Sunglass Filter Categories: Which Lens From 0 to 4 Is Used Where?

A sunglass filter category tells you how much visible light a lens lets through, with a number from 0 to 4. The higher the number, the darker the lens: category 0 is almost clear, while category 4 is made only for extremely bright places such as glaciers and high mountains. The right category is chosen according to where and when you will wear the glasses.

What is a sunglass filter category?

A sunglass filter category is a class number between 0 and 4 that shows what percentage of the visible light falling on a lens reaches the eye. This percentage is called visible light transmission. The lower the transmission, the darker the lens and the higher the category number.

The classification is defined in EN ISO 12312-1, the standard for sunglasses used in Europe and internationally. The standard sets five categories and gives each a range of transmission. This means lenses from different manufacturers can be compared on the same scale: two different pairs marked category 3 have lenses in the same range of darkness.

The category is only about brightness. It does not tell you the colour of the lens, whether it is polarised or how much ultraviolet (UV) light it filters. So you cannot decide whether a pair of glasses is protective by looking at the category alone.

Filter category table: how much light does each lens let through?

Category 0 lenses let through 80-100% of visible light and category 4 lenses only 3-8%; the other three categories sit between these two ends. The table below sums up the transmission range of each category, what the lens looks like and where it is used.

The ranges follow on from each other, so two lenses in the same category can also differ in darkness. A category 3 lens with a transmission close to 8% is noticeably darker than one close to 18%.

Which category is used where?

Categories 0 and 1 are used in overcast weather and when there is little sun, category 2 in moderate sunshine, category 3 in strong sun and category 4 only in extremely bright places such as high mountains and glaciers. The rule is simple: the stronger the light, the higher the category you need.

Categories 0 and 1: overcast weather and little sun

Category 0 lenses let through 80-100% of light and have no noticeable effect against dazzle in strong sun. Clear or very lightly tinted lenses and fashion glasses worn indoors and in overcast weather belong to this group. Category 1 lenses, with 43-80% transmission, give light shade on cloudy days with little sun. Lightly tinted lenses through which the eyes are easy to see are mostly in one of these two categories.

Category 2: moderate sunshine

Category 2 lenses let through 18-43% of light and suit moderate sunshine. They are a comfortable choice on spring and autumn days, in partly cloudy weather and on walks around town where you often move in and out of the shade. They can also be worn for daytime driving.

Category 3: strong sun, the beach and the sea

Category 3 lenses let through 8-18% of light and suit places with strong sun. The beach, the sea, boats, outdoor sports and mountain walks are this category's territory. It is the most common category for sunglasses and is also used for daytime driving.

Category 4: high mountains and glaciers

Category 4 lenses let through only 3-8% of light and are made for extremely bright places. Snow and ice-covered areas at high altitude are the main example. They are too dark for everyday use: in the shade and indoors they restrict vision noticeably.

Which category suits an Antalya summer and the beach?

For the beach, the sea and the poolside in an Antalya summer, category 3 lenses are suitable. In the summer months the sun is strong; sand, water and light-coloured surfaces reflect light back and increase the brightness. Category 3 brings this intense light down to a comfortable level, and it does not stop you seeing where you are going when you move under a parasol or into the shade.

On a holiday day around Belek and Kadriye, the setting changes often: the beach in the morning, a shaded market in the afternoon, a walk in the early evening. When the light fades and on shaded streets, category 2 may be more comfortable. For people who want to manage with one pair, gradient lenses that are dark at the top and light at the bottom are another option. You can read how lens colour affects vision in our article on sunglass lens colours.

Glare coming off the water surface is a separate matter from the category. The property that filters this reflection is polarisation; of two lenses in the same category, one may be polarised and the other not. This is explained in detail in our article what are polarised sunglasses.

Why can you not drive with category 4 sunglasses?

Category 4 lenses are not suitable for driving or road use because they let through only 3-8% of visible light. With a lens this dark, the road, pedestrians and traffic signs cannot be picked out well enough in places where the light drops suddenly, such as a tunnel entrance, the shade of trees or a covered car park.

Category 2 and 3 lenses are used for daytime driving. There is a separate rule for night and dusk: lenses with a visible light transmission below 75% are not worn when driving at these times. This limit covers all of categories 2, 3 and 4 and most of category 1. When it starts to get dark, you need to take your sunglasses off. Topics such as lens colour, polarised lenses and dashboard displays when driving are covered in our article on sunglasses for driving.

Where on the glasses is the category number printed?

On most glasses the category number is printed on the inside of the temple, next to the CE mark. To find it, you can follow this order:

1. Turn the glasses over and hold the inside of the temples up to the light.
2. Find the CE mark. The category is usually right next to it, as a single digit or as an abbreviation such as Cat. 3.
3. If you cannot find it on the temple, look at the label, the box and the information leaflet that came with the glasses.
4. If there is no category information anywhere, ask the seller before you buy.

In Türkiye and the European Union, non-prescription sunglasses count as personal protective equipment and carry the CE mark. The print on the inside of the temple can wear off with use. In that case the category of the lens cannot be reliably judged just by looking, because the lens colour and a mirror coating change how dark it appears.

Does the filter category show UV protection?

No, the filter category does not show UV protection. The category tells you how much visible light is reduced, while UV protection tells you how much invisible ultraviolet light is filtered. They are two separate properties of the lens.

A UV filter can even be colourless. So a light lens in category 0 or 1 can have UV400 protection, while a very dark lens may have no UV filter at all. A dark lens without a UV filter has a further drawback: the pupil widens behind the dark lens, which can let more ultraviolet light into the eye.

The EN ISO 12312-1 standard takes 380 nanometres as the UV limit. The UV400 label goes beyond this and indicates that the lens does not let through ultraviolet light up to 400 nanometres. What the label means and how it is checked is explained in our article what does UV400 mean.

How do you choose the right category?

The right category is chosen according to the brightness of the place where you will wear the glasses most. You can follow this order when deciding:

1. Decide where you will wear the glasses most: the beach and the sea, around town, driving or the mountains.
2. For strong sun and the waterside, consider category 3; for changing light and shaded places, category 2.
3. If you will also wear the glasses when driving, rule out category 4.
4. Whichever category you choose, check for UV400 and the CE mark.
5. If possible, try the glasses in daylight. A lens that looks comfortable indoors may not be enough outside, and one that is comfortable outside may feel too dark indoors.

Sensitivity to light varies from person to person. In the same setting one person may be comfortable with category 2 while another needs category 3. The settings in the table are a starting point; the final decision is made by trying the glasses in real light.