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Security lighting to prevent intrusions may be counter-productive. Turning off lights halved the number of thefts and burglary in Övertorneå Sweden. [2] [3] A test in West Sussex UK showed that adding all-night lighting in some areas made people there feel safer, although crime rates increased 55% in those areas compared to control areas and to the county as a whole.
The most common type of floodlight was the metal-halide lamp, which emits a bright white light (typically 75–100 lumens/Watt). Sodium-vapor lamps are also commonly used for sporting events, as they have a very high lumen to watt ratio (typically 80–140 lumens/Watt), making them a cost-effective choice when certain lux levels must be provided. [4]
An emergency light is a battery-backed lighting device that switches on automatically when a building experiences a power outage. In the United States, emergency lights are standard in new commercial and high occupancy residential buildings, such as college dormitories, apartments, and hotels.
The next major drop in price came about in the 1880s with the introduction of electric lighting in the form of arc lights for large space and street lighting, followed by incandescent light bulb-based utilities for indoor and outdoor lighting. [3] [5] Over time, electric lighting became ubiquitous in developed countries. [6]
Like other gas-discharge lamps such as the very-similar mercury-vapor lamps, metal-halide lamps produce light by ionizing a mixture of gases in an electric arc.In a metal-halide lamp, the compact arc tube contains a mixture of argon or xenon, mercury, and a variety of metal halides, such as sodium iodide and scandium iodide. [7]
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