Light Bulb Glossary


A unit expressing the rate of flow of electric current. ↑Top

(Design) Amperes

The approximate current which the light bulb will draw at design volts ↑Top

ANSI (American National Standards Institute)

The organization that develops voluntary guidelines and produce performance standards for the electrical and other industries. ↑Top

Average Rated Life

An average rating, in hours, indicating when 50% of a large group of light bulbs have failed, when operated at nominal light bulb voltage and current; manufacturers use 3 hours per start for fluorescent bulbs and 10 hours per start for HID bulbs when performing light bulb life testing procedures; every bulb type has a unique mortality curve that depicts its average rated life. For PHOTO-OPTIC light bulbs average rated life refers to the operating period after which on statistical average, 50% of the bulbs will perform within their specified values. ↑Top


A device used with an electric-discharge light bulb 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. Ballasts have two primary functions: 1) start the light bulb and 2) control operation of the light bulb once it has started. High frequency electronic ballasts operate light bulbs more efficiently (30 - 40% at equivalent light output) and eliminate the hum and visible flicker normally associated with standard magnetic ballasts. Electronic ballasts also typically have better power quality than magnetic ballasts (higher power factor and lower THD). ↑Top

Ballast Efficacy Factor (BEF)

Relative light output (ballast factor) divided by input power (watts). Used to measure the level of efficiency of similar ballast models. For example, the OSRAM SYLVANIA QT2X32IS which has a ballast factor of 0.90 and input watts of 59 (BEF=1.53), is more efficient than competitors' electronic ballasts with ballast factor of 0.875 and input watts of 62 (BEF=1.41). ↑Top

Ballast factor (BF)

Relative light output as compared to a reference ballast (i.e. BF of 0.90 would yield 90% of a light bulb's rated lumens. The measured ability of a particular ballast to produce light from the light bulb(s) it powers; ballast factor is derived by dividing the lumen output of a particular light bulb/ballast combination by the lumen output of the same light bulb(s) on a reference ballast. ↑Top

Ballast life

Ballasts are designed to have a life expectancy of 60,000 hours. To maximize life, ambient temperature should be kept as low as possible. It is also important to maintain effective dissipation of heat using the lighting fixture as a heat sink for the ballast enclosure. ↑Top

Ballast losses

Power consumed by a ballast that dissipates as heat instead of being converted into light. Electronic ballasts operate more efficiently than magnetic or hybrid ballasts. A typical ballast loss for a standard two light bulb magnetic ballast is 20 watts, which an electronic equivalent would only be 7 watts. ↑Top

Ballast types

There are three types of lighting ballasts: 1) Magnetic: an inefficient device that uses a core and coil assembly transformer to perform the minimum functions required to start and operate the light bulb; 2) Hybrid or "low frequency electronic": essentially a magnetic ballast with a few electronic components that switch off voltage to the light bulb coil once the light bulb has started. A minimal increase in efficiency is obtained via more expensive magnetic core material and the absence of power to the light bulb coils during operation; 3) High frequency electronic: a ballast that operates light bulbs at frequencies above 20,000 Hz. Maximum efficiency is obtained through the use of electronic circuitry and optimum light bulb operating characteristics. ↑Top


The light bulb base mechanically holds the light bulb in place in the application. The light bulb base directly or indirectly (via a cable or lead-in wires) conducts electricity from the circuit to the light bulb and can be designed to dissipate heat. Light bulb bases should be operated within specified temperature range. ↑Top

Beam angle

Also called the beam spread; the angular dimension of the cone of light from reflectorized light bulbs encompassing the central part of the beam out to the angle where the intensity is 50 percent of maximum. ↑Top

Beam Spread

Also called the beam angle; the angular dimension of the cone of light from reflectorized light bulbs encompassing the central part of the beam out to the angle where the intensity is 50 percent of maximum. Black Light: A fluorescent light designed to emit invisible ultraviolet (UV) light. ↑Top


Hard, soft or quartz glass enclosure, which can contain a vacuum, elemental inert gas or metal and a means of light generation (filament or electrodes). ↑Top

Candela (cd)

The unit of measure indicating the luminous intensity (candlepower) of a light source in a specific direction; any given light source will have many different intensities, depending upon the direction considered. ↑Top


Negative electrode. ↑Top

Candlepower distribution

A curve that represents the variation in luminous intensity (expressed in candelas) in a plane through the light center of a light bulb or luminaire; each light bulb or light bulb/luminaire combination has a unique set of candlepower distributions that indicate how light will be spread. ↑Top

