How to tell if your eclipse glasses are safe and which ones to never use

The ISO 12312-2 standard in plain words, a ten second test that exposes fake glasses, and why sunglasses, X-ray film and smoked glass can cost you your eyesight.

In 40 words. Safe eclipse glasses carry the ISO 12312-2 certification, block 99.997% of light and let you see nothing but the Sun. Sunglasses, X-ray film, CDs and smoked glass all fail, letting through infrared that burns the retina painlessly.

Staring at the Sun does not hurt. That is the whole problem. Your retina has no pain receptors, so the damage happens in silence and you notice hours later, when it is done. With Spain's eclipse on August 12 days away, this is everything you need to know about glasses.

The only phrase that matters is ISO 12312-2

Real eclipse glasses meet the international standard ISO 12312-2, which requires blocking about 99.997% of visible light and, crucially, the ultraviolet and infrared you cannot see. Look for the certification printed on the frame next to the maker's name. Without that print they are not eclipse glasses, they are a toy.

The ten second test (do it before eclipse day)

Put them on at home under the brightest light you have.

1. A powerful LED bulb should appear as a faint dot, or not at all.
2. If you can make out furniture, windows or your own hand through them,
3. they are fake. Through genuine glasses you see the Sun and almost
4. nothing else.
5. Hold the lenses against the light. A single scratch, pinhole or crease
6. means the bin, because damaged film lets concentrated radiation through.

What never works (no matter what your uncle says)

• Sunglasses, however dark or expensive. They pass thousands of times
• more light than your retina can take.
• X-ray film, photo negatives, CDs and DVDs, classic myths that do not
• filter infrared.
• Candle-smoked glass, the grandparents' trick, same problem.
• Pointing your phone or camera without a filter. Besides risking the
• sensor, the screen tempts you into "just one glance" at the real Sun.
• The only valid homemade options are welder's glass shade 14 (the
• common lower shades do NOT work) or pinhole projection, a card with a tiny
• hole projecting onto another card.

Where to buy (and where not to)

Buy from opticians, planetariums, astronomy shops or pharmacies, channels accountable for what they sell. On marketplaces, distrust glasses with no brand, no printed ISO or anonymous third-party sellers. Every eclipse brings recalls of counterfeits with the certification falsely printed on. If the price looks too good, your eyes are the discount.

With kids, two rules

1. Child size or an elastic band, because slipping glasses mean a guaranteed
2. glance at the Sun.
3. One adult per child during partial phases. The spike in eye-clinic visits
4. after every eclipse is mostly minors.

When can I take them off?

Only inside the path of totality, and only during totality itself, about 76 seconds in 2026. When the last ray disappears and night falls, glasses off. The corona is safe for the naked eye. The instant the first flash returns, glasses back on. In partial-eclipse areas the glasses never come off.

Keep them, they work for 2027

If the film is intact, with no scratches or folds, modern ISO 12312-2 glasses do not expire with time, and Spain hosts an even longer total eclipse on August 2, 2027. Store them flat, in their sleeve, away from heat.

Frequently asked questions

What certification should eclipse glasses have?

ISO 12312-2 (sometimes written ISO 12312-2:2015), printed on the frame with the manufacturer's name. Without that print they must not be used to look at the Sun.

Can I use sunglasses to watch a solar eclipse?

No. Even the best category lets through visible and infrared light thousands of times above what a retina can tolerate when aimed at the Sun.

How do I know my eclipse glasses are fake?

Test them at home. Through real ones you only see the Sun, or a strong bulb as a weak dot. Seeing anything else, furniture, windows, your hand, means fake. Check the film for scratches and pinholes too.

When is it safe to look at the eclipse without glasses?

Only during totality, inside the band where the Sun is 100% covered. In Spain's August 12, 2026 eclipse that phase lasts about 76 seconds. Before and after, always glasses.

Sources

• IGN, official guidance for the 2026 eclipse
• NASA, solar eclipse safety