Lighting Terminology

 

AMPERE : The ampere, or "Amp" for short, is a measurement of the quantity of electrons that move past a given point in a circuit, over a specific period of time. Another way of describing an ampere is a that it's an electrical current that's equal to one coulomb per second.

ANSI: Abbreviation for American National Standards Institute.

ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers

BAFFLE: A light baffle is a a translucent or opaque element that is used to control light distribution over an angle, and can be adjusted as needed..

BALLAST: A ballast is a common device that's used in fluorescent and HID lighting. The ballast basically provides the starting voltage to a fluorescent tube, while at the same time regulating and limiting the current through the lamp during operation. Fluorescent tubes will sometimes fail to illuminate, or will flicker on and off,  because of a faulty ballast. This condition is also referred to as ballast cycling.

BRIGHTNESS – similar to “Candlepower,” brightness is light that's perceived as being dimmer or brighter. This is not really a unit of measure, it is rather something everyone's aware of when they step out of a dark room into the bright sunshine.

CANDELA: A Candela is a unit of luminous intensity, relative to the specific direction and the intensity of the light source in question.

CANDLEPOWER:  Basically the same as brightness, only candlepower is an actual unit of measure. Candlepower measures the intensity of a light source, and in a specific direction, and is expressed in candelas (see above). The brightness of light at a specific point is measured in candlepower.

CBM: Abbreviation for Certified Ballast Manufacturers Association.

CEC: Abbreviation for California Energy Commission.

COLOR TEMPERATURE: The color temperature is a measure of the color appearance of a light source as it relates to a reference source that's heated to a particular temperature, and is expressed in the thermal unit Kelvin. This is also what is referred to when someone says that lighting has "warmth" or "coolness."  As a rule, light sources above 4000K are considered "cool," while sources below 3200K are considered "warm."

COMPACT FLUORESCENT:  Compact fluorescent lamps, or CFLs for short, are small fluorescent lamps that are rapidly taking the place of traditional incandescent lighting. CFLs have a range of advantages, including the fact that they use much less power than incandescent bulbs, and they last up to 10 times longer as well.

CONTRAST:  Contrast in lighting is the relationship between the luminance of an object and its background.

CUT-OFF ANGLE:  This refers to the angle from a light fixture's vertical axis, at which point a louver, reflector or other shielding device cuts off the direct visibility of a light or lamp.

DAYLIGHT COMPENSATION:  This is a dimming system used in buildings that get a lot of ambient light during daylight hours. These type of dimming systems use a photocell to read the available light, and dim the overhead lamps when ambient daylight is present, thus saving energy.

DIFFUSE: This is a term that refers to the dispersing or scattering of light.

DIFFUSER: Typically a diffuser is a translucent piece of plastic or glass covering the light source in a fixture. The light that is transmitted through the diffuser will then be dispersed or scattered, reducing glare and softening it into a more comfortable light.

DOWNLIGHT: This refers to a type of overhead or ceiling luminaire where the majority of the light is projected downward. These luminaire are typically recessed, and often feature an open shielding device or reflector.

ELECTROLUMINESCENT:  This is a light source technology that provides a uniform brightness, while at the same time consuming a small amount of energy.  An example of an electroluminescent light fixture would be the glowing exit signs used in most modern buildings.

EMI: This is an abbreviation for the high frequency interference (or electrical noise) can can be thrown off by some types of fluorescent lamps or other electronic components and that interferes with the operation of electrical equipment such as communication devices. EMI, which is measured in micro-volts, can usually be eliminated or at least controlled by filters.

ENERGY-SAVING LAMP: These are energy saving lamps such as compact fluourecents (CFLs) that operate at a lower wattage and thus consume less energy than conventional lamps.

FLUORESCENT LAMP: These are lamps that don't use filaments as a light source. Instead, fluorescent lamps are glass tubes filled with argon gas, along with an inert gas such as krypton. When enough electrical current is applied to each end of the tube, an arc is produced that excites the phosphors inside the lamp, causing the tube to glow and give off visible light.

FOOTCANDLE (FC): The English unit of measurement of the illuminance (or light level) on a surface. One footcandle is equal to one lumen per square foot.

