• A control circuit required for the operation of many different types of bulbs including, but not limited to high intensity discharge and fluorescent bulbs. A ballast generally plays a part in not only starting one or more light sources but also in controlling the power supplied. Ballasts can be designed to accomplish a wide variety of purposes such as dimming and even switching between multiple light sources. The physical design of a ballast depends on its application which may call for special mounting methods or a special shape such as a cylinder shape for mounting inside poles or a long skinny form for mounting inside freezer doors.
  • Design Technology

    The two primary classes of technology for ballasts are magnetic and electronic
    • Magnetic

      The largest single component is a magnetic transformer, which is made of wires wound around magnetic (iron/steel) cores both of which add to the significant weight of a magnetic ballast. Philips states that using magnetic fluorescent ballasts which operate at 60Hz as opposed to electronic
    • Electronic

      Rely on solid state technology to accomplish many of its functions. This change to smaller electronic components results in a much lighter weight compared to magnetic ballasts.
    • Example weight comparison (Sign Ballasts):
      06154D D DSB-2448-46BLTP
      22 lbs
      28696C D ESB-1040-14-120/277HF
      7 lbs
  • Mounting

    Fluorescent (including Compact), HID electronic, HID F-can
    Mounting feet for screw mounting (essentially all can ballasts)
    Threaded studs (Compact fluorescent) Blue arrow: "Bottom Leads" (BL)
    HID Core and Coil Ballasts
    Mounting brackets with screws
    Ignitor & capacitor straps (using screws)
  • Wire & Connections

    • The wires coming from a ballast are called "wire leads" and are used to connect ballasts to a power source, the lampholder(s) and to other auxiliary gear. Ballast wire leads have two core constructions, solid and stranded core. These are simply called "solid wire" and "stranded wire".

      Less wire means a lower capacity for current or "ampacity". The cross sectional area (CSA) of wire, which essentially is the amount of copper showing when a wire is cut in 2, is stated as a value of American Wire Gauge (AWG) or said simply as "gauge". The smaller the gauge value the more CSA, i.e. 10 gauge is larger than 12. Because of the space lost between strands, stranded wire must have an overall greater diameter than solid in order to have a similar CSA. The image to the right compares the overall diameter of a solid wire to a 7 core stranded wire with the same CSA.

      Stranded wire is more flexible than solid wire and thus can be pulled through conduit much easier but solid wire is preferable (or even necessary) in some cases specifically because of its rigidity, especially when making certain types of connections (below).
    • Fluorescent, compact fluorescent & electronic metal halide

      Use solid core input and output leads. Leads are color coded to match the wiring diagram. Most compact fluorescent ballasts do not have pre installed wire leads but instead have "push-in connectors" and may include pre-stripped separate leads. A common offering today is a compact fluorescent kit that offers multiple wiring and mounting options.

      See detailed image here.
    • HID Core & Coil

      Have stranded core input and output wire leads. Leads may or may not be color coded (most commonly are not) but always have the appropriate information printed on them to allow matching the lead to the wiring diagram.

      See image here. Always have pre-installed leads.
    • Connectors

      In a few cases installers use "ballast disconnects" also called "quick connects" which allow for quick connection/disconnection. These do not come pre installed. Image: a type of ballast disconnect/quick connect

      Another type of connector that is seen on rare occasions is what is referred to as a "molex" connector. These are generally special ballast made for specific applications. Image: molex connectors (highlighted)
    • Aluminum wire

      Aluminum wire is a common cost saving alternative to copper wire. For decades, aluminum wire was used in most all ballasts but to increase efficiency and decrease size aluminum wire was replaced with copper wire. Because aluminum has a lower conductivity than copper it must be 1.6 times the diameter to handle the same current load. Aluminum wire is never used for ballast input or output leads.

      Today aluminum is still used in ballasts but to prevent a significant increase in size, copper wire is used for the higher current winding(s) in a ballast that can accept more than one input voltage (multi-tap) (120, 208, 240 and 277 volt in a 5-tap for example) and aluminum wire would be used only for the lowest current (480 volt).

