What is The Visible Spectrum?
11/03/2004
The definition of The Visible Spectrum is as below: The region of the electromagnetic spectrum that can be perceived by human vision, approximately the wavelength range of 0.4 mm to 0.7 mm.
Visible light is made up of electromagnetic waves, vibrations of electric and magnetic fields that propagate through space. In contrast to slow-moving ocean waves to which they are compared, electromagnetic waves travel at the speed of light (which is 300 million metres per second, or 669.6 million miles per hour!).
Diagram 1 : Electromagnetic Wave
Every electromagnetic wave exhibits a unique frequency, and there is a wavelength associated with that frequency. For instance, diagram 1 (above) is an image which represents an electromagnetic wave corresponding to the colour red. The frequency is 428,570 GHz (pronounced gigahertz), which can also be stated as 428,570 billion cycles per second. Therefore, when a user looks at a red printout produced by an Oki printer, their eyes receive over four hundred trillion waves every second from the red area of that printout.
The wavelength of red light is around 700 nanometres long, which means that one wave spans only 7/10 000 000 (or 7 ten millionths) of a metre.
All electromagnetic waves are classified according to their characteristic frequencies, into what is known as The Electromagnetic Spectrum. Just as red light has its own distinct frequency and wavelength, so do all the other colours. Orange, yellow, green, and blue each exhibit unique frequencies and consequently wavelengths. While we can perceive these electromagnetic waves in their corresponding colours, we cannot see the rest of the electromagnetic spectrum. Diagram 2 (below) indicates the area of the electromagnetic spectrum which is visible to us.
Diagram 2 : The Electromagnetic Spectrum
Most of the electromagnetic spectrum is invisible to us, and exhibits frequencies that encompass its entire breadth. Exhibiting the highest frequencies are gamma rays, x-rays and ultraviolet light. Infrared radiation, microwaves, and radio waves occupy the lower frequencies of the spectrum. Visible light falls within a very narrow range in between. As you can see from diagram 2 (above), the visible band of the electromagnetic spectrum is very small in ratio when compared to the entire band of the spectrum.
