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This question isn't referring to the general use of umbrella to provide protection from rain rather it concerns the optical effects of the color on lower and upper portion of umbrella.

Umbrella are also used to provide protection from sunlight (at least in regions below tropic of cancer in India) and usually they come in black color on the upper side and silvery on the lower side. What advantage does this provide? Is it just for fashion (I don't think so)? Currently I believe white is more advantageous due to:

  • white being a poor absorber of heat (via radiation) I it would cause the clothe to get less warm (than dark colors) and transmitt less radiation and hence providing higher protection.

  • white being a good reflector would be beneficial in night (considering that somethimes rain occurs at night) as it would be more visible than dark colors.

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    $\begingroup$ I agree that the more reflective the upper surface is the more it will block radiant energy. And typically what absorbs visible light also absorbs infrared radiation. As the suggested answer states, a dark surface will also more readily re-radiate energy. A singed cookie sheet will produce a different result than an otherwise identical one which still has it's metallic luster. $\endgroup$ – Steven Thomas Hatton Dec 8 '19 at 23:33
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Kirchhoff's law of thermal radiation says that the absorptivity and emissivity for a given wavelength are equal, so the silvery surface would emit less infra-red radiation.

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