中途半端な記事が論文に先行して拡散されたことで、つまらない論争になってしまったようだ。

Prof. Toshiaki Ichinose measures the wavelength of reflected radiation (obviously with a thermos-sensor) not the temperature of the fabric! White fabric reflects visible light, the black absorbs the visible part of the spectrum and reflects the infrared radiation. This is a typical error of non-physicists and has no meaning in answering the question.

Healthy Living & Beyond

2022-8-8

Science News: What colors of clothing will keep you cooler in summer? Japanese researchers experiment

Unless you can just stay inside with the A.C. blasting until mid-autumn, figuring out ways to mitigate the risk of heat exhaustion is critical, and that includes dressing appropriately. Researcher Toshiaki Ichinose, from Japan’s National Institute for Environmental Studies, conducted an experiment to see what color of clothing will keep your body the coolest in the summer sun. Now, it’s pretty common knowledge that white is the coolest and black the hottest, but unless you’re a mime odds are you don’t have an entirely black-and-white wardrobe, so what’s the order of the shades in between?

Before we get to the results, a quick refresher for everyone who’s forgotten junior high science class (or, for you precocious elementary schoolers who read SoraNews24, a sneak peak of what’s to come). We perceive objects as being different colors depending on what wavelengths of light they reflect and absorb. Objects we see as white reflect almost all wavelengths of light, and their heat energy along with them. On the other end of the scale, things we see as black absorb light of just about every wavelength, and its heat too.

For the experiment Ichinose set nine mannequin torsos out in the Japanese summer sun, each clad in a different colored polo shirt, then after five minutes of exposure checked the fabrics’ surface temperatures.

As expected, the white shirt was the coolest, with a temperature of approximately 30 degrees Celsius (86 degrees Fahrenheit), more or less the same as the air temperature during the test, followed by yellow. The next coolest shirts, in order, were gray and red, the latter a surprise since red is generally though of as a “hot” color in terms of psychological effect.

Purple ended up right in the middle of the pack, with the next, blue, again being somewhat unexpected, since in visual design it’s considered a “cool” color. Next came green, then dark green, and, finally, black, with the last two both having surface temperatures of over 50 degrees Celsius (122 Fahrenheit), more than 50 percent hotter than the white shirt.

Though the experiment was conducted in June of 2019, the fundamental laws of science still apply, and with late-summer temperatures often hitting daytime highs of 35 degrees or more in Tokyo, it’s even more important to look for any and all ways to stay cool.

Source: Weather News via Yahoo! Japan News, National Institute for Environmental Studies