How Do Metal Halide Bulbs Work?
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Fundamentals
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A metal halide bulb functions similarly to other gas discharge fixtures. The light is produced from an electric current being passed through gases. In this case, the gases through which the electricity passes are halides. A halide is a compound of a halogen atom (flourine, chloride, bromine, iodine and astatine) and another element. These bulbs run at around 25 percent efficiency, meaning that they use 25 percent of the energy intake for the actual light production.
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Emission of Light
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A metal halide bulb must have a mixture of a halide, mercury and argon gases to run. Two electrodes are on the side of the gas mixture. These electrodes are used to send an electric arc through the gas mixture. As a note, the gas is at high pressure, which means that it must be kept inside a tube that is separate from and stronger than the outer glass casing, which is meant simply to block the dangerous UV rays emitted by these lights. The actual process of making light in the lamp takes some time. As the electrodes activate, the argon gas sparks first, allowing the arc to generate heat. This heat from the arc of electricity flowing through the argon in the gas mixture vaporizes the mercury and halide gases, which create light and heat.
Electricity
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The first arc sent across the gas mixture must be of sufficiently high voltage to create the argon spark. This high voltage is directed, in most cases, by a chip that regulates the voltage. The reason this electricity creates light in the gas mixture is that the energy from the voltage energizes the electrons in the atoms of the gas. As the electrons jump up in energy, they naturally jump back down toward the nucleus of their atoms, which releases light energy in the form of photons.
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