Advanced Lighting Guidelines Glossary
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Definition
Absolute Photometry Photometry is the measurement of the properties of light, particularly intensity. Absolute photometry, used for conventional lamps and luminaires with… More »
Action Spectrum The magnitude of a given stimulus required to produce a fixed physiological response, plotted against wavelength. The action spectrum reveals… More »
Adaptation The process by which the retina becomes accustomed to more or less light than it was exposed to during an… More »
Adaptation luminance The luminance to which the visual system is assumed to be adapted. In practice, this is usually taken to be… More »
Adaptive compensation Control strategy in which light levels are reduced during evening hours to accommodate human lighting preferences at night and save… More »
Altitude The vertical angular distance of a point in the sky above the horizon. Altitude is measured positively from the horizon… More »
Amalgam An alloy of mercury with other metals. Some CFLs use a mercury amalgam rather than standard mercury. An amalgam keeps… More »
Ambient lighting Lighting throughout an area that produces general illumination that may or may not be uniform. Original Chapter Source: Luminaires Provided… More »
ANSI American National Standards Institute Original Chapter Source: Policies & Programs More »
Aperture In buildings, an aperture is an opening, such as a window or a skylight, that allows daylight to enter the… More »
Application efficiency A lighting design metric that looks at the fraction of of light (lumens) at the point of use (visual task)… More »
Aqueous humor The transparent, watery fluid between the cornea and the lens of the eye. Original Chapter Source: Health & Performance Provided… More »
ASHRAE American Society of Heating, Refrigerating, & Air-Conditioning Engineers Original Chapter Source: Policies & Programs More »
Atrium A multistoried space within a building that allows daylight to illuminate the adjacent interior spaces typically through a large overhead… More »
Auxiliaries Electrical devices that provide proper voltage to ignite light sources and regulate current during normal operation. Examples include ballasts, transformers… More »
Azimuth The horizontal angular distance between the vertical planes containing two points in the sky. The azimuth of a single point… More »
Ballast The ballast is an electrical device that performs two basic functions: 1) provides the starting voltage and 2) limits the… More »
Ballast Efficacy Factor (BEF) Sometimes called ballast efficiency factor, ballast efficacy factor is the ratio of the ballast factor to the active power (in… More »
Ballast efficiency Metric used to express the electrical efficiency of a ballast, measured as the lamp wattage divided by the input watts… More »
Ballast factor Ballast factor (BF) The ratio of the light output of a fluorescent lamp or lamps operated on a ballast to… More »
Basis of Design Document produced during the design phase, and refined over the remainder of the project, that clearly articulates the design intent… More »
Bi-level switching Control of lighting system involving dual-circuiting a lighting system, which enables two different light and power levels in addition to… More »
Binning (LED) The system used by an LED package manufacturer to separate their LEDs into groups with similar performance attributes.  LEDs are… More »
Biosphere The global sum of all ecosystems, all living things. Original Chapter Source: Policies & Programs More »
Black body locus The collection of points (locus) on a chromaticity diagram that describes the color of blackbody as a function of temperature. … More »
Brightness The attribute by which an area of finite size is perceived to emit, transmit, or reflect a greater or lesser… More »
British Thermal Unit (BTU) Unit of measurement for heat energy equal to about 1,055.06 joules, or the amount of thermal energy required to raise… More »
BTU See British Thermal Unit. More »
California?s Title 24 Building Energy Code The Energy Efficiency Standards for Residential and Nonresidential Buildings were established in 1978 in response to a legislative mandate to… More »
Candela Unit of luminous intensity. The measurement of light intensity emitted in a specific direction from a luminaire. Original Chapter Source:… More »
Candela distribution chart See candela distribution table Original Chapter Source: Luminaires Provided By: Craig DiLouie More »
Candela distribution curve Graphical representation of select data in the candela distribution table, visually depicting the relative light intensity for a single vertical… More »
Candela distribution table Element of luminaire photometric report typically presented in the manufacturer catalog sheet for the product. The table, also called the… More »
