Sunglasses lenses come in five filter categories, numbered 0 to 4. The number tells you how dark the lens is, meaning how much visible light it lets through. It does not tell you how much UV it blocks. Here is what each category means and which suits children.
The five lens categories
| Category | Visible light let through | Tint | Best for |
|---|---|---|---|
| 0 | 80–100% | Clear or very light | Indoors, night, fashion and screen glasses |
| 1 | 43–80% | Light | Overcast days, low light |
| 2 | 18–43% | Medium | Moderate sun, cloudy summer days |
| 3 | 8–18% | Dark | Bright sun, beach, water, everyday summer wear |
| 4 | 3–8% | Very dark | High mountains, glaciers, extreme glare. Not for driving. |
These categories come from the international sunglasses standard EN ISO 12312-1 and are widely used on labels around the world.
Darkness is not UV protection
A category 0 clear lens can block 100% of UV, and a category 4 lens can block very little if it has no UV filter. UV protection depends on the lens material or a UV-blocking layer, not the tint. Always look for UV400 or 100% UVA/UVB as well as the category.
In fact, a dark lens without UV protection is worse than none: it makes the pupils widen and lets more UV into the eye.
Which category for kids?
- Everyday sunny days, the beach and the pool: category 3 is the usual choice. It cuts bright light comfortably without being too dark for play.
- Cloudy days and city winters: category 2 can be enough.
- Glaciers and very high altitude: category 4, only for those conditions, and never for cycling near traffic or driving.
- Screens indoors: category 0 lenses with blue-light filtering, like screen glasses.
What about polarized lenses?
Polarization is separate from the category. It cuts glare reflected off water, sand and roads, which makes a category 2 or 3 lens much more comfortable in bright conditions. Read how polarized sunglasses work.
The checklist
- Category for the conditions (3 for most sunny days).
- 100% UV protection, whatever the tint.
- Polarized lenses for glare.
- A frame that fits, so it stays on.
Every OLIVIO&CO sunglass has polarized lenses with 100% UV protection.
