The plastic figures on the sun beds glow a bright pink. When you flip them over, using the string to pull, they only glow very dimly.


   Description of the Experiment   

The exhibit mimics what happens when sunbathers put sun cream on their skin. Instead of ultra-violet light burning their skin (and turning them pink all over) it is blocked out by suitable oils.

There is an ultra-violet lamp in the top of the exhibit which shines on the plastic figures.
The figures are made of "wonderplastic" which glows a bright pink when ultra-violet light shines on it.

The underside of the figures is covered with artificial skin (used to treat burns patients) on which sun cream has been smeared. When the figures are flipped over, this layer of sun cream gets in the way of the ultra-violet light so that the plastic does not glow.
Different grades of sun cream contain oils which absorb different amounts of ultra-violet light. "Total block" cream (no. 15 and above) is designed to cut out the UV completely.

   Duration   

The experiment lasts about 2-3 minutes.

   Conclusion   

The two figures are glowing brightly in the dangerous "sunlight". Flip them over and you discover that one of them has an invisible protective coating to fend offf the ultra violet light.

Skin is soon damaged by the dangerous ultraviolet component of sunlight. Chemical absorbers in sun creams absorb ultra violet light, so that you can stay out safely in the sun.

   Detailed Conclusion   

Many chemical changes can be brought about by light. Indeed, the whole science of photography, and the working of our own eyes is based on light-induced chemical changes. Some changes, like the burning of our skin in strong sunlight, are unwelcome and dangerous, so chemical protection has to come to the rescue!

The most dangerous part of sunlight is the short wavelength, invisible, ultraviolet light which is radiated in addition to visible light by very hot bodies. This radiation converts oxygen (O2), high up in the atmosphere, into ozone (O3) which absorbs ultraviolet light strongly. When the unstable ozone reverts to normal oxygen, ultraviolet light can convert it back to ozone again.

Gases released into the atmosphere, especially freons used in refrigerators, are now interfering with this mechanism, so more ultraviolet light gets down to the earth's surface and the need for skin protection is increasing.