- A -

Accent Lighting 
Directional lighting to emphasize a particular object or draw attention to a display item.

The process by which the human eye adjusts to a change in light level.

Additional Information 
Typical application and/or other important information including footnotes, operating information, features and benefits.

Ambient Lighting 
The general lighting present in an area --excluding task lighting and accent lighting but including general lighting and daylight streaming in.

("Amps.") A measure of electrical current. In incandescent lamps, the current is related to voltage and power as follows: Watts (power) = Volts x Amps (current).

Also called "lighting application," it refers to the particular use the lamp is being put to. (e.g. high-bay industrial application or retail lighting application.) The term can also refer in a general way to "application engineering" which deals with specific paramters and usage of light sources. (e.g. how to do a lighting layout, where to place fixtures and so on.)

A general term for a high intensity electrical discharge occurring between two electrodes in a gaseous medium, usually accompanied by the generation of heat and the emission of light

Arc Lamp 
A light source containing an arc (see above). Also called a discharge lamp, or an arc discharge lamp

Arc Length 
In High Intensity Discharge lamps this is the distance between the electrode tips, which represents the physical length of the electrical discharge.

This field designates the type of gas or vacuum filling a volume or chamber of the lamp. This chamber might contain a filament or it might refer to the bulb which contains the arc tube.

Average Rated Life - An average rating, in hours, indicating when 50% of a group of lamps have failed when operated at nominal lamp voltage and current. Manufacturers use 3 hours per start for fluorescent lamps and 10 hours per start for HID (High Intensity Discharge) lamps when performing lamp life testing procedures. Every lamp type has a unique mortality curve that depicts its average rated life. 

- B -

Baffles (Fixture) - A mechanism that regulates the flow of light in a fixture. 

Ballast - A device used with an electric-discharge lamp to obtain the necessary circuit conditions (voltage, current, and waveform) for starting and operating; all fluorescent and HID light sources require a ballast for proper operation. 

Ballast Factor (BF) 
This is the percentage of a lamp's rated lumen output that can be expected when operated on a specific, commercially available ballast. For example, a ballast with a ballast factor of 0.93 will result in the lamp's emitting 93% of its rated lumen output. A ballast with a lower BF results in less light output and also generally consumes less power.


Ballast Hum - A sound generated by the vibration of laminations in the electromagnetic field that transforms the current for discharge lamp use. 

Base or Socket 
The socket is the receptacle connected to the electrical supply; the base is the end of the lamp that fits into the socket. There are many types of bases used in lamps, screw bases being the most common for incandescent and HID lamps, while bipin bases are common for linear fluorescent lamps.

Base Temperature (Maximum) 
The maximum operating temperature permitted for the base in Celsius. Fixture manufacturers need to ensure that these conditions are satisfied in their fixture.

A style of bulb base which uses keyways instead of threads to connect the bulb to the fixture base. The bulb is locked in place by pushing it down and turning it clockwise.

Beam Angle 
The angular dimension of the cone of light from reflectorized lamps encompassing the central part of the beam out to the angle where the intensity is 50% of maximum. The beam angle sometimes called "beam spread" is often part of the ordering code for the reflectorized lamps. Example: The 50PAR30/HIR/NFL25 is a 50 watt PAR30 narrow flood lamp with a beam angle of 25 degrees

Beam Lumens 
The total lumens present within the portion of the beam contained in the beam angle.

Beam Spread (Approximate) 
For reflector type lamps. The total angle of the directed beam (in degrees horizontal or vertical) to where the intensity of the beam falls to 50% or 10% of the maximum candlepower value as indicated.

Any base with two metal pins for electrical contact. This is the typical base for a fluorescent tube of 1 to 4 feet in length. It consists of 2 prong contacts which connect into the fixture. Medium bi-pins are used with type T-8 and T-12 tubular fluorescent lamps, and miniature bi-pins are used for tubular T-5 fluorescent lamps.

A hot body with an incandescent black surface at a certain temperature used as a standard for comparison. Note that a black surface is the best radiator possible. A tungsten filament will emit slightly less radiation than a blackbody at the same temperature.

Black Light 
A popular term referring to a light source emitting mostly near UV (320 to 400 nm) and very little visible light.

Whether or not the top of the miniature lamp has a blacktop coating. The coating is used to control unwanted brightness or glare.

