Sun Exposure & Vitamin D Guides
Content last reviewed: October 2026
Explore our in-depth educational articles on solar UV radiation, skin photobiology, and the environmental and biological factors behind vitamin D synthesis. Every guide includes reference tables generated from published photobiological models.
Understanding the UV Index (UVI): How UV-A, UV-B, and Solar Angle Drive Vitamin D
What each UV Index number means in physical irradiance (mW/m²), why only UV-B triggers vitamin D synthesis, and how exposure time changes from UVI 1 to UVI 11+.
Read guide →Fitzpatrick Skin Types (I–VI), Melanin, and Sun Exposure Time
How epidermal melanin acts as a natural broadband filter, the Minimal Erythemal Dose (MED) for skin types I through VI, and why darker skin needs longer exposure.
Read guide →The “Vitamin D Winter”: How Latitude and Seasons Affect UV-B Synthesis
Atmospheric path length (air mass), ozone absorption at low sun angles, and a month-by-month breakdown of peak UV Index across latitudes from 0° to 60°.
Read guide →Solar Noon vs. Clock Time: Why 12:00 PM Is Rarely Peak UV-B
How political time zones, daylight saving time, longitude, and orbital eccentricity shift true solar noon by up to two hours from 12:00 PM on the clock.
Read guide →Sunscreen, Clouds, Glass, and Clothing: What Blocks UV-B and What Doesn't
Why ordinary glass blocks UV-B while letting UV-A pass, how cloud cover scales UV dose, how exposed skin area changes exposure time, and the sunscreen paradox.
Read guide →How Age and Body Mass Index (BMI) Influence Vitamin D Levels
Why cutaneous 7-dehydrocholesterol decreases decade by decade, why adipose tissue dilutes circulating 25(OH)D, and the adjustment factors used in the calculator.
Read guide →How the Calculator Works
This page explains, step by step, how VitaminDcalc turns your answers into an estimated sun exposure time. The goal is transparency: every factor used by the calculator is listed here, together with its limitations.
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