The emissivity of a material is the relative ability of its surface to emit
or absorb energy by radiation. The emissivity value can be from 0 to 1,0.
For instance a mirror has an emissivity of 0,1. But the “black irradiator”
has an emissivity level of 1,0. If a too high emissivity level has been set
up, the measured temperature will be lower than the real one if the object
temperature is higher than the environmental temperature. For 0,95, the
emissivity level will be 0,9.