Self-tinting glasses are clear indoors and darken by themselves in the sun. Photochromic lenses are available with your prescription, as varifocals and, without a prescription, in self-tinting sports glasses and sunglasses. Here you’ll find out how they work, where their limits are and what to look out for when buying.
Key points at a glance
- Photochromic lenses react to UV light: they darken outdoors and clear again indoors.
- Heat weakens the tint, cold makes it stronger. Behind a car windscreen, most lenses hardly tint at all.
- For driving in bright sun and for very strong light on snow or water, they are no substitute for sunglasses.
- They come as prescription lenses, as varifocals and, without a prescription, in sports sunglasses.
What are self-tinting glasses?
With self-tinting glasses, the lenses adapt to the light: clear in the office, lightly tinted when it’s overcast and dark in the sun. Strictly speaking, it’s not the glasses that change colour but the lenses. Opticians call them photochromic or phototropic lenses, and you’ll also come across terms such as self-darkening, self-dimming or auto-tinting glasses.
The advantage: if you wear prescription glasses, you don’t have to keep switching to sunglasses, for example on the way to work or when exercising in changing light. The principle was developed in the 1960s by the chemists William H. Armistead and S. Donald Stookey at the US glass manufacturer Corning.
How do photochromic lenses work?
The tint is triggered mainly by the UV light in sunlight. The lenses contain light-sensitive substances that change their structure under UV radiation and then absorb part of the visible light. When the UV radiation decreases, they return to their original state and the lens clears again.
- Mineral glass: embedded crystals of silver halide (silver chloride or silver bromide) release silver under UV light, which darkens the lens – similar to a black-and-white photo, except that the reaction reverses.
- Plastic lenses: most spectacle lenses today are made of plastic. Here, organic dye molecules in the lens or on its surface produce the tint. Under UV light they switch to a dark form and then switch back again.
How quickly do the lenses darken and clear?
Darkening is quick: the lens usually reaches most of its tint in less than a minute. Clearing takes longer, often a few minutes. So when you come indoors from the sun, a slight tint remains for a short while. The exact figures depend on the lens type.
Why cold and heat affect the tint
In the cold, photochromic lenses get darker but clear more slowly. In heat, the tint stays weaker because the molecules return to their clear state faster. That’s why photochromic lenses often get less dark on a hot summer’s day at the beach than on a sunny winter’s day.
Disadvantages and limits: driving, heat and very bright light
Self-tinting lenses are good all-rounders, but they don’t replace every pair of sunglasses. The main limits at a glance:
| Situation | What photochromic lenses do |
|---|---|
| Indoors, in the evening | Clear; some lens types keep a slight residual tint |
| Overcast sky | Light tint, as UV light also passes through clouds |
| Sun outdoors | Noticeable tint |
| In the car, behind the windscreen | Little or no tint |
| Great heat | Weaker tint |
| Cold | Stronger tint, slower clearing |
| Snow, water, high mountains | Often not dark enough – sunglasses are the better choice here |
Driving: no substitute for sunglasses
The windscreen blocks most of the UV radiation. That’s why most self-tinting lenses stay clear or only tint slightly in the car, even when the sun is dazzling. Some lens types also react to part of the visible light and get a little darker behind the windscreen, but not as dark as outdoors.
For sunny drives, sunglasses – with your prescription if needed – are therefore the more reliable choice. Sunglasses are classified into filter categories 0 to 4; category 4 lenses are not suitable for driving. Find out more in our guide to driving glasses.
Snow, water and mountains
For very intense light on the water, in the snow or in the mountains, you need sunglasses made for it: usually category 3, on glaciers and at high altitude category 4. There are also sports sunglasses with photochromic lenses designed for the mountains; the categories they cover are stated in the product description.
Self-tinting sports glasses or prescription glasses?
Whether you need self-tinting lenses with or without a prescription depends on what you’ll use them for.
Without a prescription: self-tinting sports glasses and sunglasses
Without a prescription, you’ll mainly find photochromic lenses in sports sunglasses that come fitted with them. Sports brands such as Julbo (Reactiv) and uvex (variomatic) have lenses like these in their range. When running, cycling or hiking, you don’t have to stop to change glasses when you come out of the woods into the sun. Self-tinting sports glasses are available for women and men.
With a prescription: single vision and varifocal glasses
With your prescription, photochromic lenses can be fitted into most prescription frames. Then you have glasses and sunglasses in one. Self-tinting varifocals are especially practical, because you don’t need separate varifocal sunglasses.
If you drive a lot or are often out in very bright light, prescription sunglasses with a permanent tint are a useful addition. You’ll find out what to look out for in our guide to prescription lenses for sunglasses.
The best photochromic lenses: what to compare
There isn’t one “best” lens for everyone. Which self-tinting lenses suit you depends on your everyday life. Compare these points in particular:
- Tint range: how clear is the lens indoors and how dark does it get outdoors? Lens manufacturers state how much light it lets through in its clear and its dark state.
- Speed and temperature: how quickly does the lens darken, how long does it take to clear, and how much does the tint weaken in heat?
- In the car: if you drive a lot, ask about lenses that also tint a little behind the windscreen.
- Colours: depending on the lens manufacturer, several colours are available, such as grey, brown or green. Grey changes colours the least, brown makes contrasts look a little stronger.
- UV filter and anti-reflective coating: look for full UV protection (UV400); an anti-reflective coating reduces distracting reflections. For background, read what you need to know about UV radiation.
Not to be confused: lenses with a permanent tint always stay equally dark, even indoors.
How to order glasses with photochromic lenses
At Edel-Optics, you start by choosing your frame, order it with prescription lenses and select the self-tinting option and a colour under tint. You’ll see the price of the photochromic lenses directly when choosing your lenses; it depends on the lens type and your prescription.
Popular frames at the moment include the Ray-Ban Wayfarer Ease (RX4340V), the Ray-Ban Alain (RX7239), the Miu Miu MU 01XV and the Prada PR 16ZV, and for sport and leisure the Oakley Holbrook RX (OX8156) or the Oakley Crosslink Zero (OX8076). You can see which colours and lens options are available for a model on its product page.
Miu Miu MU 01XV VAU1O1£134.56
Miu Miu MU 09XV VAU1O1£134.56
Miu Miu MU 04UV 1AB1O1£134.56
Miu Miu MU 01XV 19P1O1£134.24
Ray-Ban RX3928V 2501£86.92
Ray-Ban RX3928V 2500£86.92
Ray-Ban ALAIN (RX7239 2001)£60.29
Miu Miu MU 09XV 16K1O1£135.40Frequently asked questions about photochromic lenses
Why don’t my photochromic lenses get dark any more?
Often it’s down to the situation: behind glass, such as in the car or by a window, hardly any UV light gets through, and in heat the tint stays weaker. In addition, the ability to tint decreases over the years. If your lenses hardly get darker even in the sun, have them checked by an optician.
Are photochromic lenses good for driving?
As normal prescription glasses, yes. But in the car they hardly help against bright sun, because the windscreen blocks UV light – this also applies to what are often called transition lenses. For sunny drives, take sunglasses with you.
Do photochromic lenses work on cloudy days?
Yes. Part of the UV light gets through clouds, so the lenses tint lightly even when it’s overcast.
