• A thin piece of ferrous metal (usually steel) punched into particular shapes for use in the construction of electromagnetic transformers. Laminations are used as building blocks for the magnetic core of magnetic ballasts.

  • The most common pattern laminations used in the construction of HID Ballasts are referred to as E and I laminations as shown:

    The Lamination Assembly


A word used often in the lighting industry in place of "light bulb". In modern mainstream English however it is technically incorrect. Thus, lighting professionals dealing with the public are encouraged to use the word they will understand, "bulb".


See Lighting Layout.


A soft metal with a low melting temperature commonly used in solder to make electrical connections on light bulbs and other electrical devices such as circuit boards.

Lead Wire

The wire that runs from the end of an electrode or filament to the associated electrical contact. Most commonly these wires are made of pure molybdenum wire.

Leadership in Energy and Environmental Design

Shortened to the acronym LEED. Philips Brochure.

LED Bulb

A bulb using light emitting diodes as its light source. LED Bulbs have been designed in a sufficiently wide selection now to fill almost any need and to retrofit almost any traditional bulb. Their efficacy exceeds that of any other light source in wide use today. As their cost had dropped the advantage of their use has increased significantly. LEDs also have superior efficacy with lumen per watt values of 130 or even higher. For additional information see Light Emitting Diode.

Left-Hand Thread

Abbreviated LHT. Base designation: EL26. A threaded base with the same dimensions as a standard E26 base but with threads that spin in the opposite direction. Was Intended to deter theft and also, in prisons, to prevent misuse.
Left Hand Thread
Right Hand Thread


  • Multi-Phase Power
  • Bulb

Leg Spacing

  • The spacing between the two legs of a u-bend fluorescent bulb.

  • The most common leg spacing is 6" but 1 5/8" and 3" also exist in "common use". There are however other spacings that are used for sign applications. These bulb's descriptions begin with "FTU" and are manufactured exclusively by Voltarc.

Leg Support

The hardware the spans the distance between the ends of two legs of a fluorescent u-bend bulb.



  • 1992 - Energy Policy Act (Abbreviated as EPACT92)
    • This law was drafted with heavy influence on the part of GE, Philips and Sylvania and as such created a number of short term advantages for them. This was done by changing requirements in such a way that only the technologies that they possessed could meet them.
    • Mandated for general service incandescent reflector bulbs the use of the BR shape including BR25, BR30, BR38 (for outdoor use, replaced the PAR38. Also called BPAR) and BR40.
    • The standard wattages for Indoor reflector bulbs, 75, 100 and 150 were replaced with 65, 85 and 120 respectively.
    • Established minimum efficacy levels that effectively banned the manufacture of incandescent general service PAR30 and PAR38 bulbs. This gave way to the mainstream offering of tungsten halogen bulbs in PAR shapes. Tungsten halogen bulbs were uncommon higher end bulbs at and prior to this time.
    • Established minimum efficacy levels for fluorescent bulbs that effectively banned the manufacture of 40 watt 4 foot linear and u-bend fluorescent bulbs and 75 watt 8 foot fluorescent. These were replaced with 34 and 60 watt bulbs respectively.

      In order to attempt to avoid confusion, for many years the 34 watt versions were still referred to as "F40" as opposed to "F34".

