There are many words which are used when it comes to Lighting that many people may not completely understand.  The goal of this glossary is to provide definitions for several of these words to eliminate any potential confusion.  Simply click on the letter associated with the terms you’re looking for the definition of and you’ll be directed to all listings under that letter.

Accent Lighting – Concentrated light on a subject which highlights it and causes it to stand out from its surrounding. Depending on degree of drama desired, accent light should minimally be 10x the general light or ambient light.

Ampere – A unit expressing the rate of flow of electric current.

ANSI (American National Standards Institute) – The organization that develops voluntary guidelines and produces performance standards for the electrical and other industries.

Audible Noise (Sound) – All fluorescent lamp ballasts produce some noise. Most brand ballasts are sound rated A (up to 75% quieter than magnetic types) and are acceptable for most applications. Care should be taken when mounting the ballast to reduce vibration.

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; manufacturers use 3 hours per start for fluorescent lamps and 10 hours per start for HID lamps when performing lamp life testing procedures; every lamp type has a unique mortality curve that depicts its average rated life. For Photo-Optic specialty lamps, average rated life refers to the operating period after which on statistical average, 50% of the lamps will perform within their specified values.

Ballast – A device used with an electric discharge lamp to obtain the necessary circuit conditions (voltage, current and waveform) for starting and operating a lamp. All fluorescent and HID light sources require a ballast for proper operation. Dimming ballasts are special ballasts which, when used together with a dimmer, will vary the light output of a lamp. Photo-Optic discharge lamps are either designed for AC operation (sine wave and/or square wave with recommended operational frequencies below 1KHz) or DC operation (current regulated or power regulated). Please see lamp specifications for correct ballast or electronic control gear selection.

Ballast Basics – Ballasts have two primary functions: 1) start the lamp and 2) control operation of the lamp once it has started. High frequency electronic ballasts operate lamps more efficiently and eliminate the hum and visible flicker normally associated with standard magnetic ballasts. Electronic ballasts also typically have better power quality than magnetic ballasts.

Ballast Factor (BF) – The measured ability of a particular ballast to produce light from the lamp(s) it powers; ballast factor is derived by dividing the lumen output of a particular lamp/ballast combination by the lumen output of the same lamp(s) on a reference ballast.

Ballast Life – Ballasts have an average life expectancy. 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 heatsink for the ballast enclosure.

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 lamp; 2) Hybrid or “low frequency electronic”: essentially a magnetic ballast with a few electronic components that switch off voltage to the lamp coil once the lamp has started. A minimal increase in efficiency is obtained via more expensive magnetic core material and the absence of power to the lamp coils during operation; 3) High frequency electronic: a ballast that operates lamps at frequencies above 20,000 Hz. Maximum efficiency is obtained through the use of electronic circuitry and optimum lamp operating characteristics.

Base – The lamp base mechanically holds the lamp in place in the application. The lamp base directly or indirectly (via a cable or lead-in wires) conducts electricity from the circuit to the lamp and can be designed to dissipate heat. Lamp bases should be operated within specified temperature ranges.

Beam Angle – The angle between the two directions for which the intensity (candlepower) is 50% of the maximum intensity as measured in a plane through the nominal beam centerline (center beam candlepower or CBCP).

Beam Spread – In any plane, the angle between the two directions in the plane in which the candlepower is equal to a stated percent of the maximum candlepower in the beam.

Brightness – (See Luminance.)

Bulb – 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).

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.

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

Center Beam Candlepower (CBCP) – The intensity of light produced at the center of a reflector lamp beam, expressed in candelas.

Class of Lamp – Incandescent lamps are classified as type B or type C. The type B lamp is one in which the filament operates in a vacuum. The type C lamp is one in which the filament operates in an atmosphere of inert gas. For gas-filled lamps which can be operated in any position, the lumen maintenance is best when lamps are operated base up. For the vacuum type lamps which have no restrictions on operating position, the lumen maintenance is the same in all operating positions.

