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Light cone
A light cone is the set of spacetime events reachable from a given event by light, dividing spacetime into regions of possible and impossible causal influence.
Light curve analysis
Light curve analysis is the set of techniques for measuring and modeling a celestial object's brightness over time, revealing periods, masses, and shapes of variable stars, planets, and asteroids.
Light dark matter
Light dark matter is dark matter with particle masses below about 1 GeV, far lighter than WIMPs, so conventional nuclear-recoil detectors cannot see it; electron-scattering experiments like DarkSide-50 search for it.
Light extraction efficiency
Light extraction efficiency is the fraction of photons generated inside an LED that escape the semiconductor chip rather than being lost to total internal reflection or reabsorption.
Light field imaging
Light field imaging is an imaging method that records both where light rays strike the sensor and their directions, enabling refocusing, depth maps, and 3D reconstruction after capture.
Light field microscopy
Light field microscopy (LFM) is a snapshot 3D imaging method in which a microlens array lets one camera exposure record a specimen's 3D volume, suited to fast biological dynamics.
Light meter
A light meter, also called an exposure meter or luxmeter, measures light falling on or reflected from a subject and converts the reading into camera exposure settings.
Light pillar
A light pillar is a vertical shaft of light above or below a light source, caused by flat plate-shaped ice crystals in cold air reflecting it; over the Sun it is called a sun pillar, over the Moon a moon pillar.
Light pollution
Light pollution, also known as photopollution or obtrusive lighting, is the harmful effect of artificial light at night, including skyglow and glare, on astronomy, ecosystems, and health.
Light scattering
Light scattering is the deviation of light from a straight path when it interacts with particles, macromolecules, or colloids, also used to measure size and molar mass.
Light-activated active nematics
Light-activated active nematics are active nematic liquid crystalline materials whose activity can be switched or patterned by light, typically microtubule films driven by kinesin motors that assemble only under blue light.
Light-cone coordinates
Light-cone coordinates, also called null or light-front coordinates, are coordinates on spacetime defined along the directions light travels, turning boosts into simple rescalings and underpinning Dirac's 1949 front form of dynamics.
Light-dragging effects
Light-dragging effects are phenomena in which a moving medium or rotating mass partially carries light, or spacetime, along with it: the Fresnel–Fizeau drag in moving water and the gravitational frame-dragging (Lense–Thirring) effect of general relativity.
Light-driven molecular motor
A light-driven molecular motor is a synthetic molecule that converts absorbed light into continuous, directionally controlled rotation, first demonstrated in 1999 by Ben Feringa and co-workers.
Light-driven rotary molecular motors in liquid crystal networks
Light-driven rotary molecular motors in liquid crystal networks are synthetic molecules that rotate unidirectionally under light inside liquid-crystal films, turning nanoscale motion into macroscopic work.
Light-front quantization
Light-front quantization is a quantum field theory method in which fields are quantized at fixed light-cone time, allowing relativistic bound states like hadrons to be computed directly in Minkowski space.
Light-front quark model
The light-front quark model (LFQM) is a relativistic quark model that quantizes hadrons on the light front, computing decay constants, form factors, and parton distributions for mesons.
Light-gas gun
A light-gas gun is a laboratory launcher that uses compressed hydrogen or helium to accelerate small projectiles to hypervelocities of 2 to 9 km/s, simulating orbital debris impacts.
Light-induced conical intersections
A light-induced conical intersection (LICI) is a degeneracy between two laser-dressed electronic states of a molecule, created by resonant light, with position set by laser frequency and coupling strength by intensity.
Light-induced superconductivity
Light-induced superconductivity, or photoinduced superconductivity, is the phenomenon in which intense mid-infrared or terahertz laser pulses drive a material into a transient superconducting-like state above its equilibrium transition temperature.
Light-shining-through-walls experiments
Light-shining-through-walls experiments are laboratory searches for axion-like particles and hidden photons, converting laser photons in a magnetic field and regenerating them behind an opaque barrier.
Light-year
A light-year is a unit of distance equal to how far light travels in one year, about 5.88 trillion miles, used by astronomers for interstellar distances.
Lightest supersymmetric particle
The lightest supersymmetric particle (LSP) is the lightest superpartner predicted by supersymmetry. In R-parity-conserving models it is stable and the leading cold dark matter candidate.
Lightning
Lightning, also called lightning discharge, is a giant spark of electricity in the atmosphere or to the ground, heating the air it passes through to 50,000 degrees Fahrenheit.
Lightning detection network
A lightning detection network is a system of ground-based radio sensors that locates lightning strokes by their electromagnetic signals, computing position, time, and peak current.
Lightning mapping
Lightning mapping is a set of observational techniques that locate VHF radiation sources from lightning discharges in three dimensions and time, using networks of GPS-synchronized radio receivers.
Lightning records
Lightning records are officially evaluated extreme lightning events, certified by the World Meteorological Organization and Guinness World Records, including an 829 km flash across the United States in 2017.
Lightning strike
A lightning strike is an electrical discharge between a cloud and the ground, carrying currents of tens of thousands of amperes for a fraction of a second.
Lightwave electronics
Lightwave electronics is an emerging field in which intense optical light waves steer electron motion on femtosecond to attosecond timescales, aiming at petahertz processing speeds.
Lignin depolymerization
Lignin depolymerization is the chemical or biological breakdown of lignin, the abundant aromatic polymer in plant cell walls, into phenolic monomers and oligomers for use as chemicals and biofuels.