Abbreviated as F. The SI unit of measurement of an item's ability to store a charge. In lighting this is used to quantify a capacitor's ability to store a charge.

Federal Communications Commission

Abbreviated as "FCC".
"FCC (Federal Communications Commission) Regulations - Legally enforceable U.S. government standards for EMI and RFI that must be met by highly frequency electronic devices used in this country for Class A (industrial) or Class B (residential) applications." - Advance Ballast Glossary


A type of double ended base used most commonly in double ended miniature bulb applications.


Field Angle

Not to be confused with beam angle. 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 10% of the beam's maximum intensity. These two angles are then added together to equal the total field angle. The intensity of the light emitted between the beam angle is sufficiently low that it is considered excess wasted light. This measurement is different from beam spread which is similar but is measured to 50% of the beam's maximum intensity.


  • The thin conductive wire inside a light bulb most commonly made of tungsten which is a naturally occurring metallic element with a very high melting temperature. A major contributing factor to the inefficiency of traditional incandescent bulbs is the escape of heat from the filament. Thus the smaller the effective volume of a filament the higher its efficacy will be. By designing an incandescent filament in such a way that it occupies as small an area as possible a larger amount of the generated heat is able to be converted into light by incandescence. In order to accomplish this goal filaments are coiled or in some cases even double coiled (called a "coiled coil" (CC))
  • While efficiency is important, in some cases other considerations outweigh efficiency. An example of this would be in applications where significant shock or vibration will be common. In these applications filaments must be much longer in order to accommodate additional mounting supports and also to avoid short circuiting the filament itself by inadvertent touching. Another example where efficiency can take a backseat is in the case of higher voltage bulbs. In these bulbs the filaments are significantly longer and thus in some cases require creative engineering to manage to fit the filament into the bulb at all.

Filament Evaporation

The process of tungsten leaving the filament as a result of evaporation that is caused by the extremely high temperature that it reaches.

Filament Notching

The condition of the filament that results from filament evaporation. Over time, filament evaporation results in the filament's surface becoming "notched". Notching is just one condition that results in an incandescent and/or halogen bulb becoming inoperative.

Filament Voltage

Voltage applied to fluorescent electrodes to preheat the filaments for operation.


  • See Optics.
  • (Ballasts) "Functional grouping that limits interference feedback into the power source and protects internal ballast components." - Advance Ballast Glossary

Fixture (Lighting)

  • Light fixtures are technically called "Luminaires" but this isn't the most common industry speak. "Fixture" refers to the entire lighting system which may include, but would not be limited to a ballast, driver or transformer, instant restrike system, emergency battery backup power supply, reflector, optics, louvers, fuses, mounting hardware as well as other components.
  • Indoor Interior Fixtures
    • Carriage
    • Chandelier
    • Exit Signs & Emergency Fixtures
    • Lay-in
    • Panel Lighting
    • Recessed
    • Rope & Tape Light
    • Track Lighting
    • Troffer
      • According to Merriam-Webster: Origin and Etymology of troffer blend of trough and coffer. First Known Use: 1942
      • See Fixture > Lay-in.
    • Vanity
    • Wraparound
  • Indoor Commercial & Industrial Fixtures
    • Dock Lights
    • Explosion Proof
    • High Bays
    • Horticultural
    • Strip
    • T-Bays
    • Vaportight
  • Outdoor Landscape/Accent Lighting
    • Bullet Style
    • Bollard
    • Malibu
    • Pool
    • Security
    • Step Light
  • Outdoor Commercial & Industrial Fixtures
    • Canopy
    • Flood
    • Parking Lot
    • Roadway
    • Shoebox
    • Sign Lighting
    • Sports Lighter
    • Vandal Guard
    • Wall Pack
    • Work Light


"Rapid visible light change occurring in fluorescent lighting systems. It is virtually indistinguishable in lamps operated by electronic ballasts because of their high operating frequency." - Advance Ballast Glossary


A common misspelling of fluorescent.

Fluoresce (Fluorescent)

To fluoresce is to absorb a shorter wavelength of the electromagnetic spectrum such as ultraviolet and then to emit a longer wavelength such as light (sometimes redundantly referred to as "visible light").