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 light 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.

Color Temperature (CT) – Color temperature, which is measured in Kelvin, indicates whether a lamp 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 (>5000K) features more blue light and is referred to as “cool.”

Constant Wattage Autotransformer (CWA) – Employing two coils, this HID ballast is less efficient than reactor types, but has better voltage regulation. Most popular type in use.

Compact Fluorescent Lamps (CFL) – Compact fluorescent lamps employ small diameter tubes that are bent so they begin and end in a single base. This allows them to be produced in a wide variety of configurations, greatly extending the applications for fluorescent lighting.

Correlated Color Temperature (CCT) – A specification of the color appearance of a lamp, relating its color to that of a reference source, black body radiator, heated to a particular temperature, measured in degrees Kelvin (K); CCT generally measures the “warmth” or “coolness” of light source appearance.

Current – A measure of the rate of flow of electricity, expressed in amperes (A).

Directional Lighting – Illumination on the work plane or on an object predominantly from a single direction.

Double-Ended – Lamps that have two bases opposite one another for series electrical connection, mechanical mounting and heat dissipation.

Driver – Electronics used to power illumination sources. Ballast.

Efficacy – The rate at which a lamp is able to convert power (watts) into light (lumens), expressed in lumens per watt (LPW or lm/W). See also LPW Performance.

EMI/RFI – Electronic Ballasts contain circuits that limit electrical noise conducted onto the power line or radiated through the air, otherwise referred to as EMI/RFI. Many of our ballasts comply with FCC 47 CFR Part 18, non-consumer limits for commercial applications. Ballasts for residential application must meet consumer limits. We have a complete line of magnetic ballasts for residential use.

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

Filament – A tungsten wire purposely positioned inside a lamp bulb, that when heated electrically generates radiation in the visible, infrared and ultraviolet ranges. Tungsten material is most often used, as it has great tensile strength, is very durable, and can be heated very near its melting point without evaporating rapidly. Lamp filaments are offered in a variety of designs optimized for specific applications.

Fixture – (See Luminaire.)

Floodlight – A reflector lamp with a relatively wide beam pattern. Also a luminaire consisting of lamp and reflector at fixed distance providing a wide field of illumination.

Fluorescent Lamp – A low pressure mercury vapor discharge light source. The electric discharge generates ultra-violet (UV) energy, which is absorbed by a phosphor and converted to visible light.

Footcandle (fc) – A unit of illumination equal to 1 lumen per square foot.

Frequency – 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).

General Lighting (Ambient Lighting) – Lighting designed to deliver a predominately uniform level of light throughout an area.

Glow to Arc Transition – In order to achieve full rated lamp life, a ballast should start a lamp so that the time from when the lamp begins to glow to the time the lamp arc strikes should be as short as possible. Instant start ballasts typically accomplish this task within 50 millisecond

Grounding – The ballast case and fixture must always be grounded. The grounding helps assure safety, proper lamp starting, and acceptable EMI/RFI performance. Install ballast in accordance with national and local electric codes.

Halogen Lamps – High pressure tungsten filament lamps containing halogen gases. The halogen gases allow the filaments to operate at higher efficacies than incandescent lamps. Halogen lamps also provide brighter, whiter light with better color characteristics, longer service life and improved energy efficiency.

Harmonic – 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.

Hertz (Hz) – A unit of frequency equal to one cycle per second; see frequency.

High-Intensity Discharge (HID) Lamps – Lamps in which an arc passing between two electrodes in a pressurized tube causes various metallic additives to vaporize and release large amounts of light. All HID lamps offer outstanding energy efficiency and service life. Metal halide lamps also offer good to excellent color rendering index (CRI).

Illuminance – 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.

Incandescent Lamp – 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 lamps are enclosed in a vacuum or gas-filled bulb. They provide low initial cost, good color rendition and excellent optical control.

