UV rays are strongest during the middle of the day, specifically between 10 a.m. and 2 or 4 p.m., when the sun is highest in the sky. This time frame is often referred to as the "peak" hours for UV radiation. During these hours, UVB rays, which cause sunburn, are at their strongest, and UVA rays that penetrate the skin are also fully present. The sun's UV intensity is highest because the sun's rays travel the shortest distance through the atmosphere at this time. This period accounts for the majority of daily UV exposure and carries the highest risk of skin damage and sunburn, especially in locations closer to the equator or at higher altitudes.
UV strength varies by season, location, altitude, and cloud cover, but the daily peak period remains between late morning and early afternoon. Tools like the UV Index help indicate the strength of UV radiation throughout the day, showing the greatest risk during these peak hours. The "Shadow Rule" is a simple way to gauge peak UV times: if a person's shadow is shorter than their height, UV rays are at their strongest.
In summary, the strongest UV rays typically occur from about 10 a.m. to 2-4 p.m., with the peak around solar noon when the sun is highest in the sky.