Metal-halide lamp

Metal halide lamps are bulbs from the group of gas discharge lamps. You are an evolution of the mercury vapor lamps. By the addition of rare earth compounds and color rendering and luminous efficiency can be increased. In addition, xenon or neon is included as a starter gas.

• 7.1 Use in Lamps

General

The metal halide lamp reaches over other high-pressure gas discharge lamps have a very high color rendering index of up to 90 ( at Osram HMI lamps for the film range up to 96 ), very high light output of up to 117 lumens per watt (lm / W) with good and up to 110 lm / W with very good color rendition and heard in addition to the sodium vapor lamps and LED lamps to the most efficient lamps at all. You can convert up to 38% of its electrical power consumed in visible light and has a service life of up to 30,000 hours on electronic ballasts.

It requires like almost all high-pressure lamps for a few minutes until the full light output, is available in various color temperatures from 2700 K to 20,000 K available with color rendering index of 60 to 96 Furthermore, colored lamps for lighting effects are produced.

They were invented in 1964/1965 by Gilber Reiling at General Electric, who invented in 1992 the first Ceramic Metal Halide Lamps ( CMH), followed in 1993 with their Philips Ceramic Discharge Metal (CDM). From Osram HCI she was baptized and is produced in Berlin-Spandau. When it is called Sylvania HSI.

Main areas of application is the lighting of expenses (shop light), light sets for film and television, theater lighting, lighting trade fair / warehouses, industrial halls and stadiums, architecture and aquarium lighting, traffic and outdoor lighting. They are increasingly replacing high-pressure mercury lamps, which they consider more than twice the light output and much better color rendering and save at least half of the energy at the same luminosity.

Metal halide lamps must be operated with a ballast. They are available with power ratings from 10 W to 24 kW, and (single and double ended, different base sizes and color temperatures ) in different designs. Despite the name similarity to the light generation and construction differs in principle from the halogen lamps with which they are sometimes confused.

Types and designs

The heart of the metal halide lamp is the discharge vessel ( burner tube, discharge tube ) with the two opposite electrodes. It is often used in an evacuated glass envelope ( bulb ), which serves to protect and heat insulation and the two electrode terminals leads outwards to the socket. There are one-sided and double-ended types that differ primarily in performance.

Common base:

• G8, 5 ( Quetschsockel or pin base ) with 20 to 70 W
• G12 ( ceramic base ) with 20 to 150 W
• G22 ( ceramic base ) with 250 and 400 W
• RX7S ( two-sided ceramic base ) with 70 to 250 W
• FC2 ( two-sided ceramic base ) with 250 to 400 W
• E27 ( screw ) with 35 to 150 W
• E40 ( screw ) 250 to 3500 W

In professional fields (film, TV, theater, etc. ) have the following base forms and services and programs:

• GX9, 5 or GY9, 5 ( ceramic base ) with 125 to 400 W.
• G22 ( ceramic base ) with 575-1200 W
• PG47 ( ceramic base ) with 250 to 1500 W
• G ( X) 38 ( ceramic base ) with 1200-12000 W
• G ( X) 52 ( ceramic base ) to 18000 W as a new development; Usually, however, usually double-ended lamps are used in this performance class.
• G ( X) 38 ( ceramic base ) 24000 W double-ended.

Furthermore, a distinction is made between the quartz and ceramic technology, the manufacturer-specific types of burners and color reproduction index and color temperature. Quartz discharge vessels are generally formed from a piece of quartz tube, that is in the form of a tube having been crimped ends with side exhaust tube through which the vessel is evacuated. This ancient technique has, however, production-related high volume fluctuations, which leads to high power, luminous flux and color variations. Tipless shaped ellipsoidal quartz burner (from Venture and Sylvania ) achieve higher volume constancy and thus color and light flux constancy and reach either very high light output (up to 110 lm / W at color reproduction 65) or high color rendering index of 85 to 90 at 80 lm / W. Ceramic discharge vessels (Ceramic Metal Halide Lamps ) have grown since 1993, they allow much higher internal temperatures and pressures and thus a continuous spectrum at the same time with very good color rendering over 90 and excellent light output over 100 lm / W. The new generation of these lamps is so that the top of the lamp technology with 35, 70, 150, 250 and 400 W Represent hot CMH General Electric, Philips CDM, HCI Powerball Osram CeraArc by Iwasaki, C -HIT of Ushio BLV. The burner or the discharge vessel of CDM lamps is, as can be seen in the adjacent figure, cylindrical ( see picture), the CMH are inside at the ends of double-walled, the illustrated also in Figure HCI Powerball almost spherical elliptical and the CeraArc elliptic around which arc. ( for example, the Powerball or Osram CDM - T 250 W Philips ).

