![]() ![]() Newton hypothesized that light was made up of "corpuscles" (particles) of different colors, and that the different colors of light moved at different speeds in transparent matter, with red light moving more quickly in glass than violet light. Newton observed that, when a narrow beam of sunlight strikes the face of a glass prism at an angle, some is reflected and some of the beam passes into and through the glass, emerging as different colored bands. Newton first used the word spectrum ( Latin for "appearance" or "apparition") in print in 1671 in describing his experiments in optics. Two of the earliest explanations of the optical spectrum came from Isaac Newton, when he wrote his Opticks, and from Goethe, in his Theory of Colours, although earlier observations had been made by Roger Bacon who first recognized the visible spectrum in a glass of water, four centuries before Newton discovered that prisms could disassemble and reassemble white light. For this reason, plant species whose life cycles are linked to insect pollination may owe their reproductive success to their appearance in ultraviolet light, rather than how colorful they appear to our eyes. For example, many insects, such as bees, can see light in the ultraviolet, which is useful for finding nectar in flowers. The eyes of many species perceive wavelengths different from the spectrum visible to the human eye. The "visible window" is so called because it overlaps the human visible response spectrum the near infrared (NIR) windows lie just out of human response window, and the Medium Wavelength IR (MWIR) and Long Wavelength or Far Infrared (LWIR or FIR) are far beyond the human response region. The response of the human eye is defined by subjective testing (see CIE), but the atmospheric windows are defined by physical measurement. Wavelengths visible to the eye also pass through the "optical window", the region of the electromagnetic spectrum which passes largely unattenuated through the Earth's atmosphere (although blue light is scattered more than red light, which is the reason the sky is blue). Brown, pink, and magenta are absent, for example, because they need a mix of multiple wavelengths, preferably shades of red. The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. A light-adapted eye generally has its maximum sensitivity at around 555 nm (540 THz), in the green region of the optical spectrum (see: luminosity function). In terms of frequency, this corresponds to a band in the vicinity of 400-790 terahertz. The corresponding wavelengths in water and other media are reduced by a factor equal to the refractive index. A typical human eye will respond to wavelengths in air from about 380 to 750 nm. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. The visible spectrum (or sometimes called the optical spectrum) is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. List of terms related to Visible spectrum Risk calculators and risk factors for Visible spectrumĬauses & Risk Factors for Visible spectrum US National Guidelines Clearinghouse on Visible spectrumĭirections to Hospitals Treating Visible spectrum Ongoing Trials on Visible spectrum at Clinical Ĭlinical Trials on Visible spectrum at Google Articles on Visible spectrum in N Eng J Med, Lancet, BMJĬochrane Collaboration on Visible spectrum ![]()
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