Know How

Eye Protection 101 - How to Choose Sunglasses

Sarthak Madan

Last updated: 25-10-2018

Last week, we told you about protecting yourself from sunburn and worse in our Sun Protection 101 blog. Surprise, surprise - your eyes need protection from harsh UV rays as well.

India receives almost 3000 hours of sunlight in a year, which is why it’s really, really important to have a good pair of sunglasses that protect your eyes from UV rays in the outdoors. When those UV rays are reflected by the snow on your next winter trek, you’ll be glad you’re not wearing your Ray-bans.

Apart from protecting your eyes from UV rays, wearing sunglasses during the day while hiking ensures better vision at night, reduces eye strain and provides a layer of defence against the wind, rain, snow and other flying debris.


The most important component of your sunglasses are the lenses. A good pair of sports sunglasses will block 100% of UV light, and an appropriate amount of visible light. While choosing your sunglasses, the single most important thing to consider is the Visible Light Transmission (VLT).

Visible Light Transmission (VLT) and Lens Categories

VLT is the amount of visible light the lenses on your sunglasses will allow to pass through to your eyes. Lenses are divided into categories based on their VLT properties. VLT depends on the color, thickness and material of the lenses. Each category of lenses is suitable for different conditions and activities.

Eye Protection 101 - How to Choose Sunglasses

Cat 3 or Cat 4 lenses are suitable for most situations you will encounter while trekking, cycling or engaging in other adventure sports. Don’t know how to find out what category your sunglass lenses are? The last number of the serial number printed on the inside of the frame is the category of the lens - for example, the sunglasses in the picture below have Category 4 lenses.

Eye Protection 101 - How to Choose Sunglasses

The good news is you don’t always have to choose. Some sunglasses are capable of functioning well in a diverse range of situations.

Photochromic Lenses

Photochromic lenses automatically adjust to varying levels of intensity and brightness of light. They actually turn darker in bright conditions and lighter in dim conditions. The bad news is that they’re slightly more expensive than single category lenses, and they don’t always work great in extremely cold conditions.

Interchangeable Lenses

Some sunglasses also come with lenses that can be switched out and replaced with another Category of lenses. Typically, such sunglasses will come with 3-4 pairs of interchangeable lenses that can be switched out depending on the situation. The downside is that you may end up carrying more than you need to.


A frequent problem that you may have to deal with in the outdoors is condensation build up on the inside of the lenses, or sweat falling from your forehead into the sunglasses, both of which hamper visibility and are just generally irksome to deal with.

Some lenses come with anti-fog coating which prevents condensation from building up, and a hydrophobic (water-repellent) coating, that helps sweat or rainwater slide off the surface of the sunglasses.

From multiple years of personal experience however, these coatings are not as effective as physical solutions. Choose a pair of sunglasses that come with vents in the lenses - the airflow provided by the vents is the most effective way of preventing condensation from building up inside the lenses. As far as sweating is concerned, some lenses come with a removable foam attachment at the top that seals the gap between the lenses and the forehead - this prevents water or sweat from sneaking inside the sunglasses, with the foam absorbing all the water.

Eye Protection 101 - How to Choose Sunglasses


If your sunglasses don’t fit your face well, you’ll constantly be adjusting them and having them fall of your face. Keep the following points in mind to ensure you buy sunglasses which fit you well.

  • Curvature: Some sunglasses have straight temples, while other have curved ones. The amount of curvature will affect how secure the sunglasses are against your head.
  • Adjustability: Some sunglasses have adjustable temples - this means you can adjust the ends of the temples up, down and even sideways to ensure you have a good fit.
  • Nose and Ears: Make sure the sunglasses fit snugly around your nose and ears, but aren’t tight enough to pinch or cause discomfort.
  • Cords: Most sport sunglasses will have a headband-style cord that attaches to the temples and goes around the back of your head, ensuring you won’t lose your sunglasses even if they fall off your head.

Eye Protection 101 - How to Choose Sunglasses


A common concern for people with vision impairment is whether to carry spectacles or contact lenses while trekking.

Most people who use contact lenses do so because of the superior clarity. It's also cumbersome to wear sunglasses over bulky spectacles or use clip on sunglasses. Clip on sunglasses also do not offer the same quality of UV protection as compared to dedicated outdoor sunglasses.

On the other hand, the downside of using contact lenses while trekking is that you need to ensure your hands are clean while applying, replacing or removing contact lenses. Lens solution also tends to freeze in subzero temperatures.


While you are the best person to make the choice between contact lenses and spectacles for yourself, there are a few precautions you can take whatever decision you make.

If you prefer wearing contact lenses, keep the lens solution on your body, in your jacket or pant pockets, while trekking and sleeping to prevent them from freezing. It also won't hurt to carry a spare set of lenses.

If you go for spectacles, make sure you sunglasses are wide enough to use over your spectacles if the need should arise.

It is also a good idea to carry a spare set of spectacles as backup should you lose your primary pair of lenses or specactles, or if your lens solution freezes.

Sarthak Madan

I work with Bikat Adventures as an expedition leader and technical content writer. Sometimes, I fly. Read more

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  • Aruna Rihal | 10 January 2019

    Really informative! thanks. Can you please add about wearing contact lenses in winter/Himalayan treks?

  • Sarthak Madan | 12 February 2019

    Hey Aruna, I've updated the article with a section for people who use spectacles or contact lenses. The best solution is to carry you lens solution and spare contact lenses on your person, in your pant or jacket pockets, while trekking and while sleeping!