In infrared thermography, which property is most directly associated with the rate of energy emission from a surface?

• A. Reflectivity
• B. Emissivity
• C. Thermal conductivity
• D. Specific heat

Answer: (B)

Emissivity is the property that describes how efficiently a surface emits thermal radiation compared with a perfect blackbody. In infrared thermography, what you detect is radiated energy from the surface, which follows E = εσT^4, so the emission rate scales directly with emissivity. A surface with high emissivity radiates more energy at a given temperature, making it appear hotter in IR images, while a low-emissivity surface radiates less energy and can look cooler even if the temperature is higher. Reflectivity affects how much energy is reflected rather than emitted, so it doesn’t set the emission rate itself. Thermal conductivity and specific heat relate to how heat moves through or stores energy in the material, not how much energy is radiated from the surface.