      For a specific lighting system and thus a specific power consumption, the higher the operating voltage the lower the operating current. The proportional current load of a 5 tap HID ballast for its voltages are as follows: 120 volt - 100% [maximum current load], 208 volt - 58% of max, 240 volt - 50%, 277 volt - 43% and 480 volt - 25%.
      The difference in diameter results in 4 wire gauge difference. i.e. 14 AWG copper has the same ampacity as 10 AWG aluminum.
  • Power Input

    • Certain specific voltages are made available either directly by the utility company or as a result of transformers raising or lowering voltages for various uses. By using standard transformers, specific voltages are provided for use in residential, commercial and industrial installations. In residential installations the voltages are 120 and 220, smaller commercial installations voltages are often 120/240 (both are accessible) and larger commercial/industrial voltages are often provided as 120/208 and/or 277/480. These specific voltages represent essentially all of the 60Hz AC voltages in use in the United States today. Of these voltages 120 and 277 are by far the most commonly used to provide power to lighting systems. Ballasts are designed to accept standard input voltages with most electronic ballasts accepting a range of voltages such as 120 volts to 277 volts [and all voltages in between] while some others accept a variety of specific voltages via separate input leads.
    • Fluorescent

      For decades magnetic fluorescent ballasts only accepted a single voltage for which it was designed and so multiple versions of the same ballast each designed to operate at a different voltage had to be stocked (120 and 277 volt mostly). The introduction of electronic ballasts led to the development of circuitry that allows the ballast to sense the input voltage and adjust accordingly. This type of circuit has a standard range and is stated as "120 to 277". 120 to 277 means that it runs any voltage from 120 volts up to 277 volts. This is obviously different from "120 or 277". Because the circuit is able to sense and adjust to the incoming voltage it only makes use of 2 input leads.
    • HID

      (*.Tap refers to here): Other ballasts, most commonly core and coil high intensity discharge, make use of a system referred to as "multi-tap". This design allows the ballast design to provide more than one "hot" lead for making an electrical connection. The appropriate input lead is used for the voltage being supplied. Using the wrong lead can cause a number of bad results some of which can be dangerous.

      Dual tap
      two input leads
      120 and 277 volt
      four input leads
      120, 208, 240 and 277 volt
      five input leads
      120, 208, 240, 277 and 480 volt

      Image: conceptual cross section of a 5 tap ballast coil (not actual)
    • Tolerance

      All power systems have what is called a "tolerance" level. This is how far out of bounds values can go before the system starts to react negatively. This tolerance amount is stated as a plus-minus value such as +/- 10% or +/- 10 volts which means that it may be under/over 10% or under/over 10 volts respectively.

      Example: a device is rated to accept 120 to 277 volts and its input voltage tolerance is stated to be +/- 10%. That means that the device can accept 108 to 304.7 volts
  • Ballast to Lamp (BTL)

    • Abbreviated as BTL. The length of the wire from the point where the output leads exit the ballast can or ballast coil to the base of the bulb.
    • Application

      Remote mounting a ballast, which means installing it farther from its bulb(s) than usual, often involves long runs of wire between the ballast and bulb. BTL is the length of the aforementioned run. Possible applications for remote mounting could be applications with sensitive noise requirements, tall poles such as roadway lighting where the ballast is mounted at the base, underwater or underground applications or even large signs.
    • Effects

      The smaller the gauge of a wire the higher its resistance and thus has more voltage drop. Additionally, for ballasts that require an ignitor, the longer the wire run the more significantly the ignitor's starting pulse is weakened. Both of these issues can adversely affect the life and performance of the bulb, ballast or other auxiliary gear, prevent the bulb from starting altogether or even in more significant instances a fire hazard.
    • Accessing BTL Data

      Ballast manufacturers can provide maximum BTL lengths as needed for their applicable products and may list that information in catalogs or websites. In catalogs this seems to be listed as "Remote Mounting Distance to Lamp" (Advance/Philips)
    • Equipment

