Wavelength of Visible Light Spectrum
Before going into depth of information about the visible light spectrum, let us get some basics cleared like what do you mean by wavelength and frequency.
What is the Wavelength and Frequency of a Wave?
A wave is a disturbance traveling through any medium. For example, a wave in the ocean, is a disturbance caused by wind, traveling through the sea water. Standing on the seashore, you must have observed waves sloshing back and forth. It consists of a peak and a trough, or what you could call a mountain followed by a valley. Rarely do you find a single wave or a single disturbance traveling. A wave is a periodic phenomenon. What you normally observe is a wave train, that is a string of waves, one following the other. The 'wavelength' is distance between two consecutive peaks or troughs of a wave train. The 'frequency' of a wave is the number of waves passing a point in a second.
Light as an Electromagnetic Wave
A light wave is a kind of wave, which does not require a material medium for propagation! They can travel through vacuum. Light waves are traveling disturbances in electromagnetic field. Electromagnetism is a study of dynamic electromagnetic fields that are light waves. A changing or fluctuating electric field, creates a magnetic field and a fluctuating magnetic field creates an electric field. That is how an electromagnetic wave, that is light, travels. That is how we see each other, because that is how visible light travels!
Radio waves, which enable radio communication, microwaves used in the oven for heating, infra red waves that enable viewing using night vision goggles, gamma rays emitted by radioactive nuclei, X-rays that enable skeletal imaging and visible light from the Sun are all electromagnetic waves! The primary difference among them is that they are electromagnetic waves carrying, different amounts of energy. Also, they differ in their wavelength and frequency, which is a function of energy.
So electromagnetic waves make a spectrum which is a gradation of waves according to their wavelength or frequency. Out of this spectrum, one particular band of waves, is called 'Visible Light'. This band is called 'visible' because these are the only electromagnetic waves which we can see! This is so because our eyes have a mechanism like a receptor, which responds to only this part of the electromagnetic spectrum.
That is the reason why we cannot see radio waves, infra red or gamma rays, because our eyes do not have the mechanism that could detect these waves. There may be alien civilizations who could 'see' radio waves or ultraviolet waves! All depends on the mechanism of and tuning of the receptors in the eyes. Now let us see the numerical values for the wavelength of visible light.
Wavelength of Visible Light in Angstroms
An 'Angstrom' is 10-10m. The wavelength of visible light starts from 3800 Angstrom and extends up to 7500 Angstrom. These are the wavelengths to which the human eye responds. The color or wavelength to which our eyes respond readily is 5550 Angstrom (green color). The colors that we identify are different wavelengths of visible light. Not surprisingly, evolution has bestowed us with eyes that respond to the wavelength range in which Sun radiates its energy. The wavelength range of different colors in the visible electromagnetic spectrum is as follows:
- Violet: 3800 - 4500 Angstrom
- Indigo: 4200 - 4500 Angstrom
- Blue: 4500 - 4950 Angstrom
- Green: 4950 - 5700 Angstrom
- Yellow: 5700 - 5900 Angstrom
- Orange: 5900 - 6200 Angstrom
- Red: 6200 - 7500 Angstrom