What does the term "spandrel glass" refer to?

The term "spandrel glass" specifically refers to opaque glass that is used in building facades to conceal structural elements such as beams, columns, and floor slabs. This glass is typically installed in areas of the building where the transparent glass would expose unsightly structural components, ensuring a more aesthetically pleasing appearance on the exterior.

Spandrel glass is often utilized in conjunction with vision glass—transparent glass used for windows—to create a cohesive look while still addressing functional requirements. It plays a crucial role in modern architecture by providing a uniform facade while helping to hide necessary elements without compromising structural integrity or design.

The other options describe different types of glass that serve other purposes. Transparent decorative glass is used for aesthetic enhancement, glass used solely for windows is primarily for visibility and light transmission, and low-emissivity glass is specifically designed to improve energy efficiency by reflecting heat. These do not align with the primary function of spandrel glass, which is focused on enclosures and concealment rather than visibility or efficiency.