      • Venture Lighting states the max BTL of their part number V90Y8412T which is a magnetic 250W pulse start metal halide ballast (HID, ignitor required) as 2 feet
      • GE states the max BTL of their part number 71421" GE232MAXP-N+ which is an electronic fluorescent ballast as 18 feet with 18AWG or lower gauge wire.
      • Advance/Philips BTL for non-pulse start metal halide magnetic ballasts ('16-'17 catalog) (yes, these are some big numbers)
        Maximum One-Way Length of Wire between Lamp and Ballast(in feet) (Voltage Drop Limited to 1% of Lamp Voltage)
        Metal Halide
        1-400 / 2-400
      • Special "long-range" or "remote" ignitors (2 different names from 2 different manufacturers for the exact same thing) that can be remote mounted up to 50 feet away are available from Advance/Philips as well as others.
    • Starting

      • The minimum starting temperature of a lighting system depends on both the bulb and the ballast. Certain bulbs and ballasts are designed for or are preferable in special applications such as those in low temperatures. Additional measures such as using special auxiliary gear, jacketing to enclose a bulb and/or special enclosed fixtures to preserve the bulb's heat can be used to start and operate bulbs in specialty applications where the temperature falls below the bulb's normal starting range.
      • Fluorescent

        If a fluorescent lighting system is operated in an area with ambient temperatures that are near or below rated temperatures strange phenomena may occur such as Striations and the Swirling Effect. These aren't harmful however, just psychedelic.

        Standard bipin fluorescent bulbs when used with standard ballasts are designed to start at between 50°F to 60°F and above. Reduced wattage bulbs such as F34T12 (lowered to 34 watts from 40) , F32T8/25W or F32T8/28W (lowered from 32 watts to 25 or 28 watts respectively) are more sensitive to temperature than full wattage bulbs.

        As a general rule instant start ballasts will start bulbs at lower temperatures than rapid start ballasts. All slimline (single pin) fluorescent bulbs are instant start and start down to 0°F and thus have been commonly used in cooler applications.

        Ballasts for high output (HO) and very high output (VHO) bulbs are specifically designed to start those bulbs at temperatures down to -20°F.
      • HID

        Standard HID lighting systems are able to start in lower temperatures than standard fluorescent bulbs. The voltage required to start HID lamps increases as the temperature decreases. When using standard auxiliary gear standard metal halide bulbs (probe start) should be able to start at -20°F while pulse start metal halide bulbs should be able to start down to -40°F.
    • Warmup

    • Restrike

      • Mercury and metal halide:
        4 to 10 minutes
        High pressure sodium:
        1 minute
        In tight or enclosed fixtures, mercury and metal halide lamps could take up to 20 minutes to cool down.
      • Instant restrike high pressure sodium restrike performance values from Osram-Sylvania
        Time from Power Return (Minutes)
        % Light Output
    • Wiring Diagram

      All ballasts have wiring diagrams attached or included. Their only purpose is to show which wires should be attached to what. Unless otherwise specifically and clearly stated, a wiring diagram is not meant to suggest what means or method(s) should be used to fasten/connect the referenced wires, specifically which lampholder should be used, how the ballast or bulbs should be mounted/secured, what sort of fixture a ballast can or cannot be mounted in, recommended applications, etc.
    • Total Harmonic Distortion

      Abbreviated THD. "Harmonic distortion occurs when the wave-shape of current or voltage varies from a pure sine wave. Except for a simple resistor, all electronic devices, including electromagnetic and electronic ballasts, contribute to power-line distortion. For ballasts, THD is generally considered the percent of harmonic current the ballast adds to the power distribution system. The ANSI standard for electronic ballasts specifies a maximum THD of 32% for commercial applications. However, most electric utilities now require that the THD of electronic ballasts be 20% or less. Almost all Philips Advance electronic ballasts are rated for either less than 20% THD or less than 10% THD." - 2016-2017 Philips Ballast Catalog

