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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.
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.
Metal-halide and ceramic metal-halide lamps can be made to give off neutral white light useful for applications where normal color appearance is critical, such as TV and movie production, indoor or nighttime sports games, automotive headlamps, and aquarium lighting. Low-pressure sodium-vapor lamps are extremely efficient.
These lamps are advantageous over other lamps such as mercury and metal halide lamps because low-pressure sodium lamps emit lower intensity, monochromatic light. Observatories can filter the sodium wavelength out of their observations and virtually eliminate the interference from nearby urban lighting.
A street lamp mounted on a bracket and column A high pressure sodium street light fixture. Street light interference, sometimes called high voltage syndrome, is the claimed ability of individuals to turn street lights or outside building security lights on or off when passing near them. [1]
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]
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]
Additionally, various colors are used to identify what type of lamp the fixture uses. A yellow sticker indicates the lamp is a sodium vapor lamp (HPS/LPS). A blue sticker indicates the lamp is mercury vapor (MV). A red sticker indicates the lamp is metal halide (MH). A sticker that is half-red and half-white indicates a pulse start metal halide ...