Center Beam Candlepower (CBCP)

The intensity of light produced at the center of a reflector light bulb, expressed in candelas. ↑Top


Compact Fluorescent Light bulb or Compact Fluorescent Light Bulb. ↑Top

Color rendering index (CRI)

The Color Rendering Index (CRI) measures the effect a light source has on the perceived color of objects and surfaces. High CRI lights makes virtually all colors look natural and vibrant. Low CRI causes some colors to appear washed out or even to take on a completely different hue. ↑Top

Color temperature (CT)

Color temperature, which is measured in Kelvin (K), indicates whether a light bulb has a warm, midrange or cool color appearance. "Warm" light sources have a low color temperature (2000-3000K) and feature more light in the red/orange/yellow range. Light with a higher color temperature (>4000K) features more blue light and is referred to as "cool." ↑Top

Compact Fluorescent Light Bulbs (CFL)

Compact fluorescent light bulbs employ small diameter tubes that are bent so they begin and end in a ceramic base. This allows them to be produced in a wide variety of configurations, greatly extending the applications for fluorescent lighting and offering innovative energy efficient lighting solutions. ↑Top

Correlated Color Temperature (CCT)

A specification of the color appearance of a light bulb, relating its color to that of a reference source heated to a particular temperature, measured in degrees Kelvin (K); CCT generally measures the "warmth" of "coolness" of light source appearance. ↑Top


A measure of the flow of electricity, expressed in amperes (A). ↑Top


Decorative light bulbs, such as candelabra or post lights, in a variety of shapes and bases. ↑Top


When disposing of spent light bulbs, always consult federal, state, local and/or provincial hazardous waste disposal rules and regulations to ensure proper disposal. ↑Top


Light bulbs that have two bases opposite one another for series electrical connection, mechanical mounting and heat dissipation. ↑Top


The rate at which a light bulb is able to convert power (watts) into light (lumens). A watt of electricity is the amount of power in and a lumen or light is the amount of power out. Represented in lumens per watt and found by dividing the light output in lumens by the electrical power input (to the light bulb). Also see LPW performance. ↑Top

Electronic ballasts

The electric arc in any fluorescent system is generated by a ballast. The ballast starts the light bulb, then limits its operating current and provides power factor correction. Modern electronic ballasts perform these functions with great efficiency and provide other control functions as well. ↑Top


Ballasts contain circuits that limit electrical noise conducted onto the power line or radiated through the air, otherwise referred to as EMI/RFI. ↑Top

End Foot Candles (EFC)

A measure of that portion of the total light output of a T-2 light bulb that passes through a .250" orifice placed at the end of the light bulb. ↑Top


A measure of work done by an electrical system over a given period of time, often expressed in kilowatt-hours (kWh). ↑Top

Festoon Bulbs

Festoon bulbs have a unique shape and are usually a low-voltage bulb. They come in frosted or clear glass. If using festoon light bulbs for task lighting or indirect lighting (under cabinets and shelves, over cabinets, or inside cabinets), frosted light bulbs are best. ↑Top


A tungsten wire purposely positioned inside a light bulb, that when heated electrically generates radiation in the visible, infrared and ultraviolet ranges. Tungsten material replaced carbon almost universally, as it has great strength, and is very durable. However, the basic reason for its selection as the best filament material is the fact that it can be burned very near its melting point without evaporating rapidly. Light bulb filaments are offered in a variety of designs optimized for specific applications. ↑Top


A reflectorized light bulb whose emitted beam pattern is enlarging. Also a luminaire consisting of light bulb and reflector at fixed distance providing a wide field of illumination. ↑Top

Fluorescent light bulb

High efficiency light bulb that uses 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 that makes up the structure of the light bulb. The phosphors transform the UV to visible light. ↑Top

Footcandle (fc)

A unit of illuminance equal to 1 lumen per square foot. ↑Top


The number of times per second that an alternating current system reverses from positive to negative and back to positive, expressed in cycles per second or hertz (Hz). ↑Top

Full Spectrum Daylight

Full spectrum light bulbs are designed to reproduce natural light and are thought by some to be beneficial to health by reducing stress, depression and headaches, amongst other things. Full spectrum bulbs are most often used in desk light bulbs and floor light bulbs. ↑Top


