Lens categories 0 to 4, explained.
Sunglass lenses are sorted into five categories by how much light they let through. Category 0 lets through over 80 percent. Category 4 lets through 3 to 8 percent and is not for driving.
Where the categories come from.
They come from the international standard for sunglasses, ISO 12312-1. It puts sunglass lenses into five groups by the share of light that passes through them.
The five, from clear to very dark.
Category 0 is clear or a very light tint: over 80 to 100 percent of light gets through.
Category 1 is a light tint: over 43 to 80 percent.
Category 2 is a medium tint: over 18 to 43 percent.
Category 3 is a dark tint: over 8 to 18 percent.
Category 4 is a very dark tint: over 3 to 8 percent.
Which ones are for driving.
For road use and driving, a lens must be in category 0, 1, 2 or 3. Category 4 is not for driving. Australia's product safety regulator says the same of category 4.
At dusk or at night, a lens that lets through less than 75 percent of light is not suitable for the road. So categories 2, 3 and 4 are not for driving after dark, and nor is a category 1 lens that lets through less than 75 percent.
Darker does not mean more UV blocked.
How dark a lens is tells you nothing about how much UV it blocks. The College of Optometrists calls the idea that a darker lens protects more a common misconception.
To check UV, look for a label that says the lenses meet the standard, or that they block 99 or 100 percent of UV.
Polarised lenses cut glare reflected off smooth surfaces such as water and roads. Polarisation has nothing to do with blocking UV either.
How dark is dark.
A fixed lens stays at one point.
A lens that darkens by itself moves between two points, slowly.
The aim for Photenic: you choose the point, and it gets there in a moment.
| Category | Light let through |
|---|---|
| Category 0 | over 80 to 100 percent |
| Category 1 | over 43 to 80 percent |
| Category 2 | over 18 to 43 percent |
| Category 3 | over 8 to 18 percent |
| Category 4 | over 3 to 8 percent |
Sources:
- The College of Optometrists: Tints and driving
- Australian Competition and Consumer Commission, Product Safety Australia: Sunglasses and fashion spectacles mandatory standard
- The College of Optometrists, Look After Your Eyes: Sunglasses
- American Academy of Ophthalmology: Recommended Types of Sunglasses
Other guides
Where Photenic fits.
Photenic is being made for this gap: a tint you set, on the glasses you already own. It is in development.