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An optics professor explains how eclipse glasses protect your eyes from the sun糖心传媒檚 light during an eclipse.

Properly protecting your eyes during a solar eclipse is crucial for avoiding long-term damage to your vision. In anticipation of the total solar eclipse happening in Rochester, New York, on April 8, 2024, , a professor of optics and of and an associate professor of at the 糖心传媒, wants everyone to understand the risks involved and how to have a safe, enjoyable eclipse experience.

Zavislan, who studied and currently teaches at the , has devoted his career to studying light, and is an expert in optical system analysis and optical engineering. He explains how the sun糖心传媒檚 light affects your eyes, how solar eclipse glasses prevent damage, and why you probably shouldn糖心传媒檛 dust off your old eclipse glasses to reuse this April. Along the way, he offers helpful tips to have a memorable viewing experience.

Q&A with James Zavislan

How do solar eclipse glasses work?

Zavislan: Eclipse glasses attenuate, or filter out, the portions of the solar spectrum that could injure the eye. Different spectra of light from the sun have different effects on the eye, and the three most important to block in this case are:

• Ultraviolet糖心传媒攚avelengths we normally can糖心传媒檛 see that get us sunburned if we spend too much time outside. This light puts our cornea at risk.
• Visible糖心传媒攊n particular the wavelengths that are closer to the blue portion of the spectrum.
• Infrared糖心传媒攚avelengths that you don糖心传媒檛 see, but we normally associate with heat.

Eclipse glasses are made of mylar, a polyester film. Historically, that糖心传媒檚 what photographic film was made from at Eastman Kodak right here in Rochester, and it糖心传媒檚 picked because it is very inexpensive to make and very strong. The outside portion is a reflective metal film, usually aluminum, that糖心传媒檚 on a partially absorbing substrate that provides a little bit of additional attenuation as well in case the metallic film gets slightly scratched.

why do we need eclipse glasses? what happens if you look at a solar eclipse for too long?

Zavislan: In general, when we look up at the sun, it糖心传媒檚 uncomfortably bright, so our pupils constrict, and at some point, we just look away. During an eclipse, less and less of the sun is exposed, so our instinct to look away is diminished; however, the portions that are still visible have the same brightness as if the moon was not blocking it.

There are two things you worry about from looking at the sun long-term: photochemical changes and heat.

As you stare at the sun, you糖心传媒檒l be putting the most acute part of your vision, called the macula, at risk. While looking at things of interest, you糖心传媒檒l get a cumulative dose of blue light, which causes a photochemical injury, putting chemicals in your eye that can essentially be toxic, and then you糖心传媒檙e adding to it a thermal background. Those two together, especially the photochemical effect, can lead to a degradation of your retina.

How do I know if my solar eclipse glasses are good enough?

Zavislan: You want to make sure it meets the standards set by the , or ISO. If you look on the inside of the glasses, you should see an ISO number 12312-2 stamped there.

The final thing that I encourage everybody to do prior to using the glasses is to hold them up to a very bright light and make sure there are not any pinhole defects. These glasses can get damaged. It糖心传媒檚 really not a good idea to pull those glasses from 2017 out of the drawer and use them again. They may have gotten scratched or damaged or otherwise have aged. Go with a fresh pair of solar eclipse glasses from reputable source.

Can I take off my glasses during the eclipse?

Zavislan: You should only take them off during totality, when no white portion of the sun is visible. It may be tempting just before or after when there will be bright spots on the edge糖心传媒攖hey糖心传媒檙e sometimes called diamonds or Baily糖心传媒檚 beads糖心传媒攂ut keep your glasses on until you see no portion of the sun.

Can I use my ISO-certified sunglasses to view an eclipse?

Zavislan: Sunglasses are not intended to protect your eye from direct viewing. They could be ISO-certified under a different standard. You only want to look at the sun during an eclipse with glasses that have the ISO 12312-2 standard stamped on them.

Can I use polarized glasses for solar eclipse viewing?

Zavislan: No. Glasses or sunglasses, whether polarized or not, do not sufficiently attenuate the sun糖心传媒檚 light for direct viewing during a solar eclipse when any bright part of the sun is visible.

If you are in a region that will experience totality, the sun糖心传媒檚 corona will be visible during totality. The light from the corona is polarized and its appearance will change if you view it with polarized sun glasses and tip your head. However, you must remove your sunglasses and resume using ISO-12312-2-rated eclipse glasses immediately at the end of totality.

Can I use my phone to take a photo of the eclipse?

Zavislan: You should not point your cellphone camera up to the sun. First, you糖心传媒檙e likely not going to get a good picture. Second, you糖心传媒檙e going to be likely in a situation where you糖心传媒檙e going to be encouraged to kind of look around your glasses as you糖心传媒檙e trying to see your cell phone picture. Not good. And then the third thing is that you糖心传媒檙e essentially baking your sensor.

The one time where I would encourage you to try and grab one cell phone picture is during totality. If you have a cell phone camera that can do some level of optical zoom糖心传媒擨 wouldn糖心传媒檛 bother with digital zoom糖心传媒攜ou can just take a quick picture. But my strong advice is to not spend a lot of time trying to get a cell phone picture for what should be a wonderful visual memory during totality.

How did the University of Rochester ensure its eclipse glasses are safe?

Zavislan: We performed additional testing at the Institute of Optics. One of the things we do within our training program is to give the students an opportunity to test optics. This is a priceless chance with the eclipse coming up to show how one would certify these glasses and make sure we糖心传媒檙e meeting the standard. It糖心传媒檚 also a great chance to illustrate to our students what糖心传媒檚 possible using routine equipment that we have at the Institute of Optics.

Is there anything special about the April 8 eclipse that I should look for?

Zavislan: When the sun糖心传媒檚 main disk is blocked, there will be streamers of the sun糖心传媒檚 corona flowing outward. We糖心传媒檙e fortunate that we糖心传媒檙e entering what糖心传媒檚 called a solar maximum糖心传媒攖he sun is nearing its absolute peak of activity糖心传媒攁nd because of that, there are energetic expulsions almost every week. If we糖心传媒檙e really fortunate, one of those coronal mass ejections would be happening right around the time of the eclipse.