A mental framework or concept that helps us interpret and organize new information.
Chapter 6 Distribution of Light
Angle of Incidence
The angle between a ray of light striking a surface and a line perpendicular to that surface.
Term describing dispersed light distribution. Refers to the scattering or softening of light.
A translucent piece of glass or plastic that shields the light source in a fixture. The light transmitted throughout the diffuser is redirected and scattered.
The angle from a fixture's vertical axis at which a reflector, louver, or other shielding device cuts off direct visibility of a lamp.
Describes light leaving a fixture and entering the illuminated space without first bouncing off of any architectural elements such as the ceiling or walls.
Glare produced by a direct view of light sources. It is often the result of fixtures with inadequate shielding.
A type of ceiling luminaire, usually recessed, where the light is directed downward.
The angle, measured in degrees, between vertical and the centerline of the beam of light illuminating an object.
The effect of brightness or differences in brightness within the visual field sufficiently high to cause annoyance, discomfort or loss of visual performance.
Lighting designed to provide a uniform level of illuminance throughout an area, exclusive of any provision for additional task-specific lighting requirements.
A light distribution pattern or luminaire in which all of the light is directed upward to bounce off of the ceiling.
Describes rays of light bouncing off of multiple surfaces within a room.
The ratio of light reflected from a surface to the light incident on the surface. Reflectances are often used for lighting calculations.
Glare resulting from reflections of bright objects on polished or glossy surfaces. Also called Veiling Reflection.
A device used to redirect the light output from a source, primarily by bending the waves of light.
A light distribution pattern or luminaire in which 60% or more of the light is directed downward and 40% or less of the light is directed upward.
A light distribution pattern or luminaire in which 40% or less of the light is directed downward and 60% or more of the light is directed upward.
A term describing the light reflection characteristics of a material. Light is reflected directionally, with some amount of scatter.
Describes a mirrored or polished surface. The angle of reflection is equal to the angle of incidence. This word describes the finish of the material used in some louvers and reflectors.
Describes a material that diffuses light passing through it so that objects cannot be seen clearly through it.
The percentage of light that passes through a translucent or diffusing material.
Describes a material with no diffusion of the light passing through it so that objects are clearly seen through it.
A glare reflection from a specular surface that partially or completely obscures the object being observes. Examples include reflection of a luminaire on a glossy magazine page.
Describes a material through which light does not pass.
The angle measured from the ceiling plane to the line of sight where the bare lamp in a luminaire becomes visible. Higher shielding angles reduce direct glare.
Chapter 7 Lamps
A tube made of glass, clear quartz or ceramic that contains the arc stream in a fluorescent or HID lamp.
A device used to operate fluorescent and HID lamps. The ballast provides the necessary starting voltage and regulates the current during operation.
The angle through the center of the beam where the light level has fallen to 50% of the beam’s maximum brightness (typically at the center of the beam)
A small fluorescent lamp that is often used as an alternative to incandescent lighting. Also called PL, Twin-Tube, CFL, or BIAX lamps.
The electronic device regulating electricity to LEDS. Also known as a power supply.
A light source consisting of a tube filled with argon, along with krypton or other inert gas along with mercury. When electrical current is applied, the resulting arc causes the mercury to emit ultraviolet radiation that excites the phosphors inside the lamp wall, causing them to radiate visible light.
A metal component, usually aluminum, used to draw heat away from an LED and dissipate it.
High Intensity Discharge (HID)
Lamp An electric discharge lamp in which an electric arc through a gas filled chamber produces light without intermediate steps. Generic term describing mercury vapor, metal halide, high-pressure sodium, and low-pressure sodium light sources and luminaires.
High Pressure Sodium Lamp
A high intensity discharge (HID) lamp whose light is produced by radiation from sodium vapor.
HOT RESTART or HOT RESTRIKE
Restoring the arc in an HID light source after a momentary power loss. Hot restart occurs when the arc tube has cooled a sufficient amount.
The light output of a lamp when installed.
A fluorescent circuit that ignites the lamp instantly with a very high starting voltage from the ballast. Instant start lamps have single-pin bases.
The average life of a lamp, in hours, based on an operation cycle of three hours on, then off.
Light Emitting Diode (LED)
A solid-state lighting device that emits a directional beam of colored light. White LEDs combine blue LEDs and phosphors.
A lamp (typically compact halogen) that operates at lower than 120V, typically 12V, and requires the use of a transformer.
A type of high intensity discharge lamp in which light is produced by passing an electric arc through a combination of metal halide and mercury vapors.
Parabolic Aluminized Reflector (PAR)
A sealed lamp unit having a parabolic shaped reflector, light source (typically incandescent or metal halide) and a lens. PAR lamps are available in a variety of beam angles.
A type of ballast/lamp circuit that uses a separate starter to heat up a fluorescent lamp before high voltage is applied to start the lamp.
A compact fluorescent lamp with a double twin tube configuration.
