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Illustrated Glossary of Lighting Terms by Pegasus Associates LightingIllustrated Lighting Glossary Pegasus Associates Lighting provides easy-to-understand definitions for about 100 common lighting terms, some with illustrations.
Accent Lighting: lighting that is used to accent or highlight a particular object such as a work of art. To be effective accent lighting should be approximately four or five times the level of ambient light in the area. House plants can be accented by aiming an uplight at the wall behind the plant, creating a dramatic silhouette of the plant against the wall. To learn more about this topic click on this link: Accent Lighting.
Alabaster: genuine alabaster is a very fine variety of gypsum (hydrous calcium sulfate) found in nature. It is translucent and its color is often white, pearly, or silky colorless but it sometimes has subtle reddish-brown bands running through it. It is often used for decorative objects such as light fixtures or figurines. Some light fixtures use faux alabaster, which is usually man-made glass. Both genuine and faux alabaster can be very attractive. The faux alabaster is generally much less expensive while real alabaster can lose some of its coloration over time.
Ambient Lighting: general lighting that usually lights up an entire space Ballast: an electrical device used with fluorescent or HID (high intensity discharge) lamps to supply sufficient voltage to start and operate the lamp but then to limit the current during operation.
Base: the portion of the lamp (light bulb) that provides a means of physically connecting the lamp to a socket or lampholder.
Beam Spread: a measure of the spread of light from a reflectorized light source, a special-shaped lamp with a reflective coating inside the bulb to direct the light forward. The beam spread may be very narrow (narrow spot), very wide (wide flood), or something in-between (narrow flood, for example). Examples of "reflectorized light sources" are MR11, MR16, PAR20, PAR30, PAR38, R40, ER30, and BR30 lamps. CSA: the Canadian Standards Association, like UL and ETL in the USA, is a not-for-profit membership-based association serving business, industry, government, and consumers in Canada and the global marketplace. It is an organization that works in Canada and around the world to develop safety standards that address real needs, such as enhancing public safety and health, advancing the quality of life, and helping to preserve the environment.
Cable Lighting System: a low voltage lighting system where the mechanism holding the light fixtures and conducting electricity to those fixtures is a pair of cables.
Cathode: an electrode that emits electrons. A fluorescent lamp cathode emits or discharges electrons to the cathode at the other end of the lamp (light bulb).
Chandelier: a chandelier is often the focal point of the dining room. As such it should be hung about 30 inches above the tabletop and should be at least 6 inches narrower than the table on each side.
Colored Glass Filter: this term means that the glass is formed with the color in the glass as opposed to the color being coated on the surface. This is accomplished by mixing various metal oxides in the glass composition. These colored glass filters are primarily used for aesthetic purposes in lighting. They are not designed for the precise control of the spectral bands, as are optical color filters (dichroic filters). To learn more about this topic click on this link: Colored Glass Filters. Color Rendering Index (CRI): a measure of a lamp’s ability to render colors accurately. The scale ranges from 1 (low pressure sodium) to 100 (the sun). A CRI of 85 is considered to be very good.
Color Temperature: a measure of the color appearance of a light source which helps describe the apparent "warmth" (reddish) or "coolness" (bluish) of that light source. Generally, light sources below 3200K are considered "warm;" while those above 4000K are considered "cool" light sources. The color temperature of a lamp has nothing to do with how hot the lamp will get or how much heat is given off by the lamp. The letter, K, stands for Kelvin.
These tables may help you better understand the concept of Color Temperature.
Compact Fluorescent Lamp (CFL): a generic name used for a whole family of small, single-ended fluorescent lamps with a folded, bridged, or spiral glass tube design and with high color rendering (CRI > 80) and a long life (> 8,000 hours).
Cornice Lighting: a lighting system comprised of light sources shielded by a panel parallel to the wall and attached to the ceiling and distributing light over the wall.
Cove Lighting: a lighting system comprised of light sources shielded by a ledge or recess, and distributing light over the ceiling and possibly the upper part of the wall. To learn more about this topic click on this link: Cove Lighting.
Direct Current: electric current without alterations. DC current is usually supplied by a battery, a transformer, or photovoltaic cells.
