I checked on the Cassidy site and found the following:
All of our frames are equipped with a crystal clear .060" thick acrylic (Lucite) front, which have many advantages over glass. The main advantage being that acrylic will not shatter like glass can, thus being much safer to handle and ship. Another advantage being the protection it provides your chips from the harm that light can cause. Our acrylic naturally filters out 45% of Ultraviolet rays to prevent your chips from the effects of light. NOTE: It's always a good idea to keep your chips away from direct and/or constant sources of light.
Fred