Candela per square meter (Cd/m2) Unit of luminance in the metric system. The English unit equivalent is candelas per square foot (Cd/ft2). Original Chapter Source:… More »
Candlepower The measure of the intensity of a light source in a given direction, measured in candelas (Cd). Candlepower distribution curves… More »
Carbon neutral Total operations that release zero carbon dioxide into the atmosphere. Original Chapter Source: Luminaires Provided By: Leslie North More »
Cataract A common cause of partial sight. Cataract is the formation of an opacity in the eye, usually in the lens,… More »
Cathode sputtering The process by which cathode material is slowly eroded away by electron mercury ion bombardment. Original Chapter Source: Sources Provided… More »
Chorio-retinal injury Thermal damage to the retina produced by focusing visible and infrared radiation up to 1400 nm onto the retina. Original… More »
CIE Commission Internationale de l'Eclairage (International Lighting Commission) Original Chapter Source: Luminaires Provided By: Naomi Miller More »
Circadian rhythms Circadian rhythms are physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness… More »
Circadian system The physiology of the body that controls the 24 hour variation in hormonal balance and, consequently, activity and behavior. Original… More »
Circumsolar area The region of very high brightness around the solar disk. Original Chapter Source: Daylighting Provided By: Kosta Papamichael / CLTC More »
Clerestory The part of a building rising clear of the roofs or other parts, whose walls contain windows for lighting the… More »
Closed loop Photocontrol system that measures combined daylight/electric light level on a representative task surface in the controlled space and adjusts light… More »
CMH lamp The designation for ceramic metal halide lamps in which the arc tube material is a ceramic rather than quartz. Original… More »
Coefficient of utilizaton (CU) Coefficient of Utilization (CU) is the percentage of light generated by the lamps in a luminaire that reaches the work… More »
Color Rendering Index (CRI) A scale of values from to 100, indicating how a light source makes a material color look compared to… More »
Color Temperature or Correlated Color Temperature (CCT) A specification of the apparent color of a light source relative to the color appearance of an ideal incandescent source… More »
Commissioning A systematic process that ensures that all elements of the lighting control system perform interactively and continuously according to documented… More »
Compact Fluorescent Lamp (CFL) A fluorescent lamp using compact folded or spiral tubes. Some models include integral ballast and screw base which allows them to… More »
Context parameters Parameters beyond the control of designers that affect performance. Original Chapter Source: Daylighting Provided By: Kosta Papamichael / CLTC More »
Continuous dimming Control of the intensity of a light source without abrupt transitions between light levels. Original Chapter Source: Controls Provided By:… More »
Contrast Also known as luminance contrast, it is the relationship between the luminances of an object and its immediate background. [Source:… More »
Contrast magnitude The ratio between two adjacent luminance values. Original Chapter Source: Daylighting Provided By: Kosta Papamichael / CLTC More »
Contrast sensitivity The reciprocal of threshold luminance contrast. Original Chapter Source: Health & Performance Provided By: Peter Boyce More »
Control panel Cabinet-type enclosure containing a series of relays that receive low-voltage ON/OFF signals from another device and respond by switching the… More »
Control station Control stations enable aggregation of control of multiple dimmers into a single interface between the user and the controller (dimming… More »
Control zone A luminaire or group of luminaires controlled simultaneously by a single controller. Original Chapter Source: Controls Provided By: Craig DiLouie More »
Controller Generic term describing the device in a control system that electrically changes the output of the lighting system. Original Chapter… More »
Cooling loads The rate at which heat must be removed from a building or space to achieve thermal comfort for the occupants.… More »
Core body temperature The inner temperature of the body that is stabilized by thermoregulation. Original Chapter Source: Health & Performance Provided By: Peter… More »
Cornea The transparent front surface of the eye. Original Chapter Source: Health & Performance Provided By: Peter Boyce More »
Correlated color temperature A specification of the apparent color of a light source relative to the color appearance of an ideal incandescent source… More »
Cosine sensitivity The property of cosine corrected light meters in which the sensitivity to light decreases with the cosine of the angle… More »
