The UV Index measures solar radiation intensity that causes sunburn. Originally developed for public health, UV data is now essential for outdoor activity apps, skincare applications, and any feature helping users manage sun exposure.
UV Index Scale
The UV Index scale is open-ended but typically ranges 0-11+. Low (0-2): Minimal danger for average person. Moderate (3-5): Moderate risk—wear sunscreen. High (6-7): High risk—reduce sun exposure during midday. Very High (8-10): Very high risk—extra protection needed. Extreme (11+): Extreme risk—avoid sun exposure during midday hours.
Factors Affecting UV
UV intensity varies by: Time of day (highest 10am-4pm), Season (higher in summer), Latitude (higher near equator), Altitude (increases ~10% per 1000m elevation), Cloud cover (clouds block some UV, but not all), Reflection (snow reflects 80% of UV, sand 15%, water 10%). A cloudy day at high altitude can have higher UV than a sunny day at sea level.
Skin Type Considerations
Sun sensitivity varies dramatically by skin type. The Fitzpatrick scale (I-VI) classifies skin by reaction to sun. Type I (pale, always burns) may burn in 10 minutes at UV 10, while Type VI (deeply pigmented) may tolerate 60+ minutes. For personalized recommendations, consider letting users input their skin type.
Building UV Features
Useful UV-related features include: Time-to-burn calculators (UV × skin type × SPF), Safe sun exposure windows (morning/evening vs midday), SPF recommendations by UV level, Vitamin D optimization (some sun exposure is beneficial), Shadow length rules (if shadow is shorter than height, UV is high).