How Fluorescent Ballasts Work

Over the past few years, fluorescent lamps have become the lighting of choice for contractors looking to save on both energy and maintenance costs. Although fluorescent lighting may cost a bit more upfront when it comes to initial installation, it makes up for it in the amount of energy saved when compared to traditional incandescent lighting.

A fluorescent lamp generates light through the use of two elements -- electricity and mercury vapor. A current of electricity – also known as the arc – passes through the vapor, resulting in an ultraviolet light. That light then bounces off a phosphor layer on the inside of the lamp, which makes the bulb light up.

This entire process is regulated by a fluorescent ballast, which is found in the fixtures for fluorescent lamps.

What is a Fluorescent Ballast?

Quite simply, the ballast keeps the fluorescent lamp from burning out. Without a ballast, the fluorescent lamp would literally just keep increasing the electric current flowing through it until it self-destructed. The job of the ballast is to control the amount of current running through the lamp so that does not happen.

Another job of the ballast is to provide the energy -- or voltage -- the lamp needs to get going. The ballast gives the lamp the amount of voltage it needs to create the current – or arc – between its electrodes, and then automatically lowers and monitors the voltage to make sure there is the perfect amount to keep the light going.

Fluorescent ballasts come in a variety of types to meet the needs of different fixtures. For instance, ballasts will specify how many fluorescent lamps they can regulate at one time (such as one or four) and what types of lamps they work with (such as T5, T8, T10 or T12). Additionally, the fluorescent ballast will also state the amount of voltage it can accommodate (such as 120 or 277 volts).

How a Fluorescent Ballast Works

When a fluorescent lamp is turned on, first the lamp's electrodes are heated and release electrons, which the mix with the mercury gas and other gases that may be in the lamp. When this happens, the electrons actually bump into atoms that are in the gas, releasing wavelengths of ultraviolet light that are consumed by the fluorescent coating on the inside of the lamp. This then ultimately produces the light we can see.

The job of the fluorescent ballast is to manage this entire process by giving the lamp the voltage it needs to get the process done, but at the same time making sure it doesn't take in so much that it burns out. That is because a fluorescent lamp is inherently has a negative resistance, meaning it will just keep on taking in voltage until its power supply can't take anymore. To combat this, the ballast supplies the opposite resistance -- positive -- to restrict the current.

In its simplest form, a ballast uses magnetic energy that erupts into the lamp when it is turned on, stimulating the electrodes to make a current and the lamp glows. Today's fluorescent ballasts are mainly electronic, and they have a number of positive attributes including energy efficiency, reduced flicker of light, and even dimming capabilities.

Types of Fluorescent Ballasts

There are a also a few different types of fluorescent ballasts to know about. One of the more popular types of ballasts is the instant-start ballast. Rather than warming up the lamp's electrodes gradually, the ballast a rather large initial voltage to get it going. Although this helps save energy since there's less energy used when compared to other ballast types, the downside is it can result in the lamp degrading quicker, so this type of ballast is normally recommended for fixtures that will not be turned off and on all the time.

A rapid start ballast works differently from an instant start as it does allow the lamp time to preheat by initially using a low voltage. Then when the lamp's cathodes are nice and warmed up, the voltage is increased and the lamp is lit. One plus of rapid start ballasts is they can be used in a parallel lamp service. That means if you have four lamps running on the one ballast and two go out, the other two will continue working.

And the programmed start ballast operates much like the rapid start -- gradually heating up the lamp's cathodes before initializing the ignition of the lamp. However, it is able to warm the cathodes at an even higher temperature, allowing less burn out and for it to be used with fixtures that will be turned on and off even more frequently.