Term Definition
AC Alternating current (ac) moves in a single direction; however, that direction is reversed at regular intervals. Alternating current is the prevailing electrical current in use today.
accent lighting A technique that emphasizes a particular object or draws attention to a particular area. Accent lighting usually utilizes the tight beam control of PAR lamps or MR lamps. Also called highlighting.
amalgam CFL Amalgam technology (two or three metals alloyed with mercury) is used in compact fluorescent lamps to control mercury vapor pressure, thus controlling lumen output.
ambient lighting Lighting that is designed to provide a substantially uniform light level throughout an area, exclusive of any provision for special local requirements.
amperage The amount of electrical current through a conductive source.
ANSI American National Standards Institute
arc See Arc discharge.
arc discharge An electrical discharge through an ionized gaseous atmosphere. Fluorescent and HID lamps are examples of light sources that use an arc to produce light.
arc tube An envelope, usually quartz or ceramic, that contains the arc of a discharge light source.
ASHRAE/IESNA Standard 90.1-1999 An industry benchmark of energy application standards for buildings, created by the American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) and the Illuminating Engineering Society of North America (IESNA).
asymmetric light distribution A light distribution pattern in which lumen output is directed more strongly toward one side than another.
baffle A single opaque or translucent element that shields the direct view at certain angles of a light source, absorbs or block unwanted light, or reflects or redirects light.
beam spread The width of a light beam, expressed in degrees. The beam of light from a reflector-type lamp (PAR, R, ER, or MR) can be thought of as a cone. The beam spread is the angular width of the cone. Common beam spreads are known as spot, narrow, narrow flood, and flood.
blackbody A temperature radiator of uniform temperature whose radiant exitance in all parts of the spectrum is maximum obtainable from any temperature radiator of the same temperature. Correlated color temperature (CCT) correlates with the apparent color of a blackbody radiator at a given temperature.
bollard luminaires A low, pole-mounted luminaire, usually for outdoor use. Bollards commonly are used to light pathways.
capacitor A device, the primary purpose of which is to introduce capacitance into an electric circuit.
ceiling-mounted diffuser ceiling-mounted diffusers attach directly to the ceiling and have a clear or translucent cover that diffuses the image of the lamp and distributes the light evenly into a space.
cell louver See louver.
chromaticity The dominant or complementary wavelength and purity aspects of the color taken together, or of the aspects specified by the chromaticity coordinates of the color taken together.
coefficient of utilization The ratio of luminous flux (lumens) calculated as received on the work plane to the total luminous flux (lumens) emitted by the lamps alone.
cold cathode An electric-discharge lamp whose mode of operation is that of a glow discharge. It has electrodes so spaced that most of the light comes from the positive column between them.
coldest spot Fluorescent lamp operation depends upon the mercury pressure inside the bulb, and this pressure is determined by the temperature of the coolest point of the lamp.
color filter The predominant method of producing colored light is the use of color filters with a 'white' light source. The white source contains all of the colors of the spectrum; the filter absorbs the unwanted parts of the spectrum and transmits the wavelengths that make up the desired color.
color wheel Dichroic glass filters used in illuminators to change the color of the light conducted through the fibers.
contactor A device for repeatedly opening and closing electrical circuits. Electrically, relays and circuit breakers also fulfill the same function.
cove luminaire An architectural luminaire that directs light from sources that are mounted in a cove to the ceiling or upper wall. A cove is a ledge or shelf on the wall, or a recess in the wall.
dedicated base See Dedicated CFL.
dedicated CFL A dedicated compact fluorescent lamp is one in which the ballast is hard-wired to lamp holders within a luminaire. Since the lamps fit into specially keyed sockets, this type of system ensures that compact fluorescent lamps will be used in the luminaire.
diffuser A device to redirect or scatter the light from a source, primarily by the process of diffuse transmission.
diode A device with two electrodes, in particular an anode and a cathode, and a nonlinear current/voltage characteristic.
direct glare Excessive brightness from a source of light in the line of sight. Luminaires with poor optical control can be sources of direct glare.
disability glare Excessive brightness from a source of light in the line of sight. Luminaires with poor optical control can be sources of direct glare.
discomfort glare Glare that produces discomfort. It does not necessarily interfere with visual performance or visibility.
