Lexan is a polycarbonate. Deciding whether to use Lexan or polycarbonate is like deciding whether the glass is half full or half empty.
Probably your best bet would be Plexiglas. The reason why is that Plexiglas is unaffected by UV light from the Sun. So much so, if fact, that exterior water based (latex) wood stains have to have UV blockers added to them to provide protection to the underlying wood. Without those UV blockers, then the acrylic film the exterior stain would form on the surface of the wood allows UV light from the Sun to pass easily through it, and the result is that the wood deteriorates under that acrylic film.
Since UV rays from the Sun have a lot of energy in them, they tend to deteriorate whatever they hit. In the case of clear Plexiglas, the ray goes right through the Plexiglas without harming it, and it deteriorates whatever is under that Plexiglas.
Plexiglas is the trade name for rigid plastic panels made from polymethyl methacrylate. And, in fact everything made from polymethyl methacrylate is referred to as being "acrylic". If a rigid panel of polymethyl methacrylate plastic is made by the Rohm & Haas company, it's sold under the trade name "Plexiglas". If an identical panel of the same kind of plastic is made by DuPont, it's sold as a sheet of "Lucite". If you're in Britain and you buy exactly the same thing made by ICI Ltd. (Imperial Chemical Industries), then you're buying a sheet of "Perspex". Plastics are confusing because the same plastic made by 5 different companies will be sold under 5 different trade names, and if the same plastic is made into a rod or film, it'll be sold under yet other different trade names.
What I can tell you is that polycarbonate (Lexan) is stronger than polymethyl methacrylate (Plexiglas), and that's the reason it's now used to make airplane windows, whereas they used Plexiglas for that back in WWII. Both are shatterproof so both will stand up equally well to baseball size hail stones.
I think your best bet would be to look in your yellow pages under "Greenhouse Equipment & Supplies" or "Solariums and Sunrooms" and you should find someone knowledgeable about the pros and cons of both polymethyl methacrylate and polycarbonate and whatever else they may be using nowadays. I do know that most greenhouses do use Plexiglas instead of glass because of the risk of hail, but whether there are any advantages in using polycarbonate instead is something I don't know.