Light source

A light source is any object that emits electromagnetic radiation within the visible spectrum or other areas of the electromagnetic spectrum.


A list of natural light sources might include:

  • Solar Radiation: This is the most abundant natural light source, originating from the sun’s nuclear fusion process. This light travels to Earth in various wavelengths, including visible light, ultraviolet (UV) light, and infrared (IR) radiation.
  • Bioluminescence: Bioluminescence involves living organisms such as fireflies, deep-sea creatures, and some fungi emitting light through chemical reactions.
  • Triboluminescence: This less common form of light emission occurs when certain materials, like sugar or quartz, are subjected to friction or stress, causing them to glow briefly.
  • Chemiluminescence: This chemical reaction produces light as a byproduct. It is seen in glow sticks, fireflies, and certain biological processes. The chemical reaction excites the electrons within these molecules, causing them to jump to higher energy levels. When they return to their ground state, they release energy in the form of light.
  • Atmospheric phenomena: Lightning, auroras, and airglow (faint nighttime glow) are examples of light produced by interactions between atmospheric gases, charged particles, and electromagnetic fields. These processes involve various mechanisms like electron excitation, recombination, and collisions.

A list of natural artificial sources might include:

  • Incandescent light: This traditional lighting method relies on heating a filament (usually tungsten) to high temperatures until it glows, emitting a warm, yellowish light. Incandescent bulbs are less efficient than many other options.
  • Fluorescent light: These tube-shaped lamps use fluorescent coatings that convert ultraviolet radiation from a mercury vapour discharge into visible light. They come in various colour temperatures and offer higher efficiency than incandescent bulbs.
  • LED lighting: Light-emitting diodes (LEDs) are popular due to their high efficiency and long lifespan. They convert electrical energy directly into light with minimal heat generation, and their colour temperature can be tailored to various applications.
  • Gas-discharge lamps: These encompass high-intensity discharge (HID) lamps, sodium-vapour lamps, and metal halide lamps. They use electrical discharges in different gases to create high-intensity lighting with colour spectra that suit applications such as street lighting and stadiums.

Here is a list of key sub-atomic processes involved in the generation of both natural and artificial light, categorized by the nature of the process:

Electron Transitions
  • Atomic emission: Excited electrons in atoms lose energy by dropping to lower energy levels, emitting photons (light) with specific wavelengths. (Natural: Stellar light, Auroras; Artificial: Fluorescent lamps, Gas discharge lamps)
  • Recombination: Electrons recombine with positive ions (missing electrons), releasing energy as photons. (Natural: Nebulae; Artificial: LEDs, Semiconductor lasers)
Radiative Decay
  • Nuclear decay: Certain radioactive decay processes (alpha decay, gamma decay) involve the direct emission of photons from the nucleus. (Natural: Radioactive materials; Artificial: Nuclear reactors, Radioisotope tracers)
  • Annihilation: Particle-antiparticle collisions result in complete mass conversion to energy, often releasing high-energy photons (gamma rays). (Natural: Cosmic ray interactions; Artificial: Positron emission tomography (PET) scans)
Collisional Processes
  • Bremsstrahlung: Charged particles interacting with other charged particles or strong electric fields decelerate, emitting photons. (Natural: Stellar interiors, Black hole accretion disks; Artificial: X-ray machines)
  • Synchrotron radiation: Charged particles moving at high speeds in magnetic fields experience acceleration and emit characteristic light spectra. (Natural: Pulsars, Magnetars; Artificial: Synchrotrons, Particle accelerators)
Other Processes
  • Cherenkov radiation: Charged particles travelling faster than light in a medium emit a faint bluish glow due to this specific radiation. (Natural: Cosmic rays in water; Artificial: Cherenkov detectors)
  • Piezoluminescence: Certain materials emit light under pressure due to electron transitions induced by mechanical stress. (Natural: Quartz crystals; Artificial: Ultrasonic cleaning devices)
  • Sonoluminescence: Cavitation bubbles collapsing in liquids can produce brief flashes of light due to various mechanisms (exact processes still debated). (Natural: Shrimp snapping claws; Artificial: Sonoluminescence research)
  • Chemical reactions: Some chemical reactions directly convert chemical energy into light through specific mechanisms (chemiluminescence) involving excited molecules. (Natural: Fireflies, Deep-sea creatures; Artificial: Glow sticks)
  • Plasma: Hot, ionized gases (plasmas) exhibit various processes leading to light emission, including recombination, Bremsstrahlung, and interactions with charged particles. (Natural: Stellar atmospheres, Lightning; Artificial: Plasma torches, Fusion reactors)
Light sources
Emission mechanism DescriptionExamples
LuminescenceLight emission due to the excitation of electrons in a material.Electrons within a material gain energy and then release light as they return to a lower energy state.Bioelectroluminescence
- Fluorescence
- Phosphorescence
Blackbody radiation (Type of thermal radiation)Electromagnetic radiation (including visible light) emitted by any object with a temperature above absolute zero.Electromagnetic radiation (including visible light) emitted by any object with a temperature above absolute zero.All objects above temperature of absolute zero.
ChemiluminescenceLight from natural and artificial chemical reactions.Light from natural and artificial chemical reactions.Bioluminescence
Chemiluminescent reactions:
- Luminol reactions
- Ruthenium chemiluminescence
Nuclear reactionLight emission as a byproduct of nuclear reactions (fusion or fission).Light emitted as a byproduct of nuclear reactions.Nuclear reactors
Stars undergoing fusion
Thermal radiationLight emission due to the thermal excitation of atoms and molecules at high temperatures.Light emission due to the thermal excitation of atoms and molecules.Sun
Incandescent light bulbs
TriboluminescenceLight emission due to mechanical stress applied to a material.Light emission due to the mechanical stress applied to a material, causing the movement of electric charges and subsequent light emission.Sugar crystals cracking
Adhesive tape peeling
Quartz crystals fracturing.
Natural light source
Deep-sea creatures
Glowing mushrooms
Bioluminescence Light emission from biological organisms.Involves the luciferase enzyme.
Nuclear FusionLight emission as a byproduct of nuclear fusion reactions in stars.Electromagnetic spectrum (visible light, infrared, ultraviolet).
Thermal radiationLight emission due to the thermal excitation of atoms and molecules during the combustion of a fuel source.Burning of a fuel source, releasing heat and light.
Artificial light source
Fluorescent lights Highlighters
Safety vests
Chemiluminescence Light emission from chemical reactions.Fluorescence (absorption and re-emission of light).
Glow sticks
Emergency signs
ChemiluminescenceLight emission due to phosphorescence - a type of chemiluminescence.A type of chemiluminescence where light emission is delayed after the initial excitation.
Glow sticks
Light sticks
Chemiluminescence Chemiluminescence Light emission from a chemical reaction that does not involve combustion.
Tungsten light bulbs
Thermal radiationHeated filament radiates light and heat.Light emission from a hot filament.
Fluorescent lamps
LED lights
ElectroluminescenceExcitation of atoms by electric current.Light emission when electric current excites atoms in a material.
Neon signsElectrical DischargeDischarge of electricity through gas.Light emission when electricity flows through a gas.
Sugar crystals cracking
Pressure-sensitive adhesives
TriboluminescenceLight emission from friction or pressure.Light emission due to mechanical forces.
Fluorescent paint Highlighters
Safety vests
PhotoluminescenceAbsorption and subsequent re-emission of light at a lower energy.Absorption and re-emission of light.