Two-way lamps are usually hot restrikable (see below) as well as many with G22 and other large pedestals, all non- ( Edison ) screw and the small single-ended lamps due to the small distances between the ports.

For particularly high color rendering index (up to 95, for film and television ) was the so-called Osram HMI lamp introduced (other manufacturers: MSI or RSI). HMI stands for medium -arc iodide Hydrargyrum, ie for mercury arc length middle iodine, and often used as a synonym for daylight-like headlights.

Most metal halide lamps are designed for use in enclosed luminaires: Since the discharge vessel is under high pressure, must be prevented in the case of bursting shards flying around. There are more and more metal halide lamps with Berstschutzzylinder ( shroud ) of quartz around the discharge vessel for use in open luminaires, spare a shield. Metal halide lamps with quartz burner without pistons or with quartz bulbs give off high levels of UV radiation. Therefore, from 400 W and all types without protective glass bulb an additional UV-absorbing glass is necessary, especially with HQI -TS.

The different shapes and power forms are usually characterized by the lamp designation system ILCOS and are described in more detail there.

Quartz or ceramic

Seen from the user side, the ceramic technology ( reference numbers eg: HCl, CDM; ... dependent on the manufacturer and not standardized names ) have the advantage of color stability over the life span, while in the older quartz technology (HQI ), the color spectrum is usually in the course of operation shifts toward green.

The difference here, especially in the material used for the burner tube. Quartz is due to its high melting temperature and hardness of good materials for severe, central area, but is displaced from the aforementioned reasons of translucent ceramic (sapphire glass), which now represents the state of the art. Another advantage of the newer ceramic burner is the higher light output of up to 100 lm / W ( lumens per watt ), compared to about 80 lm / W with quartz burners.

Operation

Metal halide lamps have to be operated as all gas discharge lamps with a ballast that limits after ignition when an arc is formed, the current to a constant value. It turns a lamp voltage of typically 100 to 150 volts. This depends, inter alia, by the lamp being used. Commonly used are Drosselvorschaltgeräte whose advantages are the simple, robust construction and relatively low cost, as well as electronic ballasts (EVG ) who have less losses, the lamps can boot up faster (40 -second startup time is reached to 90 % of the luminous flux ), which prolongs the life of the lamps and the luminous flux is reduced with the burn time. ECG regulate network voltage fluctuations, dampen voltage peaks etc. and mainly give flicker- free light, which is absolutely necessary for the use of metal halide lamps in offices and workplaces. Many metal halide lamps, especially CDM -TC, all 20 W and many high-power types may be operated only with one ECG. Most electronic ballasts operate lamps with square-wave AC voltage from 80 to 400 Hz, suitable for all types. Most ECG 250 W high-frequency devices. High frequency is not suitable for the thick, cylindrical CDM discharge vessels, it is already at the start-up to acoustic resonances and possibly an explosion. There are also dimmable ECGs: Especially the metal halide lamps of the new generation are getting better dimmable, at appropriate dimmable ballasts up to 50%. Since certain operating conditions such as temperature and partial vapor pressures of the metals electrodes in the arc during continuous operation should be fulfilled, metal halide lamps, however, are not arbitrary dimmable.

To ignite an igniter is required, which in the current path is ( Superimposed ignition ) and as long as the firing pulses of about 5 to 80 kV provides (depending on the lamp power ) until the lamp ignites. Double ended lamps are often hot restrikable (german hot restrike ): they can with very high voltages also be re- ignited when they have cooled. If metal halide lamps are turned off without this capability or without use a suitable ignitor, they first have to cool down before they can be re-ignited. The cooling takes depending on power rating and design of the lamp about 10 to 15 minutes.

In the first minutes after the ignition, the mixture of metals, halogens and the rare earths must first be heated to melt the solid components and evaporate. During start-up (run up, high burning ') increases the luminous flux to reach its normal value after 40 seconds to 5 minutes.

The headlamps Xenon headlights in the car it is not pure metal halide lamps, since metal salts and mercury are included together with the xenon only in very small quantities (a few milligrams). They are primarily used to reduce the color temperature and so should the light spectrum of the rather bright purple xenon in the direction of sunlight ( 5000 to 6000 Kelvin) move.

