We’re often asked what the difference is between a lens class and a lens category and it is easy to confuse the two. The following should help clarify the difference:
LENS CLASS
The Class of the lens refers to the refractive properties of the lens – these must be exceeded to meet the required optical level. Another way of looking at it is the level of distortion of the lens. There are also different optical distortions that give rise to various distortion effects. There are spherical, prismatic, cylindrical and astigmatic distortions. Lenses can be 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 Classes are perfectly good for every-day wear 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 equates to a percentage of the VLT (Visible Light Transmission) that is, how much light the lens lets through. The higher the VLT the lighter the lens, and conversely the lower the VLT the darker the lens tint will be, blocking more light coming through to the eye. The majority of sunglass/eyewear lenses fall within one of five lens categories:
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