Initial Lumens – is a measure of how much light the lamp is emitting near the beginning of its life.

Input Voltage – Power supply voltage required for proper operation of fluorescent or HID ballast.

Instant Start (IS) – Instant start ballasts apply high voltage across the lamp with no preheating of the cathode. This is the most energy efficient starting method for fluorescent lamp ballasting because they provide maximum energy savings and start lamps without delay or flashing. IS ballasts use 1.5 to 2 watts less per lamp than rapid start ballast. Other IS ballast benefits typically include parallel lamp circuitry, longer remote wiring distance, easier installation due to less complicated wiring, and capability to start lamps at 0 degrees (versus 50 degrees F for rapid start).

Kelvin – A unit of absolute temperature equal to 1/273.16 of the absolute temperature of the triple point of water. One kelvin degree is equal to one Celsius degree. In lighting, Kelvin is the unit of measure for Color Temperature. (See – Color Temperature)

Kilowatt Hour (kWh) – The measure of electrical energy from which electricity billing is determined. For example, at the rate of $0.11 oer kWh, a 100-watt lamp operating for 2000 hours will cost $22.00 (100×2000/1000 = 200kWh x.11 = 22.00).

Lamp – Manufactured light source, synonymous with light bulb; the three broad categories of electric lamps are incandescent, fluorescent and high-intensity discharge.

Lamp Current Crest Factor (LCCF) – The ratio of peak lamp current to the RMS (average) lamp current. Lamp manufacturers require a LCCF of less than 1.70 in order to achieve full lamp life.

Lamp Disposal – When disposing of spent lamps, always consult federal, state, local and/or provincial hazardous waste disposal rules and regulations to ensure proper disposal.

Lamp Flicker – Cyclic variation in output of a light source. High frequency electronic ballasts provide a minimal level of lamp flicker. Lamp flicker from magnetic ballasts may cause eye fatigue for some people.

Lamp Fuse – Wire or device designed to protect a lamp from over-voltage or over-current conditions. Photo-Optic lamps are fused in their applications to prevent lamp overpowering. Certain lamps contain their own internal fuse. Please ensure lamps in your specific application are fused with respect to their power source.

Lamp Lumen Depreciation Factor (LLDF) – The multiplier to be used in illumination calculations to relate the initial rated output of light sources to the anticipated minimum rated output based on the relamping program to be used. (See Lumen Depreciation and Mean Lumens.)

Light Emitting Diode (LED) – A solid state semiconductor device that converts electrical energy directly into light. On its most basic level, a semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.

Lamp Dimensions – Bulb designations consist of a letter or letters to indicate shape and a number to indicate the approximate diameter in eighths of an inch.

LED Driver – See “Driver.”

Lens – A glass or plastic element used in luminaires to change the direction and control the distribution of light rays.

Light – Radiant energy that is capable of producing a visual sensation.

Light Center Length (LCL) – Light Center Length is the distance from a reference point on a lamp base (usually the eyelet) to the center of the light source. For high intensity discharge lamps, it is the distance from the center of the filament or center of the arc to the point shown below for the base indicated:

•              All Screw Bases: Bottom base contact

•              Medium and Mogul Prefocus: Top of base pin

•              Medium BiPost: Bottom of bulb

•              Bayonet Candelabra and Medium Bayonet: Top of base pins

•              SC or DC Prefocus: Plane of locating bosses of prefocusing collar

•              Mini-Can: Intersection of 45 degree taper with max. diameter of base

Light Loss Factor (LLF) – A factor used in calculating illuminance after a given period of time and under given conditions. It takes into account temperature and voltage variations, dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures and atmosphere conditions. Formerly called maintenance factor.

Low Temperature Starting – Instant start and programmed rapid start electronic ballasts have the capability to start fluorescent lamps at temperatures down to 0°F providing the following conditions are met: 1. The ballast is operated at rated nominal line voltage; 2. Ballast cannot be tandem/remote wired for low temperature starting applications. Please note, starting time may increase at 0°F ambient temperatures. Enclosed fixtures are recommended as fluorescent lamps have reduced light output at cooler ambient temperatures. (See specifications for each model’s starting temperature rating.)

