Prescription Glasses and the Brilliance of Photochromics

If you wear prescription glasses, you’ve probably come across glasses which darken in response to sunlight.

Photochromic lenses—more commonly known as transition glasses—are seamlessly integrated, and often unnoticed in most prescription glasses today. Whilst they only began to gain popularity in the 1990s, today—1 pair is sold every second—that's over 125 million pairs a year!

Various coloured tints are available: gray, green and brown. Worldwide, gray is the most popular tint, while brown is preferred by many Europeans.

Photochromic glass was invented in the 1960s by American glass works company, Cornering Glass Works. Still in operation, they now specialise in glass screens for devices such as the iPhone.

Photochromic lenses are a great investment for those who spend a large portion of their time outdoors, driving, or who have a light sensitivity. Even better, they remove the need for prescription sunglasses!

Transition lenses work due to their special photochromic properties. Yet to an extent, the colour change is also driven by changes in temperature (Thermochromic). As UV light is often accompanied by heat, photochromic lens often won’t work in very hot conditions.


Initially colourless, these lenses have a special layer of photochromic optical dye. On an atomic level, the particles are separated into two halves, sitting at opposite angles to each other. In the presence of UV light, these two halves join to become one larger particle, and the UV light is absorbed. This causes the level of light which can pass through the lens to diminish, resulting in a darker tint. This effect can be reversed so it becomes colourless again.

Glass—whether as windows or car windshields—blocks most UV rays. Traditional photochromic lenses only responded to UV light, so they didn’t provide enough tint to allow full vision when driving. This caused eye strain due to their low tint level. Similarly, they only reacted to UV light, not artificial light. 

Through pioneering technological advances, Cornering Glass Works created Transition Xtractive photochromic glasses, which also react to natural light. It blends photochromic optical dyes, so that inside a car, it achieves more than half the level of tint compared to its predecessors. Heat durability is also improved, enabling the lenses to withstand temperatures over 32°C.

Leave a comment below and tell us if you’ve worn transition glasses before. Do you love or hate them?

Where do you think this technology will go? What are the possibilities for the future?