Metal halide lamps: types, device, pros and cons + rules of choice
Despite the development of LED technology, metal halide lamps (IPL) continue to hold their market niche due to its unique characteristics. Their internal structure can vary greatly depending on the intended scope of application.
Therefore, before choosing the IPF, it is necessary to thoroughly understand the principles of operation and features of these devices.
How are metal halide lamps arranged?
MGL have a complex internal structure. Externally, it is a glass cylinder with a base, although some models resemble a pear-shaped incandescent lamp.
Inside the shell is another working capsule of glass or transparent ceramics, as well as conductive elements and resistors.
The outer flask is usually filled with nitrogen, and the inner flask is filled with an inert gas under pressure, a small amount of mercury, and additives of metal halides. This design determines the name of the product.
Sodium iodide or scandium is mainly used as metal halides. They serve to correct the light spectrum and affect the scope of application of metal halide lamps. In the off state, mercury and additives are in a solid precipitated state on the glass walls.
It will not turn on itself when connecting to the electrical network. To do this, use the starting-adjusting devices (PRA), which provide the necessary starting current and voltage until the appearance of the effect of thermionic emission in the internal flask.
Light emission mechanism
The inclusion of IPF occurs in stages. At the beginning, due to the starting current, which is 10-20 times greater than the worker, a minimum electrical discharge in the inert gas environment occurs in the internal flask.
After that, for 3-6 minutes, the heating of mercury and metal halides occurs, which, evaporating, passes into the ionized phase. The current at this time is about 2 times the working one. Ions increase the conductivity of the air mixture, and provide a gradual output of the lamp to the nominal luminosity.
Due to the two-flask device, a stable high temperature is maintained in the working capsule, which prevents the precipitation of metal vapors on the walls.
After shutdown, the IPM must necessarily cool down, and metal vapors should settle on the walls of the inner flask. Only after that will it be possible to re-start the lamp.
This restriction is a significant disadvantage, so metal halide lamps are not used for domestic needs, where it is often necessary to turn on / off the lighting.
Gravity also affects the condensation processes in MGL, so many models require a clearly defined location in space.
The principle of operation of discharge lamps is not simple, but it allows you to achieve the correct spectrum and powerful light flux. In addition, the use of control gear allows you to stabilize the characteristics of the emitted light when the parameters of the electrical network.
Construction Varieties of MGL
Metal halide lamps are used to illuminate both corridors and rooms, as well as large open industrial sites. Therefore, their power varies from 10 to 2000 watts.
Lamps with high power consumption are usually connected to the network of 380 V and are used only on industrial objects. The most popular models have a small power of 35-250 watts.
There are no uniform international standards for marking IPL, but in most cases the letter M stands for "metal halide", and H informs about the content of mercury in the lamp.
Domestic manufacturers can use their abbreviation: D - arc; And - iodide, P - mercury. After specifying the model, the type and diameter of the base are usually indicated.
Metal halide lamps have a different design. Below are the options for classifications of these products, depending on their technical parameters:
- By type of orientation: vertical (BUD), horizontal (BH), universal (U).
- The size of the bulb: BT - bulb-tube, R - reflex, E or ED - ellipsoidal, ET - ellipsoid-tube, T - tubular, PAR - parabolic.
- According to the color of radiation: white, yellow, purple, green and others.
- By type of construction: baseless - with flexible current leads, single-base, two-base.
The external performance of a metal-halide lamp has little effect on its efficiency, because the direct radiating element is in a protected internal flask. It is he who determines the characteristics of the emitted light.
Technical features of lamps
The specifications of the IPF are quite varied. They depend on the metal halide lamps used in the production of materials and the electrical parameters of operation. These devices have distinct advantages and disadvantages that you should be aware of when buying.
General operating parameters
Metal halide lamps are not exactable to external temperature and continuity of operation. They can burn for weeks at sub-zero temperatures without experiencing overloads.
The main parameters that characterize the IPF are:
- color rendering index (CRI);
- work resource;
- light flow;
- type of base;
- Colorful temperature;
- the ratio of the luminous flux to electrical power;
- working temperature.
The color rendition index is considered an important feature of the IPF. CRI characterizes the presence in the emitted spectrum of different wavelengths and the uniformity of their intensity.
This indicator is measured as a percentage of similarity with natural daylight. Modern IPF color rendering index is 85-95%, and the majority of household LED-devices - 70-85%.
Some lamps deliberately distort the color rendition to give the light the necessary properties. For example, sodium MGL used for plant growth, have a CRI of only 50-60%.