GLARE: This refers to the contrast or differences in brightness within a person's field of vision, such as a ray of sunshine streaming in through a car windshield. Glare is typically annoying, and can even be dangerous if it impairs a person's ability to see clearly.

HID: An abbreviation that stands for "high-intensity discharge."  This typically refers to a type of lamp or luminaire that utilizes utilizes high pressure sodium or mercury vapor in the process of producing light.

HIGH OUTPUT (HO): High output lamps or ballasts are generally designed to produce more light by operating at higher current levels of 750 mA or more.

HIGH PRESSURE SODIUM LAMP: As mentioned above, a high pressure sodium lamp is a type high intensity lamp (HID) where light is generated by the radiation from given off from sodium vapor (and mercury).

IESNA: An abbreviation for the Illuminating Engineering Society of North America.

ILLUMINANCE: Illuminance, or light level, is a photometric term that refers to the amount of light incident on a plane or surface. Illuminance can be expressed either as lumens per square meter (lux) or as lumens per square foot (footcandles).

INCANDESCENCE: refers to the emission of light from an object as a result of it being heated.

INDIRECT LIGHT: this is typically an upward distribution of light which produces illumination on the horizontal workplane via reflection from the upper walls and ceiling.

INSTANT START CIRCUIT: This is a circuit in a fluorescent fixture that ignites a fluorescent lamp almost instantly by using a very large starting voltage, usually produced by an electronic ballast. 

INTENSITY: or luminous intensity, is defined as flux per solid angle in a given direction, and is measured in candelas (cd).

KELVIN: the unit of absolute temperature used to designate the color temperature of a light source.

KILOWATT: a unit of power equal to 1000 watts.

LED: or light emitting diode. LEDs are becoming increasingly popular as light sources in everything from flashlights to exit signs in buildings. The many advantages of LEDs include the fact that they use very little power, and have a very high rated life.

LENS: a transparent glass or plastic element used in luminaires to control the direction and distribution of transmitted light by refraction.

LIFE-CYCLE COST: This refers to the total costs associated with buying, operating and maintaining a lighting system over the average life of that system.

LOW CONTRAST: refers to a lighting condition where a large proportion of diffuse light is combined with a small amount of focused light.

LOUVER:  Typically a grid-type assembly that is used to control light output from a fixture. The louvers can range in size from small-cells to the large-cell anodized aluminum louvers used in parabolic fluorescent fixtures.

LUMEN: the unit of measurement of luminous flux equal to the light emitted in a solid angle by a uniform point source of one candela intensity.

LUMINAIRE: a complete lighting unit consisting of a housing, lamps, light controlling elements, lamp holder, and other related parts such as a ballast or transformer. Can also be referred to as a fixture.

LUMINANCE: A measurement of the intensity of light entering the eye, per unit of projected area. Luminance is expressed as footlamberts (English units) or candelas per square meter (Metric units).

MERCURY LAMP: Or mercury vapor lamp, is a type of high intensity discharge (HID) lamp in which light is produced by an electric discharge through mercury vapor.

METAL HALIDE: Another type of HID lamp in which most of the light is produced by an electric discharge through the combined vapors of metal halides and mercury in the arc tube.

MONOCHROMATIC: having or consisting of only one color or hue, or radiation of a single wavelength or very small range of wavelengths.

NADIR: A reference straight down, or 0 degree angle.

NIST: Abbreviation for National Institute of Standards and Technology.

OCCUPANCY SENSOR: A motion, ultrasonic, or infrared sensor that controls the light in a room as it becomes occupied. 

OPAQUE: blocking the passage of light. Neither transparent or translucent.

PARABOLIC LUMINAIRE:  This refers to a popular type of fluorescent fixture

PARABOLIC LUMINAIRE:  This refers to a popular type of fluorescent fixture that has a parabolic louver, usually composed of curved aluminum baffles. This parabolic shape produces a light distribution that reduces glare, and gives better overall light control.

PENDANT LUMINAIRE: a luminaire that's suspended from the ceiling by a support chain, cable, rod or cord.

PHOTOSENSOR:  A light sensing photocell device that's used to control dimmers in response to available light levels. For example, a photosensor would dim the luminaires in a room during daylight hours when ambient light levels rise.

