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A high-pressure sodium street light in Toronto A high-pressure sodium-vapor lamp An HPS lamp that isn't entirely off. A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm. Two varieties of such lamps exist: low pressure and high pressure.
Metal-halide (MH) lamps; Ceramic MH lamps; Sodium-vapor lamps; Xenon short-arc lamps; The light-producing element of these lamp types is a well-stabilized arc discharge contained within a refractory envelope arc tube with wall loading in excess of 3 watts per square centimetre (19 W/in 2). Mercury-vapor lamps were the first commercially ...
High-pressure lamps have a discharge that takes place in gas under slightly less to greater than atmospheric pressure. For example, a high pressure sodium lamp has an arc tube under 100 to 200 torr pressure, about 14% to 28% of atmospheric pressure; some automotive HID headlamps have up to 50 bar or fifty times atmospheric pressure.
Meanwhile, high-pressure sodium vapor lamps cost only $44 a year to operate, with a standard life expectancy of 15,000 hours, which also helped to lower labor and maintenance costs. [1] According to the Edison Tech Center, sodium vapor lamps are "the most ubiquitous lamp for street lighting on the planet." [17]
While most high-mast lights are high-pressure sodium, other lamp types such as mercury vapor, metal halide and LED, have also been used. Some units have the lighting surrounded by a circular shield to prevent or reduce light pollution or light trespass from affecting neighborhoods adjacent to the highway.
After warming up, when the volatile compound used for light emission is vaporized and the pressure increases, reignition of the discharge requires either significantly higher voltage or reducing the internal pressure by cooling down the lamp. [7] For example, many sodium vapor lamps cannot be re-lit immediately after being shut off; they must ...
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