The classical meaning of the word "glass" is extended in this Standard to cover "organic glass" and some crystalline optical materials.
inorganic as well as organic, appear as optical elements: e.g. windows, lenses, prisms, solar-cell covers and filters.
Optical materials can be grouped as:
-inorganic glasses - such as silicates, alumino-silicates and boro-silicates;
-organic "glasses" - polymers based on acrylic and methacrylic polymers, poly-carbonate and some polystyrene grades;
-crystalline optical materials - pure silica, sapphire and transparent fluorides.