A short, thick post with a light at its top, used for grounds and outdoor walkway lighting.

A loose way of referring to a lamp. "Bulb" refers to the outer glass bulb containing the light source.

Bulb Material or Coating 
The type of glass (or quartz) used in the glass envelope surrounding the light source. The material can also have coatings applied to achieve particular performances.

Brightness can refer to any of several technical terms used in lighting and is, therefore, ambiguous

- C -

Compact Fluorescent Lamp (CFL) 
The general term applied to fluorescent lamps that are single-ended and that have smaller diameter tubes that are bent to form a compact shape. Some CFLs have integral ballasts and medium or candelabra screw bases for easy replacement of incandescent lamps.

Case Quantity or Standard Package Quantity 
Number of product units packed in a master case. Also known as Standard Package Quantity.

Cathode Resistance 
Resistance of the cathode in a Fluorescent lamp. It is measured "cold" before the lamp is turned on (Rc) or "hot" after the lamp is turned on (Rh). The ratio of the hot resistance to the cold resistance is also measured (Rh/Rc).

Center Beam Candlepower (CBCP) 
Refers to the luminous intensity at the center of the beam of a blown or pressed reflector lamp (such as a PAR lamp). Measured in candelas.

Ceramic Metal Halide (CMH?) 
A type of metal halide lamp that uses a ceramic material for the arc tube instead of glass quartz, resulting in better color rendering (>80 CRI) and improved lumen maintenance.

A GE brand name for metal halide lamps designed to operate on HPS ballasts, allowing a user to switch from the yellowish color of HPS to the white color of metal halide without changing ballasts. These products are available in both quartz metal halide and ceramic metal halide (CMH) versions.

Measure to identify the color of a light source, typically expressed as (x,y) coordinates on a chromaticity chart.

Chromaticity Coordinates 
A system for measuring the color of the light emitted from a light source--either a primary source like a lamp or a secondary source like an illuminated object. Usually two numbers, x and y coordinates ranging from 0 to 1 specify the chromaticity.

Coefficient of Utilization (CU) 
In general lighting calculations, the fraction of initial lamp lumens that reach the work plane. CU is a function of luminary efficiency, room surface reflectance and room shape.

Color Rendering Index (CRI) 
An international system used to rate a lamp's ability to render object colors. The higher the CRI (based upon a 0-100 scale) the richer colors generally appear. CRI ratings of various lamps may be compared, but a numerical comparison is only valid if the lamps are close in color temperature. CRI differences among lamps are not usually significant (visible to the eye) unless the difference is more than 3-5 points.

Color Rendering Indicator 
Draws attention to the fact that this is a lamp with high color rendering, which helps objects and persons illuminated to appear more true to life.

Color Rendering Index (CRI) - Color rendering is the ability of a light source to produce color in objects. The CRI is expressed on a scale of 0-100, where 100 is the best in producing vibrant color. 

Color Temperature - Originally, a term used to describe the "whiteness" of incandescent lamp light. Color temperature is directly related to the physical temperature of the filament in incandescent lamps, so the Kelvin (K) (absolute) temperature scale is used to describe it. Although it may not seem sensible, a higher color temperature (K) describes a visually cooler, bluer light source. More recently, the term "chromaticity" has been used in place of color temperature. 

Cool White - Reference to the color tone or appearance of light produced by a lamp for a specific color temperature. Cool White is the least expensive and most widely used fluorescent lamp color in lighting today. Its name comes from the cool, airy atmosphere it creates wherever it is used. Modern, efficient and business-like, it is popular in stores, classrooms, offices, corridors and factories. 

Correlated Color Temperature (CCT) - A term used for discharge lamps, where no hot filament is involved, to indicate that the light appears "as if" the discharge lamp is operating at a given color temperature. CCT generally measures the "warmth" or "coolness" of light source appearance using Kelvin(K) temperature scale. 

Compact Fluorescent Lamp (CFL) - A fluorescent type bulb that has the ability to be utilized in an incandescent fixture, and still maintain the efficiency and qualities of a standard fluorescent bulb. These bulbs generally offer 75% savings in electricity while maintaining comparable light levels. Compact Fluorescent bulbs require a special adapter/ballast or may have one built in. Average life span is 10,000 hours. 

