How Sunloop UV works out the numbers
Last updated
This page explains where each number on Sunloop UV comes from and how often it changes.
The UV index
The UV index is a scale set by the World Health Organization. It measures how strongly sunlight can burn skin, weighting each UV wavelength by how much damage it does. It runs from 0 at night to 11 and above on the strongest days. In northern Australia, summer values of 14 or more are common.
Forecasts for every place
Our forecasts come from Open-Meteo, which publishes hourly UV index forecasts based on the Copernicus Atmosphere Monitoring Service model. The model accounts for the sun’s angle, ozone and forecast cloud.
We group nearby places into grid areas of roughly 10 kilometres and fetch one forecast per area. Every suburb, town and beach in that area shares the same forecast. We refresh forecasts about once an hour.
Live readings in capital cities
ARPANSA runs UV sensors in each capital city that report every minute. On capital city pages, and as the “nearest live reading” on other pages, we show the latest ARPANSA observation alongside the forecast. A live reading can differ from the forecast on patchy days, when cloud moves through faster than a model can predict.
Sun protection times
Sun protection is recommended when the UV index is 3 or higher, following WHO, ARPANSA and Cancer Council guidance. For each place we find the first and last forecast times in the day when UV reaches 3, rounded to the nearest 10 minutes, and show that window as the day’s sun protection times. If UV stays below 3 all day, we say so.
Categories and colours
We use the five WHO categories and their standard colours: Low (0 to 2), Moderate (3 to 5), High (6 to 7), Very high (8 to 10) and Extreme (11 and above). The category name always appears as text, so the colours are never the only way to read a level.
Times and time zones
Every time on a place page is shown in that place’s local time, with the zone named. Queensland, Western Australia and the Northern Territory don’t use daylight saving time, so their times can differ from neighbouring states for half the year.
UV history
From launch we store each place’s daily peak UV and protection window. That record builds the history shown on place pages and our seasonal summaries.
Limits
Forecasts are estimates. Reflection from water, sand and snow, altitude and local shade all change how much UV reaches you. Treat every number on Sunloop UV as a guide, and protect your skin whenever you’ll be outside for long periods.