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LightLight is a type of energy that communicates information about the world. When this energy is emitted or reflected by objects, it can be collected—as occurs in the human retina—and processed to make observations, identify surroundings, and produce data. This has enabled humans to develop scientific models for a broad range of phenomena, which have been used to explain nature and create nearly every piece of technology in existence.
Historically, observations of light bouncing off mirror-like surfaces suggested it was composed of a stream of particles—later called photons—while its ability to bend and spread around obstacles indicated it was instead a wave. The development of theories in electromagnetism and quantum physics reframed light as exhibiting properties of both waves and particles, known as the wave-particle duality. The variety of optical characteristics in different types of light (e.g., color) results from variations in the properties of waves and photons, such as frequency and energy.
The continuum of all electromagnetic radiation across these variations is known as the electromagnetic spectrum, which consists of radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. All electromagnetic radiation travels at 299,792,458 meters per second—one of the fundamental constants of the universe—in the absence of matter. However, differences in the properties of these bands make each useful for distinct applications, including telecommunications, food preparation, sterilization, medical imaging, and radiosurgery.Explore Light
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The air around lightning can be five times hotter than the sun's surfaceAt that temperature, lightning can almost instantly boil all the water in a tree, causing it to explode! But how is that kind of energy created, and how do humans survive lightning strikes? Click the title of this resource to find out. 1440Dizziness may describe lightheadedness and imbalance, not the spinning of vertigoDizziness is defined as an altered sense of spatial orientation, and may include feeling like you might fall over. Vertigo is associated with feeling like you are spinning or your surroundings are spinning. Cleveland ClinicLIghter-colored eyes have heightened risks for macular degenerationPeople with blue eyes appear to be at elevated risk of developing the disorder, perhaps because more light can penetrate their eyes. But the most significant modifiable factor heightening the risk for macular degeneration is smoking. Docs Who LiftIn LIGO's interferometers, light cancels itself out in the absence of gravitational wavesThe devices are designed so that a laser is split into two beams that later recombine, canceling each other out and producing no signal. Changes in the lengths of the arms due to passing gravitational waves result in an interference pattern whose properties reveal features of the objects that created the waves. SYFYBud Light was created to compete in the lower-calorie light beer marketArguably sparked by Miller Lite's successful 1975 launch, Anheuser-Busch rolled out Bud Light in 1982. The brand faced controversy in 2023 after a sponsorship deal with transgender influencer Dylan Mulvaney, sparking a Bud Light boycott. The Atlantic'Zeitgebers' like light are external cues for the circadian clockGerman for "time giver" or "time cues," common external zeitgebers include sunlight, food, and physical activity. The timing of these external influences can shift circadian clocks or lead to irregularities: A 2018 study, for example, found that later light exposure and meals were linked to later timing of peak activity and bedtimes. National Library of MedicineArtificial lighting and modern practices like working late are linked with sleep shiftsAn analysis of five adults participating in a German reality program that tasked them with living in a Stone-Age-like settlement for 2.5 months, provided some insights into how modern conditions may have shifted our circadian rhythms. The participants slept about 90 minutes more under these conditions, and went to bed earlier and rose earlier, raising questions about how circadian rhythms, sleep, and sleep quality are affected by modern lifestyles. Journal of Clinical Sleep MedicineEmulating Earth’s light-dark cycle is important for astronaut health and safetyAstronauts aboard the International Space Station experience 16 daily sunrises, but scientists have learned to try to promote circadian rhythms by phasing through several light settings aboard the ISS to improve astronauts’ sleep and productivity. NASAArtificial lightning can improve the yield of shiitake mushroom growersResearchers have found that shockwaves produced from lightning strikes homogenously break internal filaments called hyphae, transitioning the mushrooms from a vegetative growth to a fruiting phase. Repeated minor shocks near mushroom logs mimicked this effect. Physics WorldLightning may kill as many as 320 million trees each yearIgnoring the effects of tree loss resulting from lightning-induced wildfires, researchers at the Technical University of Munich developed a quantitative model to estimate the loss of these organisms due to cloud-to-ground strikes, based on global lightning data and forest structure. They expect the