Excessive brightness that may be caused by either direct of indirect viewing of a light source. Germicidal Light bulbs: Germicidal light bulbs offer ultraviolet technology that is a non-chemical approach to disinfection. In this process of disinfection, nothing is added which makes this development simple, economical and requires very low maintenance. ↑Top

Glow to arc transition

In order to achieve full rated light bulb life, a ballast should start a light bulb so that the time from when the light bulb begins to glow to the time the light bulb arc strikes should be as short as possible. ↑Top


The ballast case and fixture must always be grounded. The grounding helps assure safety, proper light bulb starting, and acceptable EMI/RFI performance. ↑Top

Halogen Light Bulbs

(Tungsten-halogen light bulb) high pressure light bulbs containing halogen gases which allow the filaments to operate at higher temperatures and higher efficacies. Halogen light bulbs use a filament, but since it is sealed in a pressurized capsule containing halogen gas, the light bulb provides brighter, whiter light with better color characteristics, longer service life and improved energy efficiency. ↑Top


An electrical frequency that is an integer multiple of the fundamental frequency; for example, if 60 Hz is the fundamental frequency, then 120 Hz is the second harmonic and 180 Hz is the third harmonic; some electronic devices, such as ballasts or power supplies, can cause harmonic distortion, directly affecting power quality. ↑Top

Heat Light Bulbs

Light bulbs used to increase the temperature in a focused area. They are most often used in the food industry and outdoor waiting areas. ↑Top

High-intensity discharge (HID) Light Bulbs

In HID light bulbs, an arc passing between two cathodes in a pressurized tube cause various metallic additives to vaporize and release large amounts of light. All HID light bulbs offer outstanding energy efficiency and service life. Metal halide light bulbs also offer good to excellent color rendering index (CRI). ↑Top

Hot ignition

The restarting of a previously operating light bulb shortly after turn-off. Hot ignition is a high performance feature in many OSRAM discharge light bulb types. ↑Top


Light arriving at a surface, expressed in lumens per unit area; 1 lumen per square foot equals 1 footcandle, while 1 lumen per square meter equals 1 Lux. ↑Top

Incandescent Light Bulbs

A light source that generates light utilizing a think filament wire (usually tungsten) heated to white heat by an electric current passing through it. Regular incandescent light bulbs produce light by passing an electric current through a filament in a vacuum or gas-filled bulb. They provide low initial cost, good color rendition and excellent optical control. ↑Top

Instant Start

A light source using the principle of incandescence. When an electric current passes through a filament wire (usually tungsten), the heated wire glows. Filaments of standard incandescent light bulbs are enclosed in a vacuum or gas-filled bulb. They provide low initial cost, good color rendition and excellent optical control. ↑Top

Instant start (IS) vs. rapid start (RS)

Instant start (high voltage is applied across the light bulb with no preheating of the cathode) is the most energy efficient starting method for fluorescent light bulb ballasting. IS ballasts use 1.5 to 2 watts less per light bulb than rapid start ballast (low voltage is applied to the cathodes prior to light bulb ignition and is maintained throughout operation). Other IS ballast benefits typically include parallel light bulb circuitry, longer remote wiring distance, easier installation due to less complicated wiring, and capability to start light bulbs at 0 degrees (versus 50 degrees F for rapid start). ↑Top


A measurement that quantifies the effect of non-linear equipment, such as lighting ballasts, on an electrical system. Lighting systems should be designed so that the transformer rating is sufficient for the ballast used (typically K-factor <4). ↑Top

Kilowatt (KW)

A measure of electrical power equal to 1000 watts. ↑Top

Krypton Light Bulbs

A premium light bulb that uses krypton gas instead of argon. ↑Top


Manufactured light source; synonymous with light bulb; the three broad categories of electric light bulbs are incandescent, fluorescent and high-intensity discharge. ↑Top

Light Bulb Current Crest Factor (LCCF)

The ratio of peak light bulb current to the RMS (average) light bulb current. Light bulb manufacturers require a LCCF of less than 1.70 in order to achieve full light bulb life. Values less than 1.70 do not achieve higher than rated light bulb life. ↑Top

Light Bulb Disposal

When disposing of spent light bulbs, always consult federal, state, local and/or provincial hazardous waste disposal rules and regulations to ensure proper disposal. ↑Top

Light Bulb Flicker

High frequency electronic ballasts provide a minimal level of light bulb flicker. Light bulb flicker from magnetic ballasts can cause eye fatigue for some people. ↑Top


