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A unit expressing the rate of flow of electrical current.
American National Standards Institute (ANSI)
A consensus organization which coordinates voluntary standards for the physical, electrical and performance characteristics of lamps, ballasts, luminaires and other lighting and electrical equipment.
Average Rated Life
A average rating, in hours, indicating when 50% of a large group of lamps have failed, when operated at nominal lamp voltage current; manufacturers use 3 hour per start for fluorescent lamps and 10 hour per start for HID lamp when performing lamp life testing procedures; every lamp type has a unique mortality curve that depicts its average rated life.
The angular dimension of the cone of light from the reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out of the angle where the intensity is 50% of maximum. The beam angle sometimes called the "beam spread" is often part of the ordering code of reflectorized lamps
Ballast
A device used with a electric-discharge lamp to obtain the necessary circuit conditions (voltage, current and waveform) for starting and operation; all fluorescent and HID lamp sources require a ballast for proper operation.
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 lamps on a reference ballast.
Base
The end of the lamp that inserts in the socket.
Bulb
The outer jacket or envelope of a lamp.
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. The term has been retained from the early days of lighting when a standard candle of a fixed size and composition was used as a basis for evaluating the intensity of other light sources.
Candlepower
Luminous intensity expressed in candelas. Plots of luminous intensity called candlepower distribution curves are used to indicate the intensity distribution characteristics of reflector type lamps.
Chromaticity
Measure to identify the color of a light source, typically expressed as (x,y) coordinates on a chromaticity chart.
Color Rendering Index (CRI)
An international system used to rate a lamp's ability to render object colors. The measure of a light sources ability to render the color of objects "correctly". The higher the CR (based upon a 0-100 scale), the better colors appear. CRI ratings of various lamps may be compared, but a numerical comparison is only valid if the lamps are also rated for the same chromaticity. CRI differences among lamps are not usually significant (visible to the eye) unless the difference is more than three to five points.
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 (absolute) temperature scale is used to describe color temperature. For discharge lamps where no hot filament is involved, the term "correlated color temperature" is used to indicate that the light appears "as if" the discharge is operating at a given color temperature. Chromaticity is expressed either in Kelvins (K) or as "x" and "y" coordinates on the CIE standard Chromaticity Diagram. Although it may not seem sensible, a higher temperature color (K) describes a visually cooler, bluer light source. Typical color temperatures are 2800K (incandescent), 3000K (halogen), 4100K (cool white or SP41 Fluorescent), and 5000K (daylight-simulating fluorescent colors such as Chroma 50 and SPX 50).
A short name for 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 HID lamps, but the circuits are quite different.
Elliptical Reflector (ER) Lamp
An incandescent lamp with an elliptically-shaped reflector. This shape produces a focal point directly in front of the lamp which reduces light absorption in some types of luminaries. It is particularly effective at increasing efficiency of baffled downlights.
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 using 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 invisible light.
Footcandle (fc)
A unit of illuminance or light falling onto a surface. One lumen falling on a surface of one square foot produces one footcandle.
A short name for the 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 higher temperature chemical reaction involving tungsten and the halogen gas recycles evaporated particles of tungsten back onto the filament surface.
Halogen-IR(HIR)Lamp
Term for a new form of high-efficiency tungsten halogen lamp. HIR lamps use shaped filament tubes coated with numerous layers of materials, which selectively reflect and transmit infrared energy and light. Reflecting the infrared back onto the filament reduces the power needed to keep the filament hot.
High-Intensity Discharge (HID) Lamp
A general term for mercury, metal halide and high-pressure sodium lamps. HID lamps contain compact arc tubes, which enclose various gases and metal salts operation at relatively high pressures and temperatures.
High-Pressure Sodium (HPS) Lamp
HPS lamps are high intensity discharge light sources, which produce light by an electrical discharge through sodium vapor operating at relatively high pressures and temperatures.
The "density" of light (lumens/area) incident on a surface. Illuminance is measured in footcandles or lux.
Incandescent Lamp
A light source which generates light using a thin filament wire (usually tungsten) heated to white heat by an electric current passing through it.
Instant Start
A type of fluorescent lamp-ballast circuit designed to start fluorescent lamps as soon as the power is applied. Originally, instant-start circuits were developed to eliminate separate mechanical starter devices. Slimline fluorescent lamps operate only on instant start circuits.
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 the type of small light fixture such as a table lamp.