      These lower wattage versions had specific names and slash designations that varied from manufacturer to manufacturer:
      • GE: Watt-Miser (/WM) Ex: F40/CW/WM
      • Philips: Econo-Watt (/EW) Ex: F34/CW/EW
      • Osram Sylvania: Super Saver (/SS) Ex: F40/CW/SS
    • This law introduced the exemption for fluorescent cold temp or "zero degree" bulbs. This really applied to high output (HO) and very high output (VHO) fluorescent bulbs.
    • This law played a large role in the creation of Energy Star (created in 1992).
    • Useless trivia: This law was also responsible for the introduction of "low flush" toilets.
  • 2005 - Energy Policy Act
    • Banned the manufacture of Mercury Vapor ballasts after January 1st 2008.
    • Established minimum power factor ratings of 0.90 for fluorescent ballasts designed to operate 34 watt 4 foot and 60 watt eight foot fluorescent bulbs. Established minimum ballast efficacy factor values for these ballasts as follows:
      Application for operation o
      Ballast input voltage
      Total nominal lamp watts
      Ballast efficacy factor
      One F34T12 lamp
      Two F34T12 lamps
      Two F96 T12/ES lamps
      Two F96 T12HO/ES lamps
    • This law set into motion regulations that would ban the sale of common T12 magnetic fluorescent ballasts for use in OEM applications (fixture manufacturers installing the ballasts in new fixtures for sale).
      These magnetic ballasts were required to:
      • be labeled "FOR REPLACEMENT USE ONLY" on the ballast itself,
      • have wire leads that were the length of the bulb or shorter, and
      • be packaged in smaller carton quantities to prevent OEM use.
  • 2007 - Energy Independence and Security Act (Abbreviated as EISA)
    • Signed into law in 2007 by George Bush Jr
    • This is the law that people say "outlawed" incandescent bulbs. In all actuality it didn't outlaw incandescent bulbs; it created efficiency requirements that were sufficiently high that they couldn't be met by traditional incandescent bulbs. In order to reach the new standards high performance halogen bulbs had to be used. Over a period of a few years the requirements expanded to include progressively lower wattages. The bulbs that couldn't meet the requirements were said to have been "phased out".
      Wattage Before Regulation
      Wattage After Regulation
      Regulation Effective Date
      72 or less
      January 1st, 2012
      53 or less
      January 1st, 2013
      43 or less
      January 1st, 2014
      29 or less
      January 1st, 2014
    • Added regulations for 150-500 watt probe-start metal halide ballasts in specific applications. The requirements of the regulations resulted in pulse start technology taking over as the "standard" technology.


Visible radiant energy. Light is transmitted in the form of photons in varying amounts of primary colors of the visible spectrum are Red, Green and Blue which are collectively referred to as the RGB Color Model.

Light Center Length

Abbreviated as "LCL". The distance from the appropriate reference point on the base of a bulb to the center of the bulbs light source such as a filament or arc tube. The LCL of North American bulbs is measured in inches while every other country uses millimeters.

Light Emitting Diode

Abbreviated as "LED". A semiconductor light source that has over time evolved into a highly efficient and compact light source. While most light sources emit light in a spherical pattern and must then make use of inefficient optics to direct the light LEDs have the distinct advantage of naturally generating their light in a highly focused directional pattern.

See LED Bulb.

Light Source

In general conversation a light source is often considered something that either emits light or that appears to emit light. In this context, examples of light sources would be the sun, the moon, a light bulb or even a mirror. Of those examples however, only the sun and a light bulb emit light; the moon and a mirror both appear to emit light but actually only reflect light. In the lighting industry the phrase light source refers to either the sun or to a device that emits artificial light. Note that artificial light sources may in addition to a component that emits light such as a Light Emitting Diode (LED) or incandescent filament include various optics such as a reflector to direct the light being emitted.

Line Interrupt

"A brief stoppage in the flow of current supplied by the electrical distribution system." - Advance Ballast Glossary

Long Lamps

Name used to refer to fluorescent bulbs that are longer than 96 inches long (F96). More specifically this refers to F108 (9'), F117 (117") and F120 (10') fluorescent bulbs.

Long Life

A generic name applied to bulbs that have a longer life than what is normal for a particular product type.

Long Neck

A bulb with a longer neck than normal. This refers specifically to PAR30 shaped bulbs which come in both short neck (/SN) and long neck (/LN) versions.
Long Neck
Short Neck

Low Temperature

Commonly said as "low temp". Commonly used to reference fluorescent bulbs and ballasts, specifically those designed for use at refrigeration temperatures, around 40 degrees, or lower.