    • Ballast Efficacy Factor

      Abbreviated as BEF. "Measure used to compare various lighting systems based upon light output and power input." - Advance Ballast Glossary
    • Ballast Factor

      "Measure of light output from lamp operated by commercial ballast, as compared to a laboratory standard reference ballast." - Advance Ballast Glossary.
    • Ballast Loss

      The amount of power consumed solely by the ballast in a lighting system. Ballasts consume power in a number of different ways including, but not limited to, stray electromagnetic interference, harmonic distortion, sound, vibration and heat.
    • Ballast Noise (Hum)

      "Sound made by operating Core & Coil assemblies in both electromagnetic and electronic ballasts, generated by the vibration of laminations in the electromagnetic field that transforms the voltage and current used by discharge lamps. The sound made by high frequency electronic ballasts is lower and any noise made by models with electronic power factor correction circuits is inaudible." - Advance Ballast Glossary
    • Electromagnetic Interference

    • Fluorescent

      • Fluorescent Ballast Starting

        • Preheat Start
          Preheat start ballasts are simply referred to as "preheat ballasts". They require the use of fluorescent starters to start bulbs.

          Those designed for use with non-compact fluorescent bulbs rarely include thermal protection, often abbreviated as "TP", which is designed to protect a ballast from overheating in the case that the system begins to cycle (attempting to start again and again after the bulb is extinguished). Those designed for use with compact fluorescent bulbs however always have thermal protection. Preheat compact fluorescent bulbs always have only 2 pins and have a starter built into the base of the bulb and thus don't require an external starter to be used.

          Preheat fluorescent bulbs are never single pin. All of the following bipin linear bulbs are preheat:

          F13T5 and below
          F18T8 and below, F22"T8/D/4
          F17T8 700 and 800 series bulbs, Philips manufactured a F17T8/CW/28" bulb for appliance applications that was preheat start but it is interchangeable with F18T8 bulbs.
          F20T9 and below
          F20T10 and below
          F25T12 and below
          F20T12 bulbs can be operated on trigger start ballasts.
          A video of a preheat ballast starting a bulb

        • Trigger Start
          A ballast designed to start the largest of the bulbs considered in the USA to be preheat start like F20T12 and F30T12 bulbs in a rapid manner like a rapid start ballast. Refer to the videos showing rapid start and preheat start for a comparison.
        • Rapid Start
          "Lamp starting method in which lamp filaments are heated while open circuit voltage (OCV) is applied to facilitate lamp ignition." - Advance Ballast Glossary. Rapid start ballasts both operate and start bulbs more gently than preheat or instant start but generally have a lower starting temperature. Rapid starting is faster than preheat but slower than instant start.

          A video of a rapid start ballast starting a bulb
        • Programmed Start
          "An electronic lighting circuit similar to rapid start that provides precise heating of the lamp filaments and tightly controlling the pre-heat duration before applying starting voltage to ignite the lamp." - Advance Ballast Glossary. Programmed start both operate and start bulbs even more gently than rapid start and have a higher starting temperature. Programmed start ballasts start bulbs faster than rapid start and preheat and possibly as quickly as instant start.
      • Fluorescent Specialty Ballasts

        • Cooler, Freezer/Zero Degree
          These ballasts are designed to operate in low temperatures.
        • Dimming
          Dimming ballasts do as one would expect; they dim the bulbs they operate. Modern dimming ballasts almost exclusively make use of 0 - 10 volt dimmers. These are dimmers that send signals to the ballast from 0 to 10 volts
        • Door
          Door ballasts are often manufactured specifically for applications and are for use in cooler/freezer/low temp applications. Anthony ballast is an example of a company that manufactures a number of door ballasts.
        • Emergency
          Emergency ballasts have batteries installed that will operate generally only one bulb but at a reduced light output for a period of time. They include LED indicator lights for visual inspection from below and push buttons for required periodic testing. Pressing the button disconnects input power to the fixture thus allowing for a test of the emergency ballast's functionality. If it is working it will light the bulb until the button is released. Generally these should be tested once per month.
    • HID

