Before LEDs, most lighting fixtures were power by different kinds of ballasts.
Ballasts provide the right voltage to start the lamp and then regulate the electrical current to the lamp while it is running. They are required for fluorescent and HID light sources. LEDs are usually powered by a driver.
Below are some common terms related to ballasts and drivers.
The opening through which the ballast in a luminaire can be installed or replaced, either through the aperture or from
above the fixture.
Ballast Efficacy Factor: Sometimes called ballast efficiency factor, ballast efficacy factor is the ratio of the ballast factor to the active power (in watts), usually
expressed as a percent. It is used as a relative measurement of the system efficacy of the fluorescent lamp/ballast combination.
Ballast Rated Life: The number of hours at which half of a group of ballasts fail
under standard test conditions. Rated life is a median value of life expectancy; any ballast, or group of ballasts, may vary from the published rated life.
Common Ballast Types
Instant start: They power the lamp through high voltage without needing to heat the filaments, making them more energy efficient and good for lamps that are on a lot.
Rapid start: They use low voltage to preheat the filament until the lamp starts,
making for a short delay in starting. They are recommended when you
have frequent on/off switching.
Dimmable ballast: In fluorescents, these ballasts – which are mostly electronic - have the ability to maintain electrode heat to excite the gas in the lamp even
when input voltage is varied.
Programmed start: These electronic ballasts heat the lamp cathodes before the lamp ignites. They allow for frequent switching and are good for use with occupancy sensors.
Hybrid: Also called cathode-disconnect ballasts, use a magnetic core and coil
transformer and electronic switch for the electrode-heating circuit, making them cheaper than electronic ballasts.
ANSI Ballast Type: Is a ballast type used to operate a lamp in accordance with the American National Standards Institute (ASNI) standard.
Transformer: A lighting transformer is a device used to convert electrical energy from a higher to a lower voltage or vice versa. While they were first invented
in the nineteenth century and have become more sophisticated, they still perform the same basic function of transforming voltage or electrical current for various purposes. When used with incandescent or halogen lamps, they typically step 120-V distribution downward to 12V, although 5.5V and 24-V models are also offered.
Electromagnetic Transformers: Rely on the relationship between magnetism and electricity to transform voltage and current.
Electronic Transformers: Are designed for low voltage applications,
are more compact and operate at lower temperatures.
Isolation Transformers: They separate one circuit from another and are used in situations where sensitive equipment needs be isolated from potentially dangerous high voltage.
An LED driver or power supply provides a similar function as a ballast does for a fluorescent or HID lighting system or a transformer used in a low voltage bulb. The driver regulates the power and provides the LED lighting system with the right amount of electricity to perform optimally.
Common LED Drivers
Constant Current drivers: They fix the current of the system and vary the voltage to the LED depending on the load. Low voltage DC constant current drivers are recommended for most applications since they are safe, efficient and reliable and have more dimming and output options.
Constant-Voltage drivers: They require a fixed voltage and add the LED loads until the maximum output currents are reached. Applications for constant voltage drivers include: under cabinet lighting, rope-lighting, backlit ad signs, traffic information signs and large screen LED displays.