Transparent Grey "Smoked" Polycarbonate, aka lexan, is a tough and durable plastic material which is hundreds of times stronger than glass and many times stronger than acrylic. Polycarbonate will meet those demanding applications where glass and acrylic fall short.
Transparent Grey (Light) - Approximate light transmittance under lab conditions (ATSM D 1003) - 50%
Transparent Grey (Dark) - Approximate light transmittance under lab conditions (ATSM D 1003) - 18%
The Term lexan is commonly used to describe polycarbonate. Actual name brand will depend on current stock.