Definition of Lighting Terms to Simplify Maintenance Lighting Purchases

Definition of Lighting Terms to Simplify Maintenance Lighting Purchases


Watts divided by volts.


American National Standards Institute.  The organization that develops voluntary guidelines and produces performance standards for the electrical and other industries.  A unique code developed and assigned by the American National Standards Institute.  This code describes the class and electrical characteristics of lamps and ballast as well as fixture requirements.  The ANSI CODE consists type of lamps as

M=Metal Halide
L=LPS and followed by the ballast number.

Metal halide lamps are followed by the fixture requirement (O, E, S, F).


The dimension of the arc discharge measured from one electrode tip to the other is called Arc Length.  It is useful for optical design of reflectors and effects fixture efficiency as well.


An average rating, in hours, indicating when 50% of a large group of lamps have failed, when operated at nominal lamp voltage and current.  Average life is defined as the total operation hours at which 50% of any group of lamps is still under operation.  There are exceptions for most High Pressure Sodium and Mercury Vapor Lights, which 65% of the lights are operating at the end of the life.  The average life of a lamp is based upon vertical operation of representative lamps operated under controlled conditions at least 10 hours per start.  Exception is MH1500 which based on 5 hours per start.

Line voltage, and all the variations regarding lamp operation conditions could have an impact on lamp life.  Regular operation lamp with off time less than 15 minutes will shorten lamp life.


A device which provides the necessary starting voltage and appropriate current to a fluorescent or high intensity discharge (HID) luminaire.


A ratio used to calcculate the expected real-world performance of a lamp.  Calculated as the difference between the expected performance of a lamp with a commercial ballast versus the measured performance of that lamp with a reference ballast.  Rated Lamp Lumens x Ballast Factor = Net Lumens.


E26 Medium - Medium (MED) bases are usually used on lamps in E27 bulbs and are limited to 200W maximum.

E39 Mogul - Mogul (MOG) bases are usually used on lamps in ED28 and bigger and are limited to 1500W.

EX39 Exclusionary Mogul Base - Exclusionary Mogul Bases (EX MOG) are bases used on metal halide lamps having shrouded arc tubes permitting them to be used in open fixture applications.  These bases are compatible with exclusionary or standard mogul sockets.

Rx7s / R7s Recessed Single Contact - Double-ended HID lamps are recessed single contact (RSC) bases have similar contacts to provide maximum electrical contact.


Glass enclosure contains chemical elements as a lighting source.  Each bulb description consists of both a letter to indicate the bulb shape and number to show the maximum bulb diameter in 1/8" increments.  For instance, BT37 bulb indicates a blown shape with tubular top, 37/8 of an inch or 4 5/8" in diameter.  HID bulbs are made of glass designed to resist thermal shock in normal applications.  They must be shielded from direct contact with liquids (such as rain) during operation to avoid bulb breakage.


Color Rendering Index (CRI) is an international scale (numbering system) up to 100 indicating the relative color rendering quality o a light source when compared to a standard reference light source of the same chromaticity (color temperature).  The CRI expresses the degree to which colors will appear "familiar" or "natural" under the light source selected.  In general, the higher the CRI number, the better the color rendering properties of the light source being measured.  The color rendering index of any two like sources should only be compared if those sources have the same correlated color temperature (CCT).


The correlated color temperature of a light source, expressed in Kelvin (K), is a means of describing the appearance or chromaticity of the source.  The correlated color temperature of the light source contributes to the visual appearance of the lighted space.  "Warm" light sources have a low color temperature (2000-3000K) and features more light in the red/orange/yellow range.  Light with a higher color temperature (>4000K) features more blue and is referred to as "cool."

With new installations, or group relamps, all color performance evaluations should be made after at least 100 hours of operation (at recommended operating cycles) to allow the lamps to stabilize.  Additional changes in chemistry within the arc tube over the life of the lamp may also cause the color temperature to shift as the lamp gets closer to the end of it's rated life.  To minimize color variation within an installation, it is recommended that HID lamps be group re-lamped and run on equal operating cycles.


A device which senses the amount of daylight in a room and controls the luminaire accordingly.


Developed by the American National Standard Institute (ANSI), the fixture requirement code describes the type of fixture required for each lamp type.  See lamp warnings for additional information and proper operating instructions.

E = Lamps classified as E-type are to be used ONLY in suitably rated enclosed luminaires.

