What is the very practical, non-fashion reason that A-list celebrities constantly wear dark sunglasses on red carpets?

A break from the lights

A red carpet can be a surprisingly harsh place to look around. Photographers fire flashes from close range, while video crews add steady lamps so faces remain visible on camera. Dark lenses cut some of that glare, making it easier to keep looking toward the cameras without squinting as much.

The flashes are not usually a danger to healthy eyes; the practical benefit is comfort, not protection from eye damage. And sunglasses cannot erase every burst of light. They simply reduce the overall brightness reaching the eyes, especially between flashes.

The cameras keep asking for a look

That relief matters because a celebrity may be photographed from several directions while pausing, turning, and walking under the lights. Sunglasses also make it less obvious where someone is looking, which can be useful when photographers are calling for attention from multiple spots at once.

So the glasses can serve a real on-the-job purpose: they soften the visual assault of a brightly lit carpet and offer a little control over a face being scrutinized from every angle. The practical detail is that, amid all the posing, the lenses are doing some of the work of a visor.