AC Ballasts vs DC Ballasts

A high-intensity discharge lamp, also called an HID lamp, is a light bulb that produces light with an electrical discharge. To do this, an arc of electricity is required between two electrodes made of tungsten. These are contained inside either semi-transparent or transparent quartz. It is filled with a mixture of gas and metal salts.

An electrical arc strikes the gas, which then heats and evaporates the metal salts, thus forming plasma. The plasma is a very intense light, much brighter than a filament type bulb. The plasma also consumes less power, which is one of the reasons for its increased popularity in various applications. One of the most popular applications for these types of headlamps is on cars, though their use is spreading to other areas. The downside of this is the cost, but manufacturers are working hard to help reduce the cost of these new headlamps.

Replacing lamps with the new HID lamps requires a conversion kit. Initially the available choice was the AC HID conversion kit. Today a lot of the manufacturers have introduced what they call a DC HID conversion kit. There are several differences between AC and DC conversion kits for HID discharge lamps.



Basic Principle

Electricity flows in both directions. An AC ballast will reverse the polarity on the same electrode so there is an equal distribution of ions. Electricity only flows in one direction. A DC ballast moves the positive ions to the negative side only.


Produces a stable color that does not flicker at all. Light can flicker some and the color of the light can flicker, as well.

Bulb Life

An average AC HID lamplasts about 3,000 hours. An average AC HID lamp lasts about 1,000 hours.

Bulb Protection

Bulbs are typically encased in a shockproof case. DC HID bulbs typically do not have a protective case.


Designed for maximum performance. Designed for low-cost performance.

One thing that should be noted about HID conversion kits is that the AC conversion kits are the only ones that are specifically made for use in an automobile. Most manufacturers will not recommend a DC conversion kit for use in an automobile.

A DC Battery and an AC Conversion Kit

When buyers are shopping for a conversion kit, their first question is usually “Why do I want an AC conversion kit for my automobile when the battery in the car uses a DC current?” This is a good question. A car battery uses a 12V DC power, but the conversion kit comes with a ballast that converts the DC power into AC power. This electricity is then transferred to the HID lamp.

So why go to all the trouble of converting the power from the battery from DC to AC? The main reason for this is that AC power puts much less strain on the internal components of the HID lamp. The alternating current flow puts less strain on the components while also producing a more intense light at less power consumption cost, since they can operate at lower temperatures.

Why a DC Conversion Kit?

The biggest reason that buyers are going with the DC conversion kits for their HID lamps is cost. Again, it should be noted that DC conversion kits are not recommended for automobiles. They do not need to convert the electricity from a DC power source and are thus cheaper to manufacture. The downside is that they burn out faster than an AC conversion kit.

Deciding Between the AC Conversion Kit and the DC Conversion Kit

Deciding between the two really comes down to the specific application that the HID lamps will be used for. If constant light intensity is a priority, then the AC conversion kit would be the logical choice. On the other hand, if this is not a huge issue then the DC conversion kit should be the choice. The other big factor to consider is the amount of use. If the HID lamps are going to be rarely used, then it may not be worth the extra money to invest in an AC conversion kit due to the upfront investment. For any kind of normal use, however, the choice should be the AC conversion kit for the HID lamp.

Other Applications for AC and DC Conversion Kits

There are plenty more applications for using conversion kits other than for HID lamps. The other common use is for any object that uses battery power. An example might be for an electric golf cart. Electric golf carts run on rechargeable batteries. These batteries, much like automobile batteries, use DC power, so a conversion kit is needed in order to convert DC into AC power. Converting to AC power for objects like a golf cart allows for more power and a faster response during operation.


Conversion kits have been around for many years, but they have only increased in popularity recently due to the giant increase in available products that run off battery power. This is a trend that will surely continue, which should help to drive the cost down even more.

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