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.

Lumen Depreciation – 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. See Lamp Lumen Depreciation Factor, LLDF and Mean Lumens.

Lumens (lm) – 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 lamp provides about 840 lumens.

Luminaire – A light fixture; the complete lighting unit, including lamp, reflector, ballast, socket, wiring, diffuser and housing.

Luminaire Efficiency – The ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein.

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).

Luminous Efficacy – The expression of efficiency in converting power (watts) into light (lumens). Expressed as lumens per watt or l/w.

Lux (lx) – A unit of illuminance equal to 1 lumen per square meter.

Maximum Case Temperature – All electronic ballasts have a maximum allowable case temperature. Applications in which the case temperature exceeds this maximum void all warranties.

Maximum Overall Length (MOL) – The total length of a lamp, from top of bulb to bottom of base.

Mean Lumens – Lumen output of a light source after the source has been used. Mean lumen values for fluorescent and HID lamps are typically measured at 40% of their rated lives. Most high pressure sodium and mercury lamps are measured at 50% of their rated lives. All measurements are made on ANSI reference ballasts. Mean lumens are not typically measured for incandescent and tungsten halogen lamps.

Multi-Location Control – Multi-location dimmers can be used with accessory dimmers (Smart Remotes) for full control of the lights from up to 10 locations.

NAED – A five-digit number used to identify a specific lamp. This NAED number in this catalog is labeled Product Number and should be used when ordering products. NAED is the abbreviation for National Association of Electrical Distributors.

Nanometer (nm) – A unit of length equal to 10-9 meters; commonly used as a unit of wavelength.

Nominal Length – A measurement of fluorescent lamp length based on the length of the lamp plus the proper allowance for standard lamp  holders.

Nominal Watts – Wattage used to describe a lamp. Also see Power and Watt.

OFR – Abbreviation for “ozone free” technology. Lamps with the designation OFR do not generate ozone during operation.

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.

Operating Position – Some lamps are specified/ designed to be operated in certain positions, i.e., horizontal or base up. Lamps may be operated in any position unless otherwise indicated.

Ordering Abbreviation – Provides a shorthand description of the lamp, using a unique code which can be used when ordering a lamp if the Product Number is not known. An example would be: CF15EL/R30/830/MED, which translates to a 15-watt Soft White DULUX® EL reflector electronic self-ballasted compact fluorescent lamp with an R30 reflector, 82CRI, 3000K color temperature and a medium screw base.

PAR Lamps – Pressed aluminized reflector lamp, with the outer bulb formed from two pressed glass parts that are fused or sealed together. PAR lamps may be incandescent, halogen, or HID types.

Parallel vs. Series – Wiring configurations for ballasts. Ballasts with parallel lamp circuitry have the benefit of companion lamps remaining lit, even if one of the lamps operated by the ballast should fail. Systems with series lamp wiring (magnetic ballasts and many rapid start electronic types) result in all lamps operated on the ballast going out if one should fail.

Photocell – A transducer used to detect and measure light and other radiations.

Photometry – The science of measuring visible light in units that are weighted according to the sensitivity of the human eye known as the Visual Wavelength factor. Photometric theory does not address how we perceive colors.

Photo-Optic Specialty Lamps – Photo-Optic specialty lamps employ a variety of technologies to meet the very precise levels of performance required by the entertainment industry, science, medical and other high-tech fields.

Power – The rate at which energy is taken from an electrical system or dissipated by a load, expressed in watts (W); power that is generated by a utility is typically expressed in volt-amperes (VA).

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.

Power Failure Memory – A feature of dimming controls that ensures the last selected light level will be preserved after a power outage.

