The Nature of Light
Light consists of packets of energy that stream constantly from the sun in all directions. These packets are called photons. Each photon is a discrete entity of electromagnetic radiation with a characteristic frequency of electromagnetic field vibration and a wavelength. The wavelength and frequency of a photon are directly related to the energy. For any two photons, the one with more energy is the one that has the highest frequency of vibration. Since it is easier to measure the wavelength than the frequency of field vibration, the energy of light us usually described as wavelength. For visible light, units of nm (10-9 meters) are most common. The shorter the wavelength, the greater the frequency of a photon and the greater its energy.
Electromagnetic radiation is produced in a great array of wavelengths, complimenting amounts of energy per packet. Visible light (the wavelengths detected by the human eye) is in the wavelength range of 400 to 700 nm (Figure 1, Wavelengths; note that differences in wavelength scale are exaggerated).
Electromagnetic radiation such as ultraviolet light, x-rays and gamma radiation, have shorter wavelengths than visible light. These shorter wavelengths lead to much more energy per photon, giving them the energy potential for damaging biological molecules and tissues and are considered health hazards. Electromagnetic radiation with wavelengths longer than 700 nm include infrared light, microwaves, radar, TV and radio transmissions. This radiation has lower energy and therefore less potential to damage biological molecules and tissues.
Within the visible range of 400 to 700 nm light, the human eye is able to discern different wavelengths of light and we give them the names of various colors. An example would be a rainbow in which white sunlight is diffracted into its component wavelengths of light. The colors visible are Red, Orange, Yellow, Green, Blue, Indigo and Violet. Each color has a different wavelength, but natural colors rarely consist of single wavelengths.
Familiar examples include the light reflected from new dark blue denim (about 460 nm), light reflected from a lush lawn (about 550 nm), light from the orangish sodium vapor used in some street lamps (about 595 nm), and the scarlet light reflected from the jersey of a Nebraska linebacker (about 650 nm). You can visualize the colors of the spectrum by going to the following site: http://www.cs.rit.edu/~ncs/color/a_spectr.html