Rapid Start (RS)
The most popular fluorescent lamp/ballast combination used today. This ballast quickly and efficiently preheats lamp cathodes to start the lamp. Uses a "bi-pin" base.
A lamp in which the outer glass envelope is coated with a reflecting material. Also referred to as an R-lamp. Variations include the ER and BR. Generically, this may also include other shapes that have reflectors such as MR and PAR.
Solid State Lighting (SSL)
Refers to LED and OLED light sources.
A device that increases or decreases electrical pressure. In lighting this typically refers to a device that converts 120V to 12V.
Tungsten Halogen Lamp
An incandescent lamp with a lamp envelope made of quartz and a fill gas of one or more halogens (namely iodine, chlorine, bromine, and fluorine), which slow the evaporation of the tungsten. Also, commonly called a quartz lamp or halogen lamp.
Abbreviation for National Electrical Manufacturers Association.
Chapter 8 Color
The perceived color of an object resulting from the color content of the light source, the object’s reflectivity and the eye’s adaptation to the illuminated environment.
An idealized object that is a perfect absorber of all energy that strikes its surface, and that is an ideal emitter of energy whose spectral power distribution curve is based on its temperature.
The saturation or purity of a color
The visual system’s process of adjusting perceived color based on target and surround colors.
Refers to the color of a light source independent of its brightness.
The perception of objects as having the same color under differing lighting conditions
Color Rendering Index (CRI)
A measurement of the effect of a light source on the color appearance of an object compared to its color appearance under a reference light source. The evaluation is abased on eight color samples, but is calculated mathematically, not visually. Expressed on a scale of 0 to 100, where 100 indicates no color shift. A low CRI rating suggests that the colors of objects will appear unnatural under that particular light source.
The effect of a light source on the apparent color of an object
A numerical indication of the warmth or coolness of white light. Specifically, it is the absolute temperature of a blackbody radiator having a chromaticity equal to that of the lighting source, expressed in kelvin. Strictly speaking, this applies only to incandescent light sources. See Correlated Color Temperature.
Correlated Color Temperature (CCT)
CCT describes the color temperature of non-incandescent light sources.
The general color attribute of red, blue, yellow, green etc.
Two or more light sources of the same color but having different spectral power distribution curves.
The sorting of LEDs by their color or color properties.
Chapter 9 Luminaires
A directional light used to emphasize an object or draw attention
The opening in a light fixture through which light enters a space.
A vertical blade or parabolic curved element of a lighting fixture used to block light distribution at high angles to prevent glare.
A type of ceiling luminaire, usually recessed, where the light is directed downward.
The outer enclosure of a luminaire.
A fluorescent fixture; usually a 2' x 4' fixture that sets or "lays" into a suspended ceiling grid.
Transparent or translucent medium that alters the direction of light passing through it. Usually made of glass or acrylic.
Grid type of optical assembly used to control light distribution from a fixture. Can range from small-cell plastic to the large-cell anodized aluminum louvers used in parabolic fluorescent fixtures.
A complete lighting unit consisting of a lamp or lamps, along with the parts designed to distribute the light, hold the lamps, and connect the lamps to a power source. Also called a fixture.
A term referring to the components of a light fixture (such as reflectors, refractors, lenses, louvers) or to the light emitting or light-controlling performance of a fixture.
A set of printed data describing the light distribution, efficiency, and zonal lumen output of a luminaire.
The term used to describe any luminaire that is installed so that the body of the luminaire is above the surface of the ceiling.
The part of a light fixture that shrouds the lamps and redirects some light emitted from the lamp.
A luminaire that is only partly above the ceiling.
Describes any luminaire installed on the surface of the ceiling, wall, floor or piece of cabinetry or furniture.
Describes a luminaire that hangs from the ceiling into the room.
The term used to refer to a recessed fluorescent light fixture (combination of trough and coffer).
A luminaire that directs light nearly parallel to the face of a wall to illuminate the surface.
A luminaire designed to illuminate vertical surfaces.
A type of fluorescent fixture that has a louver composed of aluminum baffles curved in a parabolic shape. The resulting light distribution produced provides reduced glare and better light control when compared to lay-in fluorescent fixtures.
Chapter 10 Daylighting
The upper portion of a wall containing openings to admit daylight into a building.
The intentional use of daylight as a significant daytime illuminance source for a building’s interior.
An energy-saving technique used in areas with significant daylight contribution in which a dimming system responds to a photocell by reducing the output of the lamps when daylight is present. As daylight levels increase, lamp intensity decreases.
The raised section of a building’s main roof. The sides of monitors usually contain clerestory windows or louvers to light or ventilate the area below.
Daylighting provided by vertical fenestration mounted below the ceiling plane.
Chapter 11 Documentation
A technique in which a light fixture is set on a shelf or in a recess below the ceiling. Light from the fixture is directed out of the recess to reflect off of the ceiling and into the illuminated space.