DMX controller Digital multiplex (DMX), an industry standard control protocol for the transmission of dimmer intensity or other data using a digital multiplex method.
downlight A directional luminaire that directs light downward.
electrodes The structure that serves as electric terminals at each end of electric discharge lamps.
Electroluminescence A light source technology used in exit signs that provides uniform brightness and long lamp life (approximately eight years), while consuming very little energy (less than one watt per lamp).
electromagnetic field See electromagnetic spectrum.
electromagnetic spectrum A continuum of electric and magnetic radiation encompassing all wavelengths.
electronic transformer Electronic transformers use electronic circuitry, which is capacitive by nature. Electronic transformers are compact, lightweight, and quiet.
Extruded Aluminum Aluminum that is pressed through a die to shape it. The process is commonly used to shape metal pieces used in fabrication of equipment, tools, and lightweight consumer goods such as lighting fixtures.
fascia A flat, horizontal band or board.
fluorescence The ability of some materials, such as phosphors, to convert ultraviolet energy into visible light.
flux See Luminous Flux.
group relamping Group relamping entails replacing all of the lamps in a system together after a fixed interval, called the economic group relamping interval. Group relamping can reduce the cost of operating a lighting system while keeping illuminance levels close to the design value.
halides The metal-halogen compounds, known as halides, remain stable at high temperatures, and do not cause deterioration of the quartz arc tube, which they would do if left in their elemental forms.
halogen lamp An incandescent lamp that employs a halogen-gas additive to improve lamp life and efficacy.
harmonics A sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental frequency. For example, a component of the frequency, which is twice the fundamental frequency, is called the second harmonic.
HID lamp High intensity discharge lamp: an electric lamp that produces light directly from an arc discharge under high pressure. Metal halide, high pressure sodium, and mercury vapor are types of HID lamps.
high pressure sodium lamp An HID lamp in which radiation from sodium vapor under high pressure produces visible light, characterized by a golden-yellow color.
IESNA Illuminating Engineering Society of North America.
ignitor A device, either by itself or in association with other components, that generates voltage pulses to start discharge lamps without preheating of electrodes.
incandescence The self-emission of radiant energy in the visible spectrum due to the thermal excitation of atoms or molecules.
index of refraction Ratio of the velocity of light in a vacuum to that in the medium. Thus n = c/v and is a number greater than one. Indexes of refraction are a function of the wavelength of the incident light.
infrared energy See infrared radiation.
infrared radiation Any radiant energy within the wavelength range of 770 to 106 nanometers is considered infrared energy.
injection molding The process for manufacturing plastic lenses whereby hot liquid plastic is injected into a lens mold of the desired shape and size.
IR filter A device for changing, by transmission or reflection, the magnitude or spectral composition of the flux of IR incident upon it.
Kilopascal The pascal (Pa) is the standard international unit of pressure. One pascal is equal to one newton per square meter. A kilopascal (kPa) is one thousand pascals.
light output Luminous flux, measured in lumens. The light output rating of a lamp is a measure of its total integrated light output. See also lumen.
line voltage The 110-120-volt household current, generally standard in North America.
louver A series of baffles used to shield a source from view at certain angles, to absorb or block unwanted light, or to reflect or redirect light. The baffles are usually arranged in a geometric pattern.
low voltage A lamp that nominally operates at 6, 12, or 24 volts. A transformer must be used to convert the 120-volt line voltage to the lower voltage.
lumen depreciation The decrease in lumen output that occurs as a lamp is operated, until failure.
luminous flux The rate of flow of light, measured in lumens. The overall light output of a lamp.
magnetic transformer Employed for both single and multiple lamp operation, it uses the principle of inductance (the ability of a device to store energy in the form of a magnetic field) to produce the voltage change.
maintained illuminance Initial illumination level from luminaires adjusted for depreciation of lamp lumens by aging, effects of dirt accumulation on luminaire surfaces, and other factors.
metal halide lamp An HID light source in which radiation from a mixture of metallic vapors produces visible light, characterized by a white color.
multifaceted reflector A low voltage halogen reflector lamp that is used in lighting applications where precise beam control is required, such as accent lighting. Some MR lamps, such as projection lamps, are designed for line-voltage operation.
multilevel ballast Multilevel ballasts allow fluorescent and HID lamps to be switched between two or more lighting levels. The device that activates the change in light output may be a photosensor, an occupancy sensor, or a timer.
