Sun Screen Strength A student in the science fair tried sun
screen on light sensitive plastic beads... they all turned
color, indicating the screen didn't work. Is this a valid test
of the strngth of sun screen? Ideas? What would be the effect if
no-sun screen was used. Would the beads change color to a larger
extent? What would happen with the beads using lower/higher SBF
sunscreens.? What is sun screen trying to filter out? All light,
or just (invisible) ultraviolet? What do the beads detect? Only
ultraviolet, or visible light? I think you can answer these
questions, and from that answer your original Richard Barrans
Jr., Ph.D. I assume that the beads were subjected to sunlight
and they changed color. These are some possible explanations for
the stated observations. The beads could be visible light
sensitive and change color when exposed to visible light. In
that case, the observation does not prove anything. The beads
could be sensitive to both UV and visible light, in which case,
the sun screen could stop