Downlight: a small light fixture recessed into the ceiling that usually concentrates the light in a downward direction. Synonyms: recessed downlight, “can”, recessed can. To learn more about this topic click on this link: Recessed Lighting.
Efficacy: a measure used to compare light output to energy consumption. Efficacy is measured in lumens per watt. A 100-watt light source producing 1750 lumens of light has an efficacy (efficiency) of 17.5 lumens per watt (L/W).
Filament: a tungsten wire that incandesces or lights up when an electric current runs through it.
Flexible Track Lighting System: a low voltage or a line voltage lighting system where the suspended track (sometimes called a monorail) holding the light fixtures in place and also conducting electricity to those fixtures can be bent into creative shapes.
Fluorescent Lamp: a low-pressure mercury electric-discharge lamp (light bulb) in which a phosphor coating on the inside of the glass tubing transforms some of the ultraviolet energy created inside the lamp into visible light. To learn more about this topic click on this link: Fluorescent Lamps.
Foot-Candle: the amount of light reaching a subject. The commonly United States unit of measurement of lighting level (illumination) is the foot-candle (fc). The international unit of measurement of lighting level (Illumination) is the lux (lx). The relationship between the lux and the foot-candle is 1 fc = 10.76 lux.
Four-Way Switch: a wall switch that allows three switches like this to control one lighting system. Whenever you flip one of the four-way switches in a given circuit, the light changes its state; that is, if the light was on, it then turns off and if the light was off, it then turns on. General Lighting: substantially uniform lighting of a space without providing for special local lighting requirements like task lighting or accent lighting.
Glare: direct glare is caused by light coming directly to the eye from a light source. Indirect glare is light reflected from a surface in the direction of the eye. Both can harm vision and cause visual discomfort or disability.
Halogen Lamp: a type of incandescent lamp (light bulb) that contains halogen gases (such as iodine, chlorine, bromine, and fluorine), which slow the evaporation of the tungsten filament. Also, sometimes called a tungsten halogen lamp or a quartz lamp. The glass envelope that surrounds the filament of a halogen lamp should not be touched with bare hands. The natural oil from human hands will only help to shorten the life of halogen lamps. If you should accidentally touch the glass bulb, you should thoroughly remove your fingerprints with methylated spirit (denatured alcohol). To learn more about this topic click on this link: Halogen Lamps.
HID Lamp: high intensity discharge (HID) lamps (light bulbs) have a longer life and provide more light (lumens) per watt than most other light sources. Available in mercury vapor, metal halide, high pressure sodium, and low pressure sodium types. Incandescence: light emission by a heated filament.
Incandescent Lamp: lamp (light bulb) in which light is produced by means of an element heated to the point of incandescence by the passage of an electric current.
Infrared Radiation: a type of invisible radiation for which the wavelengths are longer and frequency lower than those for visible radiation.
Instant Start: refers to fluorescent lamps that start instantly without pre-heating the cathodes and without the need for starters.
Inverse Square Law: a law that states that the illuminance (E) at a point on a plane perpendicular to the line joining the point and a source is inversely proportional to the square of the distance (d) between the source and the plane, E = I/d². Lamp: a light source such as an incandescent, halogen, or fluorescent lamp. A lamp is sometimes called a “light bulb” or simply a “bulb”. To learn more about this topic click on this link: Halogen Lamps.
Layers of Light: layers of light in a given space are created by introducing task lighting (lighting by which people perform tasks), accent lighting (lighting used to highlight specific objects), decorative lighting (lighting created by very attractive light sources), and general lighting (lighting that fills the space). This technique (long favored by cameramen and cinematographers) can eliminate ugly shadows in the room and on your face.
LED: light emitting diode. A small electronic device that lights up when electricity is passed through it. LEDs are quite energy-efficient and have very long lives. They can be red, green, blue or white in color. To learn more about this topic click on this link: LED Fixtures.
Light Fixture: a complete lighting unit consisting of a lamp (light bulb) or lamps, a housing, and a connection to the source of electrical power.
Light Trespass: also known as "spill light". Light that is emitted into an unintended area.
