Glossary of Terms
Lamp Measurement Terms

MOL – Maximum overall length in inches
LCL – Distance from the light center to the bottom, measured in inches
Dia – Maximum overall diameter in inches
Common Lighting Terms & Definitions
AMP – Watts Divided by Volts.
ANSI – American National Standards Institute. The organization that develops voluntary guidelines and produces performance standards for the electrical and other industries.
AVERAGE RATED LIFE – An average rating, in hours, indicating when 50% of a large group of lamps have failed, when operated at nominal lamp voltage and current.
BALLAST — A device which provides the necessary starting voltage and appropriate current to a fluorescent or high intensity discharge (HID) luminaire.
BALLAST FACTOR — A ratio used to calculate 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.
CRI — Color Rendering Index, sometimes CIE. The ability of a light source to accurately render an object’s color in comparison with a natural light source. Measured on a scale of 1 -100 with 100 being the ideal.
COLOR TEMPERATURE – The temperature at which a black body would emit radiation of the same color as a given object. With higher color temperature, the light is whiter or bluer.
DAYLIGHT SENSOR — A device which senses the amount of daylight in a room and controls the luminaire accordingly.
HID — High Intensity Discharge lamps. Includes HPS, PSMH and MH lamps.
HPS — High Pressure Sodium HID Lighting.
INITIAL LUMENS – The lumens produced by a lamp after an initial burn in period (usually 100 hours).
INPUT WATTS — The total wattage required by both the ballast and the lamp in a luminaire.
INSTANT START– Ballast starting type. Applies high voltage across the lamp with no preheating of the cathode.
KELVIN TEMPERATURE— 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.
LAMP — The source of light in a fixture, colloquially called a “light bulb.”
LUMENS – A unit of luminous flux; overall light output; quantity of light, expressed in lumens.
POWER FACTOR – A measure of the effectiveness with which an electrical device converts volt-amperes to watts;devices with power factors (< 0.90) are “high power factor” devices.
T5 — 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.
T8 — 1” diameter fluorescent lamps.
T12 — 1 1/2” diameter fluorescent lamps.
THERMAL CHARACTERISTICS — The manner in which a luminaire manages heat, either dissipating heat or retaining it.
High Intensity Discharge
The catalog format and related terminology are designed to help readers easily understand the information presented in this section. Lamp identification is simplified by listing the lamp families in ascending wattage, followed by an alphabetical bulb designation. Performance ratings are based on tests conducted under controlled conditions using AC circuits and auxiliary equipment, ensuring compliance with the latest ANSI specifications. However, actual lamp performance may vary under typical service conditions. Please note that ratings and specifications are subject to change without prior notice.
ANSI CODE – ANSI CODE is a unique code developed and assigned by the American National Standards Institute. This code describes the class and electrical characteristics of lamps and ballasts as well as fixture requirements. The ANSI CODE consists type of lamps as S=HPS, H=Mercury, M=Metal Halide, L=LPS and followed by ballast numbers. For metal halide lamps are followed by the fixture requirement (O,E,S,F)
ARC LENGTH – The dimensions 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 affects fixture efficiency as well.
AVERAGE LIFE (HOURS) – 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 lamps, which 65% of the lamps are operating at the end of the life). The average life of a lamp is based upon the vertical operation of representative lamps operated under controlled conditions of at least 10 hours per start (except MH 1500 which is based on 5 hours per start).
Following list shows the reduced lamp life caused by lamp operating cycles less than 10 hours per start.
5 hours/start–Approximately 75% of rating
2.5 hours/start–Approximately 55% of rating
1.25 hours/start–Approximately 40% of rating
Line Voltage, and all the variations regarding lamp operation conditions such as bulb base or base temperatures could have an affect on lamp life. Regular operation lamp with off time less than 15 minutes will shorten lamp life.
BASE
E26 Medium– Medium (MED) bases are usually used on lamps in E17 bulbs and are limited to 200W maximum.
E39 Mogul – Mogul (MOG) bases are usually used on lamps in ED28 and larger but limited to 1500W maximum.
EX39 Exclusionary Mogul Base – Exclusionary Mogul Base (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/R7 Recessed Single Contact – Double-ended HID lamps with recessed single contact (RSC) bases have silver plated contacts to provide maximum electrical contact.

BULB – Glass enclosure contains chemical elements as lighting source. Each bulb description consists of both a letter to indicate bulb shape and number to show the maximum bulb diameter in 1/8 inch increments. For instance, BT37 bulb indicates a blown shape with a tubular top
3-7 /8 of an inch or 4-5/8 inches 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.
LIGHT CENTER LENGTH (LCL) – The light center length of HID lamps is a measurement from the center of the arc tube to the bottom of the lamp base.
MAXIMUM OVERALL LENGTH (MOL) – 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).
WARM UP TIME – 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.
WATTS – A unit of electrical power which equals to 1 joule per second. Lamps are rated in watts to indicate power consumption.
COLOR RENDERING INDEX (CRI) – Color Rendering Index is an international scale (numbering system) up to 100 indicating the relative color rendering quality of 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).

CCT (Correlated Color Temperature) describes a light source’s appearance, measured in Kelvin (K). “Warm” light (2000-3000K) has more red, orange, and yellow tones, while “cool” light (>4000K) has more blue tones. CCT influences the visual feel of a space.

HOT RESTRIKE – 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. The Arc Tube within the lamp must cool down before it can restart, HID lamps have hot restrike times ranging from 1-15 minutes depending on the product type.
FIXTURE REQUIREMENT
Developed by the American National Standards 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 containment testing and may be used in open luminaires.
S = When operated within 15° of vertical, this lamp may be operated in an open luminaire provided the installation is not near people of flammable or combustible material, otherwise it must be operated in suitably enclosed luminaires.
LUMENS (lm) – A unit of luminous flux, overall light output, and 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.
LUMEN DEPRECIATION – The decrease in the 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.