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Understanding How Anti-Fog Glasses Works!

Team StoryWeavers|August 7, 2020|

It’s the last round of the medley swimming competition and two swimmers – A and B are in a close tie. Suddenly A, who was in the lead bumps into the pool wall and loses the lead to B. The reason – he had fogged-up glasses which blocked both his vision and his dream of winning the competition. Have you heard of such a scenario? Most likely not, and the reason is that we have something called anti-fog glasses!

Fogging of glasses is as old a problem as glasses themselves. Not only in swimming but in many other professions like fire fighting, construction work, factory work and even in the medical profession. In fact, with the current pandemic, anyone who wears spectacles would be facing this issue whenever they step out when used along with a face mask.  Before we explore the possible solutions to this problem, first let’s understand exactly why do we have this problem

The quick answer to this problem is – condensation.  The fog formed on glasses consists of small droplets of liquid water. This happens because the warmer water vapour from the air condenses on the colder glass surface. The droplets are thick enough to distort our vision. This is the reason why eyewear fogs every time one steps out of an air-conditioned room into the warm outdoors. This problem of condensation of moisture droplets on the lenses persists until the eyeglasses warm up to a temperature nearing the surrounding air. Similarly, when you wear a mask, warm breath escapes through the edges on the top, and reaches the glasses, resulting in your glasses fogging up. In fact, the popular method to clean glasses by blowing air on it, fogging it up and then cleaning them with soft tissue, works on the same principle.

One of the ways to deal with this problem is by heating up the surface of the glass. This solution works with bathroom mirrors, usually found in some expensive hotels and in the rearview mirrors in cars. The warm glass surface doesn’t allow condensation to happen in the first place. There have been several patents about using similar technology for eyewear, one really interesting of the lot by a gentleman named Mr William Ryden who patented his ‘Defogging Eyeglasses’ in 1992. His patent numbered US5319397A involved heating the lenses of the eyeglasses, by making the lenses a part of an electrical circuit. Electric current is supplied to the electric circuit from a power source external to the eyeglasses.

A picture from William Ryden’s patent

Other solutions to this foggy problem work on the idea of lowering the water’s surface tension i.e the force with which water molecules are attracted to each other. In fog, water forms beads because the attraction of water molecules for each other is greater than the attraction towards the surface. 

Keeping this in mind, the other possible solutions to prevent glasses from fogging up is to introduce some substance (read anti-fog coating)  that gets in between the water molecules and the glass surface and prevents them from sticking to each other. An anti-fog coating contains hydrophilic ingredients, i.e, “water-loving” ingredients. They want to absorb water and spread it throughout the coated surface. That keeps water droplets from becoming big enough to be visible, or, in other words, big enough to be seen as fog.  The best part about this solution is that you can try it at home on your spectacles!

Soapy Water

Materials needed:

  1. Spectacles (without blue light filter or anti-glare filter)
  2. Any mild liquid soap like baby shampoo or hand wash
  3. Water
  4. Soft tissue paper or microfiber cleaning cloth towel

Methodology:

Just before wearing a face mask, take microfiber cleaning cloth/soft tissue and add a drop or two of the liquid soap on it. Rub your glasses with this cloth/tissue until the glass looks clear, and then rub off the excess.  Then, let the spectacles air dry or gently dry off the lenses with another soft tissue before putting them back on. Voila! Your anti-fog glasses are ready.

In 2011, a British surgeon named Sheraz Shafi Malik published a paper stating that washing your glasses with soapy water and letting them air dry can prevent glasses from fogging up. What actually happens here is that soap acts as a surface-active agent (anti-fog coating) and the soapy water leaves behind a thin layer of soap that stops the water molecules from forming big droplets. Although this does is not a permanent solution, the technique reliably works for up to half an hour, beyond which you may have to repeat the procedure.

CAUTION: If your glasses are anti-glare or have a blue light filter, do not try the soapy water method, as the soap may damage the anti-glare or blue light protection film.

Now for those of you who face the challenge of foggy glasses while wearing a mask, here’s a hack to avoid it.

Taping the mask

Materials required:

  1. Surgical mask (do not try this with N-95 mask or any other cloth mask)
  2. Microporous medical tape or band aid (do not substitute this with duct tape or any other non-porous tape)

Methodology:

Put on the surgical mask. Tighten the nose clip on the mask around your nose. Now take a small piece of the microporous tape and put it on top of your nose where the nose clip bends. The tape should seal the top of your mask. Your anti-fogging mask is ready.

What happens with this method is that the hot breath coming from your mouth, all the way up to your glasses gets redirected to the other openings of the mask (sideways). So the breath doesn’t fog up your glasses. 

CAUTION: It is important to note that one should not try this with N-95 masks and even cloth masks, as these masks have tight edges and sealing off the top may make you feel breathless. Similarly, using any other tape than medical tape may irritate your skin. This method is a favourite amongst many surgeons and medical staff at hospitals.

Due to condensation, fogging is usually less of a problem in summers, as the outdoor temperature gets closer to the temperature of your breath. Until then you can try out the above mentioned DIYs. Try both of them and share with us what worked best for you in the comment section!

About the Author


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Charu Verma

Charu, a feminist and an accidental writer, is yet to master the art of writing about herself. Always curious to learn new stuff, she ends up spending a lot of time unlearning the incorrect lessons. She enjoys all sorts of stories – real, fictional, new, old, hers and would love hearing yours too. Feel free to ping her at storyweavers@byjus.com to share anything that you think is worth sharing.

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