The best (and riskiest) hours for sun

By Trung Hieu Lam, developer of UV Tracker · Published 1 September 2026

The UV day-curve

UV intensity follows the sun's angle, not the air temperature. It rises from sunrise, peaks within roughly an hour of solar noon (when the sun is at its highest point for your location, not necessarily 12:00 on the clock), and falls off toward sunset. Temperature lags behind — the hottest part of the afternoon is often past the UV peak, which is exactly why "it doesn't feel that hot yet" is a misleading signal.

The 10-to-4 window

As a rule of thumb, UV exposure is highest roughly between 10 a.m. and 4 p.m. local time — extra caution during that window covers most of the day's cumulative UV dose, even though the exact peak shifts with season and latitude.

The shadow rule

A simple check that doesn't need a meter: if your shadow is shorter than you are tall, the sun is high and UV is likely high too. A shadow longer than you are tall means the sun is lower in the sky and UV is generally lower.

Seasons and latitude

UV is generally higher in summer and closer to the equator, where the sun sits higher in the sky for more of the year. But it's rarely zero outside those conditions — spring and even clear winter days can still carry meaningful UV, particularly at higher altitude or with snow reflection.

Morning and evening sun

Early morning and late afternoon UV is typically much lower than midday — check the safe sun time tables or the calculator at a low UV index to see how much that changes your numbers.

Plan with a number, not a feeling

"It doesn't feel sunny" and "it's not that hot yet" are both weak signals for UV. UV Tracker's sky scan gives you an actual reading for right now, wherever you are.

UV Tracker measures the UV where you stand — sky scan for local conditions, one photo for your skin type, and your safe sun time on one card. Free forever.