First successful low intensity discharge mercury vapor lamps was invented in by an American engineer Peter Cooper Hewitt , but the first HID mercury lamp was developed later, in Higher pressure inside the bulb helps to increase the efficiency of the lamp and also decreases its dimensions.
The lamp creates light by producing an arc between two electrodes through vaporized mercury in a high pressure tube made from fused quartz. Because the lamp operates at a high pressure, it can produce light directly from the arc.
The discharge tube is covered by a larger glass bulb which is serving the purpose of insulating the heat inside the tube for better performance and protecting everything outside the bulb from ultraviolet radiation. The outer bulb can be either clear or coated with a phosphor cover to improve the color rendering of the lamp. Adding a phosphor coating to the outer bulb improves the color rendering and makes color of objects in the light to appear more natural.
High intensity mercury vapor lamps were mostly used as a street lighting in early days, but have been widely replaced by sodium vapor lights or recently by led flood lights. Because of the long life span of up to hours and high intensity, these lights were also used to illuminate large indoor areas such as factories, arenas, warehouses and similar.
Today, other types of HID lights such as sodium vapor and metal halide and also LED lights have replaced the older mercury vapor lamps in most applications due to higher efficiency, better color rendering, increased durability and safety, and longer life span. However, mercury vapor bulbs are still used in applications such a landscape lighting, parking lot lighting and in security lighting. Mercury vapor lamps illuminating.
The arc tube of a mercury vapor lamp is made from fused quartz glass that can withstand extremely high temperatures. Inside the arc tube are two main electrodes made from tungsten, and near the main electrode that is located closer to the ballast is a starting electrode used to start the arc, it is connected to the other main electrode through a resistor.
Starting electrode helps to reduce the amount of voltage the lamp requires to start. The arc tube is filled with argon gas that is ionised to create arc and solid mercury that gets heated and vaporizes as the pressure and heat inside the tube increases. The argon gas strikes quickly but it can take few minutes until the mercury vaporizes and produces intense light in a bluish color.
The outer bulb that protects the inner parts is made from a borosilicate glass and may be coated with a fluorescent coating to improve the color rendering of the lamp. Ballast is used to limit the current passed to the arc and prevent lamp from breaking. Mercury vapor lamp construction. Source — eyelighting. First stable metal halide bulbs that could stand higher operating temperatures were invented in early s by Robert Reiling who improved the previous experiments of Charles P.
Later, metal halide lamps became one of the main artificial lighting sources to be used for illuminating large areas both indoors and outdoors. As metal halide lamps basically originated from mercury vapor bulbs, the construction and in some ways also their looks are pretty similar to mercury vapor lamps.
Metal halide lamps are high pressure discharge lamps that produce light by creating an electric arc through vaporized mercury similar to mercury vapor lamps and metal halides such as silver iodide, silver bromide sodium iodide and others. These metal halides help to achieve higher light output, better efficiency and improve color rendering, making MH lamps in many ways superior to mercury vapor lamps.
The metal halide bulb consists of a compact arc tube located inside a larger glass bulb. The arc tube itself is made from fused quartz to withstand the high operational temperatures created from the high pressure up to 50 and more psi inside the arc tube.
Inside the arc tube there is a mixture of argon gas, mercury and halide salts. At first, the discharge happens through the gas till the tube heats enough for mercury to vaporize. While mercury vaporizes the temperature inside the tube keeps building until all metal salts inside the tube vaporizes too, each giving off a different color.
The combination of these colors makes the metal halide lamps produce intense, white light at color temperatures around K. Metal halide lamps are almost twice as efficient as mercury vapor lamps , but not as efficient as high pressure sodium lights.
A watt metal halide bulb will produce around lumens, while the same wattage HPS lamp can produce up to lumens. However, metal halide lamps have the shortest lifespan of high intensity discharge lamps , loosing to both mercury vapor and HPS lamps. On average, the lifespan of a metal halide lamp is from to hours. Because of such advantages as good color rendition, production of very clean, white light and high lumen output, metal halide lamps are used in large variety of applications both indoors and outdoors.
Here are some of the most common uses of metal halide lamps:. Metal halide lamps illuminating. The structure of a metal halide lamp consists of a small arc tube made either from quartz or sintered alumina ceramic, inside of the arc tube contains a gas, mercury and metal halides.
The discharge tube is enclosed inside a larger bulb made from glass, similar to mercury vapor bulbs, which protects the smaller parts from outer impacts and helps to keep more heat inside the bulb, as well as can be used to block ultraviolet radiation generated inside the lamp. The discharge arc tube has both ends sealed with two main electrodes made from tungsten residing at both ends.
