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Linsheng Explains The Use Of Metal Halide Lamps

Update:11-03-2019
Summary:

Any MH lighting system has four basic components (not i […]

Any MH lighting system has four basic components (not including mounting hardware and wiring):

light;

Ballast

Socket and

reflector.

Metal halide lamp

The metal halide lamp is a HID (high intensity discharge) lamp; the mercury vapor and high pressure sodium lamps are also HID lamps. However, mercury vapor and sodium lamps are generally not used in coral reef hobbies, but are widely used in the horticulture industry. Metal halide lamps for aquarium hobbies are often characterized and sold based on different attributes, such as:

The name of the manufacturer/light;

The nominal wattage of the lamp;

The type of method used to mount the lamp, and the number of ends of the socket used to mount the lamp;

The color temperature of the lamp.

Metal halide lamps come in two basic configurations; those with and without a housing. In the former, the basic structure of the lamp is an inner envelope (called an arc tube), which contains an arc, and the outer casing (called a bulb) filters out ultraviolet radiation (UVR) and shields the inner arc tube. These lamps are usually single-ended (SE) and screwed into the socket using a threaded mounting. The second lamp configuration has no housing and usually has two ends (dual end, DE) that need to be plugged into the socket, as will be discussed later.

The internal arc tube contains electrodes and various metal halides, as well as mercury and inert gases that make up the mixture. Typical halides used are some combination of sodium, cesium, indium, bismuth and cesium iodide. These iodides control the spectral power distribution of the lamp and provide color balance by combining the spectra of the various iodides used.

Light is generated by creating an arc between two electrodes located inside the inner arc tube. The internal arc tube is usually made of quartz, which is a very harsh environment with a high temperature close to 1000 ° C and a pressure of 3 or 4 atmospheres. To activate the metal halide lamp, a high starting voltage is applied across the electrodes of the lamp to ionize the gas before it flows and starts the lamp. The outer jacket is typically made of borosilicate glass to reduce the amount of UV radiation emitted from the lamp. It also provides a stable thermal environment for the arc tube and contains an inert atmosphere that prevents the arc tube assembly from oxidizing at high temperatures.

Recently, some manufacturers' catalogues have begun to list ceramic metal halide lamps. These are the facts that their internal arc tubes are made of ceramic material rather than quartz. Ceramic lamps can withstand higher arc temperatures and better maintain lamp life. As far as I know, there are currently no aquarium lamps with ceramic casings.

A feature of HID lamps is that they require several (from three to five) minutes to warm up, and during this warm-up period, the output of the lamp varies in intensity and color temperature. The color temperature of the lamp after startup may take 15-20 minutes to stabilize. After any power interruption (1/20 second or longer), the hot light will not restart immediately and must be fully cooled before restarting. This time delay is called the re-arc time and the MH lamp may take 10-20 minutes.

  Focus on the characteristics that affect the choice of fixtures and their associated hardware. Metal halide lamps have a number of factors that vary by many factors: their wattage, color temperature, mounting base, bulb shape, electrical characteristics, working position, and manufacturer. When using an MH lighting system, it is best to first select the bulb and then select other components based on the particular bulb selected. In addition, you should consider the types of fixtures that may be used in the future. Recently, this has become even more important as many lighting system manufacturers sell specific ballasts for specific luminaires.

The first choice to make is the power of the MH lamp to be used. Typical MH lamps are available in 70 watts, 100 watts, 150 watts, 175 watts, 250 watts, 400 watts and 1000 watts. The most commonly used family aquariums are 150 watts, 175 watts, 250 watts and 400 watts. 70 watts are more popular with nano coral reefs. The first determinant of the choice of lamp wattage depends on the type of corals that are maintained, their lighting requirements, and the depth of the aquarium. In general, for bulbs with similar color temperatures, the higher the wattage of the bulb, the more light it produces.

Once the appropriate power is determined, the next step is to determine the type of fixture based on how the fixture is installed and its startup requirements. Common classifications in coral reef hobbies are single-ended (SE) and double-ended (DE). Single-ended lamps typically have screws at one end and are designed to be mounted in a single socket. On the other hand, the double-ended lamp is designed to be mounted in a pair of sockets, one at each end. Furthermore, DE lamps do not have a large outer casing typically found on single-ended lamps that are used to limit the UV radiation of the lamp. Double-ended lights require additional safety glass to be installed in the fixtures of the luminaire so that they are safe for your tank residents.

Metal halide lamps are sensitive to the way they are mounted due to the sensitivity of the curved tubes. The luminaire is designed to operate optimally only in a particular direction. However, a lamp labeled "General Light" can be operated in any position, but when the lamp is used in a vertical position, the life and light output of the lamp will decrease. For best performance, the position-oriented bulb is optimal if you know the working position of the bulb in advance. Various codes are used to indicate the recommended burning position of the lamp (eg, U = universal, BH = basic level, BUD = basic / lower (vertical), etc.). Most modern aquarium lights are often general purpose lamps and are typically used for horizontal burning locations. When using the lamp in a horizontal position, it is preferred to orient the lamp such that the exhaust tip on the inner arc tube (which is affectionately referred to as the nipple) points upward.

Start metal halide lamp

Linsheng stated that the start-up requirements for metal halide lamps are important because they affect the type of ballast required for the lamp. Two methods are used to activate the MH lamp: probe start (standard start) and pulse start. Probe activation refers to the method used to ignite an arc in an arc tube. Conventional or probe-activated metal halide lamps have three electrodes - two for holding the arc and a third for the internal starter electrode or probe. The high open circuit voltage from the ballast induces an arc between the starting electrode and the working electrode at one end of the arc tube. Once the lamp reaches full output, the bimetal switch is turned off to short the probe, thereby interrupting the arcing.

The pulse-on MH lamp does not activate the probe electrode. The igniter in the pulse start system provides a high voltage pulse (typically 3 to 5 kV) directly on the working electrode of the lamp to activate the lamp, thereby eliminating the probe and bimetal switch required for the probe start lamp, as shown in Figure 2. . In the absence of a probe electrode, the area of shrinkage (or sealing) at the end of the arc tube is reduced, which allows for increased fill pressure and reduced heat loss. In addition, the use of a lit igniter reduces tungsten sputtering by heating the electrodes faster during startup, thereby reducing the warm-up time of the lamp.