What is a Metal Halide Lamp?

All About Metal Halide

Since the 1960s, the metal halide (MH) lamp has been a used as a viable light source for a number of applications, from illuminating sports fields, to parking lots and street lighting, to general indoor lighting for retail stores and factories. Their ability to emit a vividly white light, plus their long light life and tripled luminous efficacy when compared to traditional incandescent lamps, have made them the premiere choice for years.

However, with new technologies emerging such as fluorescent lighting and LEDs, many contractors may be confused about which lighting solution is best for their particular project. Here at ShineRetrofits.com, we want to make sure our customers have all the information they need to make educated choices about their lighting.

To help with that, here's a look at just what MH lamps are, how they work, their pros and cons, and some other additional information to help you make the best decision.

What is a Metal Halide (MH) Lamp?

An MH lamp is a type of HID (high-intensity discharge) lamp. Mercury vapor lamps are also a type of HID lamp.

In a nutshell, a MH lamp works when an electrical arc goes through a gaseous mix, causing light to be produced. With an MH lamp, that mix of gases will normally include mercury, xenon or argon, and a variety of metal halides. Metal halides are produced as a result of combining halogen with a metal. In MH lamps, that is normally metals that have been mixed with iodine or bromine. Additionally, the type of metal halides used helps determine the color temperature of the light emitted.

The MH lamp itself is built with two main sections -- the outer bulb and the inner arc tube. It's with the inner arc tube that the magic happens. When the MH lamp is turned off, the mercury and metal halides are dormant and condensed inside the arc tube. There are two electrodes at either end of the arc tube -- when voltage is supplied to the MH lamp, a current of electricity starts at one electrode and passes to the next. This begins to heat up the mercury, causing it to vaporize, and actually helps the electrical current to grow. Things are now heating up, causing the metal halides to turn into gas. The metal halide atoms begin to move away from the arc, and in doing so white light is created.

Being this entire process is rather intense, the MH lamp needs materials that can withstand it. For that reason, the inner arc tube is normally made of ceramic or quartz. And the outer bulb is generally made of borosilicate glass and helps to minimize the amount of UV (ultraviolet) radiation that is generated when the MH lamp is turned on. Some lamps may also use a phosphor coating on the outer bulb to help with this as well.

History of the MH Lamp

The basis for the MH lamp started all the way back in 1912 when a researcher by the name of Charles P. Steinmetz was the first person to take a mercury vapor lamp and use halide salts in an attempt to produce a better colored light. Although he was able to get the color he wanted, sadly he was unable to achieve a steady electrical current in the lamp.

It wasn't until 1962 that scientist Robert Reiling took the work of Steinmetz and built upon it, ultimately producing the first dependable MH lamp. It was Reiling who decided to use a quartz inner arc tube, realizing the high temperatures and pressures involved with an MH lamp required such a material.

Although the MH lamp was ready to go in 1962, high price points kept it out of the hands of most consumers until much later when prices came down. By 2005, MH lamps had become extremely popular and saw quite a jump in sales.

MH Lamp Pros & Cons

Just like with any lighting solution, there are both pros and cons to using MH lamps. First, let's look at the pros.

• Indoors & Outdoors -- Because the surrounding temperature really has no impact on how an MH lamp operates, it can be used both indoors and outdoors, making it very versatile.
• Longer Lamp Life -- Generally, MH lamps will last about 10 times longer than traditional incandescent bulbs, usually lasting for between 15,000-20,000 hours.
• Lots of Colors -- MH lamps produce a much whiter, more "natural" light to begin with. However, with the ability to use different metal halides, MH lamps are able to come in a wide variety of colors and color temperatures.
• Energy Efficiency -- When compared to incandescents and other older lighting technologies, MH lamps use less energy and have a higher luminous efficacy.

