[Flieger]

Originally Posted by nynor

black is the best color to wear when it is hot.

Originally Posted by nynor

The Physics that Explain Why You Should Wear Black This Summer

sorry, but its physics. black is the coolest color to wear.

Nu-uh!

At least not in Southern California. I've worn black shirts in the sun and they are HOT! White is much better.

Convection is the dominant method of heat rejection (aside from the phase-change in sweating) for people, animals, and things less than 500 degrees because radiation is proportional to the 4th power of the absolute temperature.

True, black is the best color for radiating heat if you consider a hot blackbody in a vacuum without any irradiation. The SR-71 was painted black because at 90,000 ft. the air is so thin there isn't much convective cooling. The compressive heating of the air at Mach 3+ also made the plane VERY hot through conduction/convection in the localized high density air, so radiation was a significant contribution to cooling (along with the fuel). The sun was a minor factor in heating, unlike spacecraft which are painted white to reflect the sun and reduce the need for cooling.

However, black is also the best color for absorbing radiation. The sun puts out way more watts than a person. The black absorbs both your radiation and the sun's. It gets hotter than a white object and at the temperature of you or your clothes it is going to be re-radiated at infrared wavelengths from both sides of the fabric. So you get a heat-lamp pointed at you as well as away from you. Black is hotter than white so more radiation in both directions than white.

White just reflects what you put out so you don't gain or loose heat through radiation. White doesn't absorb as much solar radiation. It reflects like a mirror meaning it doesn't get as hot and cause as much radiation towards you as black does. There is a reason why solar ovens and solar thermal powerplants use parabolic mirrors pointed at a black body.

Convection rules, though. So getting airflow over your skin is the best way to keep cool. Otherwise the hot fabric will make you warm through convection (and conduction where it touches your skin).