Light Sources: Mechanism, examples, and everyday applications

Footnote: Cerenkov radiation and Synchrotron radiation are not included in the table because they are not conventionally classified as light sources.


Here are some Wikipedia links to less familiar sources of light:

  • Bioluminescence: Bioluminescence is the production and emission of light by living organisms.
  • Bremsstrahlung: Bremsstrahlung from German bremsen ‘to brake’, and Strahlung ‘radiation’) is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic energy, which is converted into radiation (i.e., photons). The term is also used to refer to the process of producing the radiation. Bremsstrahlung has a continuous spectrum, which becomes more intense and whose peak intensity shifts toward higher frequencies as the change of the energy of the decelerated particles increases.
  • Cherenkov radiation: Cherenkov radiation is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium (such as distilled water) at a speed greater than the phase velocity of light (speed of propagation of a wavefront in a medium) in that medium.
  • Electroluminescence: Electroluminescence (EL) is an optical and electrical phenomenon, in which a material emits light in response to the passage of an electric current or a strong electric field.
  • Particle Collisions: High-energy photons (light) are produced during particle collisions in particle accelerators. A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies and to contain them in well-defined beams.
  • Particle–antiparticle annihilation: Particle–antiparticle pairs can annihilate each other, producing photons. Since the charges of the particle and antiparticle are opposite, total charge is conserved. For example, the positrons produced in natural radioactive decay quickly annihilate themselves with electrons, producing pairs of gamma rays, a process exploited in positron emission tomography.
  • Scintillation: In condensed matter physics, scintillation is the process where a material, called a scintillator, emits ultraviolet or visible light under excitation from high energy photons such as X-rays or gamma rays or energetic particles such as electrons, alpha particles, neutrons, or ions.
  • Sonoluminescence: Sonoluminescence is the emission of light from imploding bubbles in a liquid when excited by sound.
  • Synchrotron Radiation: High-energy light emitted by charged particles accelerated in synchrotrons.
  • Radioactive decay: Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay. The weak force is the mechanism that is responsible for beta decay, while the other two are governed by electromagnetism and the weak nuclear force.
  • Triboluminescence: Triboluminescence is a phenomenon in which light is generated when a material is mechanically pulled apart, ripped, scratched, crushed, or rubbed (see tribology). The phenomenon is not fully understood but appears to be caused by the separation and reunification of static electric charges.

A light source is a natural or man-made object that emits one or more wavelengths of light.

  • The Sun is the most important light source in our lives and emits every wavelength of light in the visible spectrum.
  • Celestial sources of light include other stars, comets and meteors.
  • Other natural sources of light include lightning, volcanoes and forest fires.
  • There are also bio-luminescent light sources including some species of fish and insects as well as types of bacteria and algae.
  • Man-made light sources of the most simple type include natural tars and resins, wax candles, lamps that burn oil, fats or paraffin and gas lamps.
  • Modern man-made light sources include tungsten light sources. These are a type of incandescent source which means they radiate light when electricity is used to heat a filament inside a glass bulb.
  • Halogen bulbs are more efficient and long-lasting versions of incandescent tungsten lamps and produce a very uniform bright light throughout the bulb’s lifetime.
  • Fluorescent lights are non-incandescent sources of light. They generally work by passing electricity through a glass tube of gas such as mercury, neon, argon or xenon instead of a filament. These lamps are very efficient at emitting visible light, produce less waste heat, and typically last much longer than incandescent lamps.
  • An LED (Light Emitting Diode) is an electroluminescent light source. It produces light by passing an electrical charge across the junction of a semiconductor.
  • Made-made lights can emit a single wavelength, bands of wavelengths or combinations of wavelengths.
  • An LED light typically emits a single colour of light which is composed of a very narrow range of wavelengths.