Constant Color A GE Registered name for lamp families which show very little color shift over life. Generally applies to GE's PRECISE MR-16 and GE's CMH (Ceramic Metal Halide) lamps.

Cool White 
A term loosely used to denote a color temperature of around 4100 K. The Cool White (CW) designation is used specifically for T12 and other fluorescent lamps using halophosphors and having a CRI of 62.

An illuminance meter that measures the light level correctly irrespective of the angle the light is coming from.

Cost of Light 
Usually refers to the cost of operating and maintaining a lighting system on an ongoing basis. The 88-8-4 rule states that (typically) 88% is the cost of electricity, 8% is labor and only 4% is the cost of lamps.

Crest Factor (Max Current) 
The ratio of the peak lamp current to average lamp operating current (RMS). The lower the current crest factor is, the gentler the ballast is on the lamp.

Current Type (AC/DC) 
Whether the operational voltage is based on Alternating Current or Direct Current.

- D -

Daylight - Reference to the color tone or appearance of light produced by a lamp for a specific color temperature. The bluish white appearance of this lamp is similar to natural daylight. It makes rooms very cool and often gives a store or office a blue-white radiance. It is often used over white goods. 

Daylight Harvesting 
Lighting design for building interiors that makes of daylight as a way of reducing energy consumption.

Daylight Lamp 
A lamp resembling the color of daylight, typically with a color temperature of 5500 K to 6500K

Whether or not the lamp lumens can be varied while maintaining reliability.

Dimmer, Dimming Control 
A device used to lower the light output of a source, usually by reducing the wattage it is being operated at. Dimming controls are increasing in popularity as energy conserving devices.

Distance Between Legs 
For U-shaped Fluorescent lamps, this measurement is the average distance between the inner walls of the legs.

Distance Between Leg Centers 
For U-shaped Fluorescent lamps, this measurement is the average distance between the centers of each leg.

Distance Outside Legs 
For U-shaped Fluorescent lamps, this measurement is the average distance to the outside of each leg.

- E -

Eccentricity (Maximum) 
In High Intensity Discharge lamps the Bulb to Arc Angle is the angle off of center between electrodes and bulb. The Bulb to Base Angle is the angle off of center that the bulb is from the base.

Economic Life - The number of hours a group of lamps will burn before it is economically and aesthetically advisable to group relamp (typically 60% to 75% of rated life). 

Efficacy - Efficiency of a light source expressed in lumens per watt (LPW or lm/W). 

Electrical Discharge 
A condition under which a gas becomes electrically conducting and becomes capable of transmitting current, usually accompanied by the emission of visible and other radiation. An electric spark in air is an example of an electrical discharge, as is a welder's arc and a lightning bolt.

Electromagnetic Ballast 
A ballast used with discharge lamps that consists primarily of transformer-like copper windings on a steel or iron core.

Electronic Ballast 
A short name for a fluorescent high frequency electronic ballast. Electronic ballasts use solid state electronic components and typically operate fluorescent lamps at frequencies in the range of 25-35 kHz. The benefits are: increased lamp efficacy , reduced ballast losses and lighter, smaller ballasts compared to electromagnetic ballasts. Electronic ballasts may also be used with high intensity discharge lamps.

Elliptical Reflector (ER) Lamp 
An incandescent lamp with a built-in elliptically-shaped reflecting surface. This shape produces a focal point directly in front of the lamp which reduces the light absorption in some types of luminaires. It is particularly effective at increasing the efficacy of baffled downlights.

Eye Sensitivity 
A curve depicting the sensitivity of the human eye as a function of wavelength (or color). The peak of human eye sensitivity is in the yellow-green region of the spectrum. The normal curve refers to photopic vision or the response of the cones.

- F -

Filament - Tungsten wire positioned inside a bulb which generates light when heated. 

Field Angle 
The angular dimension of the cone of light from reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out to the angle where the intensity is 10% of maximum.

Fluorescent Lamp - A high efficiency lamp utilizing an electric discharge through low pressure mercury vapor to produce ultra-violet (UV) energy. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube which makes up the structure of the lamp. The phosphors transform the UV to visible light.

Filament Design 
Filaments are designated by a letter combination in which C is a coiled wire filament, CC is a coiled wire that is itself wound into a larger coil, and SR is a straight ribbon filament. Numbers represent the type of filament-support arrangement.

