COLD LIGHT.
To answer these questions, we must first determine what constitutes a luminescence.
All naturally occurring sources of light can be divided into two groups. The first of these are sources that emit light when heated - the sun, the filament incandescent lamps, incandescent particles of coal, etc. The second group - sources emitting light without heat. In this group are called luminescent sources, and they create glow-cold, to stress that it is not radiated by heated bodies.
The processes occurring in the luminescence can be simplified, "described as follows. It is known that atoms of all elements consist of a positively charged nucleus and electrons orbiting a nucleus in their orbits. The farther from the nucleus of the orbit, the more energy is rotating in the orbit of the electron. If the atom was given some energy, then it means that one or more of its electrons have moved to more distant orbit from the nucleus, or, as is usually said to be excited atom. This state is very short - about hundred-millionth of a second or less, after which the electrons return to their original orbits, and the absorbed energy is given in the form of light radiation.
It follows that the luminescence process consists of absorption of energy, matter particles stay in the excited state and emission of light, and that the luminescence depends on the type of atoms, i.e., the structure of matter.
If the source of energy that causes the luminescence, energy is released as a result of chemical processes, the phenomenon is called chemiluminescence. Chemiluminescence associated with the vital processes of organisms is called bioluminescence.
If the causative agent of luminescence is the light energy that is photoluminescence. Usually not visible photoluminescence excited by ultraviolet rays or blue-violet part of the spectrum.
Photoluminescence of biological objects are divided into intrinsic and induced. Intrinsic luminescence has cartilage, nails, skeleton, chlorophyll and other plant and animal tissues and substances. Sometimes in the theater, if your eyes tear from the scene, you can watch an unusual sight - in the dark room lit brightly enough teeth viewers and their nylon shirts. This happens in cases where the performance when you make use of fluorescent paint and invisible ultraviolet light, which excites their luminescence, falls into the hall. Intrinsic luminescence of certain biological objects (white blood cells, proteins, etc.) Turns out to be invisible to the eye because the light emitted in the ultraviolet spectrum. Detecting the luminescence is possible only by means of photomultiplier tubes that have sufficient sensitivity to the corresponding region of the spectrum. Many of the objects, which do not luminesce, are treated with special dyes, luminescent-fluorochromes. This luminescence is induced.
Since the luminescence is associated with the properties of substances, it can be used to find these materials and study them. Based on this and fluorescence analysis. He quickly got into a number of areas of physics and engineering, in biology and medicine. The luminescence spectrum makes it possible to determine the composition of the objects, their physiological state, and the intensity, the number of luminescent substances.