When looking for sunglasses and eyewear, you may have come across the terms lens class and lens category. It’s easy to get confused between these terms but they refer to two different properties of lenses.
LENS CLASS
Lens Class refers to the refractive properties of the lens – its ability to meet the required optical level and how much distortion the lens may have. In other words it’s about the quality of the visual experience the lens provides. Lenses are sub-divided into three classes.
Optical Class 1 is the best visual experience with minimal, if any distortion.
Optical Class 2 provides an ‘average’ visual experience with some level of distortion
Both Optical Classes 1 & 2 are perfectly good for every-day wear sunglasses and necessary to meet CE/UKCA standards.
Optical Class 3 is rarely seen and provides a low-quality visual experience. A cheap, poor-quality sunglass sold by a street market vendor might be an example.
LENS CATEGORY
The lens category number relates to the amount of Visible Light Transmission (VLT) a lens allows through, measured as a percentage. So the VLT indicates how much light the lens lets through to your eyes. A higher VLT means the lens is lighter and lets more light through, while a lower VLT means the lens is darker and blocks more light. The majority of sunglass and eyewear lenses fall within one of five lens categories – ranging from category 0 very light/clear lenses to category 4 very dark lenses.
- Category 0: 80-100% VLT
- Category 1: 43-80% VLT
- Category 2: 18-43% VLT
- Category 3: 8-18% VLT
- Category 4: 3-8% VLT
The lens category VLT can cover quite a wide spectrum such as Category 1 which is 43-80%. Some lens colours are right on the “border” e.g. a yellow lens can have 78% VLT which is on the border between Category 0 and Category 1. The following is a general guide to the categories that apply to different lens colours:
- Category 0 – Clear, Light Yellow, Yellow, Pale Orange
- Category 1 – Orange, Rose & Vermilion
- Category 2 – Purple, Red, Amber & Light brown
- Category 3 – ‘Standard’ Grey & Brown
- Category 4 – Dark Grey & Dark Brown
For more information on lens colours and their benefits, read our post what are different eyewear lens colours for.