Question
Asked 10th Sep, 2013

What is the relationship between colour of a material and its emissivity?

Because we will feel hotter if we are wearing black cloth than when we wear white cloth under the direct sunlight. But some people say this does not necessarily mean that there is a difference between the emissivity of black cloth and that of the write one and if there is a difference between the emissivity of black cloth and that of the write cloth, it is only /mainly due to their difference in color--- it may be due to the fact that they are different materials. I would be grateful to everyone who provide me with a brief summary on this topic

Most recent answer

25th Dec, 2013
Giovanni Maria Carlomagno
University of Naples Federico II
Remember that the visible light is only a part of the electromagnetic spectrum. So when you speak of emissivity, you should rather speak of spectral emissivity which means emissivity at a certain wavelength. What Martin and Machado say is true but only for the visible light which has the highest energy in the electromagnetic spectrum (see Planck's law). But, e.g., if you consider the infrared radiation between 8 and 12 microns, we measured that a white dull paint has a sligthly higher emissivity than a black dull one.
2 Recommendations

All Answers (4)

10th Sep, 2013
Robin Patrick Mooney
Trinity College Dublin
White colored materials absorb less radiation that black colored materials. Hence two materials that differ in color only - regardless of the material type - will have different emissivities.
10th Sep, 2013
David Martin
University of Amsterdam
If we're talking about clothing, then it's as you said, white reflects all visible, some uv, and some IR. On the contrary, black absorbs nearly all wavelengths of light in the uv-vis-IR region. Therefore if one was to wear an arbitrary black cloth, it absorbs radiation, and then by conduction this 'heat' is passed to your skin via air and moisture, in comparison to white cloth which will keep you cooler because there is less energy/heat which can be transferred to your skin. Obviously this neglects the potential difference in cloth thickness and/or weave between different cloths, which is why some people even in hot countries wear black.
2 Recommendations
10th Sep, 2013
Francisco J. Machado
Central University of Venezuela
Practical examples based on differences in light absorption of surfaces can be observed at oil refineries. In fact, white coated tanks usually contains volatiles products, such as gasoline, in order to get them refractories to sunlight avoiding excessive evaporation. On the contrary, those black painted are for the heavier oil fractions and crude oils, to increase sun radiation absorption and thus lowering their viscosity. Also, the so called ¨desert clothing¨ is white to decrease the effect of sunshine heat.
25th Dec, 2013
Giovanni Maria Carlomagno
University of Naples Federico II
Remember that the visible light is only a part of the electromagnetic spectrum. So when you speak of emissivity, you should rather speak of spectral emissivity which means emissivity at a certain wavelength. What Martin and Machado say is true but only for the visible light which has the highest energy in the electromagnetic spectrum (see Planck's law). But, e.g., if you consider the infrared radiation between 8 and 12 microns, we measured that a white dull paint has a sligthly higher emissivity than a black dull one.
2 Recommendations

Similar questions and discussions

Related Publications

Conference Paper
Diese Vorlesungsreihe ist eine Einführung in die Technische Thermodynamik.
Article
The main objective of this project is to study experimentally and theoretically the two-phase gas-liquid flow characteristics and its relations with the heat-mass transfer mechanism and to enhance the heat transfer rate by considering in the view of the f สำงานกองทุนสนับสนุนการวิจัย (สกว.) คุณลักษณะ การ ไหล สอง สถานะ ของ ก๊าซ - ของ เหลว และ การ เพิ...
Got a technical question?
Get high-quality answers from experts.