This article lists sources of light, the visible part of the electromagnetic spectrum. It focuses on primary light sources (which emit light) rather than secondary light sources (which reflect or transmit light).[1] Primary light sources produce photons from another energy source, such as heat, chemical reactions, or conversion of mass or a different frequency of electromagnetic radiation, and include light bulbs and stars like the Sun. Secondary light sources (e.g., cat eyes, retroreflectors) do not actually produce the light that comes from them.
A common and fundamental means of classifying primary light sources is on the basis of the mechanism(s) of light emission.[2] Light is generated when an electric charge undergoes acceleration, typically through incandescence or luminescence.[3] Light from real light sources (e.g., stars, gas mantles, limelight, phosphor-based white LEDs) is often from a combination of mechanisms. Real light sources can in turn be categorised as anthropic ("artificial") or naturally occurring.
Incandescence is the emission of visible radiation (light) due to the thermal excitation of atoms or molecules.[4] It is thermal radiation, which emerges from the conversion of kinetic energy associated with heat, resulting in continuous spectra, which extend into the visible region when temperatures are sufficiently high.[5] The lowest temperature at which thermal radiation is visible, known as the Draper point, is approximately 798K (525°C; 977°F).
Many terms exist to describe different kinds of luminescence. Their meanings can overlap (e.g., due to a sequence of events), and continue to evolve with time, sometimes leading to confusion.[6] One recent example was the initial use of shrimpoluminescence to playfully describe shrimp-induced sonoluminescence.[7]
Candoluminescence is light given off by certain materials at high temperatures (usually when exposed to a flame) that has an intensity at some wavelengths which can be higher than the blackbody emission expected from incandescence at the same temperature.
Gas mantle– Device for generating bright light when heated by a flame
Limelight– Type of stage lighting once used in theatres and music halls
Electroluminescence is luminescence caused by the action of an electric field in a gas or in a solid material.[1] Electroluminescent materials (e.g., LEDs, OLEDs) can exhibit fluorescence, delayed fluorescence, and/or phosphorescence.
Electric discharge (also termed gas-discharge[4]) is the passage of an electric current through gases and vapours by the production and movements of charge carriers under the influence of an electric field.[1] The ionized gas becomes a plasma.[10] Such light sources exhibit electroluminescence; some may additionally exhibit photoluminescence (e.g., fluorescent lamps due to phosphors) and/or incandescence (e.g., flashtubes due to high temperatures).[2]
Fluorescence and phosphorescence are typically associated with photoluminescence, but can apply to other kinds of luminescence (e.g., electroluminescence, radioluminescence) as well.
Fluorescence
Fluorescence has traditionally been defined as luminescence which essentially occurs only during the irradiation of a substance by electromagnetic radiation.[10] Any delay is typically limited to about 10 nanoseconds.[1][4] However, some kinds of fluorescence (e.g., thermally activated delayed fluorescence (TADF), triplet-triplet annihilation delayed fluorescence (TTA DF)) exhibit delays akin to phosphorescence.[11] To more clearly distinguish it from phosphorescence, fluorescence is more specifically defined as being due to an "allowed" transition generally from an excited singlet state to a ground singlet state. For brevity, the countless types of fluorescent materials that require energy from an external source (e.g., as used in high-visibility clothing) are not listed here.
Dye laser– Equipment using an organic dye to emit coherent light
Phosphor-based LED– Semiconductor and solid-state light sourcePages displaying short descriptions of redirect targets
Phosphorescence
Phosphorescence has traditionally been defined essentially as fluorescence except with greater duration of emission following exposure to electromagnetic radiation.[4] However, given the overlap with delayed fluorescence, phosphorescence is more specifically defined as luminescence involving a change in spin multiplicity, typically a "forbidden" transition from excited triplet state to ground singlet state.[10][1][11]
Photoluminescence is light resulting from absorption of photons. The phenomenon is similar to radioluminescence, with overlapping meaning for high-energy electromagnetic radiation (e.g., gamma rays, X-rays); photoluminescent materials exhibit fluorescence, delayed fluorescence, and/or phosphorescence.
Luminous paint– Paints that glow in the dark (some can also or instead exhibit radioluminescence)
Pyroluminescence (flame luminescence) is light emitted by a gas or vapor excited by high temperature, as in a flame.[19][9] At very high temperatures the collisions of atoms can cause ionization (and recombination), in which case luminescence and incandescence become indistinguishable.[20][21]
Flame test– Process in chemistry to detect certain elements
Radioluminescence, also termed scintillation, is luminescence arising from excitation by high-energy particles or radiation.[10][22] The phenomenon is similar to photoluminescence, with overlapping meaning for high-energy electromagnetic radiation (e.g., gamma rays, X-rays); scintillators exhibit fluorescence, delayed fluorescence, and/or phosphorescence.[1][23]
Aurora– Atmospheric effect caused by the solar wind
Fluoroscopy– Production of an image when X-rays strike a fluorescent screen
Radium dial– Instrument dials painted with radium-based paint
Thermoluminescence is luminescence resulting from an increase in temperature that releases trapped energy from a chemical reaction or previously absorbed radiation.[10]
Not all terms for different kinds of luminescence end in luminescence, or even orescence. Some additional types of luminescence (e.g., Bremsstrahlung, cyclotron radiation, synchrotron radiation) involve acceleration of charged particles, including but not limited to electrons; notably, this can occur in a vacuum free of atoms. Cherenkov radiation is created when a charged particle moves faster than light in a given medium (not a vacuum), similar to a sonic boom.
Annihilation– Collision of a particle and its antiparticle
Combustion is an exothermic chemical reaction that may or may not produce a flame or explosion. A flame provides visible evidence of combustion. Whereas incomplete combustion of methane can produce soot with a temperature sufficient to incandesce (giving the flame an orangish-white color), its complete combustion yields the characteristic blue flame via luminescence, as can be demonstrated by adjusting a Bunsen burner.[5] Methane burns in air at about 1,957°C (2,230K; 3,555°F);[24] a much higher temperature would be required to yield blackbody radiation with a similar bluish appearance.
↑Lohse, D.; Schmitz, B.; Versluis, M. (2001). "Snapping shrimp make flashing bubbles". Nature. 413: 477–478. doi:10.1038/35097152.
↑Garten, V.; Head, R. (1966). "Crystalloluminescence". Nature. 209: 705. doi:10.1038/209705a0.
12Matousek, Vaclav; Matuska, Radek; Vranka, Tomas; Adamec, Martin; Herentin, Tadeas; Kalacek, Jiri; Havlik, Jan (2023). "Exploring Triboluminescence and Paramagnetism: A Rapid Mn Complex Synthesis for High School and Undergraduate Chemistry Laboratories". Journal of Chemical Education. 100 (8): 3062. doi:10.1021/acs.jchemed.3c00372.
12Franca, Larissa G.; Bossanyi, David G.; Clark, Jenny; Lays dos Santos, Paloma (2024). "Exploring the Versatile Uses of Triplet States: Working Principles, Limitations, and Recent Progress in Phosphorescence, TADF, and TTA". ACS Applied Optical Materials. 2 (12): 2476–2500. doi:10.1021/acsaom.4c00041.
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