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Light bouncing off a flat surface such as a road, water or a car bonnet becomes horizontally aligned, which is what you experience as glare. A polarised lens filters that alignment out. It makes the biggest difference driving, fishing or near water, and it is a genuine optical effect rather than a coating that wears off.

Honestly, the evidence is mixed and we would rather say so. A 2023 Cochrane review pooling 17 trials found blue-light filtering lenses probably make little or no difference to eye strain at a screen. Where the evidence is stronger is evening light and sleep. We set out the research in full, including the parts that do not favour the product, on our Information page.

Every product page lists the model code and its measurements, in the order the industry uses: lens width, bridge width and temple length, all in millimetres. The quickest guide is a pair you already own, since those three numbers are usually printed on the inside of the temple arm. Match those and the fit will be close.

They are the manufacturer model code and colourway. On a Ray-Ban RB3548N 002/71 51, RB3548N is the model, 002/71 identifies the frame and lens colour combination, and 51 is the lens width in millimetres. Searching that code on our site will bring up every colourway we hold.