Which type of glass transmits visible light while selectively reflecting the longer wavelengths of radiant heat?

• A. Ordinary glass
• B. Low emissivity glass (Low-e glass)
• C. Tempered glass
• D. Laminated glass

Answer: (B)

Low-emissivity glass has a very thin coating that is highly reflective to infrared (the longer wavelengths of radiant heat) while remaining nearly transparent to visible light. This lets daylight come through, but reduces heat transfer by reflecting heat back rather than letting it pass, improving energy efficiency. Ordinary glass passes both visible light and infrared, so it doesn’t selectively reflect heat. Tempered glass is about strength and safety, not spectral control, and laminated glass is about safety interlayer or sound reduction; by itself it doesn’t provide the infrared reflectivity that Low-e glass offers.