And now we'll look at the cons:

• Warm Up Time -- With the way an MH lamp operates, when you turn it on it can't just automatically begin to emit light -- it requires a warm up period, which can take anywhere from 1 to 15 minutes. And if the lamp is completely cold, it may take a bit of time to get going.
• Cool Down Period -- If power to the lamp cuts out for whatever reason, the lamp will automatically turn off and it requires a period of about 5 to 10 minutes before it can restart again. However, newer technologies are helping to combat this issue so that the electric current arc can automatically start again.
• Arc Tube Rupture -- As the MH lamp nears the end of its life, the arc tube inside begins to deteriorate -- it may start to discolor or generate more heat than it should. Because of this, there is the chance the arc tube may rupture, which would also cause the outer glass bulb to break as well.
• Color Shift -- Another issue for aging MH lamps is color shifting -- the color of the light its producing may not be as uniform anymore.
• UV Radiation -- As we mentioned previously, the light MH lamps produce emits UV light, which can be damaging to those around it.
• Mercury -- And as we also mentioned previously, the inside of the MH lamp will normally include a small amount of mercury, which is toxic. This also means they need to be disposed of in a certain way -- the US Environmental Protection Agency (EPA) has detailed information on how to recycle mercury-containing light bulbs.

Retrofitting MH Lamps

As new technologies have been emerging offering potentially even greater benefits to MH lamps in terms of energy efficiency, cost, and light life, you may be considering retrofitting existing MH lamps to fluorescent, compact fluorescent lighting (CFL) or LED technologies for commercial applications.

As always, the end result of what you choose as your lighting solution of choice needs to meet the specific requirements of the job you need it to do. At ShineRetrofits.com, we want to make sure our customers are the most well-educated so they can make the best decision possible.

Here's a look at how MH lamps measure up to both fluorescent/CFLs and LEDs.

MH Lamp vs. Fluorescent/CFL

As we have already mentioned, MH lamps offer a number of advantages including the ability to operate under a number of environmental temperatures, long lamp life, and ability to produce a variety of colors. Additionally, they come in an array of different fixtures and are quite durable, allowing them to be used in a variety of both indoor and outdoor applications, including hazardous ones.

When compared to fluorescent and CFL lighting, these newer technologies offer a few features that definitely make up for the MH lamp's shortcomings. For example, with an MH lamp there's the warm up period when it's turned on. Fluorescents do not have that issue thanks to "instant on" technologies and re-striking capabilities where no cool down is needed.

Overall, fluorescents also rate higher when compared to MH lamps when it comes to energy efficiency -- using only about 50% of the same energy an MH lamp would need to use -- as well as an increased color rendering capability and longer lamp life.

However, switching to fluorescents does offer some possible drawbacks. For example, fluorescents have a very hard time turning on and operating in very cold ambient temperatures, which is a problem MH lamps do not have. And to replace one MH lamp usually requires multiple fluorescent lamps to produce the same amount of light.

MH Lamp vs. LEDs

As the newest kid on the lighting solutions block, there has been much excitement regarding LED lighting as it offers a number of advantages, including increased energy efficiency, very long light life, and its eco-friendliness. All of these are pros when comes to MH lamps.

However, LEDs do have some drawbacks. First and foremost is the price -- although the price point has been decreasing over the years, LEDs still require quite a larger investment than MH lamps. It is always important to remember that they should still end up costing you less in the long run due to how long they last and the little bit of energy they use.

Another disadvantage to LEDs when compared to MH lamps is their ability to produce white light. MH lamps are esteemed for their vivid white "natural" light that they emit. With LEDs, there really is no such thing as "white light" -- you have to use a number of different colors to eventually get white light, which can mean sometimes the light can be too blue.

And the last disadvantage of LEDs compared to MH lamps is ambient temperature. As we know, MH lamps have no issues and can operate in pretty much any temperature, but that is not the case with LEDs -- they are quite sensitive to the surrounding temperature, making them a bit too finicky to work in very cold or very hot areas.