Posted by Lamar Guzman on 19th Oct 2015

Why do Metal Halide Lamps Need an ANSI Coded Ballast?

In the lighting industry, there are many important components that the average lighting buyer is unaware of or simply doesn’t think about. Many people don't know how high-intensity discharge lamps like metal halide bulbs are powered. I certainly didn’t prior to joining the lighting industry.

A major component to powering  high-pressure sodium, fluorescent, and metal halide bulbs is the ballast. High-intensity discharge lamps carry a large amount of electrical discharge to create light. The job of the ballast, in this case, is to drive and sustain the power output toward the lamps. Here is a quick rundown on how a metal halide ballast operates.


First, the line voltage goes into the ballast. The most commonly used line voltages in the U.S. are 120, 208, 240, 277 or 480V. Most  metal halide ballasts operate on 120-277V. These are called 4-tap ballasts and they operate 120/208/240/277V. You will also see 120-480V ballast, which is called a 5-tap ballast. These ballasts operate 120/208/240/277 & 480V.

Each voltage has its own specific wire that should be used depending on the voltage you have in your facility. The others are not used. For example, if you have 120V in your building operating the fixture, you would choose the 120V wire and leave the other wires alone.

4- and 5-Tap Ballast

In the picture below, each of the 4 wires in the rubber band are your "taps." The wires are labeled appropriately so you know which one you need to use. The operating voltage of the lamp is defined by the ANSI (American National Standards Institute) and noted on the lamp and ballast.

Sometimes, you can determine the ballast by looking at the part number. For example, the  M400ML5AC4M500K is a 5-tap ballast, and it is also designated in the part number with the number 5. The 5-tap ballasts typically cost a bit more because they have more copper coils.

Power and Efficiency

Once you have your voltage specified, the ballast takes over all the heavy lifting. First, the input voltage enters the ballast. Then, the main control circuits convert the power into an AC signal and senses resistance within the lamp being operated. The ballasts provide the starting voltage and ignition pulses (pulse-start lamps) that are necessary to ignite the metal halide bulbs. The ballast keeps a steady set flow of electricity flowing to the high-intensity discharge lamp once the lamp has been started.

Once in operation, the resistance can be detected over one thousand times per second while adjusting the output. An important feature to pay attention to is the Ballast Efficiency. This determines how much of the power is actually being used during output.

For example, if a ballast has an efficiency rating of 80% (0.80), then this means that for every 100 watts, 80 watts are actually powering the lamps. The other 20 watts are lost in heat transfer. Another great feature is that some ballasts have EMI shielding. EMI shielding prevents things such as radios, TVs, cell phones, etc., from interfering with the signal inside of the ballast.


Common Questions—Choosing a Ballast

A question asked daily by customers is, “How do I know what ballast I need to run these lamps?”

Fortunately, manufacturers use an ANSI code system. For  metal halide bulbs, the ballast and the lamp will have a unique identifier on them. They will all start with an "M" and then have a number such as 57, 58, 59 or 110. After that number, there can be an "E" or "O." These have to do with the high-intensity discharge lamp being open-rated or close fixture rated. The typical ballast kit sold by will include a capacitor and/or an ignitor (depending on the ANSI system), 2 screws, 2 new brackets and a new core and coil transformer like the one pictured above.

Finding the ANSI Code

A popular ballast we sell is the  Keystone MH-175A-Q-KIT. When you visit that product page, you will notice there is an ANSI code M57. This is a guide to finding all metal halide bulbs matching this ballast. When searching this ANSI code you will find a lamp such as Halco MH175/U/MED/IC In the specs, you will see ANSI Code M57E. It is imperative to match up the ANSI code on your ballast with the ANSI code on the high-intensity discharge lamp. If you do not have a match the system will not operate properly.

If you still need help trying to figure out what metal halide ballast you need, you can contact us at any time. We’re here to help!