipse Task Force and a veteran of 14 total solar eclipses. “Such filters are at least 1,000 times darker than even the darkest sunglasses.”

How to Tell If a Solar Viewer Is Safe

In 2015 the International Organization for Standardization (ISO) codified these tiny transmittances in the ISO 12312-2 standard for filters for direct observation of the Sun. Solar viewers that comply with the transmittance requirements of ISO 12312-2 are safe. How can you tell if your solar viewer meets the standard? Unfortunately, a statement on the product or packaging that affirms compliance with ISO 12312-2 isn’t sufficient — anyone can print that without properly documenting the viewers’ safety.

“Properly documenting” means that the manufacturer provides reports showing compliance with ISO 12312-2 based on tests of their products at an accredited laboratory conducted with specialized equipment. Without a satisfactory test report from a properly accredited lab, you can’t be certain that a solar viewer is safe. There’s simply no way to know by examining the viewer or even by taking a quick glance at the Sun through it.

To help the public obtain properly documented, vetted viewers, the AAS Solar Eclipse Task Force has compiled a list of vendors of safe solar viewers. For every seller on the list, we’ve confirmed three things: (1) the identity of the manufacturer, (2) that the manufacturer’s viewers have been tested for compliance with the ISO 12312-2 standard by a lab properly accredited to do so, and (3) that the viewers meet the standard’s transmittance requirements across the parts of the spectrum to which our eyes are at risk from overly bright light.

Bad Actors & Sad Actors

Many sellers of eclipse glasses and handheld solar viewers state that their products meet the ISO 12312-2 standard even though they haven’t been tested properly. How do we know this? Because in the course of vetting suppliers asking to be added to our list, we’ve examined test reports posted on their websites or provided to us directly by their manufacturers –– and some of these test reports are at best questionable and at worst clearly bogus.

“I’ve seen identical reports –– to the last decimal place! –– from different labs testing different manufacturers’ products,” says Fienberg. “In many cases, these labs aren’t accredited or their accreditation can’t be verified.” Some test reports show “Pass” for sections of the standard that don’t have requirements, only descriptive text. And some test reports for cardboard-mounted viewers are presented as proof that plastic-mounted viewers are safe, or vice-versa, even though the filters in the two types of viewers are different.

Among the worst offenders are overseas manufacturers who print the name of an American manufacturer on their viewers. This is pure fraud by bad actors. But not all sellers of eclipse glasses that haven’t been tested properly are bad actors. In most cases, they simply believed their supplier when told, or when shown documentation purporting to confirm, that the products comply with ISO 12312-2. Sadly, their trust in others led them to be duped.

In response to learning that the solar viewers they’re selling haven’t been properly tested and shown to be safe, some conscientious vendors have taken it upon themselves to get the products tested by an appropriate lab. In every instance, the reports have been satisfactory, and we’ve added those sellers to our list of suppliers of safe solar viewers. “This is what makes us think that the marketplace isn’t being polluted with unsafe solar viewers,” says Fienberg. “What some people are calling ‘fake’ eclipse glasses appear to be products being promoted with misleading claims, printed with information copied from other manufacturers’ viewers, or otherwise suspicious,” he adds. “But that doesn’t mean they’re dangerous.”

Warning Signs

If you don't see a vendor listed on the AAS solar eclipse website, it does not mean that their products are unsafe. We list more than 100 sellers of solar viewers, but there are hundreds more –– especially on sites like Amazon, Etsy, and eBay — and we can’t possibly vet them all. Still, there are signs you can spot that suggest you might want to look elsewhere. The most obvious is any claim that NASA approves or endorses a product. NASA doesn’t do that. Similarly, NASA doesn’t maintain a list of suppliers of safe solar viewers and filters. The AAS Solar Eclipse Task Force does, and NASA links to our list, but NASA hasn’t vetted the suppliers.

There’s one exception: NASA chose American Paper Optics (APO) in Tennessee to make the space agency’s eclipse glasses, so APO can legitimately claim to be NASA’s supplier. Accordingly, APO’s authorized dealers can legitimately claim to use the same supplier that NASA uses.

Any seller who claims that their solar filters block 100% of ultraviolet (UV) and infrared (IR) radiation is either lying deliberately or misleading you out of ignorance. Filters that meet the ISO standard transmit small, safe amounts of UV and IR radiation. In any case, as eclipse-chasing optometrist B. Ralph Chou points out in the technical report that he wrote for the AAS, the main threat to our eyes when observing the Sun without proper protection is intense visible light, not invisible UV or IR light. (Chou also is a principal author of the ISO 12312-2 standard and has been testing and writing about solar filters for decades.)

Final Thoughts

You have only one set of eyes, so when seeking eclipse glasses or handheld solar viewers, your best bet is to start with the AAS list of suppliers so you can be sure your viewers are safe.

That said, if you’ve already bought solar viewers and don’t see the seller on the AAS list, don’t panic! It’s highly unlikely that you’ve purchased filters that are going to put your eyesight at risk.

If you don’t have eclipse glasses yet and want them, don’t wait any longer. The closer we get to the eclipse, the more likely it is that legitimate vendors will sell out and that products of questionable origin and safety will again flood the market from companies trying to make a fast buck. Note too that you can use indirect methods, with the Sun at your back, to watch the partial phases of a solar eclipse safely if you don’t have a special-purpose solar viewer.


Rick Fienberg
Rick Fienberg
Project Manager, AAS Solar Eclipse Task Force
+1 857-891-5649
Susanna Kohler, Editor, AAS Nova
Susanna Kohler
AAS Communications Manager & Press Officer
+1 202-328-2010 x127


https://eclipse.aas.org/sites/eclipse.aas.org/files/Cardboard_Handheld_Plastic_Viewers.png (384-kilobyte PNG)

Safe solar viewers come in a variety of styles, including (from left to right) eclipse glasses with cardboard frames, handheld viewers, and eclipse glasses with plastic frames. Courtesy Rainbow Symphony and American Paper Optics.

More Information

On the AAS Solar Eclipse Task Force website:

From Sky & Telescope (published by the AAS):

In the Bulletin of the American Astronomical Society:

About the AAS

The American Astronomical Society (AAS), established in 1899, is a major international organization of professional astronomers, astronomy educators, and amateur astronomers. Its membership of approximately 8,000 also includes physicists, geologists, engineers, and others whose interests lie within the broad spectrum of subjects now comprising the astronomical sciences. The mission of the AAS is to enhance and share humanity’s scientific understanding of the universe as a diverse and inclusive astronomical community, which it achieves through publishing, meetings, science advocacy, education and outreach, and training and professional development.