Preheat – A class of fluorescents requiring a starter, which allows the lamp and filaments to be properly heated before allowing the ballast to supply the correct current flow.

Product Number – (See NAED.)

Programmed Start (PS) – A method of starting fluorescent lamps where cathode heat is applied prior to lamp ignition then removed or reduced once the lamp has ignited. Programmed Start ballasts maximize the number of lamp starting cycles while maintaining energy efficiency. This is the preferred mode of lamp starting for applications with occupancy sensors and several on/off cycles per day. Additionally, the lamps will strike reliably in cold conditions down to 0°F. This type of ballast may also be referred to as Programmed (Rapid) Start.

Rapid Start (RS) – Rapid start ballasts apply a low filament voltage to preheat the cathodes. Simultaneously, a starting voltage (lower than that used in instant start) is also applied to strike the arc. When the cathodes are hot enough, the lamp will strike. The filament voltage continues to be applied throughout the operation of the lamp. Rapid start ballasts appear to have a slight turn on delay compared to instant start. They will typically not be able to start lamps reliably under 50°F.

Rated Average Life – The length of operation (in hours) at which point an average of 50% of a large sample of lamps will still be operational and 50% will not.

Reflector – A device used to redirect the light by the process of reflection. Photo-Optic reflector lamps 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.

Resistance (R) – A measure of resistance to flow of current, expressed in ohms (O).

RFI Suppression – A feature of dimming controls that reduces the amount of Radio Frequency Interference (RFI) caused by using solid-state dimmers near AM radios, telephones, intercoms and other RFI-sensitive radio components.

Shielding – A general term to include all devices used to block, diffuse or redirect light rays, including baffles, louvers, shades, diffusers and lenses.

Single-Ended – Lamps having a single lamp base or point of electrical connection.

Single Pole Switch – A type of switch or lighting control that controls an outlet or lighting fixture from a single location.

Spectral Power Distribution (SPD) – A curve illustrating the distribution of radiant power produced by the lamp, at each wavelength across the spectrum.

Spotlight – A luminaire using halogen/incandescent or a high intensity discharge (HID) lamp that produces a narrow beam angle designed to illuminate a specifically defined area. It can also be called a reflector lamp.

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

Starting Temperature (Maximum) – The maximum ambient temperature at which the lamp will start reliably.

Task lighting – Lighting designed for a specific visible operation which requires higher light levels; most often characterized by proximity to that task.

TCLP Test (Toxicity Characteristic Leaching Procedure) – Federal EPA regulations (RCRA of 1990) have defined a TCLP test to determine whether wastes are to be treated as hazardous or non-hazardous.

Total Harmonic Distortion (THD) – A measure of the distortion of an electrical wave form. Excessive THD (defined by ANSI as greater than 32%) may cause adverse effects to the electrical system. <20% THD ballasts are fine for most applications. However, in buildings with neutral problems caused by high THD loads such as computers, printers, DC supplies, etc., the <10% THD products can help reduce the overall % of Total Harmonic Distortion.

Three Way Switch – A type of switch or dimming control that is wired in tandem with another switch to control an outlet or lighting fixture from two locations.

Total Life Hours – The total lifespan of an LED (Light Emitting Diode), usually 100,000 hours.

Transformer – An electrical device by which alternating current of one voltage is changed to another voltage

Trigger Start – A circuit used to eliminate the starter and start the preheat lamp almost instantly. In this circuit each electrode is connected to a separate winding in the ballast so that the electrode is continuously heated.

Usable Light Hours – The life of an LED (Light Emitting Diode) before light output is significantly reduced, usually 50,000 hours.

Voltage (V) – A measure of electrical potential, expressed in volts (V). Voltage is the “force” that pushes electrical current through a conductor.

Warranty – A statement of manufacturer warranty. Please see Customer Service page for more information.

Watt (W) – A unit of electrical power equal to 1 joule per second. Lamps are rated in watts to indicate power consumption. Also see Nominal watts.

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