Fixture Requirements 
Describes fixture requirements for HID lamps. 
O = Open or Enclosed Fixtures 
E = Enclosed Fixtures Only 
S = Lamps operated in a vertical position (Base Up or Down) ±15o, can be used in an open fixture. Lamps burned in any other orientation must be used in "enclosed fixtures only." See additional details in the e-Catalog Help Menu under the HID category.

The periodic variation in light level caused by AC operation that can lead to strobe effects.

Used to refer to the beam pattern of a reflector lamp, which disperses the light over a wide beam angle, typically 20 degrees or more. ("Flood" as opposed to "spot")

A luminaire used to light a scene or object to a level much brighter than its surroundings. Usually floodlights can be aimed at the object or area of interest.

A physical phenomenon whereby an atom of a material absorbs a photon of light an immediately emits a photon of longer wavelength. If there is a significant delay the phenomenon is called phosphorescence rather than fluorescence. It is interesting that "phosphors" used in lamps exhibit "fluorescence," not "phosphorescence."

Fluorescent Lamp 
A high efficiency lamp utilizing an electric discharge through low pressure mercury vapor to produce ultraviolet (UV) energy. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube which makes up the structure of the lamp. The phosphors transform the UV to visible light.

Frequency (Nominal Operations) 
The stated operating frequency in Hz of a discharge lamp.

Full Spectrum Lighting 
A marketing term, typically associated with light sources that are similar to some forms of natural daylight (5000K and above, 90+ CRI), but sometimes more broadly used for lamps that have a smooth and continuous color spectrum.

- G -

Glare - Excessive brightness that may be caused by either direct of indirect viewing of a light source. 

- H -

Halogen Lamp - A short name for a tungsten-halogen lamp. Halogen lamps are high pressure incandescent lamps containing halogen gases such as iodine or bromine which allow the filaments to be operated at higher temperatures and higher efficacies. A high-temperature chemical reaction, involving tungsten and the halogen gas, recycles evaporated particles of tungsten back onto the filament surface. 

Harmonic - An integral multiple of the fundamental frequency (60HZ) that becomes a component of the current.

High bay Lighting Fixtures - High Bay Light Fixtures are ideal for general purpose lighting in areas such as warehouse facilities, assembly areas, gyms, hangars, transportation garages, loading and staging areas. Suitable for indoor applications where ceiling height exceeds 15 feet.

High Intensity Discharge(HID) - This is the general term for a mercury vapor, metal halide, or high-pressure sodium lamp. They differ from incandescent lamps in that there is no filament, but contain gas which when exposed to an electric charge, produces light. HID lamps require a ballast, which controls the electrical current that flows into the lamp. 

Hot Restart Time 
Time it takes for a High Intensity Discharge lamp to reach 90% of light output after going from on to off to on.

- I -

A GE designation for a family of metal halide lamps which will operate on a mercury ballast. Designed as a simple retrofit for mercury lamp.

An electronic device providing a high voltage pulse to initiate an electrical discharge. Typically, the ignitor is paired with or is a part of the ballast.

The "density" of light (lumens/area) incident on a surface .

Incandescent Lamp 
A light source that generates light utilizing a thin filament wire (usually of tungsten) heated to white heat by an electric current passing through it.

Infrared Radiation - Electromagnetic energy radiated in the wavelength range of about 770 to 1106 nanometers. Energy in this range cannot be seen by the human eye, but can be sensed as heat by the skin. 

Instant Start - A lamp starting method in which lamps are started by high voltage input with no preheating of lamp filaments. Some rapid start lamps are designed so that they may be instant started. 

Instant Start Lamp - A fluorescent lamp with a single pin at each end. The lamp is ignited by a high voltage without any filament heating. 

- K -

Kilowatt (kW) 
The measure of electrical power equal to 1000 watts.

Kilowatt Hour (kWh) 
The standard measure of electrical energy and the typical billing unit used by electrical utilities for electricity use. A 100-watt lamp operated for 10 hours consumes 1000 watt-hours (100 x 10) or one kilowatt-hour. If the utility charges $.10/kWh, then the electricity cost for the 10 hours of operation would be 10 cents (1 x $.10)

- L -

Lamp - The term used to refer to the complete light source package including the inner parts as well as the outer bulb or tube. "Lamp", of course, is also commonly used to refer to a type of small fixture such as a table lamp. 