Radiant energy that is capable of producing a visual sensation. ↑Top

Light Bulb

see Bulb or Lamp ↑Top

Light Center Length (LCL)

The distance from a specified reference point on a light bulb base to its light center, typically expressed in inches. ↑Top

Light Emitting Diode (LED)

A semiconductor light source that originated as indicator bulbs and have become used for all purpose lighting. LEDs release energy in the form of photons in an effect called electroluminescence. The color is determined by the energy band gap of the semiconductor. ↑Top

Linear fluorescent Light Bulbs

In a fluorescent light bulb, an electric arc passing between cathodes in a tube excites mercury vapor and other gases and produces UV radiant energy. A phosphor coating on the tube then converts this energy to visible light. Fluorescent light bulbs are very energy efficient and provide a wide range of color responses. ↑Top

LPW performance

Lumens Per Watt. The number of lumens produced by a light source for each watt of electrical power supplied to the light source. Also see Efficacy. ↑Top

Lumen Depreciation

The decrease in lumen output of a light source over time; every light bulb type has a unique lumen depreciation curve (sometimes called a lumen maintenance curve) depicting the pattern of decreasing light output. ↑Top


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


A light fixture; the complete lighting unit, including light bulb, reflector, ballast, socket, wiring, diffuser and housing. ↑Top

Luminance (L)

Light reflected in a particular direction; the photometric quantity most closely associated with brightness perception, measured in units of luminous intensity (candelas) per unit area (square feet or square meters). ↑Top

Lux (lx)

A unit of luminance equal to 1 lumen per square meter. ↑Top

Maximum Overall Length (MOL)

The total length of a light bulb, from top of bulb to bottom of base, typically expressed in inches. ↑Top

Mean Spherical Candela (MSCD)

The average value of the luminous intensity of a light source in all directions. ↑Top

MTBF - Mean Time Between Failures

A calculation of ballast life based on thermal conditions, component values, and circuit characteristics used to develop relative predictions of ballast life. ↑Top

Medium Pin

Referring to the light bulb base pin diameters. Often referencing fluorescent light bulbs (T-8F and T-12F). ↑Top

Nominal Watts

Represents the rated wattage consumption period. Represents the energy used to produce light. Watts= Volts x Amperes. Also see Watt. ↑Top

Operating Position

Some light bulbs are specified/designed to be operated in certain positions, ie, horizontal or base up. ↑Top

PAR Light Bulbs

PAR is an abbreviation for parabolic aluminized reflector. PAR Light bulbs / PAR Light Bulbs have the outer envelope formed from two pressed glass parts that are fused or sealed together. PAR light bulbs may be incandescent, halogen, or HID types. ↑Top

Parallel vs. Series

Ballasts with parallel light bulb circuitry have the benefit of companion light bulbs remaining lit, even if one of the light bulbs operated by the ballast should fail. Systems with series light bulb wiring (magnetic ballasts and many competitors' electronic types) result in all light bulbs operated on the ballast going out if one should fail. ↑Top


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

Photo-Optic Light Bulbs

Photo-Optic light bulbs employ a variety of technologies to meet the very precise levels of performance required by the entertainment industry, science, medicine and other high-tech fields. ↑Top


The rate at which energy is taken from an electrical system or dissipated by a load, expressed in watts; power that is generated by a utility is typically expressed in volt-amperes. ↑Top

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. ↑Top


A class of fluorescents requiring a starter, which allows the light bulb and filaments to be properly heated before allowing the ballast to supply the correct current flow. ↑Top


A high heat resistant glass-like material manufactured from pure silica sand. ↑Top

Rapid Start

Rapid start ballasts apply a low filament voltage to preheat the cathodes. Simultaneously, a starting voltage is also applied to strike the arc. When the cathodes are hot enough, the light bulb will strike. Rapid start ballasts appear to have a slight turn on delay compared to instant start. They will typically not be able to start light bulbs reliably under 50'F. ↑Top

Reflectance (icon)

The percentage of light reflected back from a surface, the difference having been absorbed or transmitted by the surface. See Reflection. ↑Top


If a light ray strikes a mirror- life surface, it is reflected. The angle of incidence equals the angle of reflection; this is called specular reflection. When a ray strikes a mat surface, light is reflected uniformly in all directions. This is called diffuse reflection. With the reflectors the rays of light are penciled in the proper direction. See Reflectance. ↑Top


