What term describes a surface whose emissivity is less than 1?

• A. High Emissivity Surface
• B. Blackbody Surface
• C. Superconductive Surface
• D. Low Emissivity Surface

Answer: (D)

Emissivity quantifies how well a surface emits infrared energy compared with a perfect blackbody. Any real surface has an emissivity between 0 and 1, and when it is less than 1, the surface is described as a low emissivity surface. This means it emits less infrared radiation than a blackbody at the same temperature and tends to reflect more infrared from its surroundings. A blackbody surface has emissivity of 1, so it would not be described as low emissivity. The term high emissivity would refer to a surface with emissivity close to 1, not below 1, and superconductive surfaces aren’t a radiative-emittance term.