As the installed base of indoor LED lighting continues to grow, so will the need to replace failing components, particularly the driver. While analogous to a fluorescent ballast, driver replacement is not as simple.
The majority of LED luminaires and lamps include an electronic driver that starts the light source and then regulates its operation, similar to a traditional fluorescent ballast. The driver converts AC to DC and drives current to the light source, with good performance based on matching driver output voltage and current to the LEDs.
Types of drivers
Popular for applications where the load is unknown, such as track lighting, constant-voltage drivers produce a fixed voltage output. Popular for general lighting, constant-current drivers maintain a constant current flowing through LEDs rated for a maximum current.
Otherwise, drivers may be programmable, controllable, carry various regulatory ratings, feature a design suitable for certain applications, be remotely mounted and display a range of form factors.
An LED driver’s life has a limitation similar to a fluorescent ballast—the electrolytic capacitor. It functions as a buffer to balance input AC and output DC power. The quality of this and other components determine expected life and warranties—an argument for specifying higher-quality drivers. A five-year warranty is common.
Inevitably, drivers fail, often due to defect or design. If the LED luminaire is field-serviceable, the driver can be replaced so the luminaire remains operational. The longevity of LED light sources has altered traditional maintenance. With fluorescent lighting, the lamps would typically be changed out every three to five years, with the ballast lasting far longer. In an LED system, this is typically reversed, with the driver failing before the light source. Because the light source may fail due to lumen depreciation (parametric failure), mortality is not always visibly noticeable; when the driver fails, the device no longer lights (catastrophic failure).
Another difference from fluorescent is complexity. Fluorescent ballasts are highly standardized, particularly regarding form factors. The connected lamps were similarly standardized. If the ballast is dimmable, a ballast compatible with the dimming method would be chosen.
With LED systems, form factors are far less standardized, there is a wide variety of LED sources, the driver may be installed remotely and shorter product cycles may affect availability of a specific replacement. Additionally, the driver may need to be programmed. As a result, replacing an LED driver can be more complex and time-consuming.
The industry has been moving toward programmable drivers, which consolidate units and enable tuning of factors that might include maximum output, dim levels and dimming curves. This programming may occur at the factory or in the field. In 2016, UL announced the Class P LED Driver Program, which provided luminaire manufacturers with greater flexibility in driver substitution. While not standardized, many luminaires feature drivers with common form factors.
When confronted by a driver failure, there may be a choice of replacing just the driver or the entire luminaire. If the luminaire is field-serviceable and the driver has a common form factor, driver replacement can be preferable. This process is fairly straightforward if the same driver is available; otherwise, substitutions are possible. The replacement driver must be UL-listed, electrically compatible with the specific LED load, physically compatible with the luminaire and able to work with and produce desired performance on installed lighting controls.
If the driver is constant voltage, then replacement is relatively simple: identify the voltage and then match it and the form factor, ratings, etc.
Daren Hatfield, marketing director for digital lighting components at Acuity Brands, Atlanta, provided the following guidance on the process for constant-current drivers:
Turn off power to the luminaire and access the driver compartment. Identify the driver specifications and other factors such as dimensions or IP requirements, which may be obtained from the label, by contacting the driver or luminaire manufacturer or, if available, by digitally reading the programming with an external device. Then select an equivalent (ratings, controls compatibility, etc.) replacement driver that is appropriately UL-listed and programmed to match the original settings (current, controls compatibility, etc.). The programming may require connecting to a computer or special tool. Once the new driver is programmed, it can be wired into the luminaire. Programming can be tweaked so the altered luminaire performance can match the appearance of other luminaires in the space.
“Programmable drivers not only bring longevity to installed fixtures, but also offer unique service opportunities to distributors and contractors,” Hatfield said. “There are considerations involved with replacing a driver from a regulatory, electrical and compatibility perspective, but these are not insurmountable. Contractors can differentiate themselves with the ability to deliver cost-effective and time-saving repairs at the component level by quickly understanding and adopting field-programmable driver competencies.”
About The Author
DiLouie, L.C. is a journalist and educator specializing in the lighting industry. Learn more at ZINGinc.com and LightNOWblog.com.