So, tints. A vexed issue for eyeglass wearers. 

For decades I’d been happy with transitions, going from clear to darkish, usually in green. And then I began to expand my horizons. Simply put, IMHO, tinted lenses compliment any pair of frames you own, sometimes for functionality, sometimes for the look. You can choose various depths of tint (usually expressed in their transmission percentage, i.e., how much light they let through to the eye — for instance, a 40% tint will let 60% of the light through, and so it will be paler than an 85% tint, typical for sunglasses, which only lets 15% of the light through. (NB: for driving in the UK your sunglass lenses the tint can’t be more than 92%.)

Zeiss offer a sun tint called Adaptive Sun, which start at 60% and darken to 97%. The stricture against lenses this dark behind the wheel aren’t relevant here because all windscreens filter out UV light, which is the type of light that triggers any self-darkening lens. And that was the problem I ran into. Last winter I had Kashan glaze my pair of JF Rey full frames with Adaptive Sun. Even though they were Polarised they failed to cut the road glare. This was because in the car they stayed at 60%... Consequently I reverted to my old school sunglass lenses, 85% Pioneer Green, Polarised, for my Esmont Caudron pair, and these work perfectly.

The 50% Sweet Violet tint in the Ahlem Rue de Turenne is strictly for the look, although I do appreciate the distance from my surroundings that the tint affords (a similar effect to the blue tint in my Zephirins). I also discovered that here in the UK it’s not possible for Zeiss to add a base tint to their PhotoFusion X line, so you’ll have to select from their transition colours, which at the moment stand at Grey, Pioneer Green, Burgundy, Brown and Blue.

There's been a trend for a while in somethong called Flash Coating. These can be of various densities - from a light coating that colorfully reflects glints of light when the lens is turned in a particular direction, to a heavy mirror tint that repels light altogether, the letter being IHMO the least socially friendly.

Flash tints come in a variety of colours, but here’s the hitch: reflections on the inside of the lens.. This glare can be distracting especially when they catch indoor lights and bounce them back into your eyes or create inner lens reflections. Another thing (a particular bugbear of mine), they hide your eyes. Great, if you happen to be the foreman of a chain gang in the American South, but opt for these heavy mirror tints and you can forget about having friendly IRL conversations or video calls.

For the real sticklers, with flash tints you can also have the problem of colour accuracy. Depending on the shade, the coating could well shift the colours you see, so your immediate experience of life in general will be less than ideal.

Choosing the right LTF (Light Transmission Factor). Sunglass tints are divided into four categories, defined by the amount of light they transmit to the eyes: 

CAT 0 is a completely clear lens, so 100% to 80% light gets through These would be clear or very pale lenses for indoors, overcast days, or night driving. 

CAT 1 lets in 43% to 80% of the light, pale tints for low-sun (like in most of the UK).

CAT 2 lets in 18% to 43%, so a medium tint for moderately bright days, also on the fashion side, cool enough for indoor looks if you’re schmoozing around an art opening, say. 

CAT 3 lets in 8% to 18%, true sunglasses territory, summer days by the BBQ or at the beach. 

CAT 4 lets in 3% - 8%, (e.g. Zeiss Adaptive Sun, which transitions from 40% to 3% transmission), good for extreme glare, say on the ski slopes or on the briny, but illegal in the UL for driving.

Be sure to ask your optician to show you samples of the tints on offer. Recently I ordered a pair of tinted lenses from Kashan. I’ve had two pairs from him glazed with Zeiss’s Smartlife Superb, 50% Sweet Violet, which are fine for life both indoors and out. I assumed that their 50% blue would be just as useful. Nope. Way too dark for indoors, closer to a true sunglass shade. Kashan Aziz to the rescue! Without fuss he sent them back to Zeiss with the instruction to remake them and match the paler blue that originally came with the JMM Zephirins. Et voilà, problem solved, but satisfaction delayed. The lesson here: look at sample lenses, think about what you’ll be using the tinted glasses for (driving, aesthetics, etc.), and don’t rush your choice!