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A number from 1 upward, with colour bands and a threshold at 3.
Also known as: UV level, Sun index number
A linear scale of ultraviolet strength with a published action threshold: below 3 no protection is generally needed, above it some is. The number is the useful part and the colour band is the summary of it.
An open-ended linear scale of ultraviolet radiation strength at the surface, grouped into colour bands: green for low, yellow for moderate, orange for high, red for very high and violet for extreme.
Contexts: Public information
Three is the published threshold at which protection is advised, which makes it the one number on the scale that carries an instruction rather than a description.
Reports the radiation, not the temperature. A cold clear day at altitude can carry a higher index than a hot overcast one, which is why the scale exists separately from the forecast.
UV strength and how warm it feels are unrelated.
A numeral on a coloured bar or badge running from green through yellow and orange to red and violet, often beside a sun pictogram.