Are objects colored in black a black body?
Why does black store heat?
Anyone who has ever touched a black car that has been in the sun for a few hours knows that it can get pretty hot. A light-colored car, on the other hand, heats up significantly less. This can be understood if you understand how colors are created. The color of an object is based on which parts of the sunlight it absorbs (absorbs) and which it reflects (reflects). Sunlight is white because the sun emits radiation in all wavelengths at the same time. If an object absorbs light in the green range of the spectrum, it reflects all other parts of the light and appears in a red tone. An object that neither absorbs nor reflects light, but lets it pass unhindered (transmitted), is transparent.
Black objects appear black because they absorb light from the entire spectrum and hardly reflect anything. Why does black absorb more heat? The energy absorbed by the car in the blazing sun cannot be lost and is converted into heat, which is why its surface feels hot in the sun. Physicists speak of thermal radiation here. At normal ambient temperatures, the heat radiation consists largely of infrared light, which is invisible to the human eye. A white car, on the other hand, reflects almost all of the radiation. So the light is hardly converted into heat and the car warms up much less.
Cool in black
In order not to break a sweat too much, light-colored clothes seem to be more suitable in summer than dark ones. Although it sounds paradoxical, the Bedouins, who inhabit parts of the North African and Israeli deserts, hold it the other way round: they prefer black robes. That puzzled scientists, one might think that the nomads would have found an optimal solution for how best to live in the desert.
In 1980, a team of researchers from the Israeli University of Tel Aviv and the US Harvard University therefore started a somewhat unpleasant-sounding practical test. In the Negev desert in Israel, the scientists measured how warm a test person becomes in four different outfits with outside temperatures between 35 and 46 degrees Celsius, namely in a black and a white Bedouin robe, in a beige military uniform and in shorts. The zoologists found that the subject felt the warmest in the shorts, followed by the light brown uniform. The Bedouin robes did the best, and surprisingly equally well, although the black robe - like a black car - warmed more than the white.
The main thing is that it is airy
Why didn't the test person feel warmer in black than in white? This is probably due to the fact that Bedouin robes are wrapped quite loosely. So you let air flow through between the layers, which transports the heat away and thus cools the skin. This agrees with the results of a study published two years earlier in which biologists examined whether white or black pigeons are better protected from the sun's heat.
Even with low winds of ten kilometers per hour, which we would perceive as a light breeze, the black plumage cooled better. However, if the feathers were tight so that the heat was prevented from being transported away, the white feathers performed better. Even people who wear tight-fitting clothing sweat less in the sun in white T-shirts, as Bodil Nielsen from the then August Krogh Institute in the Danish capital found out in the late 1980s. Because there is no air between the skin and the garment in such clothing, the heat produced by a black shirt cannot be dissipated. So it's coolest in summer when our clothes are loose. Then the color doesn't matter either.
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