Discharge Lamps
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DISCHARGE LAMPS Discharge Lamps are lamps which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. Characteristics They often take a few moments to turn on They come in a variety of colors, including white They are often whiter than incandescent bulbs They last longer than incandescent bulbs They sometimes hum loudly They flicker before they fail completely Low-Pressure Discharge Lamps Mercury gas has its resonance line in the UV Low-pressure mercury lamps emit mostly UV light Some gases have resonance lines in the visible Low-pressure sodium vapor discharge lamps Emit sodium’s yellow-orange resonance light, So they are highly energy efficient But extremely monochromatic and hard on the eyes. High-Pressure Discharge Lamps At higher pressures, new spectral lines appear
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Transcript of Discharge Lamps
DISCHARGE LAMPS
Discharge Lamps are lamps which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube.
Characteristics
They often take a few moments to turn on They come in a variety of colors, including white They are often whiter than incandescent bulbs They last longer than incandescent bulbs They sometimes hum loudly They flicker before they fail completely
Low-Pressure Discharge Lamps
Mercury gas has its resonance line in the UV
Low-pressure mercury lamps emit mostly UV light
Some gases have resonance lines in the visible
Low-pressure sodium vapor discharge lamps
Emit sodium’s yellow-orange resonance light, So they are highly energy efficient But extremely monochromatic and hard on the eyes.
High-Pressure Discharge Lamps
At higher pressures, new spectral lines appear
High-pressure sodium vapor discharge lamps
Emit a richer spectrum of yellow-orange colors, are still quite energy efficient, But are less monochromatic and easier on the eyes.
High-pressure mercury discharge lamps
Emit a rich, bluish-white spectrum, With good energy efficiency. Adding metal-halides adds red to improve whiteness.
High Intensity Discharge (HID) Lamps
-Diagram of high intensity sodium lamp-
Types of HIDs
Mercury Vapor (obsolete)
Sodium Vapor
High pressure Low pressure
Metal Halide
Arc tube contains argon, mercury, and metal halides. Gives better color temperature and CRI. Most common HID used today.
ADVANTAGES
Discharge lamps produce more light, less heat
Take a few minute to turn on.
Long lasting than incandescent bulbs
Low-pressure sodium vapor lamps are extremely efficient.
Mercury lamp can produce a bluish-green light, but more recent versions can produce light with a less pronounced color tint.
High-intensity discharge lamps make more visible light per unit ofElectric power consumed than fluorescent and incandescent lamps.
Metal halide and ceramic metal halide lamps can be made to give off neutral white light useful for applications
Disadvantages
Toxic mercury is present in HID. Isotopes in lamp produces alpha and beta radiation which causes
high ionization inside. But the radiations cannot escape from the lamp. The amount of gamma radiation produced by the isotopes that can
escape from the lamp is negligible.
