Also, known as self-tinting lenses, photochromic lenses tend to darken when exposed to UV light but are otherwise nearly clear when in an indoor environment. And, that is why they are sometimes called variable tint lenses and light-adaptive lenses.
Upon the exposure of sun’s UV rays, the molecules (of silver chloride or another silver halide) inside these lenses get activated, causing darkening of the lenses. Since, the molecules are self-tinting molecules, they tend to change their structure when exposed to light conditions.
But, when you are in an indoor environment, the UV rays get blocked and unable to enter inside which allows photochromic glasses to stay in their original state of transparency.
Usually, photochromic lenses darken in less than a minute after getting exposed to UV light and over the next ten to fifteen minutes, they become even darker. In the absence of UV light, these lenses become clear within a span of just two minutes and over the next fifteen minutes, they come back to their transparent state.
Whether you are going for photochromic eyeglasses frames or sunglasses, these special ophthalmic lenses offer you with the following benefits:
Because of your lifetime exposure to sunlight and harmful UV rays, there are high chances of developing cataract and other eye problems in future. And, so it is advised that you should opt for photochromic glasses or any eyewear with such type of lenses.