Glass Performance & Properties

There has been past debate on whether to use endcaps with lighting
systems directly over the water or to place the lamps over glass
with standard lamp holders.  Obviously the glass option is less
expensive. What about the performance of glass?  Are there
differences?  I happen to run across the web site of a major glass
manufacturer.  The web site I visited was located at: 
http;//www.afg.com.  There was "performance" data listed for the
glass products they make. This particular company manufactures a
"specialty lighting glass" and I found some descriptive terms
interesting like  "maximum light transmission with minimum
absorption" and "blending transmitted light".  I don't recall any
threads on this topic.  Could those of us in aquatic gardening 
using glass to cover our lamps enhance our lighting systems by using 
some of the special glasses? 

E. Keith Johnson
Johnson City, TN