We often see things fading in the sun, on longer exposure to suns heat. In case of Plastics, they degrade. Some molecules observe UV light, that energy is sufficient to break some chemical bonds this results in destroying the molecules. This breaking of bonds or rearranging the molecules is known as PHOTODEGRADATION.
On longer exposure to this UV light the process PHOTODEGRADATION takes place and Cause Pigments and Dyes to break down, eventually the colour fades.
This looks as if it is out of our concern but, in Art world, it is pretty important to preserve the valuable paintings. If these paintings are placed in a wrong spot, it may be damaged permanently.
Apart from Art work, Sunlight also degrades certain plastics like the types used in PVC Piping and Polypropylene ropes.
This results in breaking the pipes and the ropes starts snapping. Well… Wait we have some precautions to prevent these damages. We have some resistants to prevent UV like Benzophenone.