What is Emissivity Black Body?

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Emissivity is when a material’s surface radiates energy depending on the ratio of its energy to that of its emitter. A surface’s emissivity depends on its material and its nature. A clean, polished material has low emissivity. On the other hand, a rough and oxidized surface has a high emissivity. The surface’s temperature also determines emissivity. Some factors help determine the emissivity of black body and any other material. They include:

  • Emissivity of wavelength

The wavelength of different material surfaces causes their emissivity to vary. When the wavelength of polished materials increases, their emissivity decreases. Non-metallic materials show a different behavior to metallic ones causing their emissivity to vary greatly. Plastic materials also differ in wavelength, causing a variation in emissivity levels.

  • Effect of surface condition

Metallic materials have decreased emissivity once they are polished. The surface roughness and oxidation level also cause the decrease. If a metal has been subjected to high temperatures during oxidation, the emissivity values are higher and more stable. Unlike the emissivity on a black body, bright bodies have emissivity that depends on the thickness of the surface.

  • Effect of viewing angle

Most materials, black or bright, do not depend on the viewing angle to show their emissivity. 

The thermometer needs to be within the recommended temperature range of 45 degrees. It helps get accurate emissivity levels. 

  • Effect on temperature

Temperatures do not necessarily determine the emissivity of materials. This is regardless of their color, bright or black. The emissivity of certain materials will begin to vary with the change in the surface of these materials. An example is when the coating becomes damaged and causes a thinner surface.

What is the importance of emissivity?

One important factor to note is that your material is greatly important in its emissivity. The same material is also key in taking correct and reliable temperature measurements. Emissivity should be adjustable when selecting a thermal sensor or thermal imaging camera.

Emissivity is also important in helping with temperature adjustments for different materials. If temperatures are too high, normally above 45 degrees Celsius, they may alter the emissivity.

Emissivity is also important as it helps to determine if an object needs to be oxidized or not. Oxidation causes variations in temperatures. As a result, there is an effect happening to the surface’s emissivity.

If an inappropriate coating is applied to the wrong material, it gives a wrong emissivity result. Black-coated materials are higher inaccuracy when it comes to calculating emissivity. The darkest materials have the highest emissivity.


To get the correct emissivity of a material, carefully look into a few factors. For example, always ensure that the temperatures are within the recommended range of 45 degrees. All materials whose emissivity needs to be calculated should have the correct coating. A wrong coating alters the emissivity as it either thins the material or makes it extremely thick. Finally, it is important to note that materials of different colors will have different emissivity. Darker materials have higher emissivity as compared to bright materials.

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