To most, sunglasses are nothing more than lenses inside a frame. They sit on your face to protect your eyes from the sun. Simple. But not so quick. Sunglasses are significantly more elaborate than that and it’s the details that make them so powerful. Better yet, it’s the sunglass terminology that lets you know whether your sunglasses are going to do what you need them to do because, if you haven’t guessed, not all are created equally. There’s cycling sunglasses, sports sunglasses, running sunglasses, mountaineering sunglasses, polarized sunglasses, and so much more. So, let’s look through the lenses and figure out what all that jargon means for your eyewear.     Photochromic Lenses Julbo designed photochromic lenses more than 25 years ago so alpinist can conquer everest and return back from their expeditions, without eye problems. So, as you can imagine, they’re equipped with some serious technology. To put it simple, photochromic lenses are sunglasses lenses designed to adapt to light and circumstances. For example, if it’s cloudy outside, the lenses will adjust to a lighter tint and if you're at the peak of Mount Everest where the light is intense, your lenses will darken to provide optimal protection. As such, these types of lenses are incredibly versatile and ideal for all types of adventures.    Visible Light Transmission Visible Light Transmission (VLT) is the amount of light that’s subjected to your eyes through a specific pair of lens. This reading is most important when you’re purchasing sunglasses because you could be buying a pair that doesn't offer much protection at all. Here is a general guideline as to what the VLT percentages mean: 3-8% Cat.4: Perfect for extreme light conditions 8-18% Cat.3: Good for all purposes 18-43%Cat.2: Ideal for overcast and low light 43-80% Cat.1: Minimal protection 80-100% Cat.0: Clear lens   Sunglass Shields Sunglass shields are the distinguishing detail that furthers protection, field of vision, hold and ventilation. They contribute largely to your comfort and performance when wearing them, so it’s important to know what each does. Here is your crash course on shields: Side shields Provide lateral protection against intense light Protective Skirt Flexible material that conforms to your face to protect your eyes from spray Floating Cord Ensures sunglasses float is they fall in the water Floating Strap float if they fall in the water and also provides a secure headband-type fit on your head Universal Nose Clip Nose piece that ensures a perfect fit for every face shape   Sunglass Shapes The shape of your sunglasses play a huge role in the overall comfort, style and protection provided. For example, the best mountaineering sunglasses have total cover to ensure protection from the intense light coming in from all directions, whereas the best sports sunglasses have curved frames with wide temples for optimal fit. Here’s a breakdown of what each sunglass shape means: Total Cover Maximum protection against harsh sunlight, even in extreme conditions Wrap-Around Wrap around sides for good vision and protection Panoramic Wide lenses that provide a broad vision spectrum Floating Sunglasses Made to float in case you drop them in the water Asian Fit Specifically designed for Asian facial shapes   Sunglass Ventilation Ventilation isn’t always an important feature of sunglasses but it can also be one of the most important features, depending on the activity. So, if you’re looking for sports sunglasses, running sunglasses or mountaineering sunglasses, here’s what you need to know about ventilation: Front Venting Sunglasses designed with a shape and structure that allows a natural front air flow Side Venting Sunglasses designed with specific lens shape for lateral air and humidity evacuation Full Venting Sunglasses designed with aerated structure for complete air circulation to avoid fogging up   With this crash course on sunglass terminology, you’ll be able to purchase the best pair of polarized sunglasses, mountaineering sunglasses, sports goggles – whatever you need – with ease. Shop Julbo collection of premium sunglasses today.