A maximum distance that interior fixtures may be spaced that ensures uniform illumination on the work plane. The luminaire height above the work plane multiplied by the spacing criterion equals the center-to-center luminaire spacing.
Chapter 12 Controls
The unit of measurement for electric current. It is the amount of electricity moving past a given point in a circuit during a specific period. Also referred to as Amp. Amperage is equal to wattage divided by voltage.
Astronomical Time Switch
A device that provides a signal to turn a load on or off or adjust power in steps based on the time of day or based on astronomical events such as sunset or sunrise, accounting for geographic location and day of the year. Also known as an astronomical time clock.
The process of setting, refining and/or resetting building system operational parameters. In lighting this involves setting occupancy and vacancy sensors and control system presets.
Digital Addressable Lighting Interface (DALI)
A communications protocol and network in which each luminaire has a distinct address, receives dimming information and can report back to the lighting controller.
An electrical device that controls lamp intensity by regulating the flow of electricity to the lamp.
A lighting control strategy that provides two light levels–one at full-ON and one at a lower level. This may be achieved by dimming or by turning off some portion of the lighting so that uniform light level and distribution is maintained. In addition to the two ON settings, bi-level control may provide for full-OFF. Also known as bi-level switching.
A group of luminaires performing the same task and controlled in unison.
Control device that turns lights off after the space becomes unoccupied. May use ultrasonic, infrared or both technologies.
A light-sensing device used to control luminaires and dimmers in response to detected light levels.
A set of light levels saved into the memory of a lighting controller for recall by pressing the associated button on the controller.
A device that switches an electrical load on or off based on a small input current or voltage.
Control device that is manual on/automatic off to turn lights off after the space becomes unoccupied. May be ultrasonic, infrared or both.
The standard unit of measurement for electrical potential. It defines the "force" or "pressure" of electricity.
Describes a wall-mounted switch or dimmer.
The unit for measuring electrical power. It defines the rate of energy consumption by an electrical device when it is in operation.
Chapter 13 Calculations
The ballast factor (BF) for a specific lamp-ballast combination is the percentage of the rated lamp lumens that will be produced by the combination.
Unit of luminous intensity, describing the intensity of a light source in a specific direction
A measure of luminous intensity of a light source in a specific direction, measured in candelas
Candlepower Distribution Curve
A curve, plotted on polar coordinates, illustrating the distribution of luminous intensity of a lamp or luminaire in a plane through the light center.
Coefficient Of Utilization (CU)
The ratio of lumens from a luminaire received on the work plane to the lumens produced by the lamps alone
The English unit of measurement of the illuminance on a surface. One footcandle is equal to one lumen per square foot.
The English unit of luminance. One footlambert is equal to candelas per square foot.
A photometric term that quantifies light incident on a surface or plane. Illuminance is commonly referred to as light level. It is expressed as lumens per square foot (footcandles), or lumens per square meter (lux).
Lamp Lumen Depreciation Factor (LLD)
A factor that represents the reduction of lumen output over time. The factor is commonly used as a multiplier to the initial lumen rating in illuminance calculations, which compensates for the lumen depreciation.
Light Loss Factors (LLFs)
Factors that allow for a lighting system's operation at less than initial conditions. These factors are used to calculate maintained light levels. LLFs are divided into two categories, recoverable and non-recoverable. Examples are lamp lumen depreciation and luminaire surface depreciation.
A unit of light flow, or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp.
A photometric term that quantifies brightness of a light source or of an illuminated surface that reflects light. It is expressed as footlamberts (English units) or candelas per square meter (Metric units).
The metric unit of measure for illuminance of a surface. One lux is equal to one lumen per square meter. One lux equals 0.093 footcandles.
Refers to the calculated light levels of a space after factoring in light loss factors such as lamp lumen depreciation, luminaire dirt depreciation, and room surface dirt depreciation.
Room Cavity Ratio (RCR)
A ratio of room dimensions used to quantify how light will interact with room surfaces. A factor used in illuminance calculations.
A factor used in lighting calculations that compensates for the change in light output of a fluorescent lamp due to a change in bulb wall temperature. It is applied when the lamp-ballast combination under consideration is different from that used in the photometric tests.
The level at which work is done and at which illuminance is specified and measured. For office applications, this is typically a horizontal plane 30 inches above the floor (desk height).
A reference direction directly below a luminaire, or "straight down" (0 degree angle).
Chapter 14 Codes
Abbreviation for American National Standards Institute.
Abbreviation for American Society of Heating, Refrigerating and Air-Conditioning Engineers
Light Power Density (LPD)
A calculation of the watts per square foot of power used by, or allocated to, lighting. Energy conservation codes allocate LPDs based on space type or building type.
Chapter 15 Sustainability
The total costs associated with purchasing, operating, and maintaining a system over the life of that system.
Chapter 16 Light and Health
Variations with a cycle of approximately 24 hours.