The eclipse economy is in full swing. Eclipse glasses are in low supply, and counterfeit eclipse glasses being sold. How can you tell if the solar eclipse glasses you bought are safe for staring directly at the sun or fakes?
Check the ISO number
According to the American Astronomical Society (AAS), a real and safe pair of solar eclipse glasses should be labeled with ISO 12312-2 (sometimes written in more detail as ISO 12312-2:2015), which is an international safety standard that denotes the glasses reduce visible sunlight to safe levels and block UV and IR radiation.
Reputable vendor research
Unfortunately, fake glasses may also be labeled as being compliant with ISO 12312-2 because, as a general rule, people are greedy, selfish and not to be trusted. To double check the veracity of your eclipse glasses' ISO claims, you can check to see if the vendor from which you purchased the shades is trustworthy in the eyes of the AAS. See its list of Reputable Vendors of Solar Filters and Viewers.
In assembling its list, the AAS checks to make sure a manufacturer earned its ISO rating with proper, labs-based testing. It also asks manufacturers for their authorized resellers and resellers for their manufacturers. If the vendor of your eclipse shades is listed, then you are safe. But the opposite isn't necessarily true. If your vendor isn't listed, it doesn't necessarily mean they are slinging counterfeits. It just means the AAS hasn't checked them out or hasn't been able to track everything down.
So, what are you to do if your vendor isn't on the list? Perform an eye test.
Eclipse glasses eye test
First off, a pair of honest-to-goodness solar eclipse glasses should be way darker than, say, your sunglasses. According to the AAS, the solar filters of eclipse glasses are "many thousands of times darker" than ordinary sunglasses.
So, your mystery pair of eclipse glasses look pretty darn dark? That's a good start. You should not be able to see anything through them except the sun itself or something similarly bright.
What's something as bright as the sun you can use as a test? The AAS suggests you check sunlight reflected off a mirror or a shiny metal object. If sun is behind the clouds or on the other side of the earth when you want to test your glasses, you can use a bright-white LED such as the flashlight on your phone or a bare lightbulb. The reflected sunlight or bright, white, artificial light should appear very dim through a safe pair of eclipse glasses. If you can see light behind a lamp shade or a soft, frosted light bulb through the glasses through your eclipse glasses, then they aren't strong enough to stare safely at the sun.
When staring at the sun through safe solar eclipse glasses, the sun should appear comfortably bright like the full moon, according to the AAS.
If you can't find a pair of safe solar eclipse glasses, you can make a pinhole projector to view the solar eclipse. It's fun and easy and requires a few materials you likely already have in your house.
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