O = Lamps classified as O-type, comply with ANSI Standard C78.387 for a containment testing and may be used in open luminaires.

S = When operated within 15 degrees of vertical, this lamp may be operated in an open luminaires provided the installation is not near people or flammable or combustible material, otherwise it must e operated in a suitably enclosed luminaires.


HID are bulbs used in outdoor applications like parking lots, pathway, and area lighting as well as indoor for facilities like industrial warehouses.  They are two main kinds of HID Lamps - Metal Halide (produces a bright white light) and High Pressure Sodium (produces a harsh yellow light.  Their ballasts use probe start or pulse start - each is unique to the bulbs.  This category also used to include Mercury Vapor bulbs, but they are mostly obsolete.

  • Unprotected Arcs are to be used in a closed fixture.
  • Protected Arcs have a tube around the filament to protect it and can be used in an open fixture.
  • Universal Burning Position is when a bulb can be mounted vertically or horizontally.
  • H75 is when a bulb can only be mounted horizontally.
  • BU is when a bulb can only be burned base up (vertically).


HPS are the original style of outdoor lighting bulbs.  They're frequently known for the very yellow light output (typically 2200K) with high lumens and an exceptionally long life.  Most properties with exterior lighting are leaving HPS for a whiter light available from LED or Metal Halide bulbs.


In most instances, if an HID lamp experiences a momentary power interruption or sudden voltage drop, the lamp may extinguish.  A lamp that is still hot will not restart immediately.  Because the arc tube within the lamp must cool down before it can restart, HID lamps have hot re-strike times ranging from 1-15 minutes depending on the product type.


The lumens produced by a lamp after an initial burn in period (usually 100 hours)


The total wattage required by both the ballast and the lamp in a luminaire.


Ballast starting type.  Applies high voltage across the lamp with no preheating of the cathode


A numerical scale used to describe the color of light.  Light with a lower Kelvin rating will have a more yellow tint, while light with a higher Kelvin rating will have a more blue tint.  (See "Color Temperature")


The source of light in a fixture, colloquially called a "light bulb"


The light center length of HID lamps is a measurement from the center of the arc tube to the bottom of the lamp base.


A unit of luminous flux; overall light output, quantity of light, expressed in lumens.  For example, a dinner candle provides about 12 lumens and 60-watt soft white incandescent lamp provides about 840 lumens.


The decrease in lumen output of a light source over time.  Every lamp type has a unique lumen depreciation curve (sometimes called a lumen maintenance curve) depicting the pattern of decreasing light output.


The maximum overall length of single-ended lamps is the maximum distance from the top of the bulb to the bottom of the base.  For double-ended lamps, it is the maximum distance from end-to-end (excluding any lead wires.)


A measure of the effectiveness with which an electrical device converts void-amperes to watts; devices with power factors (<0.90) are "high power factor" devices.


5/8" diameter fluorescent lamps.  "T" stands for tubular, while the number "5" stands for the 5 in 5/8".  Therefore, a T8 lamp would be a Tubular 8/8, or 1" diameter lamp.


1/4" diameter fluorescent lamps.


1" diameter fluorescent lamps.


1 1/2" diameter fluorescent lamps.


The manner in which a luminaire manages heat, either dissipating heat or retaining it.


Most HID lamps do not have instant on capabilities.  It may take several minutes for the arc tube to stabilize before optimal light output is achieved.


A unit of electrical power which equal to 1 joule per second.  Lamps are related in watts to indicate power consumption. 

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What Type of Base Do I Have?

What Type of Base Do I Have?

Choosing the right base for your light bulb isn't always the easiest thing when replenishing maintenance lighting supplies.  Many bases can look the same with slight variations, for example, of how the pins insert to the socket.

Here are samples of the most common light bulb bases to assist you in ordering the correct items:

If you need any assistance selecting the proper base, please contact us.

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Tips for Preparing Your Job Site for LED Upgrades

A successful LED upgrade requires defining your priorities, making sure new bulbs will work, identifying if you need LED bulbs vs. LED integrated fixtures, and several other considerations.
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Easy Understanding of Light Bulb Measures

Easy Understanding of Light Bulb Measures

if you're looking for any type of alternative to the bulb currently being used, there are many considerations to properly sizing a light bulb.  RealLighting has easy tips to help you manage the rounds and abouts of light bulbs. 
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