Lamp Height 
Referenced by IEC as Dimension C. Also referred to as "Base Face to Top of Lamp".

Lamp Types 
Filament lamps: Incandescent, Halogen, Halogen-IR. 
Discharge Lamps: Fluorescent, HID (High Intensity Discharge) 
HID Lamps: Mercury, HPS (High Pressure Sodium), MH (Metal Halide) and CMH (Ceramic Metal Halide)

Lamp Watts - Input power used to operate lamps.

A transparent or semi-transparent element which controls the distribution of light by redirecting individual rays. Luminaires often have lenses in addition to reflectors.

Radiant energy that can be sensed or seen by the human eye

Light Emitting Diode (LED) 
A solid that directly converts electrical impulses into light. Some LED's today incorporate fluorescent materials to change the color characteristics of the emitted light.

Light Loss Factor 
The product of all factors that contribute to lowering the illumination level including reflector degradation, dirt, lamp depreciation over time, voltage fluctuations, etc.

Light Pollution 
Light that is directed to areas where it is not needed, and thereby interferes with some visual act. Light pollution directed or reflected into the sky creates a "dome" of wasted light and makes it difficult to see stars above cities.

Light Trespass (Spill Light) 
Light that is not aimed properly or shielded effectively can spill out at into areas that don't want it: it can be directed towards drivers, pedestrians or neighbors. It is distracting and annoying and can sometimes be disabling.

Low Pressure Sodium - These are also HID bulbs with a sodium gas, and produce a yellowish light. Average life span 18,000 hours. Typical usage: Security areas (work well with security cameras) Outdoor. 

Lumens Per Watt - A measurement of white light produced by each output watt. 

Luminaire - A complete lighting unit consisting of a lamp (or lamps), together with the parts designed to distribute the light, position and protect lamps and connect them to the power supply. 

Lumen Maintenance - The lumen output provided by a lamp at a given point or percentage of its life. 

Lumen Efficacy - The light output of a source divided by the total power input to that source. It is expressed in lumens per watt. 

A complete lighting unit consisting of a lamp (or lamps), ballast (or ballasts) as required together with the parts designed to distribute the light, position and protect the lamps and connect them to the power supply. A luminaire is often referred to as a fixture.

A measure of "surface brightness" when an observer is looking in the direction of the surface. It is measured in candelas per square meter (or per square foot) and was formerly referred to as "photometric brightness."

- M -

Maximum Overall Lenth (M.O.L.) - The end-to-end measurement of a lamp expressed in inches or millimeters. 

Medium Base 
Usually refers to the screw base typically used in household incandescent lamps. There is also the medium bipin base commonly used in T12 and T8 fluorescent lamps.

Mean Lumens - The average light output of a lamp over its rated life. For fluorescent and metal halide lamps, mean lumen ratings are measured at 40% of rated lamp life. For mercury, high pressure sodium, and incandescent lamps, mean lumen ratings are measured at 50% of rated lamp life. 

Mercury Vapor Lamp - A high-intensity discharge light source operating at a relatively high pressure (about 1 atmosphere) and temperature in which most of the light is produced by radiation from excited mercury vapor. Phosphor coatings on some lamp types add additional light and improve color rendering. 

Metal Halide Lamp - These HID bulbs produce a blue-white type light, these bulbs are very efficient, and long lasting, average life span 20,000 hours. 

Mogul Base 
A screw base used on larger lamps, e.g. many HID lamps.

Monochromatic Light 
Light with only one wavelength (i.e. color) present.

Mounting Height 
Distance from the bottom of the fixture to either the floor or work plane, depending on usage.

MR-16 and MR-11 
A line of low voltage compact reflector lamps used for accent and spot lighting. The 16 and 11 refer to 16 eighths of an inch diameter and 11 eighths.

- N -

National Stock Number 
The standardized part number used by the US Government for procurement.

A unit of wavelength equal to one billionth of a meter.

- O -

Open Circuit Voltage (OCV) 
Open Circuit Voltage measured across the socket the lamp screws into, with the ballast powered on. It is dangerous to stick a voltmeter into such a socket without precise knowledge of the ballast because exceedingly high voltages could be present.