Next to one of the main electrodes is a starting electrode and resistors used to start the lamp. Ends of most metal halide bulbs are coated with ceramic to reflect the heat back to the lamp and keep the arc at a specific temperature needed for halide salts to vaporise.
Keeping a higher temperature inside the arc tube allows the lamp to be brighter, more efficient and also improves the color rendering. Metal halide, similar to other high intensity discharge bulbs, require electric ballasts to operate safely.
The light in metal halide lamps are generated through a high pressure gas discharge inside the arc tube, this process happens between two tungsten electrodes on each side of the arc tube. The discharge arc is generated through the argon gas in most lamps , so it must be made conductive by a process called ignition, when high-voltage pulses are generated by an ignition device. When the lamp starts through the argon gas, the tube is still cold, so the lamp is very dim and produces blue color.
When the lamp heats up, the mercury slowly starts to vaporize making the arc produce brighter and more intense light and at the same time reducing the size of the arc. When enough heat is generated inside the arc tube, the various halide salts start to vaporize too, each producing a different color from white to green and yellow.
In combination with the blue color of mecrury and various colors of halide salts, the lamp starts to shifts its color from blue to white. All this process requires some time usually few minutes for mercury and all halide salts to fully vaporize and for the lamp to reach its full brightness. This process is called warm-up period. When a metal halide lamp reaches the end of its lifespan, it starts to change the color of the light, the brightness of the light reduces and lamp starts to go off after some period of illumination till it cannot be ignited at all.
High pressure sodium lamps are type of gas discharge lamps that produce light using sodium in an excited state. There are two types of sodium vapor lamps — high pressure and low pressure. While low pressure sodium vapor lamps are known for their high energy efficiency and monochromatic light output, in this section we are going to look the second type of sodium vapor lamps — high pressure sodium vapor lamp.
The first low pressure sodium vapor lamp was introduced in early s and while it had its advantages over other existing lighting sources, such as high efficacy, there were also some problems with these lights, such as lower brightness and very narrow light spectrum, producing an intense yellow color which made them pretty much useless for indoor and outdoor lighting where color rendering is very important.
When the first low pressure sodium lamp was introduced, it was known that by increasing the pressure inside the arc tube, a bulb with improved energy efficiency and color rendering could be achieved. Few years after this invention the first practical high pressure sodium vapor lamp was introduced by GE.
High pressure sodium lamps differ from other types of high intensity discharge lamps as they contain a mixture of xenon and sodium-mercury amalgam, which gives the lamp its orangish glow. The arc tube is made from a translucent ceramic material that can withstand high chemical activity and extremely high temperatures up to thousand degrees celsius over degrees fahrenheit. Xenon is used as the starter gas until it warms up the arc tube for mercury to vaporize, and while it vaporizes, the temperature inside the tube continues to build until the sodium starts to vaporize too, shifting the color of the lamp to more orangish.
The color of different HPS lamps can vary depending on the brand of the bulb. Because of such advantages as high efficacy and relatively long life span, these lamps are used in variety of applications , such as:. An arc is created with an initial surge of electricity, facilitated by the gas in the lamp. The arc then heats the metal salts, and a plasma is created. This increases considerably the light produced by the arc, resulting in a source of light which is more efficient at creating visible light instead of heat than many traditional technologies such as incandescent or halogen lamps.
Generally speaking, HID lamps are used primarily in applications where the most critical factor is creating as much visible light per watt as possible. Major applications include streetlights, gymnasiums, warehouses, large retail facilities, and stadiums, and plant growing rooms. Recently, these lamps have also been used in some high-end vehicle headlights. Also, some HID bulbs require an extended warm up time and are not suitable for applications where lights are turned on and off on a regular basis.
Skip to content. Account Sign In. In low-pressure discharge lamps, the working pressure is much less than the atmospheric pressure. Like the fluorescent lamps, and the sodium lamps. They produce lumens per watt. One advantage of low-pressure discharge is they have a long life span.
The low-pressure discharge lamps require the ballast to create a high voltage. Ballasts fundamentally work on the principle of inductance. With increase. The working pressure of these lamps is much higher than the atmospheric pressure. Different categories are there in high-pressure discharge lamps such as metal halide lamps, high-pressure sodium lamps, and high-pressure sodium mercury lamps.
The high-intensity discharge lamps are very efficient as compared to pressure based discharge lamps. They have a long life span and can save a lot amount of energy. The high-intensity lamps use an arc array to produce intense light. For this they need high voltage, i. The ballast helps to build up the high voltage. For this reason, when turned on, the high-intensity lamps take up to ten minutes to reach peak value. The high-pressure mercury vapor lamp, metal halide lamps, and high-pressure sodium lamps are some of the examples of high-intensity lamps.
We shall see the high-intensity discharge lamps for this case.
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