estimate to rise due to increased strikes resulting from climate change. Yale e360Lightning bolts are about as thick as a garden hoseThe conductive filament ranges from about 2.5 to 5.0 centimeters (1 to 2 inches), though its extreme brightness makes it appear much thicker and visible from miles away. Scars on individuals who suffer a direct strike produce Lichtenberg figures with similar maximum thickness. Stuff You Should KnowUnderstanding ball lightning remains an area of active researchObservations of glowing orbs of light that appear during or after thunderstorms have been documented since at least the 12th century, but their rarity and short lifetimes have made their study challenging. Some theories suggest they form when lightning vaporizes pockets of gases in the air or certain materials on the ground. Discover MagazineEvery day, lightning releases several Hiroshima bombs' worth of energy into the atmosphereIf all this lightning struck one location at once, the bolt would be the diameter of the center circle of a basketball court, turning the entire court into a crater. Its heat would ignite surfaces for miles around, and its shockwave would demolish buildings. xkcd's What If?Lightning rods provide a conductive pathway to safely steer massive electric currentsThe device is positioned higher above the ground to "catch" one of the many branching filaments of electrons from clouds before they make contact with other surface structures, which have been induced to have a positive charge by overhead storm clouds. The current is then sent to a conductive grid buried underground. How Stuff WorksBeing struck by lightning has a mortality rate of about 10%Near-immediate deaths are the result of electrical disruptions in the heart and nervous system, causing cardiac arrest, but severe skin burns, temporary paralysis, and blown eardrums are more common. About 74% of survivors are left with a long-term disability, which includes brain damage and changes in memory and mood. IFLScienceWatch lightning strike a building at 40,000 frames per secondWhen the built-up layer of negative charge at the bottom of clouds is sufficiently high, a network of charge filaments will emerge. If one of the filaments meets a rising strand of positively charged particles, a highly conductive path forms, and charges across all filaments move to the path, generating lightning AGULightning storms are more common in coastal and tropical regionsWater-abundant areas that receive increased solar radiation, such as those near the equator, experience increased rates of evaporation, which produce tall clouds as moisture rises, cools, and condenses. Mountain ranges can also steer air to higher altitudes, creating collisions between atmospheric particles that generate charge imbalances—the precursors to lightning. Ologies with Alie WardLightning forms when streams of rising and falling charged particles connectIn cloud-to-ground lightning, a buildup of negative charge at the bottom of clouds repels electrons on Earth's surface, leaving behind positively charged particles. When descending negatively charged air—the stepped leader—meets rising positively charged particles—the upward streamer—brightening runs up the connection, producing intense flashes known as return strokes. NOAAThe air around lightning can be five times hotter than the sun's surfaceThe rapid discharge of electricity—flowing electrons—between oppositely charged regions across a narrow filament can raise temperatures to 30,000 degrees Celsius (54,000 degrees Fahrenheit). If lightning strikes a tree, the speed of the temperature spike can almost immediately turn all its water into pressurized steam, causing it to explode. National Weather ServiceLightning results from the rapid flow of charges through the atmosphereLightning in storm clouds forms from the collisions between graupel—small hail particles—and smaller ice particles, which transfer electrons. Layers of opposing charges form as these differently sized particles rise and fall. When air can no longer insulate these layers, electricity discharges, equalizing these regions. NOAA SciJinksBright light therapy involves basking in 10,000 lux of light for 30 minutes each morningNothing is better than going outside and soaking up real sunlight. However, this is harder in winter, especially in very cold and cloudy regions. SAD lamps are designed to project 10,000 lux—a unit of illuminance, or how much light actually hits a surface (rather than how much is produced, like watts). This video discusses product options and practical considerations. New York TimesInfrared light is most often associated with thermal radiation and cooking foodAlthough extensively used in remote controls for electronics, where LED lights send signals wirelessly, infrared cameras allow for night vision and thermography—imaging of heat patterns in the body to non-invasively reveal blood flow for supplementary diagnostics. Infrared radiation also provides heat in toasters, saunas, and other technologies. Geeks For GeeksLight can 3D print objects within rotating cylinders of resinComputed axial lithography involves using light to project 2D computerized tomography, or CT, scans of a figure onto photo-sensitive resin, which solidifies upon exposure. As the images and the cylinder are spun at the same rate, the object is