What does emissivity measure?

Emissivity is a measure of how effectively a surface emits thermal radiation compared to an ideal black body at the same temperature. It quantifies the ability of a material to radiate heat – essentially how much thermal energy a material can emit as infrared radiation. The value of emissivity ranges from 0 to 1, where a value of 1 indicates that the material is a perfect emitter, while lower values indicate less effective thermal radiation capability.

In practical terms, this is particularly relevant in thermal imaging, where understanding a material's emissivity can affect temperature readings and the interpretation of heat distribution. Materials with different emissivity values will appear differently when measured by thermal cameras, which is crucial for accurate thermal analysis in various applications such as building inspections, industrial processes, and environmental monitoring.