Operating phase after switching on

Ignition phase

In the burner is still a mixture of mercury, halogens, sodium, thallium, and usually scandium, in lamps with excellent red rendering and calcium, rubidium or strontium, in daylight types of rare earth metals, as well as an inert gas (eg argon). This, at room temperature, partially solid, liquid and gaseous mixture is initially not ionized and therefore has a high resistance. By the high voltage of the ignitor, an arc is initially ignited. The vast number of lamps are designed here on ignition voltages up to 5kV, because at higher voltages the base as well as the ignitors and the leads by the required insulation would be too costly to implement.

Ensuring a reproducible ignition of less than 5kV, it is necessary easily vorzuionisieren the gas. For this, the burner electrodes such as the Osram HCI or Philips CDM alloyed with thorium Th232/Th228 until 2012, as krypton Kr85 is included in the internal fulfillment. Due to the radioactive decay of the starting gas in the burner is easily pre-ionized, which reduces the voltage required by a factor of 5. The caused by the emitter load is extremely low and is below 0.01 mSv. The technical progress in recent burners enables the ionization by UV light, which is generated by an auxiliary electrode outside of the burner or burners in a small discharge vessel near by corona discharge. These embodiments will be readily apparent upon consideration of the burner. According running light bulbs are free of radioactive emitters, so that the legal requirements in the production of lamps omitted and the excess of the prior art exposure to ionizing radiation completely absent.

After ignition, the resistance decreased greatly by impact ionization. In addition, the electrodes and reduce heat by their work function, whereby the lamp voltage drops even further. As first mainly mercury ions ( the mercury is used for better ignition of the lamp ) can contribute to lighting, and the gas pressure is low, the lamp is initially only slightly from the light with a high blue and ultraviolet component.

High burning

The gas discharge heats the burners, melts and evaporates the contained solid filling components. This process does not run due to the different melting and boiling points simultaneously. First, the mercury reaches its boiling point of 356 ° C and thus contributes to enhanced light emission at an early stage. The mercury reservoir is relatively abundant sized to ensure a for igniting sufficient partial pressure over the operating life of the lamp. For this reason, the spectrum of the emitted light moves initially by a blue-green region, the intense being damaged later covers a large part of the visible spectrum.

With progressive warming boil the other metals and contribute increasingly to light production. In this phase, a generous color change from greenish to white and a strong increase in brightness is observed - the lamp has reached its operating parameters.

Aging process

The aging of the lamps based on several processes. The most important, because unavoidable component is the wear of the electrodes that are charged accordingly by the arc. Tungsten atoms evaporate from the Ein-/Austrittspunkten the arc and deposited in other places from the burner.

Another process is the corrosion of the burner vessel through the various fillers. In addition, the service life due to the diffusion of gases from the burner environment can be significantly reduced. The aging process of a metal halide lamp ( Brennerschwärzung by tungsten transport from the hot electrode to the burner wall ) can be reduced in two ways.

Electronic ballasts

Ballasts typically used, electronic operation of the burner to produce a square wave voltage of the order of 100V. As opposed to a sinusoidal voltage in this case the gas in the burner is permanently ionised, which ensures a stable operation, in particular in aged light sources. During the ignition phase acicular pulses having a voltage of typically 4 .. 5 kV to the square wave signal are superimposed.

The detail view shows that the ignition pulse consists of a high-frequency vibration. This makes it possible to produce these with a small ferrite transformer, which is connected in series with the lamp in the normal operating current.

In operation, the ballast disables the ignition pulses, so that the full wave voltage and a superimposed with the 50 Hz ripple of the power system current rectangle remain for operating the burner. In ECG the mains input voltage is directly rectified and fed to a power factor correction in the form of an active PFC. At the output of PFC, a DC voltage of approximately 400 V is present, which is reduced to the operating voltage of the lamp by a controlled step-down converter. The following is an inverter, typically connected as a full bridge IGBT, which generates therefrom ... rectangular voltage with a frequency in the range 100 to 150 Hz for the operation of the lamp. The low frequency prevents damage to the burner due to acoustic resonance effects. When the gas pressure during the start phase slowly but steadily up to 40 bar increases, the burner would otherwise advised when operating at higher frequencies in resonance, which would have a strong mechanical stress result. The fairly low operating frequency provides no flicker, since the square wave voltage zero crossing traverses very steep. A disadvantage, however, some ballasts will produce an audible sound when its winding goods are excited with the frequency.