volumetrically fabricated an order of magnitude faster than layer-by-layer methods. Nature VideoStereolithography uses light to fabricate objects in layers via chemical reactionsSpecific locations in a tank of light-sensitive liquid resin are exposed to projected light, causing them to cure onto a build platform. The resulting cross-section of hardened plastic is moved slightly away from the light source, exposing it to resin once more, and the process repeats to produce successive layers. FormlabsThe reflection of light within a material is the basis for fiber opticsAs light travels from one material to another, it can be absorbed, reflected, or transmitted through, depending on the properties of the two materials. Fiber optic cables are designed to reflect light internally, minimizing data loss as information is sent at high speeds through flashes that represent zeros and ones. EngineerGuySolar sails use light as a means of propulsionPhotons possess momentum and can transfer it to objects they strike or bounce off, imparting radiative pressure, or a light-based force over a small surface area. Lasers fired at observational equipment with specially designed sails can theoretically use this mechanism to accelerate up to 20% the speed of light. Bloomberg OriginalsLight energy can be transformed into electricity in solar cells via the photovoltaic effectWhen light strikes semiconducting material, it can knock electrons out of atoms, creating a charge imbalance within the material. A wire connecting the oppositely charged regions can allow electrons to flow back, balancing the charges and producing an electric current that can be harnessed to power devices. The Engineering MindsetRayleigh scattering of light gives the atmosphere its blue skies and red sunsetsLight is deflected from its original path by atmospheric particles, where bluer light is scattered more than other colors. When the sun is at its highest point in the sky, it travels through the thinnest part of the atmosphere, scattering some blue light across the sky. A greater atmospheric path length at sunset scatters more colors, leaving only red, yellow, and orange. MinutePhysicsSpikes of light around stars are artifacts of light bending around the mirror supportsThrough diffraction, electromagnetic waves can bend around obstacles, as observed in the silver linings at the edges of clouds, where light should be blocked. Within reflecting telescopes, starlight diffracts around struts—beams holding a secondary mirror in place—and spreads perpendicular to them, creating pairs of spikes. Astronomy.comLight appears to slow down as it travels through different materialsAs electromagnetic waves interact with particles in a transparent medium, particles vibrate and generate their own electromagnetic waves. The interference of the original and generated waves, which are slightly delayed, results in ensemble light with an effective slower speed but unchanged color. Space.comLight waves can interfere and cancel each other outWhen light waves travel past one another, their peaks and valleys combine, just as overlapping ripples in water can combine to form a larger ripple. When the peak of a light wave meets the valley of another of the same wavelength and brightness, the waves combine to produce no light. VeritasiumWhen processing light, the brain can perceive colors with no natural wavelengthHumans possess receptors that are sensitive to the red, green, and blue wavelengths of light. These receptors send signals to the brain, which are processed and mixed to produce the array of colors we observe, including magenta, pink, and others that lack a corresponding natural wavelength in the visible spectrum. Emory UniversityProteins with limited light sensitivity prevent humans from seeing all types of lightSpecialized photoreceptor cells in the retina called cones each possess photopigments that activate when exposed to three ranges of visible light. Other forms of electromagnetic radiation outside the activation range do not generate signals for processing in the brain, thereby limiting average human vision to approximately 10 million colors. American Academy of OphthalmologyLight has been modeled as a wave and a stream of particles throughout historyIsaac Newton first identified white light as composed of a spectrum of colors, which he believed consisted of particles of different hues. Various light phenomena, including refraction, led Christiaan Huygens to develop an alternative wave model. Quantum mechanics validated both models through the concept of wave-particle duality. Be SmartLichtenberg figures capture lightning-like patterns within insulatorsWhen high-energy electrons from particle accelerators are fired into materials like acrylic, they form a charged plane before discharging into scarred patterns within the material. By evenly charging a cylindrical bottle through rotation during the irradiation process, a 3D figure of lightning in a bottle can be created. Electron ImpressionsBefore electric lights, Christmas trees were lit with real candlesThe practice of lighting Christmas trees with electricity didn’t begin until the late 1800s. Before that, families used wax candles on branches—a dangerous tradition that originated in 16th-century Germany. Its Red BananaLEDs emit pure colors, while incandescent bulbs filter