Low Voltage: usually 12 volts but sometimes 24 volts
Lumen: a unit of measure used to describe the amount of light that a light source produces or emits. For reference please consult the table below.
M.O.L.: maximum overall length of a lamp (light bulb) — from tip to tip.
MR11 Lamp: a halogen metalized reflector lamp (light bulb) that measures 11/8 inches in diameter and which directs a sharp, well-defined beam of light. To learn more about this topic click on this link: MR11 Low Voltage Halogen Lamps.
Neodymium: a rare earth element discovered in 1885 with an atomic number of 60 in the Periodic Table of Elements. It is a fairly common silvery metal that is used to make slightly purple glass envelopes for incandescent light bulbs, eye protection goggles for welding and glass blowing, laser rods, filters to color correct light for art displays, and lenses used by astronomers to calibrate spectrometers, optical instruments used for analyzing light. Using this substance in an incandescent light bulb makes it less "yellowish" and more like natural outdoor light; however, the use of these "daylight" light bulbs can "expose" the flaws or inconsistencies in things.
Opaque: a term that describes a material that does not transmit any visible light. A wooden door, aluminum foil, and bricks are all examples of opaque materials.
Open Circuit: an electric circuit in which the flow of electricity is interrupted due to an open circuit breaker or a blown fuse or a burned out electrical component.
Parallel Circuit: an electric circuit that has two or more paths for the electricity to flow. The light fixtures in a parallel electric circuit are "parallel" to each other like rungs on a ladder. If one of the light fixtures in a parallel circuit burns out, the other light fixtures will remain on because the electric current would still be able to flow through them.
Pendant: pendants can provide both task and general lighting. Equipped with shades or globes to avoid glare, they are suspended from the ceiling over dinette tables, game tables, kitchen counters, or other work areas. When used over end tables or night tables, they free up the space occupied by table lamps. In general, pendants should be hung about 30 inches above the tabletop and be about 12 inches narrower than the table on all sides.
PL Lamp: a nickname for a twin tube fluorescent lamp coined by Philips Lighting, a large manufacturer of lamps.
Portable Lamp: a table lamp, floor lamp, pharmacy lamp, or reading lamp which can be easily moved and plugged into a receptacle; officially called a portable luminaire (light fixture).
Radio Frequency Interference (RFI): interference to the radio frequency band cased by other high frequency equipment or devices in the immediate area. Fluorescent lighting systems and AC electronic transformers can generate RFI.
Rapid Start: a fluorescent system that does not require starters and takes 1 to 2 seconds to emit light. The ballast preheats the electrodes within the fluorescent lamp and initiates the arc without a starter or the application of high voltage.
Rated Life: The rated life of a lamp signifies the time at which 50% of a large quantity of these lamps will have burned out. That means that 50% of these lamps will burn out before the rated life and 50% will burn out after the rated life. The rated life does not mean that every one of the lamps will last at least that long. Also, please note that the Actual Life of a Lamp = the Rated Life of that Lamp x (Rated Voltage/Operating Voltage) raised to the 12th power. For example, the Actual Life of a certain lamp that is designed to be used with 130 volts is equal to the Rated Life of that Lamp (let's say 1000 hours) x (130 volts/120 volts) raised to the 12th power. The Actual Life of this lamp is, therefore, equal to (1000 hours) x (1.083) raised to the twelfth power = (1000 hours) x (2.61) = 2610 hours. This means that an incandescent lamp that has a rated life of 1000 hours and is designed to be used with 130 volts but is used with 120 volts instead will have an "Actual Life" of 2610 hours.
Romex Wire: Romex wire is used throughout your household behind walls to wire your entire house. It usually is made up of 3 wires: one wire with white insulation, one wire with black insulation, and one copper wire with no insulation and white insulation around all 3 wires holding them together. The Romex wire that is used to connect lighting fixtures is usually described as "14/2 with ground" (although this may vary with geographical location). The "14/2" refers to the two insulated wires that are 14 gauge in size and the "ground" refers to the uninsulated copper wire. Sconce: an ornamental light fixture attached to a wall. Synonym: wall sconce. Not to be confused with a scone, which is a flat, round cake of wheat flour.