      • Constant-Wattage Autotransformer (CWA)
      • Constant-Wattage Isolation (CWI)
      • High-Reactance (HX)
      • Reactor (R)
        • Will run bulbs that can operate at the supply voltage. Most common examples are 35 - 150 watt high pressure sodium bulbs which only require 120 volts to operate and thus only require an ignitor to start the bulb and the ballast to operate. Reactor ballasts are almost exclusively single tap (only one input voltage accepted). Because of the simple and conservative construction of reactor ballasts they are cheaper than others. They don't require capacitors and thus to further reduce costs ballast kits generally do not include them. However, when the appropriate capacitor is used with a reactor ballast it provides excellent power factor correction.
    • Induction


Ballast Code

See American National Standards Institute HID Codes.

Ballast Efficacy Factor

  • Abbreviated as BEF
  • "Measure used to compare various lighting systems based upon light output and power input." - Advance Ballast Glossary

Ballast Loss

See Ballast > Ballast Loss.


One word used to describe a range of wavelengths within the electromagnetic spectrum. Similar to Spectrum.


The point that a bulb and fixture contact.


When referring to a Quality Control (QC) batch it is important to use the internal lingo of simply a "QC". This is sometimes used as a slang reference to a generic grouping of bulbs such as those shipped on a particular order, received in from a third party or even a grouping of bulbs in an installation. This is an ambiguous use of this word and should not be used to avoid confusion.

Bayonet (Base)

Often referred to as a "push and twist" type of base. Bayonet bases are of either single or double contact design. All bayonet sockets are spring loaded to keep pressure against the base so that once it is twisted into place the locking notch is secured into its slot to prevent the bulb from falling out. The official names for bayonet bases always begin with the letter B or BA then a number that represents the millimeters in diameter and finally a lower case s or d for single contact or double contact respectively. A non-exhaustive list of bayonet bases:
Low Pressure Sodium
Images: single contact bayonet base bulb with its locking notch highlighted and single contact bayonet socket (top), BY22d base of a low pressure sodium bulb with its locking notch highlighted (bottom).

Beam Spread

  • An angular measurement stated in degrees (°) that is measured in two opposite directions from the center of the beam outwards to the point that the intensity of the beam reaches 50% of the beam's maximum intensity. These two angles are then added together to equal the total field angle. The shape of this beam is cone shaped.
  • The image to the right is a graphical representation of a single plane measurement of the beam spread of a reflector bulb. The angular measurements are shown around the outer edge of the graph and the intensity values are shown down the center of the graph. See Goniophotometer.
  • Total beam spread equals the sum of the measurements taken of two angles along a fixed 2 dimensional plane that both begin in the center of the beam, continue in opposite directions along the aforementioned plane and then end at the point where the beam intensity drops to 50% of the center beam intensity. This is different from field angle which is similar but is measured to 10% of the center beam intensity.
  • In the lighting industry beam spreads are very often referred to by industry standard names as opposed to degrees. The range of degrees represented by each of these names often varies based on the size and shape of the reflector in question as well as from manufacturer to manufacturer and thus they are really just used to differentiate ascending/descending beam spreads.
    Here are the most common names shown along with ranges of beam angles to which various manufacturers have applied the associated name:
    Super (Pin) Spot
    Very Narrow Spot
    Narrow Spot
    Very Wide Flood
    Wide Flood
    Medium Flood
    Narrow Flood

Bilirubin Blue Bulb

  • A special type of bulb used to treat newborn babies born with jaundice.
  • 04565B - D F20T12BB BILI BLUE
    08742B - D F40T12BB BILI BLUE
  • The following is an excerpt taken from

      "Newborn jaundice occurs when a baby has a high level of bilirubin in the blood. Bilirubin is a yellow substance that the body creates when it replaces old red blood cells. The liver helps break down the substance so it can be removed from the body in the stool.
      A high level of bilirubin makes a baby's skin and whites of the eyes look yellow. This is called jaundice.
      Sometimes special blue lights are used on infants whose levels are very high. These lights work by helping to break down bilirubin in the skin. This is called phototherapy.

