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Weatherwatch: why cooling white roofs cause neighbours to swelter | Climate crisis
(www.theguardian.com)
this post was submitted on 06 Dec 2024
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so it's blue because specifically that wavelength of light is scattered, not the rest of it. it's not reflection, it's refraction.
You are within sight of a blue LED. Does that monochromatic blue look like the blue of the sky? No. Because Rayleigh scattering diffuses higher wavelengths more, not exclusively.
Even a deep red sunset scatters enough light to overwhelm the stars.
Cooling paint emits light deep enough in the infrared that this effect becomes negligible. It proportional to frequency, to the fourth power.
The sky is not emitting light, it is refracting light, like a prism. A blue LED is emitting light at different wavelengths than the blue of the sky.
... no shit.
Like a prism, it affects all wavelengths. If it was "specifically that wavelength," "not the rest of it," it would be monochromatic. Like an LED. But it's not. Rayleigh scattering diffuses any near-visible photons, at a rate proportional to their frequency, squared, squared.
That's why cooling paint works differently than merely reflecting light. Even red light can scatter in the air and warm up the environment. Red scatters less than blue... but infrared scatters less than anything visible.
Alright, I'm trying to say that "mostly transparent" is a fine way to describe it.