UV light from the sun and other sources natural or artificial, degrade the plasticides and rubber content of the plastics used in the sheathing of the cables. It turns it brittle and will pose a risk to cracking and breaking.
The solution is shielding from light or use a type that is UV impervious. Most UV sensitive plastics will also degrade over long amounts of time but those times could be longer than the service intervals or even the life span of the installation so we don't worry too much about that for now.
As for web sites, I am right in assuming that you have a computer, you know how to use it as you found us....so go google