Metal halide lamps: advantages and disadvantages, scope

Metal halide lamps (MGL) are considered extremely popular today. This is due to their high efficiency, power and compactness. They belong to the category of gas discharge (GRL). They differ from other gas-discharge lamps in that special emitting additives (ID) are added to the MGL-structure, which are halides of metal alloys.

Specificity of MGL lamps

MLG has the same principle of operation as other gas-discharge devices - an electric arc discharge occurs between individual electrodes in a flask filled with mercury. The advantageous feature of metal halide bulbs is presence of ID in mercury vapor.

Metallic iodides are required to correct the spectral properties of an electric arc discharge. Thanks to their use, the level of quality of light emission is greatly improved. In addition, they prevent the formation of tungsten deposits on the internal surfaces of the structure. During operation of MGL bulbs, metal halides and tungsten vapors begin to interact with each other. As a result, a special gaseous mixture (tungsten iodide) is formed, which begins to evaporate from the surface of the electrodes. After deactivation of the metal halide lamp, the tungsten returns to the electrodes.

Features of the device

Construction of MGL bulbs includes several main components. These include:

• The burner (discharge tube) is the base of the lamp. This part is often made from special quartz glass or ceramics. Ceramic-type tubes have high heat resistance. The discharge torch and electrodes are located on the outer bulb.
• The outer bulb is a kind of light filter. This element is made from borosilicate glass. Such flasks are characterized by a high level of mechanical and thermal stability. They reduce the heat loss of the discharge tube, ensuring a stable thermal regime.
• Base / plinth.

It is impossible to start MGL lamps without ballast. For this purpose, ballasts (electronic or electromagnetic ballasts) are used. The use of electronic control gear allows you to achieve an even light at start-up, reducing starting and operating electric currents, as well as increasing the durability of the device.

Functioning principle

The plasma of an electric arc discharge acts as a luminous body in metal halide lamps.

The burner is filled with halogen compounds and inert gases, which, being in a cooled state, collect on its inner surfaces and look like a thin film. As the temperature rises, the halides evaporate and split into individual ions. Then the ionized atoms are irritated and create optical radiation.

In addition, inert gases have a buffer function, so the electric current can enter the discharge tube even at low temperatures. As the burner heats up, the emitting additives and mercury are evaporated, thereby regulating the spectrum of light emission and the electrical resistance of the MGL lamp.

To ionize the discharge, it is necessary to use special equipment, for example, impulse ignitors. Ignition is carried out using a transformer or inductor with high magnetic dispersion rates.

Advantages, disadvantages and applications

Experts and consumers note that the use of MGL bulbs has a lot of advantages. These include the following:

• greater durability than ordinary incandescent bulbs;
• high degree of light output;
• low power consumption;
• compactness;
• reliability of normal operation even at low temperatures;
• good color rendering.

Metal halide lamps are not devoid of disadvantages. Among them:

• impossibility of adjusting the light flux;
• long warm-up;
• the need to use IZU;
• inability to re-ignite the MGL lamp immediately after deactivation;
• sensitivity to sudden voltage drops.

Despite some disadvantages, metal-halide bulbs are used both in conventional lamps and in light-signaling equipment, which is due to the mass of useful properties.

Metal halide lamps are used in many areas:

• stage, studio and film lighting;
• decorative;
• architectural;
• utilitarian;
• street lighting, in particular in quarries, railway stations, sports facilities, etc.

Among other things, metal halide lamps are often used for the production of headlights for road transport and for lighting industrial plants.