      • The infant is placed under these lights in a warm, enclosed bed to maintain a constant temperature.
      • The baby will wear only a diaper and special eye shades to protect the eyes.
      • Breastfeeding should be continued during phototherapy, if possible.
      • In rare cases, the baby may need an intravenous (IV) line to deliver fluids.

      If the bilirubin level is not too high or is not rising quickly, you can do phototherapy at home with a fiberoptic blanket, which has tiny bright lights in it. You may also use a bed that shines light up from the mattress.

      • You must keep the light therapy on your child's skin and feed your child every 2 to 3 hours (10 to 12 times a day)."

Bipin Base

See Base.


A theoretical object that among other things would be perfectly black (which means that it would perfectly absorb all light) and that would not melt. Some materials such as tungsten (the metal filaments in bulbs are made from) and graphite are fair approximations of a blackbody.

Blacklight Blue Bulb

Abbreviated as "BLB". A fluorescent bulb that is made with a dark purple glass called "Wood's glass". The dark purple color of the glass is not a paint or coating but is due to the actual composition of the glass. The peak wavelength of BLB bulbs is most commonly 365 nm. This special glass filters out certain wavelengths in order to produce a cool purple glow. This bulb is commonly referred to by customers as simply a "blacklight" but a true blacklight is a different bulb so it is important to clarify which bulb is being referred to.

Blacklight Bulb

Abbreviated as "BL". The peak wavelength of BLB bulbs is most commonly 350 nm. BL bulbs are commonly used in "bug zappers" and also in coating curing applications.


A generic term to describe that a bulb is now inoperative. Most commonly a 'blown' bulb will have some sort of residue on the inside of the glass.

Bottom Leads

"A configuration with leads or a wire-trap on the bottom or base of the ballast. This type of configuration is usually used when the ballast is mounted onto a junction box plate." - Advance Ballast Glossary

Box Mounting(ed)

See Mounting - Fixture.

Bulb Blackening

A less descriptive name for Bulb Wall Blackening used by some in the lighting industry. See Bulb Wall Blackening.

Bulb Flaring

A visible phenomenon seen in newly installed Metal Halide bulbs. This "flaring" of light and color is a result of the relocation and reaction of the metal halides within the arc tube. This phenomenon occurs for 100 hours or less after the initial installation of the Metal Halide bulb and will cease upon the full stabilization of the arc tube's contents.

Bulb Wall

The inside surface of a light bulb's envelope.

Bulb Wall Blackening

  • Also referred to as "Bulb Wall Blackening". This is the process of a material from within the bulb depositing on in inside of the bulb wall. This process occurs in all bulbs that make use of tungsten filaments or electrodes and is a result of tungsten particles being expelled from the filament. This blackening process is most pronounced at the time that the filament is energized. Because of the high temperatures of the tungsten during operation a small amount of evaporation would occur but the degree of blackening that actually occurs is a result of the stresses and vibration caused by the sudden rush of current when the bulb is first powered on. This is why turning an incandescent bulb on and off again and again shortens its life.
  • Incandescent bulbs do suffer from lumen depreciation but not in the same ways as discharge bulbs such as fluorescent, HID and LED. The lumen depreciation of incandescent bulbs is actually caused by this bulb wall blackening effect. As additional deposits form on the inside bulb wall they begin to block more and more light.
  • When operated properly the nature of the halogen cycle in tungsten halogen bulbs prevents bulb blackening from occurring.


Burn-in Test

"Test performed on electronic products that simulates conditions encountered in actual operation." - Advance Ballast Glossary


For LED fluorescent retrofit bulbs this means that the ballast must be removed from the circuit before installing the bulb. Afterwards the bulb will be powered by the line voltage that was originally supplying the ballast.