Question

What wavelength of light is reflected from a green shirt?

Answer 1

Well, it has to be (primarily) green. But it doesn't have to be one wavelength.

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Any light of a certain color that is significantly reflected and makes it to our eyes will dominate the color spectrum that we see. It will involve wavelengths around the so-called `lambda_max`, the maximum wavelength.

(On the other hand, absorbed light will not be seen, because it doesn't travel to our eyes.)

Green light is near `"510 nm"`, around the range `500 - 520` `"nm"` or so.

So, if that color is reflected the MOST, we see green, whereas violet, indigo, blue, yellow, orange, and red light are all mostly absorbed.

Of course, that means other wavelengths are also reflected, but at lower intensities, and thus they are dominated by `lambda_max ~~ "510 nm"`.