Technical
Knowledge Base articles tagged Technical.
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How the UVA Index is calculated
The full method behind our UVA Index: how surface UVA irradiance (315–400 nm, W/m²) is derived from a radiative-transfer lookup table plus live cloud, haze, pressure and snow data, the exact formulas and assumptions, how it is validated, and which factors we leave out.
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UVA around the world: why latitude matters less than you think
Ozone barely absorbs UVA, so the equator-to-pole gradient is far shallower for UVA than for the UV Index. Peak clear-sky UVA Index for cities worldwide, why the southern hemisphere runs hotter, and what actually drives local differences.
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UVA at altitude: mountains, hiking and flying
UV rises with elevation — but UVA rises more slowly than the often-quoted 10% per 1000 m, which is an erythemal figure. Why the altitude gradient differs by wavelength, how snow and clean air compound it, and what the cockpit UVA and pilot melanoma research shows.
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Reflected UVA: snow, sand, water and concrete
Ground reflectance adds to the UVA you receive — and UV albedo is not visible albedo. Reflectance values by surface, why skiers and boaters burn under the chin, why shade fails on a beach, and how the UVA Index models surface albedo.
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How to measure UVA yourself: meters, cards and phone myths
What it takes to actually measure UVA — spectroradiometers, broadband radiometers, cheap consumer meters and photochromic cards — where each fails, why no smartphone can measure ultraviolet, and how to sanity-check any reading.
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