UV Index
Knowledge Base articles tagged UV Index.
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UV Index vs UVA Index: what each one measures
The UV Index is erythemally weighted, so it is dominated by UVB and barely registers UVA. What each index measures, the situations where a low UV Index sits alongside high UVA, and how to read the 0–11+ UVA Index scale.
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The UV Index scale explained — and what it leaves out
What the UV Index numbers mean, where the 0–11+ scale comes from, the WHO band colours and advice, how high it can actually go — and the erythemal weighting that makes it under-report UVA.
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Why UVA changes far less with the seasons than UVB
Ozone absorbs UVB strongly and UVA barely at all, so a low winter sun collapses UVB while UVA falls only modestly. Why winter and early-morning UV is disproportionately UVA, with the numbers — and why a low UV Index never means low UVA.
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