Infrared readings show cooler apparent temperature for surfaces with which combination?

• A. High emissivity and low reflectivity
• B. High reflectivity and low emissivity
• C. Low reflectivity and low emissivity
• D. Low emissivity and high reflectivity

Answer: (B)

Infrared readings are determined by both what the surface emits and what it reflects from the surroundings. The camera detects radiance that is a mix of the surface’s own emission and any ambient radiation it reflects. Emissivity controls how much a surface emits versus reflects: a high-emissivity surface is a strong emitter and largely reflects its own temperature, while a low-emissivity surface emits little and reflects more of the environment.

When a surface is highly reflective (low emissivity), it tends to pick up the ambient infrared from its surroundings. If those surroundings are cooler than the surface, the reflected radiation makes the apparent temperature drop. That’s why the combination of high reflectivity and low emissivity yields a cooler apparent temperature on infrared readings. In contrast, surfaces that emit more (high emissivity) or reflect less of the surroundings will show readings closer to their true temperature.