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UV Index Reference - Online Exposure Category & Protection

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UV Index Reference Guide

Understand ultraviolet radiation levels, exposure categories, and essential sun protection measures. Use the interactive slider to check any UV index value and get instant recommendations.

UV Index
0 3 6 8 11 15
5
Moderate
Moderate

Wear sunscreen SPF 15+, sunglasses, and a hat during midday hours.

0 – 2
Low

Minimal UV exposure risk

Protection: Sunglasses on bright days. SPF 15+ if outdoors for extended periods.

3 – 5
Moderate

Some risk of harm from unprotected sun exposure

Protection: SPF 15–30, wide-brim hat, sunglasses. Seek shade during midday.

6 – 7
High

High risk of harm from unprotected sun exposure

Protection: SPF 30+, hat, sunglasses, protective clothing. Limit midday sun (10am–4pm).

8 – 10
Very High

Very high risk — skin & eye damage can occur quickly

Protection: SPF 50+, avoid direct sun 10am–4pm, wear UV-blocking sunglasses & full-coverage clothing.

11+
Extreme

Extreme risk — unprotected skin burns in minutes

Protection: SPF 50+, stay indoors during midday. If outdoors, wear full sun protection: hat, sunglasses, long sleeves, and seek shade.

Protection Guide by UV Level
UV Index Category Color Code Burn Time* Recommended Protection
0 – 2 Low Green 60+ min Sunglasses; SPF 15+ for extended outdoor activities
3 – 5 Moderate Yellow 30–45 min SPF 15–30, hat, sunglasses; shade during midday
6 – 7 High Orange 20–30 min SPF 30+, wide-brim hat, UV sunglasses; limit 10am–4pm exposure
8 – 10 Very High Red 10–20 min SPF 50+, protective clothing, avoid midday sun
11+ Extreme Purple < 10 min SPF 50+; stay indoors 10am–4pm; full protection if outside

* Estimated time for fair skin (Type II) to burn without protection. Actual burn time varies by skin type, altitude, and surface reflection.

Key Facts About UV Radiation
Peak Hours

UV radiation peaks between 10am and 4pm. During these hours, over 60% of the day's total UV reaches the earth's surface.

Clouds Don't Block All UV

Up to 80% of UV rays can penetrate light cloud cover. Scattered clouds can even enhance UV through reflection.

Surface Reflection

Snow reflects up to 80%, sand 15%, and water 10–25% of UV radiation. This can nearly double your exposure.

Altitude Effect

UV intensity increases approximately 5–10% for every 1,000 meters (3,280 ft) of elevation gain.

Latitude Matters

UV exposure is highest near the equator and decreases toward the poles. Tropical regions experience intense UV year-round.

Ozone Layer

The ozone layer absorbs most harmful UVC and significant UVB. Thinner ozone (e.g., near poles) means higher UV at ground level.

Pro Tip: The Shadow Rule

A quick way to estimate UV intensity outdoors: If your shadow is shorter than you, UV exposure is high — seek shade. If your shadow is taller than you, UV exposure is lower and it's safer to be in the sun. This simple rule works because the sun's angle directly correlates with UV intensity at ground level.

Frequently Asked Questions

Everything you need to know about UV index and sun safety

The UV Index is an international standard measurement developed by the World Health Organization (WHO) that indicates the strength of ultraviolet radiation reaching the earth's surface at a particular place and time. It ranges from 0 (minimal UV, typically at night) to 11+ (extreme UV, common in tropical and high-altitude regions during midday). The scale is designed to help people understand their risk of UV exposure and take appropriate protective measures. Values can occasionally exceed 15 in very high-altitude equatorial locations.

The UV Index is calculated using a complex model that incorporates multiple factors: the angle of the sun (solar zenith), ozone concentration in the stratosphere, cloud cover, altitude, and ground surface reflectivity (albedo). Weather agencies use satellite data and atmospheric models to produce daily UV forecasts. The calculation weights different UV wavelengths according to their potential to cause skin damage (erythemal action spectrum), with UVB rays being more damaging than UVA.

UVA (320–400 nm): Penetrates deep into the dermis. Causes premature aging, wrinkles, and contributes to skin cancer. Accounts for ~95% of UV reaching the ground. Present year-round, even on cloudy days. Can pass through glass windows.

UVB (280–320 nm): Affects the outer skin layer. Causes sunburn and direct DNA damage. Primary driver of skin cancer. Intense during midday and summer months. Mostly blocked by glass.