MR16 lamp See Multifaceted reflector.
MR-16 lamp See Multifaceted reflector.
nanometers 1 nanometer = 1 billionth of a meter, or 1 X 10-9 m. See Wavelength.
neon Neon lamps are cold cathode lamps lacking a phosphor coating. See cold cathode.
opalescent Reflecting an iridescent light; having a colored smooth surface that gives the effect of cloudiness and diffusion due to the intentional presence of fissures, striae, and bubbles.
optical control Optical control may be provided in a number of ways. All are applications of one or more of the following phenomena: reflection, refraction, polarization, interference, diffraction, diffusion, and absorption.
PAR lamp See parabolic aluminized reflector.
parabolic aluminized reflector An incandescent or tungsten-halogen incandescent lamp with a hard glass bulb and an interior reflecting surface, a precisely placed filament, and a lens to control beam spread. The lens is hermetically sealed to the reflector. Metal halide PAR-lamps are also now available.
parabolic louvers Parabolic louvers control luminance precisely; they consist of multiple cells with parabolic reflectors, and a specular or semi-specular finish. The cells range in size from in. X in. to 1 ft. X 1 ft.
peak demand A utility customer's maximum load. For purposes of calculating utility cost, peak demand is generally based on the maximum monthly demand, where demand is measured as an average over a time interval, usually 15 or 30 minutes.
phosphors Chemical compounds that are used to coat the inside of fluorescent and some HID lamps.
photocell A device that converts light to electrical current. Based on the amount of incident light, a photocell can switch a lamp on or off or regulate a lamp's light output to maintain a preset level of light.
photometric data See Photometric report.
photometric report The lighting performance of a luminaire may be measured either by the manufacturer or by an independent testing laboratory. The results of these measurements are produced in a photometric report, which often becomes part of the catalog description of that luminaire.
photoreceptors See Retina.
pin-based CFL A pin-based CFL plugs into specially keyed lamp holders. Its ballast is hard-wired to the lamp holder within the luminaire.
plenum The space between the ceiling and the floor or roof above.
potentiometer Intensity control device used in dimmers. May be either a rotary knob or linear slide type element. A variable resistor used in analog control.
prismatic acrylic See prismatic lens.
prismatic lens Prismatic lenses incorporate a pattern of small prisms or other refractive elements to reduce the luminance of the luminaire and inhibit direct glare.
prismatic reflector See prismatic lens.
R lamp A common reflector lamp. An incandescent filament or electric discharge lamp in which the sides of the outer blown-glass bulb are coated with a reflecting material so as to direct the light. The light-transmitting region may be clear, frosted, or patterned.
rare-earth phosphors A group of phosphors containing rare-earth elements. Rare-earth phosphors are used in fluorescent lamps to achieve higher efficacy and better color rendering than can be achieved with halophosphates. RE designates a lamp containing rare-earth phosphors.
rated active power The input power (measured in watts) for a lamp-ballast combination.
reference ballast A ballast that is specially constructed, with certain prescribed characteristics, used for testing electric-discharge lamps and other ballasts.
reflected glare Glare resulting from bright reflections from polished or glossy surfaces in the field of view. Reflected glare is usually associated with reflections from within a visual task or areas in close proximity to the region being viewed.
refractor A device that transmits and redirects the luminous flux from a source. Refractors for outdoor luminaires are typically made from acrylic, polycarbonate, or glass, and when designed well, help control direct glare.
relay A device that performs the actual on or off switching of an electrical load, due to small changes in current or voltages.
