Ballast Basics on Electronic Lighting Ballasts

Introduction
High efficiency, high frequency electronic ballasts offer enhanced lighting performance and energy savings. The Electric Power Research Institute estimates that lighting consumes 20-25% of all electric power and that lighting energy accounts for 40% of the average commercial electric bill. The retrofit of existing facilities with modern lighting systems increases productivity and can save over one-half the energy of the original system.

The economics of lighting retrofits have never been better. Investment payback is often accelerated by "Demand Side Management" programs from electric utilities that offer incentives in the form of rebates for energy efficient measures. Consult with your local energy provider for available programs in your area.

Ballast Basics
Modern electronic ballasts operate at a frequency above 20,000 Hz. This high frequency operates lamps more efficiently (10-15% more light output) and eliminates the 60 cycle hum and visible flicker normally associated with electromagnetic ballasts. Modern solid-state circuitry makes the electronic ballast practical, reliable and cooler running.

Instant-Start
Instant-start electronic ballasts are the most popular type of electronic ballast today because they provide maximum energy savings and they start lamps without delay or flashing. Since they do not provide lamp electrode heating, instant-start ballasts consume less energy than comparable rapid-start, program rapid-start or programmed-start ballasts. As a result, they provide the most energy efficient solution to fluorescent lamp ballasting. The instant-start ballast uses 1.5 to 2 watts less energy per lamp than the rapid-start alternative.
Instant-start electronic ballasts provide a high initial voltage (typically 600V for F32T8 lamps) to start the lamp. This high voltage is required to initiate discharge between the unheated electrodes of the lamp. However, the cold electrodes of lamps operated by an instant-start ballast may deteriorate more quickly than the warmed electrodes of lamps operated by a rapid start, program rapid-start or programmed-start ballast. Lamps operated by instant start ballasts will typically withstand 10-15K switch cycles. Instant-start ballasts and typically wired in parallel. This means that if one lamp fails, the other lamps in the circuit will remain lit.

Rapid-Start
Rapid-start ballasts have a separate set of windings which provide a low voltage (approx. 3.5 volts) to the electrodes for one second prior to lamp ignition. A starting voltage somewhat lower than that of instant ballast (typically 405-550V for F32T8 lamps) is applied, striking an electrical arc inside the lamp. Most rapid-start electronic ballasts continue to heat the electrode even after the lamp has started, which results in a power loss of 1.5 to 2 watts per lamp. Lamps operated by a rapid-start electronic ballast will typically withstand 15-20K switch cycles. Rapid-start ballasts are typically wired in series. This means that if one lamp fails, all other lamps in the circuit will extinguish.

Program Rapid-Start
Program Rapid-Start (PRS) electronic ballasts have been designed for use with occupancy switches by providing up to 30,000 lamp starts. PRS electronic ballasts precisely heat the lamp cathodes to 650°C with virtually no glow current before applying arc voltage to the lamp. Program rapid-start ballasts are typically wired in series. However, PRS ballasts also feature series-parallel lamp operation for the 3 and 4 lamp units. This means 1 or 2 lamps will continue to operate normally in the event of a single lamp failure.

Programmed-Start
Programmed-Start (PS) electronic ballasts provide maximum lamp life in frequent starting conditions (up to 50,000 starts). PS ballasts use a custom integrated circuit (IC) which monitors lamp and ballast conditions to ensure optimal system lighting performance. Like Program rapid-start ballasts, PS ballasts also precisely heat the lamp cathodes. However, PS ballasts heat the lamp cathodes to 700°C prior to lamp ignition. This puts the least amount of stress on the lamp electrodes, resulting in maximum lamp life regardless of the number of lamp starts. Programmed-start ballasts are typically wired in series.

Ballast Factor
Light output ratings published by lamp manufacturers are based on powering the lamp with a "reference ballast" as specified by ANSI standards. The ballast factor of a particular ballast provides a measure of expected light output.
Electronic ballasts have several different ballast factors. This enables the lighting system designer to adjust the lighting level to meet the requirements of a particular application. The lighting system designer can trade watts for lumens by selecting the appropriate ballast.