Metal halide lamps (MFL) 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 an arc discharge plasma due to the fact that there are halides of certain metals inside the bulb.
How is the metal halide lamp arranged?
The main component of the metal halide lamp is a burner. This discharge vessel, made of quartz glass, emits harmful ultraviolet radiation during operation. To detain it, an external bulb is used, inside which the burner is located.
Another purpose of this outer shell is to reduce heat losses. An external bulb made of stable borosilicate glass is produced. Also inside this element are pairs of mercury and electrodes, creating an arc discharge.
Principles of metal halide lamp operation
MGF are filled with halides - special additives in the form of inert gases. The radiating components are complex compounds of cesium, rare earth metals and tin. It is as a result of the appearance of electrical discharges in the vapors of the metal that a glow occurs. Depending on the content of this or that inert gas inside the burner, the metal halide lamp is installed.
If the lighting element is in an idle state, the radiating additives settle on the walls of the discharge bulb. When the metal halide lamp is turned on, the burner surface is heated. As a result, the settled chemical elements begin to evaporate and fall into the zone of action of the arc discharge that arises between the electrodes. Here, the halogenides are affected by high temperatures, and they break up into ions. As a result of the excitation of metal particles, a glow is formed.
Classification of metal halide lamps
Metal halide lamps can be classified according to the power, color, design and type of cap.
The power of the light sources can be as follows: 20, 35, 50, 70, 150, 250, 400, 700, 1000, 2000 and 3500 watts. Each of these lamps requires its own mains voltage. Elements with a power of 2000 and 3500 W for operation need 380 V. And all other sources of lighting, for example, a metal halide lamp of 400 W, are connected to a network with a voltage of 220 V.
The indicator of the color of the radiation from the sources of illumination varies from warm white to 3000 K to daylight at 6500 K. There are also color metal halide lamps of the following shades: blue, green, orange and purple.
According to their design, these lighting elements can be single-capped, single-ended and double-ended (soffit).
The cap type can be as follows:
- E27 and E40. Standard shape with thread for lighting elements with a power of 250 to 2000W.
- G8.5 and G12. Used for light sources of low power, such as, for example, a metal halide 70W lamp.
- RX7s. It is used in lighting elements with two plinths.
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 work of the lighting element is carried out from an alternating current. A high-voltage discharge can be provided by an electronic or electromagnetic ballast.The first option is preferable, because when using it the lamp life increases, the radiated light is more even, the current intensity during start-up and operation is significantly reduced.
Advantages of metal halide lamps
Such lighting elements have the following advantages:
- Long term of functioning. The average value of this indicator varies from 6000 to 8000 hours. The maximum service life can reach 15,000 hours. This advantage is achieved through the use of halides.
- Large range of the chromaticity index of radiation. The value of this characteristic varies from 3000 K to 6500 K. This provides an opportunity to bring lighting closer to the natural one. The spectrum of radiation can be as cold, whitish, and warm, pleasantly yellowish.
- Economic benefit. The metal halide lamp is about five times more efficient than a traditional source with a filament.
- High intensity of light. For an equivalent replacement of the lamp with a filament of 600W power, a 150W metal halide lamp can be used, which will provide similar illumination. At the same time, significant energy savings are evident.
- Compact size. Small dimensions of metal halide light sources significantly expand the field of their 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 time of ignition. Lamps of low power take about three minutes to achieve maximum brightness, and light sources with a higher index need about ten minutes for this.
- Impossibility of dimming. Metal halide lamps are not designed to smoothly adjust the brightness of lighting.
- High price. Good light sources are expensive compared to traditional incandescent lamps, but it is difficult to find a replacement for them, which is suitable for quality and with a lower price.
Metal halide lamps give high-quality lighting and have good color rendition. Due to this the area of their application is extensive. Such lamps are used for lighting 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 illumination of buildings.