Sunglasses reference
Reading the optics of sunglasses
Lens category, UV filtering, polarization, and frame geometry each affect how a pair performs. This guide sets out the criteria to check before you choose.
Lens criteria
Three lens measures to read on the label
Category 0 to 4
Visible light reduction
The category rating from 0 to 4 describes how much visible light a lens lets through. It is separate from UV absorption, so a lens can block UV while remaining light.
UV400 standard
Ultraviolet absorption
UV400 indicates absorption up to 400 nanometres, covering both UVA and UVB. Check the label for this reference, since darkness alone does not show UV protection.
Polarized filters
Glare on surfaces
Polarized lenses reduce horizontal glare from water and roads. They can make some digital navigation screens hard to read, so test them at the angle you use most.
Frame geometry
Fit decides long-term comfort and coverage
Bridge width, temple length, and pupillary alignment determine how a frame sits on the face. A proper fit keeps the lenses centred over the eyes and limits light entering from the sides.
Wrap angle and temple length extend peripheral UV coverage. Measure these before you buy, and compare them with a frame you already wear comfortably.
Selection criteria
Check bridge width against your nose, temple length against your head, and whether the lens centre sits over your pupils. Confirm UV400 on the label before choosing a frame by shape alone.