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[The shadow rule and appropriate sun behavior]
Henrik F Lorentzen1, Kaare Weismann
1Dermatologisk afdeling D42, H:S Bispebjerg Hospitalet, DK-2400 København NV.
Ugeskrift for Laeger
|July 11, 2002
Summary
Seeking shade based on shadow length is a simple, effective way to prevent sunburn. When shadows are shorter than objects, avoid direct sun exposure to minimize ultraviolet (UV) damage.
Area of Science:
- Dermatology
- Environmental Health
- Physics
Context:
- Sunscreen limitations in preventing melanoma and UV damage.
- Increased sun exposure due to reduced UVB penetration and UVA protection.
- The importance of seeking shade for protection against ultraviolet rays.
Purpose:
- To examine the association between UV intensity and the ratio of shadow length to object height.
- To develop a predictive model for UV load based on astronomical data.
- To establish a simple, universal rule for sun protection based on shadow length.
Summary:
- A linear model (R=0.95) correlated UV intensity with shadow length to object height ratio.
- Calculated accumulated UV doses using solar altitude and UV intensity.
- Erythema onset varies with shadow-to-object ratio: <5 min for 0.5, 20-30 min for 1, ~1 hour for 2.
Impact:
- The 'shadow rule' (short shadows = seek shade) is a practical, universally applicable method for sun safety.
- Children can be taught this simple rule for effective sun protection.
- Provides guidance on permissible sun exposure durations based on shadow length ratios.