UVC (200–280 nm): The most dangerous type, but completely absorbed by the ozone layer and does not reach the earth's surface.

UV 0–2 (Low): SPF 15 is sufficient for most people, though daily SPF 15+ moisturizer is a healthy habit.
UV 3–5 (Moderate): Use SPF 15–30. Reapply every 2 hours if sweating or swimming.
UV 6–7 (High): SPF 30+ is recommended. Seek shade during midday hours (10am–4pm).
UV 8–10 (Very High): SPF 50+ is strongly advised. Wear protective clothing, a wide-brim hat, and UV-blocking sunglasses.
UV 11+ (Extreme): SPF 50+ is essential. Stay indoors if possible during midday. If outdoors, combine sunscreen with full-coverage clothing, hat, sunglasses, and shade.

Remember: No sunscreen blocks 100% of UV. SPF 30 blocks ~97% of UVB; SPF 50 blocks ~98%. Reapplication is critical.

Absolutely yes. Up to 80% of UV radiation can penetrate through light and moderate cloud cover. In fact, scattered cumulus clouds can sometimes increase UV exposure through a phenomenon called the "broken cloud effect," where UV rays reflect off cloud edges and create localized increases in UV intensity. This is why you can get a surprising sunburn on a partly cloudy day. Always check the UV Index rather than relying on visible sunlight alone.

Yes, significantly. The Fitzpatrick skin type scale categorizes skin into 6 types based on melanin content:
Type I (Very fair): Always burns, never tans — burn time as low as 5–10 minutes in extreme UV.
Type II (Fair): Burns easily, tans minimally — the "standard" used for most UV index burn time estimates.
Type III (Medium): Burns moderately, tans gradually.
Type IV (Olive): Burns minimally, tans well.
Type V (Brown): Rarely burns, tans deeply.
Type VI (Dark brown/Black): Very rarely burns, but UV damage (including skin cancer risk) still occurs.

Regardless of skin type, everyone is at risk for UV-related eye damage and long-term skin aging.

In the Northern Hemisphere, UV radiation peaks in late June and early July around the summer solstice (June 20–21), when the sun is highest in the sky. In the Southern Hemisphere, the peak occurs in late December around the summer solstice (December 21–22). However, in tropical regions near the equator, UV levels remain high year-round with less seasonal variation. Interestingly, the Southern Hemisphere generally experiences higher peak UV levels than similar latitudes in the Northern Hemisphere due to naturally lower ozone concentrations.

Winter: While UVB decreases in winter at mid and high latitudes, UVA remains relatively constant. Snow reflects up to 80% of UV, nearly doubling your exposure. Winter sports enthusiasts (skiing, snowboarding) should wear sunscreen, goggles, and lip balm with SPF.

High Altitudes: UV intensity increases approximately 5–10% for every 1,000 meters of elevation due to thinner atmosphere and reduced UV scattering. At 3,000m (nearly 10,000 ft), UV can be 25–30% stronger than at sea level. Mountaineers, hikers, and high-altitude residents need enhanced protection regardless of temperature.

Sunscreen should be reapplied every 2 hours as a general rule, and more frequently if you are swimming, sweating, or towel-drying. Water-resistant sunscreens maintain their SPF protection for either 40 or 80 minutes in water (check the label). Apply sunscreen at least 15–20 minutes before sun exposure to allow it to bind properly to the skin. Most people apply only 25–50% of the recommended amount — you need approximately 1 ounce (30ml, about a shot glass full) to cover your entire body adequately. Don't forget often-missed areas: ears, neck, tops of feet, and the scalp (or part line).

UV Index forecasts are widely available through multiple sources:
• Weather apps: Most smartphone weather apps (Apple Weather, AccuWeather, Weather.com) display the daily UV Index.
• EPA SunWise: The U.S. Environmental Protection Agency provides UV Index forecasts by ZIP code.
• WHO/UNEP: Global UV monitoring through the World Health Organization.
• Bureau of Meteorology: National weather services in most countries publish UV forecasts.
• Wearable UV sensors: Devices and smartwatches with UV sensing capabilities provide real-time readings.
• UV Index mobile apps: Dedicated apps like UVLens, SunSmart, and QSun provide personalized recommendations.

Remember: The UV Index forecast is typically for peak midday conditions. Adjust your protection accordingly if you'll be outside at different times.

UV Index categories follow WHO (World Health Organization) international standards.

Always combine multiple protection methods: sunscreen + shade + clothing + sunglasses + hat.

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