Properties

Metal halide lamps have a luminous efficacy of about 95 lm / W ( lumens per watt ), the average life is 750-30000 hours. Special types have only partly a lifetime of 500 to 2000 hours. Operation is possible only with a ballast.

The light color and color rendering comparable to fluorescent lamps and is determined by the mixture of components of the burner. The color temperature is typically 3000-7000 K, so both similar to incandescent and daylight-like lighting can be created. The color rendering index is 1 B to 1 A. The vast majority of metal vapor halogen lamps have the following light colors:

For special applications, such as in swimming pools or for the aquarium, there are metal halide lamps with much higher color temperatures from 10,000 to 20,000 K, as well as color spotlights. The surface temperature of the enveloping bulb is approximately 500 ° C.

Use

Find use metal halide lamps primarily for daylight-like lighting with spotlights at high duty and high required lighting levels.

Typical applications include shops and exhibitions, where especially the long operating time and the lowest possible desired heat input at the highest possible light output prohibit the use of halogen bulbs. Furthermore, the metal halide lamp found in architectural lighting, indoor lighting, stadium lighting and in the street and area lighting application.

Another important application is the film industry. Here a defined color temperature (daylight, approximately 6,500 K) and stable color reproduction is especially important. For day - indoors or outside services for lightening up to 18,000 W are used. For example, in U.S. film productions especially for night shots show the whole streets, often used Muscolights. That's 15 kW HMI Pars in a hydraulically operated 50-meter arm of a self-propelled generator.

Metal halide lamps are also used in color changing lights and moving heads as a light source. Their light output and the desired color can be adjusted with motorized adjustable color filters. For beam deflection are movable mirrors, lenses or prisms.

Also in the hobby these lamps are due to their point light source character and the resulting light - shadow - game often used by waves on the water surface for lighting medium and large aquariums. Also in the terrarium, these lamps are increasingly being used because they (the reflector type to well over 100,000 lux ) can provide with low energy consumption similar to natural light levels. HQI lamps are preferably used for emergency services, since the compact design and the high brightness of the illumination of large areas is made possible with just a few lights.

Metal halide lamps are increasingly being used for street lights, because they are more efficient than high-pressure mercury lamps. The lamps used were hitherto generally NAV -SON -LU E Na - vapor lamps, as

• Ceramic Metal Halide 70W 7400 lumens and more than 8000 lumens at twilight vision, color rendering index of 90 ... 96
• NAV -E, SON- E, LU E 70 W Lumen 5600 and less than 5000 lumens at twilight vision, color rendering index of 20 ... 25

Use in luminaires

The high pressure in the discharge vessel (risk of hot glass splinter on bursting ) and the strong UV emission usually requires an appropriate lighting design. This is often different from luminaires for incandescent or halogen lamps. Basic requirements are, for example, limiting the UV emission and the corresponding design of the luminaire parts made ​​of UV resistant material. Furthermore, the protection of the environment must be guaranteed against glass shards of a broken lamp by the light ( and the melt through an underlying plastic cover from hot shards ). Therefore, the operation of the metal halide lamp is usually only in enclosed and specially constructed lighting certainly possible. Industrially produced lamps meet these requirements. In -house designs ( by yourself), there is often a substantial danger to the environment, particularly when used according to the principle of the construction site version. Due to the need to operate metal halide lamps with a ballast, rarely one meets constructions as in the picture on the right, however, to. Only a few types of lamps provide even sufficient protection without ambient light. This is achieved through a suitably constructed, and sufficiently large outer bulb ( ellipsoid ). The lamp in the picture on the right has no such outer bulb.

A note to ("only for use in enclosed luminaires" ) is indicated on the packaging or bulbs in the data sheet.

Costs

Metal halide lamps with E27 base and 230 volts for household use with 35 watts to 150 watts of power and a luminous flux of 100 lumens per watt are available for about 50 Euros per piece in stores. With Base E40 and 230 volt lamps from 150 watts to 2000 watts available at prices between 50 and 150 euros. An HMI burner for a 18,000 -watt headlight film costs about 3000 EUR and has a specified by the manufacturer lifetime of only 300 hours.

Literature

• Hans R. Ris: Lighting for the practitioner. Bases, lamps, lighting, planning, measurement. Second, erw. Ed VDE -Verlag, inter alia, Berlin and others 1997, ISBN 3-8007-2163-5.
• Günter Springer: electrical engineering expertise. 18, completely revised and expanded edition. Europe teaching aids, Haan - Gruiten 1989, ISBN 3-8085-3018-9.