The electromagnetic spectrum is composed of wavelengths of light between 10^-16 to 10^8 meters. The majority of this electromagnetic spectrum is invisible to the human eye. Visible light makes up only a small portion of the electromagnetic spectrum. Visible light is the part of the spectrum that is visible to the human eye and has properties unique to the section of the electromagnetic spectrum it makes up.
The range of wavelengths that the eye detects is between 400 nm (violet) to 700 nm (red). The colors between, ranging from longest to shortest wavelength, are orange, yellow, green, blue and indigo. The sensitivity of the human eye follows a Gaussian profile with maximum sensitivity to green-yellow light at 555 nm. This sensitivity drops to 1 percent at wavelengths of 430 and 690 nm at the violet and red part of the spectrum, respectively.
The frequency range of visible light can be calculated knowing the wavelength of visible light. Frequency is defined as the number of events per unit time. Light frequency is measured in Hz, or the amount of oscillations per second. Using the equation f=c/lamba, where c is the speed of light (3 x 10^8 m/s) and lamba the wavelength of light (in meters), the frequency range of visible light is calculated. This frequency range spans from 7.5 x 10^14 Hz (violet) to 4.3 x 10^14 Hz (red).
The oscillations of light carry with it an energy value. The energy of the light is directly proportional to the light's oscillation frequency and inversely proportional to its wavelength. The energy range of visible light can be calculated using the equation E=h x f where h is Planck's constant (6.63 x 10^-34 m^2 x kg/s^2) and f the frequency of light in Hz. The energy range of the visible spectrum therefore ranges from 4.97 x 10^-19 Joules (violet) to 2.84 x 10^-19 Joules (red).
Visible light appears to be white in color because it consists of almost all wavelengths of light within the visible spectrum. Light can be dispersed into its individual wavelength components using a triangular prism. Since the refractive index of a given medium is a function of the light's wavelength, the light entering the prism will bend at different angles depending on the frequency of light. Therefore, the entire visible spectrum is displayed once the light leaves the prism.
