Al -

Your experience with carbonate lenses differs from mine.

The majority of plastic lenses sold in my area are acrylic, NOT carbonate. They are very light weight and have good clarity, but they are softer and scratch rather easily. They nearly always should have a scratch resistant coating, which quite often is a thin layer of polycarbonate.

Optical polycarbonate is quite hard and is reasonably scratch resistant. Without going to "exotic" materials, there are no coatings that will improve the scratch resistance of a good quality carbonate lens, and if a seller is offering a "scratch resistant" coating he's probably selling acrylic lenses and not carbonate. (The few "exotic" coatings available are - or were recently - rather expensive, and give only marginal improvement in scratch resistance.) Good carbonate lenses don't need an additional scratch resistant coating for most users.

(If you get an anti-glare or uv coating on carbonate lenses, the coating may not be really tough, and an anti-scratch coating to protect some other coating might be recommended, even with carbonate lenses; but it should not be separately indicated on the bill.)

For most users, the carbonate lenses will be noticably heavier than acrylics, although not quite as heavy as "real glass."

Carbonate lenses are used in "safety glasses" and "safety lenses" can be very heavy, compared to ordinary glasses. To be considered "safety glasses" in the US they must bear the appropriate certification etched on the edge of the lens. If the cert markings aren't there, even good carbonate lenses should not be expected to provide eye protection if you're doing something where it's needed.

John