white lightTraditional Christmas lights produce softer, less saturated colors by partially blocking the full spectrum of light, resulting in a particularly warm glow by dimming the cooler blue tones. LEDs are designed to emit a single wavelength of light, creating intense colors that are visually unbalanced in multicolor environments. Technology ConnectionsThrough gravitational redshift, light loses energy as it leaves a massive objectJust as one becomes exhausted as they walk up a flight of stairs against gravity, light is predicted to lose energy as it travels out of a gravitational well created by an object warping spacetime. This is observable through a decrease in the frequency of light toward longer, redder wavelengths. NASALight echoes are expanding shells of reflected starlightJust as sound waves reveal the location of obstacles by reflecting off them, pulses of light emitted by stars illuminate rings of interstellar dust, giving the appearance of ejected material as the light travels outward. NASA Science‘Guiding Light’ was the longest-running scripted drama in broadcast historyThe show ran for 72 years, starting as a radio program in 1937, and eventually transitioning to television in 1952. Along the way, it launched several Hollywood stars, like Kevin Bacon, James Earl Jones, and Christopher Walken. CBS canceled the show in 2009. NPRLight can be used to slow the motion of atomsWhile photons possess energy, they also have momentum, which allows them to collide with other particles, much like billiard balls, thereby slowing them down and reducing their kinetic energy, or temperature. Using multiple lasers from different directions, particles can be cooled to within one degree of absolute zero. Physics GirlThe scattering of light in the early universe prevents seeing the beginning of timeA "cosmic fog" of elementary particles in the early universe prevented light from traveling far before being absorbed. Only 380,000 years after the big bang, when the first atoms formed, was light free to travel and reach telescopes for study. UMBCWatch a lightning storm from the International Space StationWhile passing over the Alabama and Georgia regions, NASA astronauts photographed passing thunderstorms from the ISS. The illuminated clouds are described as "nebula-like formations." IFLScienceThe light sleep stages of the sleep cycleEach night as we sleep, we progress through a predictable pattern of brain activity known as the “sleep cycle.” The sleep cycle consists of four distinct parts, and the early portion of this cycle is often referred to as “light sleep.” This helpful page written by journalist Lisa L. Lewis helps clarify what exactly “light” sleep means and why it perhaps doesn’t get the credit it deserves. After all, we spend about half the night in this stage, which researchers have discovered is critical for memory consolidation and learning. Sleep.comLighting the menorah is viewed as the most important Hanukkah ritualThis short video guides viewers through the process, from the supplies required to the order in which the candles are lit. It also covers the prayers that are recited nightly and associated blessings for each individual night. HowcastLight pollution is giving oysters insomniaOysters, bivalve mollusks that have light-detecting cells along their skin, can't sleep with all this artificial light. According to a 2022 study, oysters' sleep cycles are disturbed by light dimmer than that provided by the full moon. As with humans, it's possible that these bouts of insomnia could have adverse health effects and contribute to the development of disease over time. Hakai MagazineX-rays shed light on how Pompeii victims really diedHistorians previously theorized that much of Pompeii was suffocated by the clouds of ash that plumed out of Mount Vesuvius in 79 CE. This article disputes recent claims the volcano's blast killed victims instantly, arguing instead the victims of Pompeii had a window of time between the destructive waves to escape, but were thwarted by falling ash. Noninvasive x-rays of plaster casts of seven bodies buried by the eruption suggest the victims had survived the first phase of the eruption. Science.orgElectrical discharge from stressed rocks may produce lightningAlthough flashes of light in the sky likely result from storms or damaged transformers and power lines coinciding with geological events, some scientists theorize that fracto-luminescence, or earthquake lights, may be caused by discharged built-up static electricity. NOVA PBS OfficialA planeterrella creates artificial auroras in a jarWithin the apparatus, a large metal sphere representing the sun and a smaller sphere representing the Earth are enclosed in a near vacuum. A voltage is established between the two, which draws electrons from the "sun" to the "Earth" to mimic solar wind. A magnet inside the smaller sphere funnels these particles to the poles, recreating auroras. University of LeicesterWatch seed shrimp escape being eaten by releasing bioluminescent chemicalsWhen caught in the mouths of cardinal fish, this type of ostracod releases luciferins and photoproteins to illuminate the fish's body quickly. Feared being seen by a larger predator, the cardinal fish releases the ostracod alongside the chemicals. NowScienceNews
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