The visible Light , also called visible spectrum or optical spectrum is the part of the electromagnetic Specter which is visible for the human eye.

There is no exact limit with the visible spectrum: the human eye adapted to the light generally has a maximum sensitivity in the light of Wavelength of approximately 550 Nm, which corresponds to a yellow-green color. Generally, it is considered that the answer of the eye covers the wavelengths of 380 Nm with 780 Nm although a range of 400 Nm with 700 Nm is more common. These extremes correspond respectively to the colors purple and red However, the eye can have a certain visual answer in ranges wavelengths even broader.

The wavelengths in the visible range for the eye occupy the major part of the optical window , a range the wavelengths which are easily transmitted by the Atmosphère of the Earth.

The Ultraviolet (UV) and the Infrarouge (IR) are often regarded as " light " but are not visible by the human ones; although of comparable nature that the visible light (like the visible light, the Ultraviolet and the Infrarouge is electromagnetic waves)

Historical use of the term

Two of the oldest explanations of the optical spectrum were made by Isaac Newton, when he writes his book Opticks , and by Goethe, in its Théorie of the colors .

Newton used for the first time the term spectrum (of the Latin “appearance” or “appearance”) in a text printed in 1671 by describing its Expérience S in optics. Newton had observed that, when a small ray of white light of the Sun touches the face of a prism out of glass with a certain angle, part of the ray is deviated and another cross-piece the prism while coming out from it in the form of coloured bands. Newton made the assumption that the light was made of " Corpuscle s" (particles) of various colors, and that each color of light had its own speed in transparent medium, with the red color fastest and the slowest violet. The result was that the red light was deviated (refracted) that the violet while passing through the prism, this creating a spectrum of colors.

Newton divided the spectrum into seven named colors: Red, orange, Yellow, Green, Blue, Indigo and Purple or ROJVBIV. It chooses seven colors because of a belief coming from the former Greek philosophers, that there was a bond between the colors, the notes of music, the known objects of the solar system and the days of the week. The human eye is relatively insensitive with the frequencies of the indigo, and certain people having a good sight cannot distinguish the difference between the indigo and blue or the purple one. For this reason, some critical whose Isaac Asimov suggested that the indigo was not to be looked like a color but simply like a shade of blue or the purple one.

Johann Wolfgang von Goethe affirmed that the continuous spectrum was a made up phenomenon. Whereas Newton reduces the luminous ray to isolate the phenomenon, Goethe observed that with a larger opening, there was no spectrum. In the place, there were edges yellow-red and blue-cyan with white between them, and the spectrum appears only when these edges are sufficiently close to be exchanged.

It is nowadays generally accepted that the light is made up of Photon S (which shares certain properties of a wave and some of those of the particles in the Vide). Speed of light through a material is lower than speed of light in the vacuum, and the report/ratio speeds is known under the name of Index of refraction of material. In certain matters, known under the name of nondispersive , speed has various frequencies (correspondent with various colors) does not vary, and thus the index of refraction is constant. However, in other matters (known as dispersive ), the index of refraction (and thus speed) depend on the frequency according to a relation of dispersion. Glass is one of these matters, which makes it possible the prisms out of glass to create an optical spectrum since the white light.

Spectroscopy

The scientific study of the objects based on the light which they emit is named Spectroscopie. A very important application of the spectroscopy is the Astronomie, where the spectroscopy is essential with the analysis of distant objects. In particular, the astronomical Spectroscopie uses tools atstrong rate of diffraction to observe the spectrum with very spectral high-resolutions. The Hélium was the first detected during an analysis of the spectrum of the Sun; others chemical elements can be detected in astronomical bodies by transmission lines and of absorption, the position of the lines of the spectrum can be used to detect properties of bodies distant or going quickly. The first exoplanètes were discovered by analyzing the dust of stars to a so high resolution that the variations of their small radial swiftness of a few meters per seconds could be detected: the presence of planets was revealed by their gravitational influence on analyzed stars, like by the trajectories.

Colors of the spectrum

Although it is continuous and that there is no clear border between a color and the following one, the following table gives the approximate limits of the colors of the spectrum:

Purple 380-450 Nm

Blue 450-495 Nm

Green 495-570 Nm

Yellow 570-590 Nm

Orange 590-620 Nm

Red 620-750 Nm

See too

• spectral Band

External bonds

• Any knowledge on photosynthesis and the photovoltaïsme

Footnotes