# Visible Spectrum: Definition, Wavelengths & Colors

Have you seen the visible spectrum today? You most likely have and may not be aware of it. This lesson tells you what the visible spectrum is, its wavelengths, and its colors.
Definition of the Visible Spectrum
You see the visible spectrum every day and probably don’t even realize it. This is because we commonly refer to the visible spectrum as light, or visible light. Nearly all of us see some form of light every day.
Electromagnetic waves are grouped according to frequency. The electromagnetic spectrum is the range of frequencies over which electromagnetic radiation can be propagated. It includes all groups of electromagnetic waves. The lowest frequencies are associated with radio waves. Microwaves have a higher frequency, and then infrared waves, light, ultraviolet radiation, X-rays, and gamma rays in sequence. The visible spectrum is one group of electromagnetic waves in the electromagnetic spectrum.
Visible light is a very narrow band of frequencies of electromagnetic waves that are perceptible by the human eye. The eye contains specialized cells called rods and cones that are sensitive to the visible spectrum. As mentioned previously, most of us see visible light every day. For example, the sun produces visible light. Incandescent light bulbs, fluorescent, and neon lights are other examples of visible light that we may see on a regular basis. Visible light is probably the most important of all electromagnetic waves for most of us.
Wavelengths of Visible Light
As mentioned, electromagnetic waves are grouped according to frequency. The visible spectrum is a group of electromagnetic waves that occupy a specific frequency range in the overall electromagnetic spectrum. Frequency and wavelength are related and are inversely proportional. A higher frequency means a shorter wavelength, and a lower frequency means a longer wavelength.
When we talk about the frequency range of the visible spectrum, we usually talk about wavelength rather than frequency. This is because the frequencies of the visible spectrum are so large that it is more convenient to use wavelengths. The visible spectrum ranges from approximately 400 nanometers to 700 nanometers. A nanometer (nm) is 10^-9 meters, or one billionth of a meter, so visible light waves are extremely small.
These wavelengths correspond to frequencies in the range of 750 terahertz to 429 terahertz. A terahertz is a unit used to measure frequency, and it is 10^12 hertz. The bandwidth of the visible spectrum is relatively narrow. The longest wavelength we can see is less than twice the shortest. By comparison, the range of sound frequencies that we can hear is much larger. The highest frequency of sound we can hear is 1,000 times the lowest frequency.
Colors of Visible Light
Within the narrow band of visible light, the different wavelengths are perceived by people as different colors. The shortest wavelengths are perceived as violet and the longest wavelengths are perceived as red. There are seven wavelength ranges within the visible spectrum that each correspond to a different color.
The colors fall in an order commonly referred to with the acronym ROYGBIV. ROYGBIV can aid in remembering the order of the colors: red, orange, yellow, green, blue, indigo, and violet.

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