A device used to redirect the light by the process of reflection. Photo-Optic reflector light bulbs utilize ellipsoidal (converging light rays) or parabolic (collimating light rays) reflectors. Dichroic coated reflectors are designed to reflect visible light and pass through unwanted infrared wavelengths. ↑Top

Resistance (R)

A measure of resistance to flow of current, expressed in ohms. ↑Top


Ballasts should be installed and operated in compliance with the National Electric Code (NEC), Underwriters Laboratories Inc. (UL) requirements, and all applicable codes and regulations. As it is possible to come in contact with potentially hazardous voltages, only qualified personnel should perform ballast installation. All installation, inspection, and maintenance of lighting fixtures should be done with the power to the fixture turned off. ↑Top

Single Pin

Single pins have a mini can or D.C. bay base whereas bi- pin light bulbs have a bi- pin base. ↑Top


Light bulbs / Light Bulbs having a single light bulb base or point of electrical connection. ↑Top

Spectral Power Distribution (SPD)

A curve illustrating the distribution of power produced by the light bulb, at each wavelength across the spectrum. ↑Top


A luminaire using halogen/incandescent or a high intensity discharge (HID) light bulb that produces a narrow beam angle designed to illuminate a specifically defined area. ↑Top

Total harmonic distortion (THD)

Excessive THD (defined by ANSI as greater than 32%) may cause adverse effects to the electrical system. THD levels below 20% provide optimal system compatibility, but levels below 10% may not add any practical benefit. 10% THD types may also introduce excessive in-rush current unless circuitry is added that limits in-rush levels. ↑Top


(Toxicity Characteristic Leaching Procedure), Federal EPA regulations (RCRA of 1990) have define a TCLP test to determine whether wastes are to be treated as hazardous or non-hazardous. Trigger Start: A circuit used to eliminate the starter and start the preheat light bulb almost instantly. In this circuit each electrode is connected to a separate winding in the ballast so that the electrode is continuously heated. ↑Top

Tungsten Halogen Cycle

Halogen light sources utilizing the halogen regenerative cycle to prevent blackening of the light bulb envelope during life. ↑Top

Ultraviolet Radiation

UV light bulbs / light bulbs produce radiant energy in the range of about 100-380 nanometers (nm). ↑Top

Voltage (E)

A measure of electrical potential, expressed in volts (V). ↑Top


A unit of electrical power. Light bulbs are rated in watts to indicate power consumption. Also see Nominal watts. ↑Top

Wavelength (icon)

Distance between two successive points of a periodic wave; the wavelengths of light are typically expressed in nanometers (nm), or billionths of a meter. ↑Top

Working Distance

As a function of an elliptical reflector, light is collected and converged into a specific area a certain distance in front of the light bulb. Light bulb alignment can be provided for specific illumination and color qualities at the designated area. ↑Top

Xenon Light Bulbs

Xenon light bulbs are made from Xenon, a rare gas used in specialized light bulbs. They are known to last up to 10,000 hours. Xenon bulbs can be touched with a bare hand unlike halogen bulbs. ↑Top

Parts of an incandescent light bulb:

Globe: outer glass shell of the light bulb. Made from a fine layer of glass for maximum light efficiency. Must be strong enough to support the other parts of the bulb.

Filament: located inside the globe, the filament is shaped as a coil to allow the required length of tungsten within its environment to display the correct wavelength of light.

Wires: a wire takes the electricity from the base of the light bulb and another returns the electricity to the base.

Stem: within the inner center of the light bulb, a centralized stem made of glass and supports the filament and is connected to wires to ensure the steady flow of electricity.

Gas: inside the light bulb are inert gases (usually argon and / or nitrogen). They prevent the filament within the light bulb from burning out and support the light bulb from compression.

Base: securely supports the light bulb within an electrical source unit (like a light bulb or light fitting). The base also transfers electricity from the main source unit to the inner side of the light bulb itself. Next the base protects the inner insulation from backfiring into the unit’s main electrical source. Lastly, the base secures the globe and all of its components into the bulb itself.

Parts of a compact fluorescent light bulb:

Bulb: made up of a twisting glass tube. The design allows for more surface area, increasing the amount of light produced when the gas in the bulb hits the white coating.

Stem: identical to a conventional incandescent bulb base allowing for each type to be used in fixtures. The stem is the metal part at the bottom of a bulb which screws into an outlet.

Coating: a white coating inside the glass tubes that interacts with UV rays to produce white light.

Gas: either argon or neon; when electricity is introduced, it causes the molecules to become excited creating UV rays.