What it means and why
UV400 is a label for filtering ultraviolet wavelengths up to 400 nanometres. Nanometres measure wavelength, not prescription power. UV is largely invisible to us, so how dark a lens looks is not a reliable test of its UV protection.
Tint controls visible light; polarisation reduces certain reflections; UV filtering addresses ultraviolet exposure. A product can combine these features, but none of the three labels should be silently substituted for another.
A worked example
A pale lens with documented UV protection and a very dark lens with no reliable specifications cannot be ranked by colour alone. Look for a trustworthy protection statement and consider coverage around the eyes, since light can also arrive around the frame.
What it does not tell you
Ordinary UV-protective sunglasses are not solar-viewing filters or protective eyewear for welding. Those tasks need specific protection; do not test sunglasses by looking at the sun.
THINK IT THROUGHDoes a dark polarised lens automatically prove UV400 protection?
No. Visible tint, polarisation and ultraviolet protection need separate specifications.
Sources & reading notes
Page updated:
- National Eye Institute · Wear sunglasses ↗ Public health information
Useful for general health explanations and safety guidance; individual assessment and local advice still matter.
- National Eye Institute · Protecting your eyes from the sun’s UV light ↗ Public health information
Useful for general health explanations and safety guidance; individual assessment and local advice still matter.
- NASA · Eclipse eye safety ↗ Science education
Supports physical principles and terminology, not clinical or product-performance claims.