Open Fixture Rated 
Lamps that are approved for burning in open fixtures (as opposed to enclosed fixtures which have an acrylic lens or plate glass enclosure).

Operating Position or Burn Position 
Mercury and High Pressure Sodium lamps may be operated in any burn position and will still maintain their rated performance specifications. Metal Halide and Low Pressure Sodium lamps, however, are optimized for performance in specific burn positions, or may be restricted to certain burn positions for safety reasons. 

Operating Voltage 
For electrical discharge lamps, this is the voltage measured across the discharge when the lamp is operating. It is governed by the contents of the chamber and is somewhat independent of the ballast and other external factors.

- P -

PAR Lamp 
PAR is an acronym for parabolic aluminized reflector. A PAR lamp, which may utilize either an incandescent filament, a halogen filament tube or a HID arc tube, is a precision pressed-glass reflector lamp. PAR lamps rely on both the internal reflector and prisms in the lens for control of the light beam.

An inorganic chemical compound processed into a powder and deposited on the inner glass surface of fluorescent tubes and some mercury and metal-halide lamp bulbs. Phosphors are designed to absorb short wavelength ultraviolet radiation and to transform and emit it as visible light.

The measurement of light and related quantities.

Vision for which the cones in the eye are responsible; typically at high brightness and in the foveal or central region.

Power Factor (PF) 
A measure of the phase difference between voltage and current drawn by an electrical device, such as a ballast or motor. Power factors can range from 0 to 1.0, with 1.0 being ideal. Power factor is sometimes expressed as a percent.

Preheat Circuit 
A type of fluorescent lamp-ballast circuit used with the first commercial fluorescent lamp products. A push button or automatic switch is used to preheat the lamp cathodes to a glow state. Starting the lamp can then be accomplished using simple "choke" or reactor ballasts.

Programmed Rapid Start - A lamp starting method which preheats the lamp filaments, while not allowing the lamp to ignite, and then applies the open circuit voltage (OCV) to start the lamp. The user may experience a half to one second delay after turning on the lamps while the preheating takes place. This type of starting circuit keeps lamp end blackening to a minimum and improves lamp life performance, especially in applications where the lamps are frequently switched on and off. 

Pulse Start 
An HID ballast with a high voltage ignitor to start the lamp.

- Q -

A name for fused silica or melted sand from which many high-temperature containers are fashioned in the lighting industry. Quartz looks like glass but can withstand the high temperatures needed to contain high intensity arc discharges.

- R -

A general term for the release of energy in a "wave" or "ray" form. All light is radiant energy or radiation, as is heat, UV, microwaves, radio waves, etc.

Rapid Start Circuit 
A fluorescent lamp-ballast circuit that utilizes continuous cathode heating, while the system is energized, to start and maintain lamp light output at efficient levels. Rapid start ballasts may be either electromagnetic, electronic or of hybrid designs. Full-range fluorescent lamp dimming is only possible with rapid start systems

Rated Lamp Life 
For most lamp types, rated lamp life is the length of time of a statistically large sample between first use and the point when 50% of the lamps have died. It is possible to define "useful life" of a lamp based on practical considerations involving lumen depreciation and color shift

Rapid Start - A lamp starting method in which lamp filaments are heated while open circuit voltage (OCV) is applied to facilitate lamp ignition. 

Rapid Start Lamp - A fluorescent lamp with two pins at each end connected to the filament. The filaments are heated by the ballast to aid in starting. Some rapid start lamps may be instant started without filament heat. 

The ratio of light reflected from a surface to that incident upon it.

Reflector Lamp - An incandescent, compact fluorescent or HID lamp with a built-in reflecting surface. Incandescent and HID versions are made from a single piece of blow-molded soft or hard glass. CFL versions may be one piece or may be designed so that the inner lamp can be replaced. 

- S -

Seal Temperature (Maximum) 
The maximum operating temperature of the seal of the lamp in Celsius.

Self-Ballasted Lamps 
A discharge lamp with an integral ballasting device allowing the lamp to be directly connected to a socket providing line voltage.

Shroud - A glass cylinder that surrounds the arc tube in open fixture rated metal halide lamps. The shroud is designed to contain hot arc tube particles and glass bulb breakage, should a rupture occur. This protection reduces the risk of using metal halide lamps in open fixtures. 

