Don't let your energy savings evaporate in a cloud of lamp replacement costs. Choosing the correct ballast for the application makes all the difference.
Electronic ballasts are in wide use because of their energy savings. But, if you use them in applications where they cycle on and off frequently, reduced lamp life may eat up any savings. This is true whether you use instant or rapid start ballasts. But, a third choice can protect your investment in energy savings. The programmed start ballast can extend fluorescent lamp life by more than 50% in frequent-cycle applications.
You see rapid-start ballasts in frequent-start applications, because they minimize lamp life reduction compared to the more efficient instant start ballasts. However, the wide variety of designs can mean reduced lamp life, because of a mismatch between lamp and ballast. Let's examine the various types of ballasts and their associated starting methods.
Rapid start. Rapid start ballasts ignite lamps by providing cathode voltage (heat) and voltage across the lamp simultaneously. As the cathodes heat, you need less voltage to ignite the lamp. After you apply both voltages, the cathodes reach a sufficient temperature to do their job.
During this starting scenario, voltage across the lamps creates a glow current ( lamp current that flows during this preheat interval), which causes end blackening and degradation in lamp life.
Rapid starting doesn't guarantee the cathodes are at their proper temperatures prior to lamp ignition. If applied voltage across the lamp is too high, the lamps ignite before the cathodes are hot enough. This causes sputtering of the emissive material. After the cathode loses its emissive material, the lamp fails.
Instant start. Instant start ballasts ignite lamps by applying significant voltage across the lamp during starting. The high voltage typically ignites them within 50 milliseconds (ms). These ballasts do not heat the cathodes. You have a release of emissive material during this scenario.
Programmed start. Programmed start ballasts use a precise starting sequence. This breaks the process into unique, well-defined steps that eliminate the pitfalls of other starting methods.
The first step is the application of cathode heat. While the ballast applies this heat (preheat interval), voltage across the lamp drops to a level that reduces damaging glow current. It's important during this step that the ballast apply sufficient voltage to the cathodes, long enough for the cathode to reach at least 700 DegrC. The duration of this step is part of the ballast's preprogramming. Since the ballast keeps lamp voltage very low, the lamps cannot ignite until the cathodes heat to optimal temperature and the ballast's starting program moves to the second step.
The second step of the starting process is application of lamp voltage. After the programmed time of step one ends, the ballast applies a voltage across the lamps to ignite them with minimal loss of emissive material. Minimizing loss of emissive material prolongs lamp life. Some programmed start ballasts can eliminate glow current by not applying voltage across the lamps during this first step.
Transition phase. The time required for the lamp to move from the cathode heating stage to the full arc current stage is the transition time. The longer the transition, the more emissive mix the cathodes lose. Most rapid start ballasts have a transition time of about 80 ms to 100 ms. The time depends on the cathode's temperature and the voltage across the lamp. However, for programmed start ballasts, the transition time is as little as 30 ms. This fast transition, in addition to the preheated cathodes, prevents significant loss of cathode emissive material.
Normal operating efficiency. Instant start ballasts are the most efficient, since they don't apply cathode heat during starting or normal operation. Rapid start ballasts leave the cathode heat on -- even after the lamps ignite. Manufacturers' lamp life graphs show that instant and rapid start ballasts provide the same lamp life in continuous burn applications. This cathode heating uses power and increases the input wattage of the lighting system, with no benefit to the lamp or its owner. Some programmed start ballasts reduce the power to the cathodes, saving more energy.
Accelerated-life testing. Accelerated cycle testing of instant, rapid, and programmed starting methods yield surprising results. For, example, in 15 min on/5 min off cycles, most rapid and instant start ballasts supply about 16,000 starts with a 50% lamp survival rate. But, programmed start ballasts exceed 40,000 starts. Also, the instant start ballasts were equivalent to, or better than, the rapid start models tested.
Lamp applications flexibility. With many electronic rapid start ballasts, other lamps listed for use are usually shorter (thus requiring less voltage to ignite). These lamps instant start, because they get the higher voltage potential required for longer lamps. Many programmed start ballasts keep the voltage across the lamp (during step one) low enough so shorter lamps will not ignite until their cathodes heat properly and the ballast transitions to step two.
Lamp configuration. You can use parallel lamp operation with programmed start; failure of one lamp doesn't affect the others. With series operation, other lamps provide insignificant light when one lamp fails.
Programmed start ballasts are ideal for applications where the occupant turns lights off and on frequently. These applications include classrooms, storage rooms, restrooms, and rooms with occupancy sensors. The ballast provides the efficiencies expected from a T8 electronic system, maximizes lamp life, and reduces maintenance costs.
Sidebar: When a Retrofit Makes Sense
If your lighting system still uses F40T12 lamps and has magnetic ballasts, it will benefit from a retrofit. Energy savings can be as high as 40%, but other factors are also important in making a system upgrade.
Electronic lighting systems operate more quietly than their predecessor magnetic ballast systems. Many electronic systems also feature parallel lamp operation so when one lamp fails, the other lamps still function.
The quality of light from T8 lamps is better than that of the older F40T12 cool white and warm white options. Lamps with higher color rendering are now standard.
The light output options from electronic ballasts can allow for the right amount of light to fit a particular application. For areas where you need more light, high light output products are available. Increasing the light level or reducing the number of installed lamps you need to maintain existing light levels can save energy.