Should you wear sunglasses on cloudy days? Yes, and here is which lens

Yes, you should wear sunglasses on cloudy days, for two reasons that have nothing to do with how bright it looks. Cloud blocks visible light far more than it blocks ultraviolet, so on an overcast day most of the UV can still reach your eyes. And a uniformly bright overcast sky is glare without a source: flat, shadowless light that is tiring to look at for hours. The lens for it is not a dark one. It is a light contrast tint, brown, amber, yellow or rose, that lifts the flat scene and blocks the UV. A dark grey on a cloudy day is the wrong tool twice over.

Cloud and UV

Clouds are made of water droplets that scatter light. They scatter visible light strongly, which is why a cloudy day looks dim. They scatter ultraviolet less, so a larger share of it gets through. Under thin or high cloud most of the UV reaches the ground. Under thick, dark cloud the reduction is larger but rarely complete.

Broken cloud can do something worse. Light scattered off the edges of clouds adds to the direct light coming through gaps, and for short periods the UV at ground level can be higher than under a clear sky. This is why people burn on days that did not feel sunny.

None of that is visible. Your eyes judge brightness by visible light, and visible light is what the cloud removed. The UV is the part you cannot feel.

Why a dark lens is wrong

On a cloudy day there is less visible light to begin with. A dark lens removes most of what is left, and what is left is what you use to see the ground, the kerb, the step. Dark sunglasses on an overcast day make the world dim and no safer, because darkness was never the thing protecting your eyes; the UV block was. Our UV400 vs polarized post separates the two.

Why a contrast lens is right

Flat light is a contrast problem. With the sun hidden, there are no shadows, and shadows are how you read shape and distance. Everything sits in the same grey.

A lens that absorbs more blue than red raises contrast. Blue light scatters most, and on an overcast day the whole sky is scattered light; remove some of the blue and the scene separates again, near from far, texture from flatness. That is what brown, amber, yellow and rose lenses do, in increasing order of how light they are:

Grey does none of this. It dims evenly and leaves the flat scene flat. On a cloudy day it is the least useful tint you can wear.

Bright overcast: the white sky

There is a particular kind of cloudy day that is tiring in a way people do not expect: high, thin cloud that turns the whole sky into one bright white sheet. It is not dark, it is not sunny, and after an hour outside your eyes ache. That is glare with no source to look away from. A medium contrast lens, brown or amber, cuts it without turning the day dim. That is the T01 Brown, and it is the reason a brown lens is the more useful of the two plain tints for anyone in a cloudy climate.

The same light-tint logic applies to bright interiors, which our indoors post covers.

Polarized on a cloudy day

Polarization removes reflected glare, and on a cloudy day there is less of it: no sun, so no hard reflection off water or road. It still helps on wet surfaces, which cloudy days tend to produce. It does not hurt, with one exception: in flat light on snow, a polarizing film can hide the sheen that reveals ice. Our skiing post covers that.

Frequently asked questions