What is the wavelength of visible light?
Visible spectrum
In the early 19th century, the concept of the visible spectrum became more definite, as light outside the visible range was discovered and characterized by William Herschel (infrared) and Johann Wilhelm Ritter (ultraviolet), Thomas Young, Thomas Johann Seebeck, and others.[8]
Young was the first to measure the wavelengths of different colors of light, in 1802.[9]