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A wrist-watch which measures UVA plus UVB - should NOT be used to increase vitamin D - June 2014


Overview Skin and vitamin D has the following chart for UV when standing

Chart edited to show when shadow length = your height (sun angle = 45 degrees)
Sun Friend would indicate that you are getting a lot of UV, but only 1/4 of it is the UVB needed to make Vitamin D

Until a new version of Sun Friend is available which includes compensation for sun angle (= location & time of year & time of day)
Sun Friend should only be used to estimate vitamin D at local noon +- about 2 hours in the summer

Note: I spoke July 2015 with developers about this limitation.

Another way of seeing the huge change in UVA to UVB ratio during the day
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People wearing the UVA+UVB watch would learn to keep out of the hottest portion of the sun (which actually has the vitamin D) because their watch would (falsely) tell them that they would get lots of vitamin D is the late afternoon - when it is not as hot.

See also VitaminDWiki

Thus the use of this watch might result in decreased levels of vitamin D

Attached files

ID Name Comment Uploaded Size Downloads
5724 UVA 3X of UVB.jpg admin 28 Jul, 2015 82.51 Kb 3021
4058 UVA UVB.jpg admin 24 Jun, 2014 72.71 Kb 2002