Posted by Doug Root on 17th Jun 2020

How Does a Metal Halide Lamp Work?

To anyone who doesn’t have a close familiarity with lighting solutions or electricity, a light bulb is just a light bulb. Once you start to develop an understanding of electrical systems and the different types of lights - as well as how they are used - the truth becomes more apparent. There are many different types of lightbulbs that operate on different principles. Perhaps most surprisingly, some light bulbs aren’t even designed with the intention of providing light!

Considering all of that, you may at some point or other come across the term applied to a type of bulb known as a metal halide (or MH) lamp. Without ever having seen one in action (or recognizing one) the term may have seemed Greek. That’s alright - we’re here to shed a little light on the matter - no pun intended.

First, a little context. A metal halide lamp is a type of High-Intensity Discharge Lamp (HID Lamp) that is primarily used because of its ability to provide extremely bright white light at relative energy efficiencies. There is a fairly good chance that you have seen these lights even if you didn’t know what you were specifically looking at. Because they are capable of high discharge (hence the name) and lighting up large spaces, they are frequently used to light stadiums, sports fields and arenas, parking lots, and other large outdoor spaces at night. They are sometimes also used as street lights. So how do they work?

A metal halide lamp is made of a smaller arc tube, which is sometimes called a discharge tube, inside of a larger bulb. Arc tubes are typically made of quartz or ceramic in part because these materials can withstand the high temperatures that metal halide lamps produce.

Inside the arc tub is a mixture of mercury, metal halide salts, and a gas such as argon that helps to mediate the process. There are two main electrodes as well as a starting electrode as a part of the arc tube as well. The starting electrode helps to supply the initial current and the main electrodes sustain the operation. While the lamp is off, the mercury and halide salts are condensed within the (relatively) cold arc tube.

When you supply power to the lamp, the ballast allows a fairly high current to pass to the starting electrode which then jumps to the main electrode. This smaller arc heats up the gas inside the tub and thus the mercury and the halides. Some of the mercury is vaporized at this point and the temperature in the arc tube continues to increase. The electricity in the discharge tube has to overcome the resistance of the gas and mixture within the tube, but this becomes easier as the gas heats up. As more of the mercury gets vaporized, the electricity can arc from the main electrode nearest the starting electrode through the mercury vapor to the other main electrode on the other side of the discharge tube.

Once the arc reaches from one main electrode to the other, it stops flowing from the starting electrode to the nearer main electrode. When the arc is able to bridge the gap between the electrodes through the mercury vapor, the halides in the discharge tube will vaporize as the lamp becomes warmed up. Once this stage is reached the lamp is producing or near producing its full brightness.

That is how metal halide bulbs produce light, but there is a little more to their engineering that makes them capable of operating properly. The discharge tube is contained within an outer bulb that is typically made of borosilicate glass. The borosilicate outer bulb provides a stable environment for the inner discharge tube so that it will produce a steady stream of light, and typically contains an inert gas to prevent the inner components from oxidizing. That is, it protects them from the influence of oxygen in the atmosphere. Some MH lamps have outer bulbs coated in a material such as a phosphor to diffuse the light or to change its color or alter its color temperature.

In a nutshell, that’s how a metal halide lamp works. Lighting fixtures that have MH lamps are extremely popular in areas like those enumerated above for the clear, bright white light they produce and can sometimes be found indoors and outdoors.

Here at Atlanta Light bulbs, we’re not just your source for lighting information - we’re your source for light sources. Check out our inventory and you will find an extremely broad collection of metal halide lamps, fluorescent bulbs, incandescent bulbs, LED lighting, and even specialty bulbs and lighting solutions. Take a look through our collection to see what options for your needs, and if you have any questions at all, don’t be shy about reaching out to us. We’re here to help, and you can contact us at 1-888-988-2852.