Understanding infrared thermography reading 3 part 1 of 2

Thermal infrared radiation impinging on a surface can be absorbed, reflected,
or transmitted as illustrated in Figure 1.5. Kirchhoff's law states that the sum
of the three components is always equal to the total received radiation, E t The
fractional sum of the three components equals unity or 100 percent:
E t = E α + E ρ + E τ , (for blackbody E Ɛ = E α )
where:
E t = total energy
Likewise, the sum of the three material properties, transmissivity, reflectivity
and emissivity, also always equals unity:
τ + ρ + Ɛ =1
Charlie Chong/ Fion Zhang