Fluorescent Bulb

  • A traditional light source which relies upon a combination of phosphors, ultraviolet emissions and a control circuit such as a ballast to produce light. Most commonly fluorescent bulbs are tubular in shape the inside surface of which is coated with a white powder called phosphor. Ultraviolet emissions excite the phosphor coating which then in turn emits light. The most common source of ultraviolet emissions inside of a fluorescent bulb is from the excitation of mercury. The ultraviolet emission spectrum of mercury peaks at 254 nm. Fluorescent bulbs most commonly have a low pressure argon gas fill that supports both their starting and continued operation.
  • Starting and Operation

    • A ballast and starting circuit are required for all fluorescent bulbs. Traditional "preheat start" fluorescent bulbs such as a F15T8 style bulb require a separate capacitive "starter" to be wired in line with the ballast. "Rapid start" and "trigger start" ballasts have the starter built into the ballast. The distance between the ballast and lamp is called the Ballast to Lamp distance (BTL). If the bulb is wired beyond the length of the pre-installed wire leads it can lead to starting and/or operational problems such as shortened lamp life, flickering, strobing among others.
    • Fluorescent bulbs are quite sensitive to temperature. An excessively high or low temperature will result in an appreciable loss in light output. Furthermore, a sufficiently low temperature can prevent a fluorescent bulb from starting entirely. Starting temperatures vary based on the bulb series. Special ballasts designed to start bulbs in low temperatures are available for many different bulb series. Often times these ballasts are referred to as "low temp", zero degree, cooler, refrigeration or freezer ballasts.
  • Mercury Content

    • Large fluorescent bulbs in the past have contained as much as 50mg of mercury per bulb. In recent times however due to significant pressure from government authorities much progress has been made by manufacturers to reduce mercury content. Philips has successfully reduced the amount of mercury contained in each of their ALTO II four foot 32 watt T8 bulb bulbs to 1.7mg. For comparison, an old style mercury thermometer contained 610mg of mercury, an old style mercury thermostat contained 3,000-6,000mg while Mount Kilauea, a shield volcano on the island of Hawaii all by itself releases 270 tons of mercury per year (244,940,171,095mg).[^] That is the equivalent of the mercury contained in 144,082,453,585 4-foot low mercury T8 Philips bulbs.
    • Low Mercury Bulbs

      • In the lighting industry low-mercury bulbs are referred to as "TCLP compliant" or "low mercury". Common designations for these bulbs are "ECO" and "ALTO" (ALTO is a registered trademark of Philips Lighting Company).
      • As a result of the overzealous* efforts of Philips to lower the mercury content in their bulbs of the condition shown in the picture to the right is not uncommon when using their bulbs.

        *Their efforts are overzealous simply because:
        1. Regardless of the amount of mercury they contain, the laws in essentially all states now require that businesses of a particular size recycle all fluorescent and HID bulbs regardless of the amount of mercury they contain;
        2. The type of mercury that is being used is no longer elemental mercury and is of a type that is HIGHLY leach resistant, is so over an EXTREMELY long time period and is in Philips case contained within a specially made glass capsule that is designed specifically to prevent mercury spillage.

Fluorescent Starter

A small piece of auxiliary gear used only with preheat start fluorescent bulbs and the appropriate corresponding ballasts. Provides a high-voltage discharge to preheat the bulb's filaments and thus begin the starting process. Starters are designed to continue the starting process until the bulb is lit. Once a preheat bulb reaches its end of life the starter may no longer be able to start the bulb and thus will continue attempting again and again. These continuous attempts to start the bulb can cause overheating and/or failure of lighting system components and can even present a fire hazard. The proper course of action is to replace the bulb but in the case that a bulb is installed in an application where the end of life symptoms (continuous flickering and starting) may not be seen a type of fluorescent starter with a reset button is available. This type of starter will "trip" or open the circuit if it is unable to start the bulb. When it does so the button on the starter will pop out and will not attempt to start again until the button is pressed in again.
Common starter
Video Demo
Starter with reset button
Video Demo
Intermediate base
Video Demo
FS-85 90-100 watt starter
Compared to normal size

Fluorocarbon Coating

  • Teflon
  • FEP


Abbreviated as "fc". Technically printed as "foot-candle" but in practice it will be most often seen as simply "footcandle". Used to measure the intensity of the light falling upon a surface. This is a unit of measurement of illuminance. One footcandle equals one lumen per square foot.

See Lux


A rarely used measurement of luminance. In more recent time the unit of candelas per square meter is used.


A small area centered in the retina that is responsible for providing Photopic Vision.


A small area centered in the retina that is responsible for providing Photopic Vision.


A bulb 'dreamed up' to fill a need or application. Most commonly a non-existent bulb that combines the features of one or more bulbs.


  • The number of wave cycles that pass a given point in one second. The unit of measure for frequency is hertz.
  • See Alternating Current.

Functional Group

"Assembly of electronic components designed to accomplish a given task in the electronic ballast, such as EMI filtering, or power factor control." - Advance Ballast Glossary