HeatGuard field guide
UV index explained: what the number means
The UV index describes the strength of sunburn-producing ultraviolet radiation at a place and time. It is not a temperature scale: a cool, breezy or partly cloudy day can still have high UV.
01
Read the scale
The standard categories are low at 0–2, moderate at 3–5, high at 6–7, very high at 8–10 and extreme at 11 or above. Protection is recommended once the index reaches 3.
The number changes with sun angle, clouds, ozone and elevation. Reflection from snow, sand or water can increase personal exposure.
- 0–2: limited protection for most people.
- 3–7: seek midday shade and use protection.
- 8+: minimize unprotected midday exposure.
02
Temperature and clouds can mislead
UV radiation does not feel hot. Wind may cool skin without reducing UV, and thin or broken clouds can allow substantial radiation through. Comfort is a poor UV sensor.
HeatGuard shows UV beside heat measures so you can look for a window that lowers both burdens. A cooler hour may still require sun protection.
03
Plan around exposure
A daily maximum does not describe every hour. Check the hourly trend and consider duration. Shade, clothing, hats and sunglasses reduce exposure when the schedule cannot move.
People taking photosensitizing medications or managing a health condition should seek personalized medical guidance. HeatGuard provides environmental information, not medical advice.
- Favor earlier or later hours.
- Use shade where natural cover is limited.
- Protect children and others who may not report overexposure.
Primary sources
Continue planning
This guide provides environmental planning information. It is not medical advice, an emergency service, or a substitute for an applicable workplace, school, league or governing-body protocol.
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