List of light sources
A light source is the place emanating from the light. Light sources can be classified according to the nature of generated radiation, listed according to the beam path and differentiate according to physical characteristics such as quantum energy or wavelength distribution. Furthermore, we distinguish them according to their spatial extent as point sources or diffuse light sources and their various radiation beaming as omni or directional.
Physically differ natural light sources ( such as solar, fireflies, polar light or flash ) and man-made artificial light sources (such as oil lamps, bulbs, lasers, cathode ray tubes, light emitting diodes) well in the process. Conditions of light production, but not by the physics of the radiation generated
An active light source, and light source first -order or self-illuminating light source is a source which generates the light. These luminous objects include the sun, stars, fireflies, fire or lamps. As a passive light sources, including second or higher order light sources, consists of all the bodies that do not illuminate themselves and send out by other light sources only when illuminated and thus visible, such as the moon, reflectors such as cat eyes or other body that reflect light.
Thermal radiators provide continuous radiation with increasing temperature, the radiation maximum is shifted from the infrared through red, toward blue and ultraviolet light ( see Planck's radiation law ). The hotter a spotlight, the bluer it appears.
Subdivision on the heat source:
- Electric energy: light bulb, the Nernst lamp, the plasma of the carbon arc lamp
- Chemical energy (combustion ): oil lamp, oil lamp, including the high-powered lamp, gas lamp, fire, candle, torch: flame lit by glowing carbon or disperse the light is produced by a mantle
- Nuclear energy: sun, Thermophotovoltaischer converter ( radionuclide )
Molecules and atoms may be displaced by the supply of energy to an excited state. When they return to the ground state ( recombination), they release their energy partly as radiation with wavelengths in the visible spectral range. The optical portion of the resulting radiation is called luminescence. See also: line spectrum.
The supplied energy (excitation ) of a light source is, for example, by
- Chemical reaction, like fireflies or the light stick
- Electric current by means of gas discharge, or electroluminescence, as in light-emitting diodes, gas discharge lamps, EL sheets
- Electron bombardment, and beta radiation from a fluorescent phosphor, such as picture tubes, fluorescent displays, also by cathodoluminescence, tritium light
- Light / ultraviolet (shorter wavelength): conversion by fluorescence (fluorescent) in visible light, as in fluorescent lamps and white LEDs.
Gas discharges in rarefied gases show very sharp spectral lines. For gases under pressure ( high-pressure metal halide lamps ), the lines broaden.
Fluorescence occurs only during the stimulation on, phosphorescence, however, even after the external stimulus is already extinct. Both of these are forms of luminescence. The phosphorescence ( afterglow after lighting ) is used in safety signs, dials or as a decoration.
Generating visible light by X-ray radiation ( light screens of older devices), by gamma radiation (radioactive luminous paint ) and the synchrotron radiation and the Tscherenkowstrahlung other hand, have no meaning as artificial light sources.
Lasers are excited by electrical current, radiation of shorter wavelengths or chemical energy, but they are rarely used as a light source. Examples include infrared target illumination, blinding laser or red laser pointer.
The green light laser pointer is generated by frequency doubling of an infrared laser beam.
In addition to the light output, the color rendering index of significance even with a lot of white lamps.