restrike time Usually applied to HID light sources, the interval between the extinguishing of an arc and the time it can be reignited.
retina A membrane lining the posterior part of the inside of the eye. It comprises photoreceptors (cones and rods) that are sensitive to light and nerve cells that transmit to the optic nerve the responses of the receptor elements.
rheostat A resistance dimmer.
screwbase CFL A compact fluorescent lamp with a ballast that has a medium screwbase that fits into the standard incandescent lamp socket. A screwbase compact fluorescent lamp may either be modular, in which the lamp and ballast are separate pieces, or self-ballasted, in which the lamp and ballast are inseparable. Both types are designed to replace incandescent lamps.
service life The total time that passes, including time that a lamp is on and time that it is off, before the lamp must be replaced.
shielding Shielding conceals the lamp and controls glare within a zone called the shielding angle. This is the maximum angle that the eye is raised above horizontal without seeing the light source beyond the shielding system.
simple payback A measure of economic performance representing the number of years required for the monetary value of the energy savings to equal the investment.
soffit luminaire An architectural luminaire that directs light downward from the cornice or soffit between the wall and ceiling to light the wall surface below.
solid angle A measure of that portion of space about a point bounded by a conic surface whose vertex is at the point. It is defined as the ratio of intercepted surface area of a sphere centered on that point to the square of the sphere's radius. It is expressed in steradians.
specular A surface from which the reflection is predominantly directional. Specular surfaces are mirror-like or shiny, as opposed to diffuse.
spectrum Wavelengths of electromagnetic radiation.
spread lens A glass lens accessory used to diffuse and widen beam patterns.
steradian The solid angle subtended at the center of a sphere by an area on the surface of the sphere equal to the square of the sphere radius.
stroboscopic effect Condition where rotating machinery or other rapidly moving objects appear to be standing still due to the alternating current supplied to light sources. Sometimes called "strobe effect".
task lighting Lighting that is directed to a specific surface or area. Task lighting provides illumination for visual tasks.
torchiere An indirect floor lamp sending all or nearly all of its light upward.
track lighting A lighting system with an electrically fed linear track that accepts one or more track heads. The track heads can be easily relocated along the track.
transformer Transformers are electrical devices with no moving parts, which change distribution voltages to higher or lower levels. When used with incandescent or halogen lamps, they typically step 120V distribution downward to 12V, although 5.5V and 24V models are also offered.
translucent Transmitting light diffusely or imperfectly.
trim Baffles, cones, rims, and other treatments for apertures of downlights. Trim is usually the part of the luminaire that is visible from below the ceiling.
trim ring A plastic or metal ring used to cover and seal the edges of holes that are cut into ceilings to install recessed luminaires.
troffer A recessed luminaire that is installed in the plenum with the opening flush with the ceiling. Typically rectangular or square in shape, as in a 2-foot by 4-foot luminaire.
ultrasonic frequency A frequency lying above the audio frequency range. The term is commonly applied to elastic waves propagated in gases, liquids, or solids.
ultraviolet energy Any radiant energy within the wavelength range 100 to 400 nanometers is considered ultraviolet radiation (1 nanometer = 1 billionth of a meter, or 1 X 10-9 m).
ultraviolet radiation See Ultraviolet energy.
UL Underwriters Laboratories. An organization that tests electrical components and appliances and lists products that pass safety standards.
UV filter A device for changing, by transmission or reflection, the magnitude or spectral composition of the flux of UV incident upon it.
valance luminaire An architectural luminaire with a longitudinal shielding member mounted across the top of a window or along a wall and usually parallel to the wall, to conceal light sources giving both upward and downward distributions.
veiling reflection A reflection on the visual task that obscures visibility by reducing contrast.
wall sconce A decorative and/or functional wall-mounted luminaire.
wall washing A technique that lights a wall fairly evenly from top to bottom without spilling or wasting light away from the wall into the room.
wavelength The distance between two corresponding points of a given wave. Wavelengths of light are measured in nanometers (1 nanometer = 1 billionth of a meter, or 1 X 10-9 m).