Series Circuit: an electric circuit that has only one path for the electricity to flow. The light fixtures in a series electric circuit are connected to each other in a single line like links in a chain. If one of the light fixtures in a series circuit burns out, the other light fixtures would not remain on because the electric circuit would become an open circuit and the electric current would not be able to get to the other light fixtures. Another term for a series circuit is a "daisy chain".
Single-Pole Switch: a standard on/off wall switch that is the only switch that controls one or more light fixtures in a single circuit.
Sky Glow: also, known as "light pollution". The "haze" or "glow" that surrounds highly populated areas and reduces the ability to view the nighttime sky. Specifically, light that enters the sky from an outdoor lighting system by indirect light reflected from atmospheric particles such as fog, dust, or smog.
Specular Reflection: reflection, without diffusion, in accordance with the laws of geometrical optics, as in a mirror.
Starter: an electrical device used in conjunction with a ballast for the purpose of starting an electric discharge lamp like a fluorescent lamp or an HID lamp.
Task Lighting: lighting that is specifically installed to light an area where a task is performed.
Translucent: a term that describes a material that transmits some visible light usually with some distortion. A frosted piece of glass, a stained glass window, and paper are all examples of translucent materials.
Transparent: a term that describes a material that transmits most, if not all, of the visible light incident upon it with very little, if any, distortion. A typical glass window pane, the air, and clear plexiglas are all examples of transparent materials.
Troffer: a large recessed luminaire (light fixture) that often uses several fluorescent lamps, measures 24in by 48in, and is usually installed with the opening flush with the ceiling.
Uplight: the percentage of lamp lumens directed from a luminaire (light fixture) at or above 90 degrees.
UV Radiation: is not visible to the naked human eye and is generally considered to be that electromagnetic radiation which has a wavelength of less than 400 nanometers (nm) and greater than 100 nm. To learn more about this topic click on this link: UV Filters.
Vapor-Tight Luminaire: a luminaire (light fixture) constructed so that a specified vapor or gas cannot enter its enclosure — usually water vapor.
Voltage: the difference in electrical charge between two points in a circuit expressed in volts; the electric pressure that exists between two points and is capable of producing a flow of current when a closed circuit is connected between the two points; the rate at which energy is drawn from a source that produces a flow of electricity in a circuit; synonyms: electrical potential, electromotive force, EMF; Formulae: volts = amps x ohms, V = I x R, voltage = electrical current x electrical resistance.
Voltage Drop: the loss of voltage caused by the electrical resistance of the wire and the light fixtures in the circuit. It can become especially noticeable in low voltage circuits (where the operating voltage is 12 or 24 volts). Voltage drop may be minimized by using a thicker wire with a lower gauge, shortening the distance between the low voltage transformer and the light fixtures, and/or using a DC transformer.
Wall Grazing: a lighting term that refers to the dramatic highlight and shadow effects on surfaces such as draperies, stone, and brick. Grazing creates easily distinguishable high and low levels of light on the surface.
Wall Washing: a lighting technique that produces a relatively smooth, even level of illumination on the wall and reduces the texture of the surface.
Wattage: the amount of electrical power consumed by a lamp or light fixture measured in “watts”. One watt is equal to the power dissipated by 1 ampere of electrical current flowing across a resistance of 1 ohm or the power produced by 1 ampere of electrical current under an electromotive force of 1 volt. One horsepower is equal to 746 watts.
Xenon Lamp: a type of incandescent lamp that contains xenon gas in the glass envelope. The primary reason that this is done is to lengthen the average rated life of the lamp. Depending on the lamp a typical xenon lamp may have a rated life of 10,000 hours whereas a similar halogen lamp may have a rated life of 2,000 hours. Unlike halogen lamps, xenon lamps may be touched with bare hands without affecting the rated life of the lamp. Xenon lamps also operate at cooler temperatures than halogen lamps. Like halogen lamps, xenon lamps may be dimmed (using the right dimmer) whether the lamp is rated for low voltage (12 volts or 24 volts) or line voltage (120 volts). To learn more about this topic click on this link: Xenon Lamps.
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