Emittance data as a function of polarization, wavelength, angle, and temperature
Emissivity is the ratio of the thermal radiation of a surface relative to the radiation of an ideal black body at the same temperature (ratio between 0 and 1). An emissivity of 0 means that the material is a perfect reflector, whereas a ratio of 1 means it is a perfect emitter.
The determination of surface emissivity is important for accurate non-contact temperature measurements and for heat transfer calculations. The emissivity of a surface depends on the material (i.e., chemical and physical properties), the nature of the surface (e.g., smooth or rough), the temperature, wavelength, and angle.
Applications
Thermal emittance data is valuable for the following applications:
Emissivity Measurement Types
- Directional, near-normal emittance, when reflectance has been measured at near normal incidence (θ = 10°)
- Directional angular emittance, when reflectance has been measured at any incidence angle other than near-normal
- Total hemispherical emittance, when reflectance has been measured over a sufficiently wide range of incidence angles to permit integration over the hemisphere.
- Spectral hemispherical emittance, when reflectance has been measured over a sufficiently wide range of incidence angles to permit integration over the hemisphere.