Sunglasses lens categories and VLT: what category 3 means and why it is not a UV rating

A sunglasses lens category is a band of darkness. It is set by visible light transmission, or VLT: the percentage of visible light that passes through the lens. Category 0 is almost clear, category 4 is very dark, and category 3, which lets through roughly 8 to 18 percent of light, is the band almost all everyday sunglasses fall in. The category says nothing about UV protection, nothing about polarization, and nothing about colour. It is one number describing one property, and it is the number most makers, including the one we buy from, do not state.

What VLT is

Hold a lens up to a light. Some of the light passes through, some is absorbed or reflected. VLT is the fraction that passes, as a percentage, measured across the visible spectrum with the eye's sensitivity weighted in.

A clear lens is around 90 percent. A light tint might be 50. A typical grey sunglass lens is 12 to 15. A glacier lens is 3 to 5.

VLT is the honest measure of darkness. "Dark" and "light" as words mean little; two lenses that look similar on a shelf can be 25 and 12 percent, and that is the difference between a lens you can drive in at dusk and one you cannot.

The categories

The international standard for sunglasses groups VLT into five bands:

Category 3 is where most sunglasses sold for general use sit. Category 4 is a specialist band: it is dark enough that road-safety authorities say it must not be used for driving, and it is usually marked as such.

What category does not tell you

This is the part that matters, because the category label gets read as a quality or safety grade. It is neither.

Not UV. UV protection is a separate property of the lens material and coating. A category 3 lens can block all UV or none. A category 0 clear lens can be UV400. Our UV400 vs polarized post explains the labels.

Not polarization. Any category can be polarized or not.

Not colour. A category 3 grey and a category 3 brown let through the same total light and look completely different.

Not quality. Category says nothing about distortion, coatings or construction.

So a full description of a lens needs at least three separate statements: how dark (category or VLT), whether it blocks UV (UV400 or stated cut-off), and whether it is polarized. A label that gives one and implies the others is the thing to be wary of.

Categories 0 and 1 are also the bands for tinted lenses worn indoors for light sensitivity; our indoors post covers when that makes sense.

Category and driving

Standards bodies and driving authorities agree on two things. Category 4 lenses must not be used for driving. And no tinted lens should be worn for driving at night or in poor visibility, whatever its category. Categories 2 and 3 are the daytime driving range. Our driving lens post covers colour within that range.

What we can and cannot tell you about ours

We do not state a VLT or a category for any of our lenses. Nobody has put one on a photometer, and the frame maker does not state a figure. Rather than pick a plausible number, every product page lists transmission and category as unknown. If you need a stated category, for driving law in your country or for a mountaineering trip, ask any seller for the figure and where it came from. A category printed on a lens with no test behind it is not better than none.

Frequently asked questions