What does UV400 on sunglasses mean?

[Fort Washakie]

I often see UV400 on some sunglasses. What does this mean? Does anybody know?

[Fort Washington]

UV400 means you will have a very high level of protection from the most harmful UV sun rays. So when you are choosing sunglasses, those labelled as "UV400" are good choices for you.

[Fort Wayne]

It means the sunglasses lens can block all UV rays including UVA and UVB which is invisible but can penetrate the clouds and cause a sunburn. All sunlight up to 400 nm wavelength can be blocked by these kinds of sunglasses lenses, so you can get a full protection.

[Fort White]

UV400 protection is the highest level of protection your lens can have. It blocks 100% of all harmful light from the sun.

[Fort Wingate]

Some sunglasses have a label saying "UV400", refers to the degree of protection of the lens. Sunglasses with this label insure that the lens can protect your eyes from all harmful UV rays that are under 400 nm, so they can give you a total protection from all ultraviolet harmful radiations.

[Niskayuna]

UV400 protection is the highest level of protection your lens can have. It blocks 100% of all harmful light from the sun.