light sources (original) (raw)
Author: the photonics expert (RP)
Definition: devices generating light
photonic devices- light sources
Related: lightlaserslight sources based on nonlinear optical effects
DOI: 10.61835/44q Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn
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Contents
Introduction
This article gives a brief overview of different sources of light — going beyond only visible light by including sources of infrared light and ultraviolet light. It mostly categorizes light sources by physical mechanisms, but also by other aspects.
Light Sources by Physical Mechanisms
We first categorize technical (artificial) light sources by the fundamental physical mechanisms which they utilize.
Incandescent Sources
Incandescent light sources generate light as thermal radiation. Originally, candles and oil lamps have been widely used, but these have later been largely replaced by incandescent lamps (including halogen lamps) with an electrically heated filament. This is a simple technology, but is fundamentally very inefficient, as most of the generated thermal radiation generally lies outside the wavelength range which can be utilized. Exceptions are cases where broadband infrared light is needed, for example. It is in principle possible to modify thermal light emitters such that their emission is restricted to certain narrow wavelength regions, but this is not mature technology.
See the article on incandescent lamps for details.
As the technology of incandescent light sources is not only inefficient but also unsatisfactory concerning lamp lifetime, fluorescent lamps and light-emitting diodes have been developed to largely replace them.
Luminescent Sources
Various kinds of light sources rely on some form of luminescence, including electroluminescence, chemiluminescence, fluorescence and superluminescence:
Gas Discharge Lamps
Gas discharge lamps utilize light emission of excited species in a gas or plasma. As the excitation is generated with an electrical current, this is electroluminescence.
Such lamps often reach reasonably high conversion efficiencies, higher than for incandescent sources, and often with spectrally more concentrated output. The spectra may contain isolated spectral lines and/or broadband parts, depending on the conditions.
See the article on gas discharge lamps for details, also more specific articles on arc lamps and flash lamps.
Fluorescent lamps utilize fluorescence from a phosphor which is illuminated with a gas discharge. The function of the phosphor is to convert the original ultraviolet light to a useful spectral region, usually in the visible range. Such lamps can be quite efficient and long-lived. One may subsume fluorescent lamps under gas discharge lamps since they utilize such a discharge, although their final light generation is based on fluorescence. See the article on fluorescent lamps for details.
Chemiluminescent Sources
There are “glow sticks” which generate a modest amount of light based on chemical reactions producing excited molecules.
See the article on chemiluminescence.
Light-emitting Diodes
Light-emitting diodes (LEDs) produce electroluminescence in a semiconductor material with an appropriate band gap energy. They can be highly efficient and emit in a limited spectral bandwidth of typically a couple of nanometers.
There are different types of LEDs, including inorganic and organic LEDs (OLEDs).
See the article on light-emitting diodes for details.
Superluminescent Sources
Superluminescent sources utilize the effect of superluminescence. They are mostly either superluminescent diodes or based on fiber amplifiers.
See the article on superluminescent sources.
Sources with Cathodoluminescence or Radioluminescence
Such sources generate light from excitation by energetic particles. Examples are cathode-ray tubes, scintillators and tritium-based glow lights. Some of these are used in radiation detectors and displays.
Lasers
Lasers utilize stimulated emission of radiation in excited laser gain media. They might be subsumed under luminescent sources as the light generation is not thermal, but lasers generate laser light which usually has quite special properties, particularly related to spatial and temporal coherence.
Devices including both a laser and an optical amplifier are often called lasers as a whole.
See the article on lasers for details.
Light Sources Based on Nonlinear Effects
Various kinds of light sources are based on nonlinear optical effects. Examples include frequency-doubled lasers, optical parametric oscillators and Raman lasers.
See the article on light sources based on nonlinear optical effects for details.
Other Categories of Light Sources
Light sources can also be categorized according to other aspects, such as their use or special properties; some examples:
Quantum Light Sources
Quantum light sources generate light with special quantum properties, such as modified quantum noise properties. Examples include squeezed light sources, single-photon sources and photon pair sources.
See the article on quantum light sources for details.
Light Sources by Emission Region
Light sources can be categorized into visible light sources (including e.g. red light sources), sources of infrared light and ultraviolet light.
White Light Sources
White light sources are sources with a broad optical spectrum. Examples include incandescent lamps, fluorescent lamps, LEDs with a combination of multiple LED types, and superluminescent sources.
See the article on white light sources for details.
Coherent vs. Incoherent Sources
Light sources can be categorized by their coherence. Here, it is important to distinguish temporal and spatial coherence; note that combinations of temporally coherent but spatially incoherent emission, or vice versa, are possible.
Typical temporally coherent sources include most lasers and many light sources based on nonlinear optical effects, while typical temporally incoherent emitters are incandescent lamps and superluminescent sources (the latter usually with high spatial coherence). High spatial coherence allows for the formation of very directed light beams.
Wavelength-tunable Light Sources
Some light sources allow their emission wavelength to be tuned. Examples include tunable lasers and sources with a broadband light source followed by a monochromator.
See the article on wavelength-tunable light sources.
Pulsed vs. Continuous-wave Light Sources
Many light sources emit continuously over prolonged times, while others emit light pulses — sometimes with extremely short pulse durations; see the article on ultrafast lasers.
Light Sources for Specific Applications
Light sources are often labeled according to their application areas, for which they are tailored. Examples include illumination and projection light sources, laser pump sources, metrology light sources (e.g. optical frequency standards) and communication light sources.
Natural Light Sources
Natural light sources include:
- Sun and other stars: a powerful nuclear fusion-driven radiation source with a broad spectrum, mostly from thermal radiation.
- Fire from combustion of fuels, generates thermal radiation and some chemiluminescence.
- Lightning is electrical discharges in the atmosphere, emitting light through excited species.
- Bioluminescence is generated by chemical processes in organisms such as fireflies and various deep-sea creatures.
Frequently Asked Questions
What are the main physical principles for generating light?
What is the difference between incandescent and luminescent light sources?
Incandescent sources produce light as thermal radiation from a hot object, which is generally inefficient. Luminescent sources use non-thermal mechanisms like electroluminescence, where an electrical current excites materials to emit light, often with much higher efficiency.
How do lasers differ from other light sources like LEDs?
What is a white light source?
What is the difference between temporal and spatial coherence?
Temporal coherence is related to the monochromaticity (narrow spectral bandwidth) of light, while spatial coherence describes the ability to form a highly directed beam. Some sources can possess one but not the other.
What are quantum light sources?
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