To keep cool on a sunny day, the color of your clothes may matter more than the length or material. Have you ever wondered why you feel cooler in a long-sleeved white shirt than you do in a black T-shirt? It all comes down to color. The color of an object is determined by the wavelengths of light that object absorbs, and because absorbed light transforms into thermal energy (heat), darker colors attract more heat.
TL;DR (Too Long; Didn't Read)
The only color that does not attract heat is white because white objects reflect all visible wavelengths of light. Black – the color that absorbs all visible wavelengths of light – attracts the most heat, followed by violet, indigo, blue, green, yellow, orange and red, in descending order.
Light and Color
Light is a type of electromagnetic radiation that moves outward from the source in waves. Though we see light as uniform, it consists of a broad range of wavelengths in a variety of colors depending on frequency – some visible and some invisible to the human eye. Color is a measure of which of these wavelengths is or is not absorbed by a given object. All other wavelengths reflect off the object.
Light and Heat
Heat is a measure of the movement of molecules in an object. The more the molecules move, the warmer the object becomes. Wavelengths of electromagnetic radiation resonate with molecules when the radiation is absorbed, setting them into motion and increasing heat. The more wavelengths of radiation that are absorbed, the more heat is attracted. Even objects that reflect all colors still absorb some wavelengths of radiation. The longest of these wavelengths, known as infrared light, is invisible to the naked eye.
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White and Black
White and black stand at opposite ends of the color spectrum. White objects reflect all visible wavelengths of light, while black objects absorb all visible wavelengths. As a result, these two colors attract the least and the most heat, respectively. However, even white objects attract heat by way of infrared light – no color attracts no heat.
Rainbows and Radiation
Falling between white and black, objects of a given color attract heat based on how many wavelengths of visible light they reflect. Wavelengths of higher frequency result in darker colors, resulting in more absorbed heat. Red objects attract the least heat after white objects, followed by orange, yellow, green, blue, indigo and violet, which attracts the most heat of any visible color other than black.
Keeping Cool, Staying Warm
To stay cool during the summer and keep warm during the winter, keep this rule of thumb in mind. White, red and yellow are best for the warm months when you want to avoid attracting extra heat. In cool months, those same colors are best traded for blue, violet or black when you want to trap as much heat as possible. This is why you aren’t supposed to wear white after Labor Day.