Metal Halide Lamps: The Other Unsung Hero

Metal Halide Lamps: The Other Unsung Hero

With all the talk of LED lighting, some may have forgotten about the other efficiency trooper in the lighting world the Metal Halide lamp. With Lumens per Watt ratings upwards of 30 the Source Four HID range provides another efficient lighting solution for your next install. But what exactly is a metal halide lamp and how does it work?

Following the release of the Source Four XT, ETC now have a complete range of metal halide lighting solutions as part of its Source Four HID range. The metal halide lamp in the HID range provides the lighting punch and long throws of a theatrical fixture with the high efficiency and long life needed for an architectural application. The metal halide though is fast becoming still the unsung hero of efficient long life lighting, its solid state cousin the light emitting diode is quickly taking the spotlight. This article is going in to bat for the metal halide and the HID and will explain how it works and why it is at this point in time irreplaceable for high output, long life architectural applications.

What is it?
Metal-halide lamps, a member of the high-intensity discharge (HID) family of lamps, produce high light output for their size, making them a compact, powerful, and efficient light source. The metal halide adds rare earth metal salts to the standard mercury vapour lamp to improve the luminous efficacy and to improve the output light colour. Similarly to nearly all of the HID family the metal halide lamp operates under high pressure and temperature and requires specialty fixture design in order for them to operate safely. The Source Four body and lamp base are perfectly designed to take these lamps, as they are obviously (because of their theatrical use) able to take the intense heat and protect these pressurised lamps. These lamps combined with the ultra efficient Source Four di-chroic glass reflector create an intensely bright directed architectural fixture consuming only 150w.

How does it work?
As with the majority of other HID lamps, the metal halide is a gas discharge lamp, that is they produce light by making an electric arc in a mixture of gases. In a metal halide lamp there 3 components, the arc tube with electrodes, an outer bulb and a base. Obviously we know what the base is, and we can guess that the outer bulb refers to the outer glass that protects the arc tube but it is also used to block a portion of the UV light generated by the lamp to protect people and users. However, what is the arc tube and how does it produce such a large amount of light with such low power. The arc tube is made of fused quartz and produces light by making an electric arc in a mixture of gases. The metal halide arc tube contains the gases, argon, mercury and a mixture of metal halides. It is this mixture of halides that affects the nature of the light produced, that is the colour temperature and intensity of the lamp. The electric arc is produced by two tungsten electrodes sealed into either end of the arc tube through which current is passed. The argon gas is easily ionized and facilitates the arcing across these two electrodes. The arc produces a surge of heat which then vaporizes the mercury vapour and halides which produce light as the temperature and pressure increases. The initial arc requires a high inrush voltage provided by an electronic ballast which then stabilises to keep the lamp running at its capacity

Metal halide lamps require a warm up period after initial arc in order to reach full brightness. A "cold" (below operating temperature) metal-halide lamp cannot immediately begin producing its full light capacity because the temperature and pressure in the inner arc chamber require time to reach full operating levels. Starting the initial argon arc sometimes takes a few seconds, and the warm up period can be as long as five minutes (depending upon lamp type). During this time the lamp exhibits different coloUrs as the various metal halides vaporiSe in the arc chamber.

If a metal halide loses power even for a short moment the arc will extinguish and the high pressure within the hot arc tube will prevent the lamp restriking for a period of up to 5 minutes. This means that the lamps must be used in a constant use scenario that means they are perfect for architectural applications.

So how does the Source Four HID use the Metal Halide?
The Source Four HID utilises a 150w metal halide lamp within a standard Source Four fixture body, whether this be in the form of a zoom or fixed beam profile or a high intensity clean wash par fixture. The HID gives you the performance of a standard 2000 hour Source Four with an additional 10,000hours of use. The HID makes use of an electronic ballast which is mounted to the yoke of the fixture, and uses a power factor greater than 95% compared to some of its competitors ballasts at less than 70%, it also has an efficiency of over 90%. This creates an extremely high output, long life fixture with the proven optics that come with the Source Four brand.

ETC-Source-Four-XTThe Source Four XT expands the HID by incorporating all of these features within an IP65 housing to give this efficient lamp the ability to be used in external, all weather applications. The XT housing is completely weather resistant and incorporates the ballast within an enclosed housing at the rear of the unit.

There is no substitute for the metal halide when the application requires a high output directed white light that must be used for an extended period of time. Although an LED can provide amazing colour rendering colour mixing and wall washing capabilities and ultimately to the eye are much more exciting, the HID is still a great choice at this point in time for a high intensity theatrical style direct feature, with an extremely high efficiency and lower power usage.

                               Source Four HID                 STANDARD LED FIXTURE*
Power (w)             150w                                  110w
Lumens Output       5210lm                               2500lm
Lumens Per Watt    34                                       26
* A standard RGB fixture

We can be certain that the LED will continue to improve and that the LED gives you a greater range of features and capabilities but the Source Four HID mustn't be left by the wayside as they are a highly efficient and extremely bright lighting fixture that are perfect for architectural applications.

Visit ETC's website for more information on the entire Source Four HID range.

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