The radiation detected by a thermal camera in a non-contact temperature measurement consists of the reflection, the transmission and the emission of infrared radiation emanating from objects in the field of view of the camera. The emissivity is a dimensionless measure that indicates the ratio of the emitted radiation of the measurement object in relation to the incident radiation.
Emissivity depends on the material, the surface texture and, in some cases, the temperature of a body. In general, the higher the emissivity of a body, the easier the temperature can be measured with a IR-camera.
The following relationship applies: Emissivity + Reflection + Transmission = 1
This glossary of plastic industry is provided by PLEXPERT Canada Inc.