A tinted lens pulls down the blind; a polarised lens takes the reflection away. They are not the same thing, yet it's the most common confusion in front of a display. The first darkens everything, including what you'd like to make out; the second cuts the glare bouncing up from asphalt, a car bonnet or a puddle. Which is why the pair you put away in September as a summer accessory deserves to stay in your bag until December.

A dark lens is not a polarising filter

The tint and the polarising filter are two separate things, and one tells you nothing about the other. The tint is density: it decides how much light passes through the lens, hence categories 0 to 4, from lightest to darkest. The polarising filter, by contrast, targets one specific direction of light: the light reflected horizontally off a flat surface such as a wet road, a shop window or a car bonnet. A dark but non-polarised lens doesn't remove that reflection; it just makes it darker. Which is not exactly a win.

Through a polarised lens the wet road reads clearly while the rest of the frame stays glaringly bright
Same colour density, two different jobs.

Is the darkest lens the most protective? Not necessarily, and that's where the misunderstanding starts. In November, available light is already low: a very dark lens adds a grey filter over an already grey sky, and you lose detail – the edge of the pavement, the puddle, the cyclist filtering up the queue. In practice, choose a category suited to the light; the darkest lenses are not right for a low-light morning commute.

A light-coloured frame is portable lighting

When it comes to frames, winter plays a different tune. A translucent, ivory, honey or pearl-grey frame lights up the complexion when the sky won't, and it works with seasonal textures: the bouclé wool of a coat, the thick cotton of a trench, a cream roll-neck. Clear acetate gives that lit-from-within effect without looking as if you've just stepped out of a studio. A wrap-around frame, meanwhile, covers more of the eye contour – welcome when walking into the wind, and more comfortable under a beanie.

A translucent honey acetate frame worn with a pink coat
Honey acetate brings a little light to the face.

Do watch the thickness, though: the clearer the acetate, the more you see through it, and the more your brows or make-up show behind the rim. On a fine face, thick crystal creates a nice contrast; on a smaller face, a thin rim is more discreet and often more flattering. And if black is the only colour you'll wear, you don't have to switch sides: a dark frame with a real filter is more useful than a light frame without one.

How to check the filter without trusting the colour

So how do you decide without buying blind? Certainly not by naked eye at the shop window: the colour of the lens tells you nothing about the filter. A grey lens can be polarised, a brown one may not be, and the very pretty pink gradient on the next pair won't tell you anything either. What matters is the information provided: the lens category and whether the pair is genuinely polarised.

Two polarised lenses crossed at 90 degrees, the overlap going dark
A slow rotation is all the proof you need.

Two simple moves are enough to check a pair in store. The first is within your reach: hold the lens in front of your phone screen, turn it slowly and watch. At a certain angle the screen darkens sharply, sometimes to a blue-black – that's the filter doing its job. For the second, ask the sales assistant: opticians often have a two-lens demonstrator that you cross at 90 degrees, and the overlap goes almost entirely dark. If no one can show you either test, walk away: a pair whose filter can't be demonstrated is not a good buy, whatever the price.

The phone-screen test, quick version: screen on, lens in front, slow rotation. Does the image darken suddenly? The filter is there. Nothing changes at all? It's a tint, not a polarising lens.

What to spend

Expect to pay around £20 to £50 for a simple pair from a high-street chain, a pharmacy or a seasonal display – sometimes very pretty, sometimes with a filter, but the labelling is rarely clear. Between £60 and £150, opticians' own collections and independent brands offer decent polarised lenses, with a demonstration usually possible in store. Above £150, you are mainly paying for the frame, the design and the name: there's nothing wrong with that, it's just that the filter isn't what costs that much.

And if you'd rather avoid buying a new pair? Consider having the lenses changed in a frame you already love, if it's in good condition. It's often kinder to your budget than a new pair, avoids another purchase and gives a new lease of life to a frame that has been sleeping in a drawer. Ask for the price first: it really does vary from shop to shop.

A light-coloured pair with polarised lenses isn't a seasonal purchase to look pretty: it's the accessory that makes the road readable and the morning commute a little less dazzling. Turn the lens, compare, ask for the demonstration – and if you're torn between two frames, keep the one that makes you squint least, not the one with the prettiest lens colour.