Metal halide lamps (MGL) are high-power lighting sources with relatively low power consumption. Such devices are a type of high-pressure gas discharge elements. The formation of the light flux occurs in the plasma of the arc discharge due to the fact that inside the flask there are halides of certain metals.
How does the metal halide lamp work?
The main component of a metal halide lamp is a burner. This discharge vessel, made of quartz glass, emits harmful ultraviolet radiation. For its detention the external flask in which the torch is located is used.
Another purpose of this outer shell is to reduce heat loss. An external flask is made of resistant borosilicate glass. Also inside this element are mercury vapor and electrodes that create an arc discharge.
How does metal halide lamp work?
MGL is filled with halides - special additives in the form of inert gases. As emitting components, complex compounds of cesium, rare-earth metals and tin are used. It is precisely as a result of electrical discharges in metal vapor that luminescence occurs. Depending on the content of an inert gas inside the burner, the value of the metal halide lamp is established.
If the lighting element is in an inoperative state, radiating additives are deposited on the walls of the discharge flask. When the metal halide lamp turns on, the burner surface is heated. As a result, the deposited chemical elements begin to evaporate and fall into the zone of action of the arc discharge that has arisen between the electrodes. Here, the halides are affected by heat, and they break down into ions. Due to the excitation of metal particles and luminescence is formed.
Classification of metal halide lamps
Metal halide lamps can be classified depending on the power, radiation color, design and type of base.
The power of light sources can be as follows: 20, 35, 50, 70, 150, 250, 400, 700, 1000, 2000 and 3500 watts. Each of these lamps needs its own power supply voltage. Elements with a capacity of 2000 and 3500 W require 380 V to operate. And all other sources of illumination, for example, a metal-halide lamp 400 W, are connected to a network with a voltage of 220 V.
The chromaticity index of the radiation of light sources varies from warm white at 3000 K to daylight at 6500 K. There are also colored metal halide lamps of the following shades: blue, green, orange and magenta.
According to their design, these lighting elements can be baseless, single-base and two-base (soffit).
The type of base can be as follows:
- E27 and E40. Standard threaded shape for lighting elements with power from 250 to 2000W.
- G8.5 and G12. Used for light sources of low power, which, for example, is a metal halide lamp 70W.
- RX7s. It is used in lighting elements with two bases.
Connection of metal halide lamps
The metal halide lamp is not able to work if it is connected directly to the power system. In order for such a light source to function properly, it is necessary to use a special ballast and a pulsing incendiary device, because the lighting element is operated from alternating current. The high-voltage discharge can be provided with an electronic or electromagnetic control gear.The first option is preferable, because when it is used, the life of the lamp increases, the emitted light is more even, the current is significantly reduced during start-up and operation.
The advantages of metal halide lamps
Such lighting elements have the following advantages:
- Long service life. The average value of this indicator varies from 6000 to 8000 hours. Maximum service life can reach 15,000 hours. This advantage is achieved through the use of halides.
- Large range of chromaticity emission indicator. The value of this characteristic varies from 3000 K to 6500 K. This makes it possible to bring the lighting as close as possible to the natural one. The radiation spectrum can be both cold, whitish, and warm, pleasantly yellowish.
- Economic benefits. The metal halide lamp is about five times more efficient than a traditional incandescent filament source.
- Greater light intensity. For an equivalent replacement of a filament lamp with a filament of 600W, a metal halide lamp 150W can be used, which will provide similar illumination. At the same time, substantial energy savings are evident.
- Compact size. The small dimensions of the metal-halide light sources greatly expand their field of application.
Disadvantages of metal halide lamps
The main disadvantages of these light sources include the following:
- Significant heat dissipation. In this regard, it is recommended to install metal-halide lamps at a certain height, and the more powerful the lamp, the greater this value.
- Long ignition time. Lamps of low power need about three minutes to achieve maximum brightness, and light sources with a higher rate need about ten minutes to do this.
- The impossibility of dimming. Metal halide lamps are not designed for dimming lighting.
- High price. Good light sources are expensive in comparison with traditional incandescent bulbs, but replacing them with a suitable quality and lower price is difficult to find.
Metal halide lamps provide high-quality lighting and have good color reproduction. Due to this, their field of application is extensive. Such lamps are used to illuminate both open and closed sports facilities, stadiums, industrial buildings, concert halls. They are also used in shopping centers, hotels, restaurants, schools, offices and for architectural highlighting of buildings.