Visible light is a form of electromagnetic radiation (EM), as are radio waves, infrared radiation, ultraviolet radiation, X-rays, and microwaves. In general, visible light is defined as the wavelengths that are visible to the human eye.
Visible light is a type electromagnetic radiation, which is transmitted as waves or particles at different wavelengths and frequencies. This wide range of wavelengths is called the electromagnetic spectrum. That spectrum is usually divided into seven regions in order of decreasing wavelength, increasing energy and frequency. These regions are:
- radio waves (wavelengths greater than 0.4 inches or 10 mm)
- microwave (wavelength 0.004 to 0.4 inch, or 0.1 to 10 mm)
- infrared rays (IR) (wavelength from 0.0003 to 0.004 inches, or 740 nanometers to 100 micrometers)
- visible light, (wavelength from 0.000015 to 0.0003 inches or 380 to 740 nanometers)
- ultraviolet (UV) (wavelength from 0.000015 to 0.0003 inches, or 380 to 740 nanometers)
- X ray (wavelengths from 4 × 10^−7 to 4 × 10^−8 inches, or 100 picometers to 10 nanometers)
- gamma rays (wavelength less than 4 × 10^−9 inches, or 100 picometers)
Visible light is in the EM spectrum between infrared (IR) and ultraviolet ray (UV). It has a frequency of about 4 × 1014 up to 8 × 1014 cycles per second, or hertz (Hz) and a wavelength of about 740 nanometers (nm) or 2.9 × 10−5 inch, to 380 nm (1.5 × 10−5 inches).
Color and spectrum of visible light
Perhaps the most important property of visible light is color. Color is both an inherent property of light and a work of cells in the human eye. Objects do not “have” color, according to Physics Hypertext Book. Rather, they emit light that “seems” to be a color. In other words, writes Elert, color exists only in the mind of the viewer.
According to NASA Mission Science Website. Humans see light at the lower end of the visible spectrum, with a longer wavelength, about 740 nm, as red; we perceive light in the middle of the spectrum as green; and see light at the upper end of the spectrum, with a wavelength of about 380 nm, as purple. All other colors that we perceive are mixtures of these colors.
For example, yellow contains light from both the red and green regions of the visible light spectrum; Cyan is a blend of green and blue, and magenta is a blend of red and blue. White light contains all colors combined. Black has no light at all. According to the website of Michael Fowler, professor of physics at the University of Virginia.
How does heat energy turn into visible light?
According to NASA’s Mission Science, as objects heat up, they emit energy dominated by shorter wavelengths, which we assume change color, according to NASA’s Mission Science. For example, the flame of a soldering iron changes from red to blue when it is adjusted to burn hotter. This process of converting heat energy into light energy is called luminescence Dynamic Educational Advancement Institute (IDEA) website, WebExhibits.org.
Incandescent lamps are produced when hot matter releases some of its thermal vibrational energy such as photon. At about 1,472 degrees Fahrenheit (800 degrees Celsius), the energy emitted by a radiating object reaches infrared. As the temperature increases, the energy moves into the visible spectrum and the object appears red. As the object gets hotter, the color changes to “hot white” and finally to blue.
Visible light astronomy
The color of hot objects, such as stars, can be used to estimate temperature, according to IDEA. For example, the surface temperature of the sun is about 5,800 kelvin (9,980 F or 5,527 C). The emitted light has a maximum wavelength of about 550 nm, which we perceive as visible white (or yellowish) light.
According to NASA, if the surface temperature of the sun were colder, around 3,000 degrees Celsius, it would have a reddish color, like the star Betelgeuse. If it were hotter, around 12,000 C, it would be blue, like the Rigel star.
Astronomers can also determine what material an object is made of because each element absorbs light at specific wavelengths, known as absorption spectra. Knowing the absorption spectra of the elements, astronomers can use spectroscopy to determine the chemical composition of stars, dust clouds, and other distant objects.
Learn more about how the human brain perceives light in this video from National Geography. Follow your path through the electromagnetic spectrum with this stunning book”Light: The visible spectrum and beyond“(Black Dog & Leventhal, 2013) or conduct your own visible light experiments at home following instructions from Duckan educational website for children.
This article was updated on May 23, 2022 by Live Science managing editor Tia Ghose.
https://www.livescience.com/50678-visible-light.html What is visible light? | Live Science