Low Voltage

Any voltage less than 120 volts. Low voltage may be either AC or DC.


Abbreviated as "lm". An international standard unit of measurement (SI) for Lumnous Flux. While there is more to it than this, it essentially is the amount of light being emitted by a light source.

See Average Lumen Output.

Lumen Depreciation

The gradual loss of effective light output occurring over the life of a light source. Most light sources including, but not limited to Incandescent, HID, Fluorescent and LED light sources are subject to this factor. Additional factors that are cumulative and time and environment dependent such as dirty reflectors, bulb walls, lenses and optics can also greatly affect light output.

Lumen Maintenance

The measurement of a light source's ability to maintain its light output. A light source with excellent Lumen Maintenance would have low Lumen Depreciation and vice versa. The Lumen Maintenance of a light source is generally shown as a graph that displays the light source's Lumen Maintenance Curve.

Lumens Per Watt

  • Abbreviated as "LPW". The unit used to state the efficacy of a light source. It is calculated by dividing the lumen output of a light source by the number of watts it consumes.
    LPW = Lumens over Watts

    As an example, the efficacy of a bulb that consumes 60 watts and that produces 600 lumens is 10 LPW.

    600 Lumens over 60 Watts = 10 LPW
  • The efficacy (lumens per watt) of various light sources changes with size, average light hours, color temperature, power consumption (watts) and/or 'density' of power consumed (the ratio of the size of the light source to the power being consumed).
    • The efficacy of incandescent and tungsten halogen bulbs generally increases as the wattage and kelvin temperature increases but decreases as the design life hours are increased.
    • the efficacy of fluorescent and compact fluorescent bulbs decrease as the power density increases. Using an 8' T12 fluorescent bulb as an example, the high output version has a significantly lower efficacy than the standard output version and very high output versions have even lower efficacies. However, it is worth noting that while the efficacy of a high or very high output fluorescent bulb is lower, the lumen output they emit is significantly higher than a standard wattage bulb of the same size. Size constraints may require that a product with a higher power density be used even if it results in lower efficacy.
  • Here is a list of the efficacy of various lighting sources:
    Lumens Per Watt (Min-Max)
    Tungsten Halogen
    Compact Fluorescent Plug-in
    Compact Fluorescent Screw-in
    Fluorescent T12 4' Cool White (34W) (D)
    Fluorescent T12 4' Daylight Deluxe (40W)
    Fluorescent T12 8' Daylight High Output (110W)
    Fluorescent T12 8' Very High Output (215W)
    Fluorescent T10 800 series (40W)
    Fluorescent T8 4' 700 series (32W) (D)
    Fluorescent T8 4' 800 series (32W)
    Fluorescent T5 4' 800 series (54W)
    Mercury Vapor Self Ballasted (160W)
    Mercury Vapor (400W)
    Metal Halide - Probe Start (standard) (400W)
    Metal Halide - Pulse Start (320W)
    LED Bulbs (4' Fluorescent Retrofit)
    High Pressure Sodium (400W)
    Low Pressure Sodium (180W)

Luminaire (Fixture) Efficiency

A value between zero and one that is calculated by dividing the lumens emitted by a light fixture by the lumens of the bulb being used within.


A rarely used measurement that requires a mathematical formula to make real use of. For the satisfaction of those that may feel shortchanged if no definition is included herein here is a more detailed definition: "Formerly, a measure of photometric brightness. Luminance has a rather complicated mathematical definition involving the intensity and direction of light. It should be expressed in candelas per square inch or candelas per square meter although an older unit, the 'footlambert', is still sometimes used. Luminance is a measurable quantity whereas brightness is a subjective sensation." - GE Lighting Glossary.

Luminous Flux

See Lumen.


Abbreviated as "lx". The international standard unit of illuminance. One lux is equal to one lumen per square meter.