Visible spectrum is humanvisionPerceived spectrum.aswhite lightthroughPrismorgratingdispersionThen red, orange, yellow, green, blue, indigo and purple ribbons appear, which isVisible continuous spectrum。stayVisible areaThere are alsoLine spectrumandBanded spectrum。It's the whole thingElectromagnetic spectrumThe smallest region in the.
The whole electromagnetic spectrum includesradio waves, infrared, ultraviolet, andX-rayEtc.They have different wavelengths, of which the wavelength ranges from 400 to 760nanometerIt's just ordinaryvisible light。
Visible light source
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The main natural light source of visible light is the sun, and the main artificial light source is incandescent objects (especially incandescent lamps).The visible spectrum they emit is continuous.Gas discharge tubeIt also emits visible light, whose spectrum is discrete.Various gas discharge tubes and filters are often used as monochromatic light sources.
The range of light visible to the human eye is affected by the atmosphere.The atmosphere is opaque to most electromagnetic radiation, with the exception of visible light band and a few other bands such as radio communication band.The range of light waves that many other creatures can see is different from that of humans. For example, some insects, including bees, can see the ultraviolet wave band, which is very helpful for finding nectar.
The spectrum cannot contain all colors that can be recognized by human eyes and brain, such as brown, pink, purple, etc., because they need to be mixed by multiple light waves to adjust the intensity of red.
The wavelength of visible light can penetrate the optical window, that is, the electromagnetic wave range that can penetrate the earth's atmosphere without much attenuation (blue light scattering is more serious than red light, which is why we see the sky is blue).The response of the human eye to visible light is defined subjectively (see CIE), but the window of the atmosphere is defined by physical measurement.It is called the visible light window because it just covers the spectrum visible to the human eye.The near infrared (NIR) window is just outside the visible range of the human eye, while the medium wavelength infrared (WMIR) and far infrared (LWIR, FIR) are farther than the visible range of the human eye.
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Visible spectrogram 2
Visible light consists of seven different colors of light, namely red, orange, yellow, green, indigo, blue and purple.Different colors have different wavelengths: red light has the longest wavelength, followed by orange, yellow, green, indigo, blue and purple.That is to say, the wavelength of purple light is the shortest.
Two early explanations of spectrum came from Isaac Newton's optics and Johann Wolfgang von Goethe's chromatics.Newton first used the word spectrum in his explanation of optical experiments in 1671 (in Latin, it stands for appearance and image).Newton observed that when a beam of sunlight shot into the glass prism at an angle, part of it would be reflected, and part of it would penetrate the glass and present different color bands.Newton assumed that sunlight is composed of small particles of different colors, and these different colors have different forward speeds when penetrating materials.The speed of red light is faster than that of purple light, which causes the deflection (refraction) of red light after passing through the prism to be smaller than that of purple light, producing various spectra.Newton divided the spectrum into seven colors: red, orange, yellow, green, blue, indigo and purple.According to the ideas of ancient Greek philosophers, he chose these seven colors and linked them with notes, planets in the solar system, and days of the week.However, the sensitivity of human eyes to the frequency of indigo is relatively poor. In addition, some people with normal color discrimination ability said that they could not distinguish indigo from blue and purple.For this reason, some experts, such as Isaac Asimov, have suggested that indigo should not be regarded as a color, it is just a range of shades of blue and purple.Goethe claimed that continuous spectrum is a composite phenomenon.And Newton believed that only the visible light spectrum was a separate phenomenon. Goethe observed a broader part, and he found that there was no spectrum in the area, such as the red yellow border and the cyan blue border were white, and there would be color light overlap in the border area.So far, the public has accepted that light is composed of photons (sometimes light has the characteristics of waves, and other times it is the characteristics of particles, seeWave particle duality）All light in vacuum is a constant speed light speed, and the speed of light in other substances is lower than that of light in vacuum. The ratio of the speed of light in vacuum to that of other substances is the refractive index of the substance.In some known substances (non dispersive substances), there is no difference in the travel speed of light of different frequencies, but in other substances, light of different frequencies has different travel speeds: glass belongs to this kind of substance, so glass prisms can divide white light.The rainbow in nature is an ideal example of seeing spectrum by refraction.
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Visible spectrum imaging system, including light source system, light splitting system, image imaging and recording system, image analysis and processing system, consists of optical objective lens, liquid crystal tunable filter (LCTF)It is composed of CCD camera, light source and computer. Its core device is liquid crystal tunable filter, whose function is similar to a high-quality band-pass interference filter.With the adoption of the electronically controlled liquid crystal adjustment method, problems such as uniformity in the light plane, peak spectral transmittance, and out of band suppression have been solved, reflecting the advantages of high precision and easy real-time controlSpectral imaging technologyThe application of has played a positive role in promoting.
Commercial instruments of visible spectrum imaging system mainly include Nuance of CRIMultispectral imagerAnd the Condor hyperspectral imaging system of ChemImage Company in the United States. The spectral working range of the system is 410nm~720nm, the spectral resolution is less than 10nm, and the imaging field of view is about 260mmx250mm. The field of view is increased through optical elements.In addition, Xu Xiaoxuan, Shen Zhixue and others in China have also designed and developed a visible liquid crystal spectral imaging system with simple structure, high spatial resolution and high spectral resolution[1]。
