Emissivity of Skin: Unity & Ice | Need Help & Guidance

[msbird]

I have found from various sources that the emissivity of human skin, irrespective of pigment, is close to unity.

I am also unsure as to why ice has such a high emissivity too- perhaps my understanding of emissivity is fundamentally flawed!

Any help or guidance on this topic would be greatly appreciated!

Many thanks in advance :)

 

[craigi]

I have found from various sources that the emissivity of human skin, irrespective of pigment, is close to unity.

It sounds like was given to you as an example to avoid any misinterpretation of Black Body Radiation.

I am also unsure as to why ice has such a high emissivity too- perhaps my understanding of emissivity is fundamentally flawed!)

...and this was given to illustrate that emissivity isn't about how cold something is.


Emissivity is a measure of how readily a material emits electromagnetic radiation. Typically this is of infrared frequencies, ie heat. You maybe recall learning about how heat can be transmitted by conduction, convection and radiation. We're talking about the radiation part.

An emissivity of 1 represents the emissivity of a perfectly Black Body. Which means that it emits radiation at the maximum possible rate.

Emissivity of real materials is determined by the surface properties of the electromagnetic field for a given material. Typically smooth shiny metals have low emissivity, wheres as insulators have high emissivity.

Another source of confusion, perhaps is the relation between specular reflectivity and emissivity. It's important not to confuse diffuse reflectivity, which determines the colour of a material, with specular reflectivity, which determines how shiny it appears.