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Light Energy and Sunscreens

By: Peter T. Pugliese, MD
Posted: March 26, 2009, from the April 2009 issue of Skin Inc. magazine.

page 9 of 13

In reality, no matter what sunscreen you use, some UV still gets through to the skin. That is why sunscreen is a vital part of a comprehensive sun protection program, along with seeking the shade between high sun intensity times of day and wearing sun-protective clothing, including a wide-brimmed hat and UV-blocking sunglasses.


a. Planck's constant = 6.626 x 10-27 ergs

b. Speed of light = 299,792,458 meters per second (m/s)

c. NJ Turro's Modern Molecular Photochemistry (University Science Books, 1991) is the text I recommend about photochemistry. It is advanced and mainly for professionals or undergraduate physics students. Another good reference in photochemistry is The Science of Photomedicine (Plenum Press, 1982) edited by JD Regan and JA Parrish

d. Remember that a person's energy in food comes from the sun through plants using photosynthesis. The sun's energy is locked in the molecules of the plant, and sugar is one of these important plant molecules. When sugar is eaten, the molecule is broken down and the energy is released.