Operation
Like other gas-discharge lamps such as the very-similar mercury-vapor lamps, metal-halide lamps produce light by making an electric arc in a mixture of gases. In a metal-halide lamp, the compact arc tube contains a high-pressure mixture of argon or xenon, mercury, and a variety of metal halides, such as sodium iodide and scandium iodide,. The particular mixture of halides influences the correlated color temperature and intensity (making the light bluer, or redder, for example). The argon gas in the lamp is easily ionized, which facilitates striking the arc across the two electrodes when voltage is first applied to the lamp. The heat generated by the arc then vaporizes the mercury and metal halides, which produce light as the temperature and pressure increases.
Common operating conditions inside the arc tube are 5-50 atm or more (70–700 psi or 500-5000 kPa) and 1000-3000 °C. Like all other gas-discharge lamps, metal-halide lamps, with the rare exception of self-ballasted lamps with a filament, require auxiliary equipment to provide proper starting and operating voltages and regulate the current flow in the lamp. About 24% of the energy used by metal-halide lamps produces light (an efficacy of 65–115 lm/W), making them substantially more efficient than incandescent bulbs, which typically have efficiencies in the range 2-4%.
Read more about this topic: Metal-halide Lamp
Famous quotes containing the word operation:
“An absolute can only be given in an intuition, while all the rest has to do with analysis. We call intuition here the sympathy by which one is transported into the interior of an object in order to coincide with what there is unique and consequently inexpressible in it. Analysis, on the contrary, is the operation which reduces the object to elements already known.”
—Henri Bergson (1859–1941)
“It is critical vision alone which can mitigate the unimpeded operation of the automatic.”
—Marshall McLuhan (1911–1980)
“Waiting for the race to become official, he began to feel as if he had as much effect on the final outcome of the operation as a single piece of a jumbo jigsaw puzzle has to its predetermined final design. Only the addition of the missing fragments of the puzzle would reveal if the picture was as he guessed it would be.”
—Stanley Kubrick (b. 1928)