A metal-halide lamp is an electric lamp that generates light by an electric arc through a mixture of vaporized mercury and metal halides (compounds of metals with bromine or iodine). They are similar to mercury lamps, but contain additional metal compounds in the arc tube, which improve the efficacy and color rendition (whiteness) of the light. Metal-halide lamps have high luminous efficacy, about 75-100 lumens per watt, which is about twice the efficacy of mercury lamps and 3 to 5 times the efficacy of incandescent lamps. Metal halide lamps have a moderately long lifetime (from 6000 to 15000 hours, slightly shorter than that of mercury lamps) and emit intense white light. As one of the most effective sources of CRI white light, metal-halide lamps are one of the fastest growing products in the lighting industry.
They are used for illuminating large spaces in commercial, industrial and public buildings, such as parking lots, playgrounds, factories, shops, etc. The lamp is composed of small quartz or a ceramic arc tube which contains the gases and the arc, enclosed inside a larger glass bulb. This larger bulb has a coating which serves to filter out the generated ultraviolet light. Like other high-intensity discharge lamps, they operate at high pressure (4-20 atmospheres) and require special fixtures to operate safely as well as an electrical ballast. These lamps also require a warm-up period of several minutes to reach full light output, therefore they are not commonly used for indoor lighting, which is switched frequently.
Some types of metal-halide lamps
They are used for lighting in large public spaces such as cinemas, shopping malls, halls, etc. The lamp is placed in a special fixture for metal-halide lamps with a ceramic socket at both ends. Some models are also used for aquariums.
Lamps with sockets E27 and E40
These lamps are widely used in park and garden lighting as well as for illuminating large spaces. The high level of illumination and the daylight that they emit make them ideal for illuminating recreation grounds, halls and other public places. They also need ballast in order to start functioning.
Lamps with sockets G12, G6.35, G10
These metal-halide lamps have specific application. They are used in medicine, various types of projectors, etc. They are coupled with the socket by the two „legs“ in the lower part of the lamp. It is recommended to clean them with alcohol because they have high power and operate at high temperature, and touching the lamp with fingers leaves marks, which in turn significantly reduces the lifetime of the lamp.
A sodium-vapor lamp is a gas discharge lamp that uses sodium in an excited state to generate light. There are two varieties of this type of lamps according to their working pressure: low and high-pressure lamps. Low-pressure sodium lamps are the most efficient electrical light sources, but their yellow light restricts their use to outdoor lighting such as street lights. Sodium high-pressure lamps have a broader spectrum of light, but poorer color rendering in comparison with other types of light fixtures. Since sodium-vapor lamps cause less light pollution than mercury-vapor lamps, many cities use them. They are produced with sockets E27 and E40.
A mercury-vapor lamp is a gas discharge lamp that uses an electric arc and mercury vapor to produce light. The arc discharge is usually confined to a small quartz tube, which is placed in a borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor, in either case the bulb provides thermal insulation and protection from the ultraviolet radiation, which is generated by the light source. Mercury-vapor lamps (and similar to them) are more energy-efficient than incandescent lamps and most fluorescent lamps have luminous efficacy of 35 to 65 lumens / watt.
Their other advantages are a long lifetime of the bulb in the range of 24,000 hours, high intensity and clear white light output. For these reasons, they are used for lighting large areas, such as factories, warehouses, stadiums, playgrounds and street lights. Clear mercury lamps produce white light with a bluish-green tint due to mercury’s specific spectral lines. Mercury lamps with phosphor coated bulbs have better color rendition due to the phosphor „correction“.
Lamps with sockets E27 and E40
These lamps are used mainly for street lighting. They are powered by 220 VAC, but like other high-pressure lamps they require ballast.
Gas-discharge low-pressure lamps
Induction lamps belong to the group of low-pressure discharge lamps – fluorescent lamps or compact fluorescent lamps. They are electrodeless lamps, in which the power is transferred by electromagnetic induction inside the lamp and is converted into visible light. The electronic control is embedded in the volume of the lamp. The induction lighting provides a significant reduction of the CO2 emissions, of energy losses and power consumption. Over 20 % of the input power is converted into visible light and the power is converted 4-5 times better than in incandescent lamps. Therefore, induction lamps are currently the most efficient light source in the natural light spectrum.
The power supply of these lamps is 230V (-23% / +10%), 50 Hz. The color of the radiation is warm white 3000 Kelvin or neutral white – 4000 Kelvin. The light output is 70 lumens per watt (at 4000 Kelvin) / 120 pplm / W. Color rendering index Ra> = 80 , cos ф = 0.94 .
Other advantages of induction lights over other conventional light sources: long lifetime – from 60,000 hours (over 14 years) up to 100,000 hours; instant start; resistant fluctuations of the supply voltage; long warranty period. They are suitable both for domestic use and for warehouses and public buildings. Their only drawback is their relatively high price.
Autor: Angel Georgiev