Lamp Lumen Depreciation (LLD)
Lumen depreciation is a term that describes the normal attrition of light. Essentially, the longer a lamp operates, the less light it delivers. Different light sources have different rates of depreciation.
Louver
A framed opening, as in a wall, door, or window, fitted with fixed or movable horizontal slats for admitting air and light and shedding rain. May also refer to one of the slats used in such an opening.
Luminaire Dirt Depreciation (LDD)
Dirt or dust that accumulates on luminaires decreasing the total output of light, lowering the overall efficiency of the system.
Light
Radiant energy which can be sensed or seen by the human eye. Visible light is measured in lumens.
Light Center Length (L.C.L)
The distance between the center of the filament or arc tube in a lamp and a reference plane-usually the bottom of the lamp base. See L.C.L Reference Plane location below.
Lumen
The international (SI) unit of luminous flux or quantity of light. For example, a dinner candle provides about 12 lumens. A 60-Watt Soft White incandescent lamp provides 840 lumens.
Lumen
Maintenance
A measure of how well a lamp maintains its lamp output as it ages. Lumen maintenance is usually provided as a curve.
Lumen Per Watt (lpw)
A measure of the efficiency, or, more properly, "efficacy" of a light source. Efficacy is easily calculated by taking the lumen output of a lamp and dividing by the lamp watts. For example, a 100-watt producing 1750 lumens has an efficacy of 17.5 lumens per watt.
Luminaire
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 lamp and connect them to the power supply.
Luminaire Efficiency
The ration of total lumens emitted by a luminaire to those emitted by the lamp or lamps used.
Luminance
Formerly, a measure of photometric brightness. Luminance has a rather complicated mathematical definition involving the intensity and direction of light. It should be expressed in candelas per square inch or candelas per square meter although an older unit, the "footambert," is still sometimes used. Luminance is a measurable quantity where as brightness is a subjective sensation.
Luminous Efficacy
The light output of a light source divided by the total power input to that source. It is expressed in lumens per watt.
Luminous Flux
The luminous flux is the quantity of light flow produced by a lamp. Flux is often used to describe the total light output. It is expressed in the unit lumen.
Luminous Intensity
Luminous intensity is a measure of light at a source emitted in a certain direction. It is expressed in candelas.
Lux (lx)
The metric equivalent of the footcandle. The SI (International) unit of illuminance. One lux is equal to one lumen per square meter.
The end-to-end measurement of a lamp expressed in inches or millimeters.
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% or rated lamp life. For mercury, high-pressure sodium and incandescent lamps, mean lumen ratings are measured at 50% of rated lamp life.
Mercury Lamp
A high-intensity discharge light source in which the light is produced by the radiation from mercury, plus halides of metals such as sodium, scandium, indium and dysprosium. Some lamp types may also use phosphor coatings.
A unit of wavelength equal to 10-9 meters.
PAR is an acronym for a parabolic aluminized reflector. A PAR lamp, which may use either an incandescent filament, a halogen filament tube or HID arc tube is a precision pressed-glass reflector lamp. PAR lamps rely on both the internal reflector and prisms in the lens for the control of the light beam.
Phosphor
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.
Power Factor (PF)
A measure of the phase difference between voltage and current on alternating current circuits. Power factors can range from 0 to 1.0 with 1.0 being ideal. Power factor is sometimes expressed as a percent. A high power factor means that an electrical system or device is utilizing power efficiently. Incandescent lamps always have power factors close to 1.0 because they are simple "resistive" loads. The power factor of a discharge lamp system is determined by the ballast used. "High" power factor usually means a rating of 0.9 or greater. The power factor of "core and coil" electromagnetic ballasts may be as low as 0.5-0.6.
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.
A fluorescent lamp-ballast circuit which uses 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.
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.
Radiant energy in the range of about 100-380 nanometers (nm). For practical applications, the UV band is broken down further as follows:
Ozone Producing 180 - 220nm
Bactericidal (germicidal) 220 - 300 nm
Erythemal (skin reddening) 280 - 320 nm
"Black" light 320 - 400 nm
The international Commission on Illumination (CIE) defines the UV bands as UV-A (315-400nm); UV-B (280 - 315 nm) and UV-C (100-280)
Voltage
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 waterline.
Watt
A unit of electrical power. Lamps are rated in watts to indicate their power consumption. Power consumed over time equals the electrical energy used.