Source Size 
For Projection lamps, this is defined as the dimensions of the rectangular area, centered on the lamp axis, within which all luminous parts of the filament lie, when viewed perpendicular to the axis of the filament coil or to the plane of C-13 and C-13D filaments.

Spacing to Mounting Height Ratio 
Ratio of fixture spacing (distance apart) to mounting height above the work plane; sometimes called spacing criterion. It is OK to have fixture spaced closer than the spacing criterion suggested by the manufacturer but not farther, or you will get dark spots

A colloquial term referring to a reflector lamp with a tight beam of light, typically around 10 degrees or less. It comes from the fact that such a lamp produces a narrow spot of light as opposed to a wide flood of light.

An electronic module or device used to assist in starting a discharge lamp, typically by providing a high-voltage surge.

Starting Temperature (Minimum) 
The minimum ambient temperature at which the lamp will start reliably.

Skin reddening and inflammation caused by overexposure to sources containing UV-B and/or UV-C.

- T -

T-12, T-8, T-5 
A designation for the diameter of a tubular bulb in eighths of an inch; T-12 is 12 eighths of an inch, or 11/2 inches; T-8 is 1 inch, and so on.

Task Lighting 
Supplemental lighting provided to assist in performing a localized task, e.g. a table lamp for reading or an inspection lamp for fabric inspection.

Troffer - An inverted, usually metal, trough suspended from a ceiling as a fixture for fluorescent lighting tubes. 

Two-Pin Compact Fluorescent Lamps - Type of lamps that have the glow bottle starter built into the base of the lamp. Traditionally, 2-pin lamps are designed to work with electromagnetic ballasts. 

- U -

UL (Underwirters' Laboratories, Inc.) - Laboratory that sets safety standards for building materials, electrical appliances, and other products.

Ultraviolet (UV) Radiation 
Radiant energy in the range of about 100-380 nm. For practical applications, the UV band is broken down further as follows:

The International Commission on Illumination (CIE) defines the UV band as UV-A (315-400 nm); UV-B (280-315 nm) and UV-C (100-280 mm).

- V -

Valance Lighting 
Lighting from light sources on a wall typically above eye level, shielded by horizontal panels. The light may be upward or downward directed.

Veiling Reflection 
Effective reduction in contrast between task and its background caused by the reflection of light rays; sometimes called "reflected glare." You might have dealt with veiling reflections when you have to tilt a shiny magazine to avoid glare so as to read it, or struggled with reading a computer monitor because of the reflection of a window or a light fixture.

Visual Comfort Probability (VCP) 
For a given lighting scheme, VCP is a ratio expressed as a percent of people who, when viewing from a specific location and in a specified direction, find the system acceptable in terms of glare.

A measure of "electrical pressure" between two points. The higher the voltage, the more current will be pushed through a resistor connected across the points. The volt specification of an incandescent lamp is the electrical "pressure" required to drive it at its designed point. The "voltage" of a ballast (e.g. 277 V) refers to the line voltage it must be connected to.

A measurement of the electromotive force in an electrical circuit or device expressed in volts. Voltage can be thought of as being analogous to the pressure in a waterline.

- W -

Wall Temperature (Maximum Bulb) 
The maximum operating bulb wall temperature in Celsius.

Warm White - Reference to the color tone or appearance of light produced by a lamp for a specific color temperature. The color of the light from this lamp makes a factory, office or store seem warmer and friendlier. Together with the "white" lamp, this is the most efficient of all fluorescent colors. It is a good choice to blend with incandescent bulbs. 

Warm-Up Time - The amount of time from ignition of the lamp to 90% light output. 

Watt - A unit of electrical power. Lamps are rated in watts to indicate their power consumption. Power consumed over timer equals the electrical energy used.

Wattage Indicator Reduced 
Indicates that this is a reduced wattage option for lamps normally used in this application. Be sure to check wattage, lumens and life to determine which lamp is best suited to your needs.

The distance between two neighboring crests of a traveling wave. The wavelength of light is between 400 and 700 nanometers.

Work Plane 
Plane at which work is done and at which illumination is specified and measured; unless otherwise indicated, it is assumed to be a horizontal plane 30 inches above the floor (table-top height) having the same area as the floor.