The efficiency of the lamp does not decrease because of this, it just emits most of the energy in a given wavelength range. To give the light a yellow tint, sodium halides are used, green is thallium, and blue is indium.
With regards to performance, metal halide lamps are not far behind the LEDs. This indicator in both devices of the average price range is 100-120 lm / W.
The color temperature of MGL can be from 2500-20000 ° K. When the voltage drops in the network, it changes upwards and the light becomes colder.
With a long excess of 240 V, the lamp can simply explode due to overheating of the gas-air mixture in the inner flask.
An important quality of MGL is the stability of the luminous flux throughout the entire period of operation, which is 6-15 thousand hours. If the efficiency of LEDs after 10,000 hours of operation drops by about 50%, then for metal halide lamps - only 2-20%.
The remaining parameters depend on the specific model of the lamp and are not specific.
The advantages of metal halide lamps
The modern market of discharge lighting devices is slowly shrinking due to the onset of LED. But the unique properties of IPF for at least several decades will be in demand by consumers.
The main advantages of these lamps are:
- Excellent energy efficiency. For every watt of energy consumed, the lamp gives out more than 100 lm of light.
- High color rendering index.
- The perfected production technology minimizing breakages of internal elements of a lamp.
- Wide power range.
- Long service life.
- Resistance to high temperatures due to the absence of electronic components inside the lamp.
Metal halide lamps compete mainly with LED and fluorescent. All three technologies are actively developing, therefore, further improvements can be expected from the IPF.
Negative sides of the device
The absence of metal halide lamps in the domestic sphere indicates that they have not only positive, but also negative qualities.
The main disadvantages of the IPF are:
- The cost is several times higher than similar LED devices.
- The lack of brightness control.
- The need for cooling for 5-10 minutes before re-starting.
- Existence of external PRA which demands an additional place for installation.
- Gradual increase in color temperature during prolonged use.
- Explosion hazard at power surges.
- Sensitivity to spatial location.
- Absolute non-repairability.
- The need for special disposal due to the content of toxic substances.
- The need for time to reach the calculated luminous flux after switching on.
Thus, they have even more minuses than pluses. This narrows the scope of the IPF to industrial and public buildings and sites where continuous and high-quality lighting is needed.
Scope of lighting
The use of metal halogen houses is not only economically inefficient, but also dangerous due to the content of mercury in them. The flask may burst and the room will be filled with toxic fumes.
Due to insecurity, mainly the use of metal halide lamps is only in demand mainly for non-residential spaces:
- Filming studios, photo salons.
- Car lights.
- Architectural buildings.
- Public buildings, mall.
- Industrial shops.
- Objects under construction.
- Street lighting.
- Sports objects.
- Park areas.
- Greenhouse complexes, greenhouses.
- Night lighting country houses.
Most people do not face the purchase of IPF also because these devices are rarely sold in small hardware stores. They are acquired mainly by enterprises and entrepreneurs from specialized companies.
How to choose a metal halide lamp?
The specificity of the applications of discharge light bulbs forces a careful approach to the choice of their characteristics. The goods, of course, can always be exchanged, but it is better to immediately purchase a suitable model.
The main recommendations for the acquisition of metal halide are as follows:
- Carefully read the inscriptions on the packaging, which can inform about the limitations of the use of IPF in certain circumstances.
- The stated working position of the product must correspond to the position of the luminaire for which it is intended. The smallest resource for vertically oriented models.
- The diameter of the cap should fit the lamp holder.
- The starter body must be made of metal with a sufficient number of ventilation holes. Indeed, depending on the model, PRA consumes 10-20% of the lamp power.
- The starter is designed for a specific voltage and current, so when replacing the lamp, these factors need to be considered.
- In some cases, the critical ignition of MGL is critical, so it’s necessary to read about the time it reaches the nominal luminosity in the instructions in advance.
If a metal-halogen lamp is purchased to replace a failed one, then you can take a broken model to the store for example.
The IPF costs are expensive, so it is important to keep all the checks and invoices in case of purchase, so that you can use the warranty rights later.
Conclusions and useful video on the topic
Overview of the characteristics of metal halide lamps:
Check the operation of the metal halide floodlight:
Metal halide lamp connection:
Metal halide lamps continue to be used in many areas, despite a number of design flaws. A diverse range of radiation allows you to select them for different needs of economic activity.Therefore, the IPF will remain competitive in the niche of industrial lighting for a long time.