What Is the Visible Spectrum?

The visible spectrum is the spectrum that human vision can perceive. If white light is red, orange, yellow, green, blue, indigo, and purple colored bands after being dispersed by a prism or grating, it is a visible continuous spectrum. In the visible region, there is also a line spectrum and a band spectrum. It is a very small area in the entire electromagnetic spectrum.

The main natural light source for visible light is the sun, and the main artificial light source is incandescent objects (especially incandescent lamps). The visible spectrum they emit is continuous. The gas discharge tube also emits visible light, and its spectrum is discrete. Various gas discharge tubes and filters are often used as monochromatic light sources.

The range of light that the human eye can see is affected by the atmosphere. The atmosphere is opaque to most electromagnetic wave radiation, with the exception of visible light bands and a few other radio communication bands. Many other organisms can see the range of light waves different from humans. For example, some insects, including bees, can see the ultraviolet band, which is very helpful for finding nectar.

The spectrum cannot include colors that can be recognized by all eyes and brains, 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 range of electromagnetic waves that can penetrate the earth's atmosphere without much attenuation (blue light is more severe than red light, which is why we see the sky blue). The human eye's response to visible light is subjectively defined (see CIE), but the atmospheric window is defined by physical measurements. It is called the visible light window because it covers the spectrum visible to the human eye. The near-infrared (NIR) window is just outside the visible segment of the human eye, while the medium-wavelength infrared (WMIR) and far-infrared (LWIR, FIR) are farther away than the visible segment of the human eye.

Visible spectrum imaging system, which includes light source system, spectroscopic system, image imaging and recording system, image analysis and processing system, etc. It consists of optical objective lens, liquid crystal tunable filter (LCTF), CCD camera, light source and computer, etc. The device consists of a liquid crystal tunable filter whose core device is similar to a high-quality band-pass interference filter. With the adoption of the electronically controlled liquid crystal adjustment method, the problems of uniformity in the clear plane, peak spectral transmittance, and out-of-band suppression have been solved. It has the advantages of high accuracy and easy real-time control. The application of spectral imaging technology has begun. To a positive impetus.

Commercial instruments for visible spectrum imaging systems include Nuance multispectral imagers from CRI in the United States and Condor hyperspectral imaging systems from ChemImage in the United States. The system's spectral working range is 410nm ~ 720nm, the spectral resolution is less than 10nm, and the imaging field of view is about It is 260mmx250mm, and the optical field is used to increase the field of view. In addition, domestic Xu Xiaoxuan, Shen Zhixue and others also designed and developed a visible light liquid crystal spectral imaging system with simple structure, high spatial resolution and high spectral resolution ^[1] .