What property of aluminum leads to it appearing cooler on an infrared camera?

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

Answer: (B)

Infrared cameras read the infrared radiation a surface emits, not just its actual temperature. What you see depends on two properties: emissivity (how well a surface emits infrared) and reflectivity (how much infrared from the surroundings it reflects). Aluminum is a metal with low emissivity and high reflectivity, so it doesn’t emit much infrared by itself and it reflects a lot of the ambient infrared from its surroundings. If those surroundings are cooler than the aluminum, the camera mainly sees that reflected, cooler radiation, so the surface looks cooler than its real temperature. Surfaces with high emissivity emit more infrared on their own and tend to look warmer, while low emissivity with high reflectivity makes them appear cooler due to less self-emission and more reflection of cooler surroundings.