Fluorescent lighting is a system that relies on the compatibility between the lamp and ballast for reliable lamp starting, desired illumination level, energy efficiency, and achieving rated lamp life.
The ballast controls the voltage and current applied to the lamp(s). Beyond these basics, ballasts also have many additional characteristics that need to be considered so the selected ballast is the best match for the lamp and the application. The operational and energy efficiency of the lamp/ballast system depends on a proper match.
This post will summarize the key criteria to consider when selecting an electronic ballast for general fluorescent lighting in applications such as office, classroom, hallway, retail and warehouse. We will not address fluorescent dimming ballasts or specialty ballasts for ultraviolet lamps in this post, although many of these guidelines also apply to UV bulbs and ballasts.
Common Types of Electronic Fluorescent Ballasts
An instant start ballast applies high initial voltage (eg 600V for F32T8) to start the lamp. There is no cathode heating, simply a voltage jolt to ignite the lamp. The principal advantage of this starting method is that less energy is consumed than most other types of ballast. Instant start is generally the most energy efficient ballast for most types of fluorescent lighting. However, because of the high voltage starting method, the instant start ballast will reduce the rated lamp life in applications where frequent On/Off switching is part of normal operation – for example when the lighting is connected to occupancy sensors.
Rapid start ballasts ignite lamps by providing cathode heat and voltage to the lamp simultaneously. This approach allows lower ignition voltage that is not as hard on the lamp as the high voltage Instant start ignition. For frequent-start applications, Rapid start ballasts have traditionally been specified with the promise of minimal lamp life reduction compared to Instant start ballasts. Today, for new installations, Programmed start ballasts are preferred over Rapid start.
Programmed start ballasts use a "soft start" strategy. Each phase of the lamp ignition is broken down into small increments. A specific sequence of events powers on the light. This more sophisticated starting method allows up to 40,000 starts without degrading the lamp quality compared to less than 20,000 starts for Instant start ballasts. Today Prgrammed start ballasts are the preferred ballast choice for applications where frequent On/Off switching is the norm.
Ballast Selection Checklist
(1) Lamp Type - Wattage - Number of Lamps
The specification sheet for an electronic fluorescent ballast will indicate which lamp types and configurations the ballast is designed to operate. For example, a three lamp fixture using 32 watt T8 fluorescent lamps. Many ballasta will be compatible with several lamp types such as F17T8, F25T8, F28T8, F32T8 and possibly U-bent versions of these same lamps.
(2) Start Type
Instant or Programmed – the selection is based on the application as discussed above – if the lighting system is characterized by frequent switching because of occupancy sensors or other factors, choose Programmed Start. Otherwise, Instant Start is the usually the best choice.
(3) Ballast Factor
Normal Ballast Factor (.77 to 1.1) is the default for most general lighting.
Low Ballast Factor (<.77) may be the most appropriate ballast factor for applications where the full light output of the lamps is not required. A low ballast factor may be appropriate in these instances as a way to save energy.
High Ballast Factor (>1.1) is useful when the goal is to boost the light lightput for spaces such as warehouses or big box retail. Generally, you will get around a 10% increase in lumen output over the rated lumens of the lamps.
Multiply the rated lamp lumens by the ballast factor to get an estimate of the delivered lumens.
(4) Input Voltage
Some ballasts provide universal voltage, other specific voltage. In either case, check the input voltage requirements for the ballast (120 / 277 / 347) to make sure it includes the voltage you need.
(5) Minimum Start Temperature
Ballast specification sheets will include minimum start temperatures that will likely vary depending on the type of lamp driven by the ballast. For example, a ballast may show a 0°F minimum start temperature for F32T8 lamps, but for F32TT8ES a 60° minimum start temperature may apply and for F40T8 a 32°F min. temp. As you can see the variations can be significant. Carefully consider the typical 365 day ambient temperature where the lamp/ballast system will operate and check the ballast spec sheets for the minimum requirements.
Other Specifications to Consider
- Circuitry: Parallel is the norm. This allows other lamps to remain lit even if one lamp in the fixture goes dark.
- Anti-Striation Control: Striations are undesirable bright and dim areas that may form a standing wave pattern down the length of the lamp. Striations are more likely to develop when the lamp is operated at low temperatures. Manufacturers have developed ways to minimize these striations and often refer to an Anti-Striation feature in the ballast specification sheet.
- Sound Rating: An "A" rated ballast will hum softly; a "D" rated ballast will make a pronounced buzz. The importance of the ballast sound rating depends on the application. Libraries want the quietest ballast possible, while sound rating is probably not as important for warehouses.
- LED Transition: Some ballast manufacturers have lists of their instant and programmed start ballasts they call "LED Ready". For forward looking facility managers this may be an important factor when selecting a ballast if a transition to LED is anticipated.
- Manufacturer Warranty