PREHEAT: A preheat ballast uses a separate starter circuit to heat up a fluorescent lamp, prior to high voltage being applied to start the lamp.

REFLECTION: Reflection refers to the return of light from a surface, such as a mirror or a shiny metal plate. The angle of reflection is equal to the angle of incidence. Diffuse reflection occurs when an incident ray of light is reflected in all directions.

REFLECTOR: This refers to the part of a luminaire that shrouds the lamps and re-directs some of the light streaming out of the lamp.PARABOLIC LUMINAIRE:  This refers to a popular type of fluorescent fixture that has a parabolic louver, usually composed of curved aluminum baffles. This parabolic shape produces a light distribution that reduces glare, and gives better overall light control.

PENDANT LUMINAIRE: a luminaire that's suspended from the ceiling by a support chain, cable, rod or cord.

PHOTOSENSOR:  A light sensing photocell device that's used to control dimmers in response to available light levels. For example, a photosensor would dim the luminaires in a room during daylight hours when ambient light levels rise.

PREHEAT: A preheat ballast uses a separate starter circuit to heat up a fluorescent lamp, prior to high voltage being applied to start the lamp.

REFLECTION: Reflection refers to the return of light from a surface, such as a mirror or a shiny metal plate. The angle of reflection is equal to the angle of incidence. Diffuse reflection occurs when an incident ray of light is reflected in all directions.

REFLECTOR: This refers to the part of a luminaire that shrouds the lamps and re-directs some of the light streaming out of the lamp.

REFRACTION: The deflection of a light ray as it passes obliquely from one medium into another, such as when light passes from air into water.

RELAY: An electrical device that acts as a switch. In lighting, a relay is typically used to switch an electrical load on or off, based on a smaller change in current or voltage. An example of a solid state relay would be a transistor.

SEMI-SPECULAR: An irregular surface that partially disperses or spreads the reflected beam. Some of the light is scattered, and some of it is reflected directionally.

SHIELDING ANGLE: The zone within which shielding conceals the light source, usually performed by louvers or baffles, controlling glare.

SKYLIGHT:  The diffused and reflected light of the sky, as is passes down through an opening in the roof of a building, typically covered with a frosted or glazed plastic shield.

SPACING CRITERION: This refers to the maximum ratio of luminaire spacing, or the distance that interior fixtures may be spaced in order to ensure uniform illumination on the work plane. 

SPECULAR: Similar to a mirror, having the reflecting properties of a mirror or other smooth reflecting surface. This term is also used to describe the finish of the material used in some reflectors or louvers.

TORCHERE: a portable luminaire suitable for standing on the floor, which directs most, if not all, of it's light in an upward direction.

THERMAL FACTOR:  A factor that is often used when calculating the compensation needed for the change in light output of a fluorescent lamp due to changes in temperature.

TRANSFORMER: An electrical device with two or more coupled windings, used to convert the supply (input voltage) of electrical power at one voltage in a primary circuit, to a lower voltage (output voltage) in a secondary circuit.

TRANSLUCENT: the opposite of opaque. A translucent material has the property of transmitting diffused light but obscuring vision, as in a bathroom window.

TROFFER: A layman's term used to refer to a recessed fluorescent downlight. 

TUNGSTEN HALOGEN: A type of lamp that uses a gas-filled tungsten filament, combined with a lamp envelope made from quartz, in order to withstand the high temperatures that these lamps produce. These are also commonly referred to as quartz halogen lamps.

ULTRA VIOLET (UV):  Invisible radiant energy having a wavelength shorter than wavelengths of visible light, and longer than those of x-rays.

UPLIGHT: The opposite of downlight. An uplight is typically a luminaire that projects light upward toward the ceiling, usually along a wall, with no downward component of light.

VALANCE: A longitudinal shielding panel mounted over a windown with draperies to conceal light sources that provide both uplight and downlight.

VOLT: The standard unit of measurement of electrical potential; when applied across a resistance of one ohm, a volt will result in a current flow of one ampere.

WATT: A unit of electrical power commonly used in lighting. A watt is equal to the power produced by a current of one ampere across a potential difference of one volt.

WORKPLANE: This refers to the plane on which visual tasks are performed, typically a horizontal plane about 30 inches above the floor, or desk height.

 

 

 

 

 

 

 

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