Solar eclipse glasses work by blocking out the harmful rays of the sun, allowing you to safely view a solar eclipse without damaging your eyes. Here’s a detailed look at how they achieve this:
Material and Construction
Specialized Solar Filters: Solar eclipse glasses are made with solar filters that block out the vast majority of sunlight. These filters are much more powerful than regular sunglasses, blocking out 99.999% of visible light as well as harmful ultraviolet (UV) and infrared (IR) radiation.
Mylar or Black Polymer: The lenses of solar eclipse glasses are typically made from Mylar or a black polymer material that contains a thin layer of aluminum deposited on their surface. This metallic coating reflects away the harmful rays while allowing a minuscule fraction of sunlight to pass through, so you can safely view the sun.
How They Protect Your Eyes
Blocking UV and IR Radiation: The primary concern when looking directly at the sun is the potential damage from ultraviolet (UV) and infrared (IR) radiation. Solar eclipse glasses specifically block these types of radiation, protecting the delicate cells in your retina from being damaged or destroyed.
Reducing Visible Light: In addition to blocking harmful UV and IR radiation, solar eclipse glasses drastically reduce the amount of visible light reaching your eyes. This reduction is critical because the sun’s brightness is so intense that it can cause immediate harm to your eyesight, known as solar retinopathy, even if you don’t feel pain while looking at it.
Standards and Safety
ISO 12312-2 Compliance: To ensure they provide adequate protection, genuine solar eclipse glasses must meet the international safety standard ISO 12312-2. This standard guarantees that the glasses have been tested and proven to block the necessary amount of solar radiation.
Importance of Using Certified Glasses
Using uncertified or makeshift filters (like sunglasses, smoked glass, or exposed film) to view the sun can be dangerous. These materials cannot block the full spectrum of harmful solar radiation, despite potentially making the sun appear less bright, leading to “eclipse blindness” or retinal burns.
Ensuring your eclipse glasses are not fake and meet the ISO 12312-2 international safety standard is crucial for protecting your eyes during a solar eclipse. Here’s how you can verify their authenticity and safety:
Look for the ISO Certification
ISO Standard: Genuine solar eclipse glasses are designed to meet specific international safety standards (ISO 12312-2). Check the glasses for printed information stating they meet the ISO 12312-2 standard.
Manufacturer’s Information: Legitimate glasses should have the manufacturer’s name and address printed on them. You can research the company to ensure they are recognized and reputable in producing eclipse glasses.
Inspect the Glasses
No Scratches or Damage: Even if the glasses claim to meet ISO standards, any scratches or damage can make them unsafe. Inspect the lenses carefully; if they are torn, scratched, or punctured, do not use them.
Uniform Darkness and Color: The lenses should be uniformly dark and not show any uneven coloration or light areas. You shouldn’t be able to see anything through them except the bright sun or similarly intense light sources.
Test the Glasses
Try Them Out: Before the eclipse, test your glasses by looking at a bright light bulb. You should only be able to see the light itself with no surrounding room light or fixtures. If you can see things like household lights in detail, the glasses are not safe.
Check for Comfort: While wearing the glasses, you shouldn’t experience any discomfort or “sunny” spots that make you squint or want to look away. If you do, the glasses might not be filtering out the sun’s light effectively.
Verify with Trusted Sources
Approved Vendors: The American Astronomical Society (AAS) provides a list of reputable vendors of solar glasses. Buying from an approved vendor can reduce the risk of getting fake glasses.
Be Wary of Online Marketplaces: Glasses sold on online marketplaces can be counterfeit, even if they claim ISO compliance. It’s safer to purchase directly from recommended manufacturers or authorized retailers. The AAS Solar Eclipse Task Force has compiled a list of vendors of safe solar viewers. For every seller on the list, they 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.
AAS also provides an example of how to spot counterfeit glasses below:
The inside left earpieces of counterfeit Chinese (top) and genuine American (bottom) eclipse glasses. Much of the text on the counterfeit glasses is copied from the real ones. Note that the counterfeit glasses include the name of U.S. company American Paper Optics but not the address (though there is a spurious fragment of an unrelated address above the name), whereas APO’s glasses include both their name and address, as required by the ISO 12312-2 international standard for filters for direct observation of the Sun. Courtesy American Paper Optics and the American Astronomical Society.
Price Too Good to Be True: Extremely low prices can be a red flag for counterfeit products. While eclipse glasses should not be excessively expensive, be cautious of deals that seem too good to be true.
Ask for Documentation: If purchasing for an event or organization, ask the supplier for documentation verifying the ISO certification. A reputable supplier should be able to provide this.
What to Do if Unsure
If you have any doubts about the safety of your eclipse glasses, do not risk using them. Viewing a solar eclipse without proper protection can cause serious eye damage or blindness. Consider other safe viewing methods, such as a pinhole projector, or watch the eclipse through a live stream from a reliable source. Always prioritize safety over convenience when it comes to observing solar eclipses.