Photochromic lenses: how they work, what they don't do and when to choose them
Clear indoors, dark in the sun. How photochromic lenses work, why they stay clear in the car and when to choose them over a pair of sunglasses.
Clear indoors, dark in the sun. Without changing glasses.
Photochromic lenses react to light: they darken outdoors and turn clear again when you come back inside. They can seem like the answer to everything, but they follow precise rules. Here's how they work, what they don't do and when it makes sense to choose them over a pair of sunglasses.
How they work
Within the lens material, or in a layer on its surface, there are molecules that change shape when they're hit by ultraviolet rays. As they change shape they absorb more visible light, and the lens darkens. When UV levels drop, the molecules return to their original shape and the lens clears. The process repeats every day, without you having to do a thing.
It's ultraviolet that activates them, not light itself. That's why they stay clear behind glass that filters UV.
They darken more in the cold, less in the heat. On a mountain in winter they get darker than on a beach in August.
They darken quickly and clear more slowly. When you step back indoors, they need a few moments.
What they don't do
In the car, they barely darken. The windscreen blocks most ultraviolet rays, so standard photochromic lenses stay almost clear behind the wheel. For driving in the sun you need sunglasses, ideally with polarised lenses.
They aren't polarised. They reduce light, but they don't eliminate the dazzling glare off wet tarmac or water. That calls for a different lens, which we explain in Polarised lenses: what they are and when you need them.
They don't always replace sunglasses. On snow, by the sea and in the mountains in summer, a sun lens chosen for that light is still the right choice.
Photochromic, sun or polarised?
| Photochromic | Sun lenses | Polarised | |
|---|---|---|---|
| At home and in the office | Clear | Too dark | Too dark |
| Outdoors in the city | Darken on their own | Yes | Yes |
| Driving | Stay almost clear | Yes | The best choice |
| Glare off water and tarmac | Reduce it slightly | Reduce it slightly | Cut it out |
| One pair for the whole day | Yes | No | No |
SEIKO photochromic lenses
OCCHIO! is a SEIKO Vision Specialist. In the SEIKO range, photochromic lenses are called SENSITY: clear indoors, they darken automatically in outdoor light and offer full UV protection. They come in several colours, and the intensity and speed of darkening are chosen around how you live your day.
They can be paired with single-vision and progressive lenses. Progressives require measurements taken in our boutique, with the frame on your face: we explain them in Progressive lenses: how they work and which to choose.
Leisure Society Geiger
An example of a photochromic lens fitted from the start: the titanium Geiger, in 24K Gold and 12K White Gold finishes, comes with Blue Tint lenses that darken in sunlight. A round frame with an architectural bridge, handmade in Japan and numbered.
View the frameWhich frame to choose
Any optical frame can take photochromic lenses. Two things to bear in mind: on a large frame the lens is wider and the change in tint is more noticeable; on a clear front, the darkened lens creates a strong contrast, which can look striking. Start with women's optical glasses, men's optical glasses or clear frames. If you prefer a lens that stays dark, read Prescription sunglasses.
Do photochromic lenses darken in the car?
Only a little. The windscreen blocks most of the UV rays that activate the lens, so behind the wheel they stay almost clear. For driving in the sun, sunglasses are the better choice, ideally polarised.
How long do they take to clear?
They darken quickly and clear more slowly. Timing depends on the type of lens and the temperature: in the heat the lens clears sooner and stays less dark in the sun.
Do they protect against UV even when clear?
Yes. SEIKO SENSITY lenses offer full UV protection in every light condition, clear or dark.
Can they be made as progressives?
Yes. Progressives require measurements taken in the boutique with the frame on your face, so we make them in Crema (Italy).
Do they replace sunglasses?
For everyday use in the city, often yes. When driving, at the sea, in the mountains or around highly reflective surfaces, sunglasses are still the right choice.
Try them with your frame
In our boutique in Crema (Italy), we'll choose the colour and intensity of your SENSITY lens with you, along with the frame to fit it in. Bring your prescription, or the glasses you wear now.