Question 1

What is the UVA Index?

Accepted Answer

The UVA Index is a 0–11+ scale derived from surface UVA irradiance (the unweighted 315–400 nm band, in W/m²): the irradiance is divided by 6 so a clear-sky overhead sun reads about 11, mirroring the familiar UV Index range. Categories follow the WHO bands — Low (0–2), Moderate (3–5), High (6–7), Very High (8–10) and Extreme (11+). Unlike the standard UV Index, which is erythemally weighted and dominated by UVB, this value isolates UVA and is derived from solar geometry plus live cloud and aerosol data.

Question 2

How is the UVA Index calculated?

Accepted Answer

It combines the solar zenith angle for your location and time with a clear-sky UVA baseline, then applies live corrections for altitude, aerosol optical depth, cloud cover and surface albedo using free Open-Meteo data. The resulting UVA irradiance (W/m²) is then divided by 6 to give the 0–11+ UVA Index.

UVA Index

UVA Index through the day

Inputs

Model breakdown