Unlike the simple heated filament of incandescent lights, both LEDs and fluorescents require a buffer between the lamps and the raw power supply. Fluorescents use ballasts, while LEDs use drivers. (LED drivers can be considered ballasts as well, but most documentation prefers ‘drivers’ or ‘power supply’ to avoid confusion with fluorescent ballasts.) Both ballasts and drivers do more than simply charge up their respective lights. They are an essential element to triggering and controlling your light fixtures, from the first flip of a switch through tens of thousands of hours of performance.
What They Do
Fluorescent ballasts provide an initial spike of high voltage, generating an arc that travels from cathode to anode within the discharge tube. Once the light is on, the ballast then acts as a current regulator. LED drivers convert high voltage, ac current into the low voltage, direct current that LEDs are designed to run on. Both fluorescent ballasts and LED drivers protect the light from fluctuations in the electrical supply. Irregular drops or spikes in voltage can affect light quality and shorten the length of the lamp.
While LED lighting fixtures are a relatively recent creation, fluorescent lights were introduced in 1939. With almost 80 years of development, there have been many variations in ballast design and complexity. The older magnetic ballasts consisted of not much more than inductors, capacitors and a series resistor. This was enough to help fluorescent tube fixtures become the lighting of choice for commercial applications, but they developed a reputation for the buzzing noise they produced and the flickering that signaled the end of their productive life. Modern solid-state electronic ballasts have largely eliminated these issues, while cutting energy consumption.
Internal vs. External Drivers and Ballasts
Household bulbs usually include an internal driver (LEDs) or solid-state ballast (CFLs) so that they can be screwed into a standard E26 socket. Without that bit of backward compatibility, neither form factor would likely have caught on with consumers.
Similarly, LED tube lamps designed to replace fluorescents often have an integrated driver, allowing tubes to simply slip into existing fixtures. This is a huge selling point to commercial property owners and facility managers, as it slashes the capital investment required to switch over from an existing lighting system.
On the opposite end of the spectrum from integrated drivers, remote ballasts and drivers can be located quite far from the actual lamps, and are often used to power more than one light at a time.
LED Temperature Concerns
LEDs operate at a very cool physical temperature, in that the lamps don’t heat up the same way that incandescents do. However, the fixtures themselves generate a fair amount of heat. If a fixture is installed incorrectly, improper ventilation can cause the internal temperature to skyrocket. Although this is almost never a safety issue, the hike in temperature can cause the electrolyte gel inside the driver’s capacitors to dry out, drastically shortening the life of the lamp.
Dimming and Color
Both LED drivers and electronic fluorescent ballasts are available in dimmable models. In order to be dimmed, fluorescent ballasts must maintain the internal temperature of the discharge tube to allow for gas excitation while the voltage is varied. The process is much easier for LEDs; as the voltage is lowered the brightness of the lamps simply drops accordingly, without any loss of efficiency. This simpler technology means that dimmable LED drivers carry a lower price tag than fluorescents.
Similar to dimmable units, color-changing LEDs make the most of LED drivers. Whether the color change is accomplished by dimming an percentage of colored LEDs organized in an array, or through using red, blue, and green to create a spectrum of colors, LEDs are versatile tools for a range of hues. And since LEDs can be integrated with circuit boards relatively easily, they can be set to follow pre-programed sequences or adjusted on the fly.
As mentioned earlier, fluorescent ballasts ramp-up standard voltages for the initial firing of the arc, while LED drivers ramp them down to low-voltage levels (UL Class 2). This means that at the lamp level, there’s effectively no risk of fire or electric shock.
Both LEDs and fluorescents can be used in exterior applications, as long as the fixtures are rated for exterior use. Fluorescents need a bit more of an initial boost to light in cold temperatures, and both types of lamp should be installed with exterior-appropriate drivers or ballasts.
Finally, some LED tube inserts for existing fluorescent fixtures come in “shatterproof” options. While these lamps can still be broken, their casings of plastic and steel mean that there won’t be a pile of glass shards to sweep up if a maintenance person drops one during an installation.
With a solid understanding of how fluorescent ballasts and LED drivers fit into your overall lighting system, you’ll be better able make decisions regarding upgrades, replacements, and budget allocations for lighting maintenance.
With over a decade of construction experience, Dan Stout writes articles that help demystify the industry for both contractors and customers. Visit him at www.DanStout.com.