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Art Gallery Lighting Definition

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Lightning is a massive electrostatic discharge between electrically charged regions within clouds, or between a cloud and the Earth's surface. The charged regions within the atmosphere temporarily equalize themselves through a lightning flash, commonly referred to as a strike if it hits an object on the ground. There are three primary types; from a cloud to itself (intra-cloud or IC); from one cloud to another cloud (CC) and finally between a cloud and the ground (CG). Although lightning is always accompanied by the sound of thunder, distant lightning may be seen but be too far away for the thunder to be heard.Lightning occurs approximately 40–50 times a second worldwide, resulting in nearly 1.4 billion flashes per year.Many factors affect the frequency, distribution, strength, and physical properties of a "typical" lightning flash to a particular region of the world. These factors include ground elevation, latitude, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC, CC and CG lightning may also vary by season in middle latitudes.Sound of a thunderstormHigh-speed, slow-motion lightning video captured with a Phantom v12.1 camera at 6,200 frames per second.Because human beings are terrestrial and most of their possessions are on the Earth, where lightning can damage or destroy them, CG lightning is the most studied and best understood of the three types, even though IC and CC are more common. Lightning's relative unpredictability limits a complete explanation of how or why it occurs, even after hundreds of years of scientific investigation. A typical cloud to ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 km (3 mi) tall, from within the cloud to the ground's surface. The actual discharge is the final stage of a very complex process.[2] A typical thunderstorm has three or more strikes to the Earth per minute at its peak.Four-second video of a lightning strike, Island in the Sky, Canyonlands National Park, Utah, United States.Lightning primarily occurs when warm air is mixed with colder air masses resulting in atmospheric disturbances necessary for polarizing the atmosphere. However, it can also occur during dust storms, forest fires, tornadoes, volcanic eruptions, and even in the cold of winter, where the lightning is known as thundersnow.[4][5] Hurricanes typically generate some lightning, mainly in the rainbands as much as 160 km (100 mi) from the center.The science of lightning is called fulminology. The fear of lightning is called astraphobia.Lightning is not distributed evenly around the planet, as seen in the image on the right.About 70% of lightning occurs over land in the tropics where atmospheric convection is the greatest. This occurs from both the mixture of warmer and colder air masses, as well as differences in moisture concentrations, and it generally happens at the boundaries between them. The flow of warm ocean currents past drier land masses, such as the Gulf Stream, partially explains the elevated frequency of lightning in the Southeast United States. Because the influence of small or absent land masses in the vast stretches of the world's oceans limits the differences between these variants in the atmosphere, lightning is notably less frequent there than over larger landforms. The North and South Poles are limited in their coverage of thunderstorms and therefore result in areas with the least amount of lightning.In general, cloud-to-ground (CG) lightning flashes account for only 25% of all total lightning flashes worldwide. Since the base of a thunderstorm is usually negatively charged, this is where most CG lightning originates. This region is typically at the elevation where freezing occurs within the cloud. Freezing, combined with collisions between ice and water, appears to be a critical part of the initial charge development and separation process. During wind-driven collisions, ice crystals tend to develop a positive charge, while a heavier, slushy mixture of ice and water (called graupel) develops a negative charge. Updrafts within a storm cloud separate the lighter ice crystals from the heavier graupel, causing the top region of the cloud to accumulate a positive space charge while the lower level accumulates a negative space charge.Because the concentrated charge within the cloud must exceed the insulating properties of air and this increases proportionally to the distance between the cloud and the ground, the proportion of CG strikes (versus cloud-to-cloud (CC) or in-cloud (IC) discharges) becomes greater when the cloud is closer to the ground. In the tropics, where the freezing level is generally higher in the atmosphere, only 10% of lightning flashes are CG. At the latitude of Norway (around 60° North latitude), where the freezing elevation is lower, 50% of lightning is CG.[9][10]Lightning is usually produced by cumulonimbus clouds, which have bases that are typically 1-2 km (0.6-1.25 miles) above the ground and tops up to 15 km (9.3 mi) in height.On Earth, the place where lightning occurs most often is near the small village of Kifuka in the mountains of the eastern Democratic Republic of the Congo,[11] where the elevation is around 975 m (3,200 ft). On average, this region receives 158 lightning strikes per 1 square kilometer (0.39 sq mi) per year. Other lightning hotspots include Catatumbo lightning in Venezuela, Singapore,Teresina in northern Brazil,[14] and "Lightning Alley" in Central Florida.