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LightLight is a type of energy in the form of electromagnetic waves—vibrating electric and magnetic fields that travel perpendicular to one another. Everything in the universe emits light, which can reflect off objects or be collected and processed by biological and computer systems to make observations, identify surroundings, and produce data. Historically, observations of reflected light 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 theories of electromagnetism and quantum physics reframed light as exhibiting properties of both waves and particles, a phenomenon known as the wave-particle duality. The variety of optical characteristics across different types of light (e.g., color) results from variations in wave and photon properties, 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. 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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Light therapy was widely used as a medical treatment for various maladies in the early 1900s before it was replaced by antibiotics. The Nobel PrizeHigh-powered red light therapy—delivered directly to nerve fibers via a fiber optic needle—has been used in recent experimental research to suppress pain. NatureCertain visible light therapies, when applied at specific intensities, can be used to treat skin conditions, including acne. Mayo ClinicUnits involving light, such as light-seconds and light-years, describe the distances traveled by light across that amount of time. NASA Solar SystemRed light therapy—a treatment harnessing a specific form of energy that penetrates the top layers of skin—is marketed for skincare and wellness, but has its roots in NASA plant growth research. Health vs. HypeThe flashing green light on a smartwatch estimates a person's heart rate by measuring the amount of light reflected back to the watch as blood vessels expand and contract. Royal Society of ChemistryLight takes approximately eight minutes to travel from the sun's surface to Earth, but it takes thousands of years to reach the star's surface from its core—a distance more than 200 times shorter. TED-EdBeing near a lightning strike—even without getting struck—can be fatalBecause animal tissue is generally more conductive than soil, electricity moving along Earth's surface after a strike tends to travel up and back down an animal's legs, discharging dangerous amounts of energy along the way, with risks increasing the farther apart the legs are. This ground current accounts for about half of all lightning-related deaths and injuries in humans. SciShowDizziness 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 ClinicIn 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 WorksWatch 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. NOAALightning is the sudden flow of electricity in the atmosphere as two oppositely charged regions seek to become balanced via the movement of electrons. 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 GeeksStereolithography 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. FormlabsSpikes 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 wavelengthWhile some animals are sensitive to many forms of light, humans possess receptors that are sensitive to red, green, and blue wavelengths. These receptors send signals to the brain, which are processed and mixed to produce the array of colors we observe, including magenta, pink, and "supercolors" that lack a corresponding natural wavelength in the visible spectrum. Emory UniversityLight 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 SmartBefore 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 BananaThrough 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 ScienceChris Lighty represented some of New York's biggest rappers Lighty founded Violator—a record label and management firm—in 1996 and went on to represent Busta Rhymes, A Tribe Called Quest, Nas, 50 Cent and others. In 2012, he was found dead on the patio of his apartment. The death was ruled a suicide, though many close to Lighty believed otherwise. Mogul‘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. NPRAir sacs and lightweight bones helped some dinosaurs grow to enormous sizesAfter the Triassic extinctions, new species with birdlike anatomy evolved from smaller, early dinosaurs. This anatomy allowed for more efficient breathing and lighter skeletons, favoring the evolution of larger organisms. Insider ScienceMelanin and light scattering contribute to different eye colorsBrown eyes have high melanin, while blue eyes have low melanin. Multiple genes contribute to eye color, which can change over time due to melanin buildup. Hazel eyes can shift color depending on ambient light. ScienceAlertDirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.Humans have always been fascinated by volcanoes. One of the most stunning phenomena that occurs is volcanic lightning. Understand the science behind it! AccuWeatherJust as light bends at different angles as it travels through different materials, seismic waves move in different directions through Earth's interior, revealing the presence of layers with varying properties.It is pretty amazing how much we know about the Earth’s interior, given that we can only directly observe a tiny fraction of it. Due to our lack of access to the Earth’s interior, scientists must rely on indirect observations. One way they do this is by studying the movement of pressure waves as they travel through the interior of the Earth. SciencePrimerThe 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. UMBCBioluminescence produces new light while biofluorescence re-emits absorbed lightA chemical reaction between luciferin and oxygen—catalyzed by luciferase—produces light within bioluminescent organisms. Biofluorescence, on the other hand, involves special proteins that absorb light of one wavelength and re-emit the light at a different, typically longer, wavelength. IFLScienceFireflies light up to provide mating signals and warnings to predatorsVariations in the illumination patterns and flight paths while emitting light have been observed across firefly species. Some species instead rely on pheromones if they are primarily active during the day or have lost the ability to illuminate. Science FridayBy separating light with tools such as prisms, scientists can reveal the presence and composition of celestial matter by identifying color fingerprints unique to specific elements and molecules.By separating the light spectrum into its component wavelengths and comparing them to what is expected based on Earth-based experiments, we can determine an object's temperature, elemental and molecular composition, and motion through space. NASA GoddardWatch 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." IFLScienceHubble's first light test produced an underwhelming photographThis test represents the first time light travels entirely through an observatory's optical system and reaches its detectors, producing an image. Although the telescope's warped mirror was not discovered and announced until a month after first light, the issue was not responsible for the simplicity of the first light image. TIMELighting 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 MagazineTrack lightning strikes around the worldThe Blitzortung platform triangulates the positions of this phenomenon from stations that detect atmospheric interference in low-frequency signals that are characteristic of lightning strikes. A network of nearly 2,000 stations transmits the required data to a central server, where its software performs these calculations and generates the subsequent visualization. Blitzortung.org
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