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White light is dispersed by a glass prism into the colors of the visible spectrum. The visible spectrum is the band of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light (or simply light).
By definition, visible light is the part of the EM spectrum the human eye is the most sensitive to. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in molecules and atoms that move from one energy level to another. This action allows the chemical mechanisms that underlie human vision and plant photosynthesis.
When a beam of light crosses the boundary between a vacuum and another medium, or between two different media, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not orthogonal (or rather normal) to the boundary, the change in wavelength results in a change in the direction of the beam.
Up until the 1940s, astronomers could only use the visible and near infrared portions of the optical spectrum for their observations. The first great astronomical discoveries such as the ones made by the famous Italian polymath Galileo Galilei were made using optical telescopes that received light reaching the ground through the optical window ...
A white light source—emitting light of multiple wavelengths—is focused on a sample (the pairs of complementary colors are indicated by the yellow dotted lines). Upon striking the sample, photons that match the energy gap of the molecules present (green light in this example) are absorbed, exciting the molecules. Other photons are scattered ...
Wavelengths of commercially available lasers. Laser types with distinct laser lines are shown above the wavelength bar, while below are shown lasers that can emit in a wavelength range. The height of the lines and bars gives an indication of the maximal power/pulse energy commercially available, while the color codifies the type of laser ...
When adapted for bright conditions (photopic vision), the eye is most sensitive to light at a wavelength of 555 nm. Light with a given amount of radiant energy will have more luminous energy if the wavelength is 555 nm than if the wavelength is longer or shorter. Light whose wavelength is well outside the visible spectrum has a luminous energy ...
Light with the same radiant intensity at other wavelengths has a lower luminous intensity. The curve which represents the response of the human eye to light is a defined standard function y (λ) or V (λ) established by the International Commission on Illumination (CIE, for Commission Internationale de l'Éclairage ) and standardized in ...