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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. Low-pressure sodium lamps are highly efficient electrical light sources, but their yellow light restricts applications to outdoor ...
Diagram of a high-pressure sodium lamp A high-pressure sodium lamp, Philips Master SDW-T 100W. Various types of chemistry are used in the arc tubes of HID lamps, depending on the desired characteristics of light intensity, correlated color temperature, color rendering index (CRI), energy efficiency, and lifespan. Varieties of HID lamp include:
Compared to other lamp types, relatively high arc power exists for the arc length. Examples of HID lamps include mercury-vapor lamps, metal halide lamps, ceramic discharge metal halide lamps, sodium vapor lamps and xenon arc lamps. HID lamps are typically used when high levels of light and energy efficiency are desired.
The sodium atoms get excited due to photons from the sodium vapour lamp, with electrons excited from 3s to 3p states, absorbing light in the process. The sodium vapour lamp emits light at 589nm, which has precisely the energy to excite an electron of a sodium atom. If it was an atom of another element, like chlorine, shadow will not be formed.
A gas-discharge lamp is an electric light using a gas-filled tube; these include fluorescent lamps, metal-halide lamps, sodium-vapor lamps, and neon lights. Specialized gas-filled tubes such as krytrons, thyratrons, and ignitrons are used as switching devices in electric devices.
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English: Diagram of a high pressure sodium vapor lamp. Date: 20 December 2006: Source: ... Description=Diagram of a high pressure [[sodium vapor lamp]] ...
The neon gas used in some nixie tubes includes a small amount of mercury vapor (for various reasons), which glows blue. A Penning mixture of neon and argon is also used as a starter gas in sodium vapor lamps, where it is responsible for the faint pinkish glow before the sodium emission begins.