Visible spectrum

Unsaturated colors such as pink, or purple variations like magenta, for example, are absent because they can only be made from a mix of multiple wavelengths.

[8][9] Visible wavelengths pass largely unattenuated through the Earth's atmosphere via the "optical window" region of the electromagnetic spectrum.

[10] In the 13th century, Roger Bacon theorized that rainbows were produced by a similar process to the passage of light through glass or crystal.

[11] In the 17th century, Isaac Newton discovered that prisms could disassemble and reassemble white light, and described the phenomenon in his book Opticks.

He was the first to use the word spectrum (Latin for "appearance" or "apparition") in this sense in print in 1671 in describing his experiments in optics.

The result is that red light is bent (refracted) less sharply than violet as it passes through the prism, creating a spectrum of colors.

Newton originally divided the spectrum into six named colors: red, orange, yellow, green, blue, and violet.

For this reason, some later commentators, including Isaac Asimov,[13] have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet.

Evidence indicates that what Newton meant by "indigo" and "blue" does not correspond to the modern meanings of those color words.

[14][15][16] In the 18th century, Johann Wolfgang von Goethe wrote about optical spectra in his Theory of Colours.

Goethe used the word spectrum (Spektrum) to designate a ghostly optical afterimage, as did Schopenhauer in On Vision and Colors.

Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow and blue-cyan edges with white between them.

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.

[18] The connection between the visible spectrum and color vision was explored by Thomas Young and Hermann von Helmholtz in the early 19th century.

Subjects with aphakia are missing a lens, so UVA light can reach the retina and excite the visual opsins; this expands the visible range and may also lead to cyanopsia.

Regardless of actual physical and biological variance, the definition of the limits is not standard and will change depending on the industry.

[30] Since the melanopsin system does not form images, it is not strictly considered vision and does not contribute to the visible range.

Vertebrates tend to have 1-4 different opsin classes:[19] Testing the visual systems of animals behaviorally is difficult, so the visible range of animals is usually estimated by comparing the peak wavelengths of opsins with those of typical humans (S-opsin at 420 nm and L-opsin at 560 nm).

However, old world primates (including humans) have since evolved two versions in the LWS class to regain trichromacy.

A possible benefit of avian UV vision involves sex-dependent markings on their plumage that are visible only in the ultraviolet range.

Astronomical spectroscopy uses high-dispersion diffraction gratings to observe spectra at very high spectral resolutions.