I could find many vague definitions of UV400, but no precise definition.
Examples of vague definitions:
Investing in sunglasses that are labeled UV400 blocks 99 to 100 percent of UV light. This rating ensures that all light rays with wavelengths up to 400 nanometers, including both UVA and UVB rays, are blocked out.
If you want to go one step further and block out 99-100% of UV rays (for example if you’re keen on yachting and want to protect your eyes from the sun), then look for sunglasses with UV400. ‘UV400’ refers to UV rays at the top end of the UV spectrum, up to the 400-nanometre wavelength.
These sunglasses feature UV400 lens technology, absorbing over 99.9% of harmful UVA and UVB spectrum.
- Does UV400 guarantee that at least 99% of all wavelenths between 290 and 400nm are blocked?
- How about wavelengths shorter than UVB rays (e.g., UVC)?
- Is that 99 or 99.9% protection?