Almost everything emits, reflects, or transmits some kind of light. The Electromagnetic (EM) Spectrum is the measurement of the frequency range of EM radiation of an object. The frequency is measured in wavelengths. The wavelength ranges can extend from the size of an atom to thousands of kilometers.
The long wavelengths are low frequency and are the Radio, Microwave, and Infrared waves. The short wavelengths are the high frequency Ultraviolet, X-ray and Gamma Rays. The Visible Spectrum, or Optical Spectrum, is the range of the Electromagnetic Spectrum that is visible by the human eye.
The Visible Spectrum has no clear boundaries from one color to the next but is generally described in the following ranges:
*Nanometer - a unit of length in the metric system, equal to one billionth of a meter, which is the current SI base unit of length. It can be written in scientific notations as 1×10-9 m (engineering notation) or 1 E-9 m (exponential notation), both meaning 1/1,000,000,000 meters
Newton divided the spectrum into seven named colors: red, orange, yellow, green, blue, indigo, and violet, or ROY G. BIV. Originally only five primary colors were named: red, yellow, green, blue and violet, but later he added indigo and orange to have seven colors. The need for the number seven was derived from the belief that it should match the number of known planets, number of days in a week and the number of notes on a major scale. This theory was derived from ancient Greek Sophist philosophy.
The word Spectrum is Latin for apparition, and was coined by Newton during his experiments with light. He observed that sunlight passing though a prism produced the apparition or spectrum or, in other words, a band of colors.
Sir Isaac Newton wrote Optick's released in 1704, hailed as one of the earliest explanations of the Spectrum.
The field of optics usually describes the behavior of visible, infrared, and ultraviolet light; however because light is an electromagnetic wave, analogous phenomena occur in X-rays, microwaves, radio waves, and other forms of electromagnetic radiation. Optics can thus be regarded as a sub-field of electromagnetism.
In vision applications that use camera technology the optical fields of visible, infrared and ultraviolet are the most widely used, and with the implementation of specialized optics, filters, and lighting many solutions to imaging issues can be found. Infrared Radiation (IR) is a wavelength longer than visible light but shorter than radio waves (750nm to 1nm). Ultraviolet (UV) is shorter than visible light but longer than X-Ray (400nm to 200nm Near UV, NUV). Most cameras will fall in the near IR or near UV range and with the use of specialized lighting (LED’s), enhancement of the wavelengths is possible.
Infrared (IR) camera technology is very common in military applications and Ultraviolet (UV) solutions are used in various machine vision, and industrial imaging applications. There are also digital cameras, such as Firewire? 1394 which exploit the use of Ultraviolet (UV). Sony Electronics, Inc. offers the XCDSX910UV camera featuring Firewire? 1394, digital camera technology. This camera is ideal for use in demanding markets such as semiconductor inspection, ultraviolet microscopy, FA precision inspection and surface inspection applications.
Hitachi Kokusai Electric Inc. offers the KP-F120, a Near IR (NIR), high resolution, progressive scan camera with Camera Link, USB2.0, Firewire 1394 or LVDS digital camera interfaces. The spectral response extends beyond 1000 nm. This camera is appropriate for a wide range of applications including machine vision, agricultural inspection, medical diagnostics and research, and microscopy.
There are many cameras that fall into the near Infared (IR) and near Ultraviolet (UV) ranges. They are used in a variety of applications and provide many solutions from military to medical.