Critical fusion frequency See Flicker fusion frequency. Original Chapter Source: Light & Vision Provided By: Heschong Mahone Group / Peter Boyce More »
Cylindrical illuminance The average illuminance on the surface of an infinitesimally small, vertical cylinder. Original Chapter Source: Light & Vision Provided By:… More »
DALI (Digital Addressable Lighting Interface) A marketing term developed by DALI-AG often used generically to describe a royalty-free, non-proprietary, two-way, open and interoperable digital protocol… More »
Daylight Light originating directly from the sun or direct sunlight that is scattered by the atmosphere. Original Chapter Source: Daylighting Provided… More »
Daylight harvesting The appropriate turning off of electric lighting systems during times at which sufficient daylight is available for visual tasks that… More »
Daylight zone Area of consistent and substantial daylight availability within a building, expressed in square feet. Also called the daylight area. Original… More »
Daylighting Lighting strategies that use the sky as a light source, while shielding or reflecting direct sunlight to avoid glare, heat… More »
Daylighting control Control strategy in which lighting is either switched OFF or dimmed when photosensor-measured incoming or task light levels rise above… More »
Demand charge Utility rate structure which charges based upon peak electric demand use during the billing month. Fee rate is in $/kW.… More »
Demand response Allows customers to bid into the power supply system by reducing building consumption during pre-defined peak load conditions. Original Chapter… More »
Design parameters Parameters that designers control to affect performance. Original Chapter Source: Daylighting Provided By: Kosta Papamichael / CLTC More »
Device Settings Document listing all adjustable lighting controls in a project, identifying them by individual space or space type, and then clearly… More »
Diabetic retinopathy A common cause of partial sight caused by chronic diabetes. The effect is to damage parts of the retina. The… More »
Dichroic coatings Optically-thin layers of metalic materials applied to the lens or glass envelopes of lamps to selectively reflect or transmit certain… More »
Dielectric Nonconducting substance. Original Chapter Source: Luminaires Provided By: Leslie North More »
Diffuse daylight Daylight not originating directly from the sun or from specular reflections of the sun. Original Chapter Source: Daylighting Provided By:… More »
Diffuse reflectance The ratio of the luminous flux reflected from a surface to the luminous flux incident on the surface. Original Chapter… More »
Dim The act of reducing light intensity. Original Chapter Source: Daylighting Provided By: Kosta Papamichael / CLTC More »
Dimmable ballast Fluorescent or HID ballast specially designed to provide the ability to adjust light output by modifying the lamp current. Original… More »
Dimmer A control device for varying the light output of lamps. Original Chapter Source: Controls Provided By: Craig DiLouie More »
Direct Glare Glare caused by a light source directly visible. Original Chapter Source: Design Considerations Provided By: Leslie North More »
Disability glare Glare that causes a deterioration in visual capabilities. Disability glare is caused by light being scattered in the eye, the… More »
Discharge lamps Electric light sources which produce light by passing electrical current through an ionized gas.  Examples include neon lamps, xenon flash… More »
Discomfort glare Glare that causes discomfort. Discomfort glare does not necessarily cause a deterioration in visual capabilities. Original Chapter Source: Health &… More »
Distributed control Control strategy involving distribution of smaller control panels throughout a facility close to the loads they control. Original Chapter Source:… More »
Distributed intelligence Control system in which microprocessor intelligence and functionality is embedded in the control devices attached to the lighting network rather… More »
DMX512 A digital communications protocol most commonly used to control theatrical, stage and entertainment lighting and effects. Original Chapter Source: Controls… More »
Downlight A recessed luminaire usually using a point source, with a round or square aperture that projects light downward. Original Chapter… More »
Driver For light emitting diodes, a device that regulates the voltage and current powering the source. Original Chapter Source: Sources Provided… More »
Dual-loop photosensor Relatively new daylight harvesting technology combining open- and closed-loop photodiodes looking in different directions, with the result being greater accuracy… More »
Dual-switching A bilevel switching strategy involving dual-circuiting the inboard lamps separately from the outboard lamps in three-lamp luminaires, enabling three different… More »
Eccentricity The angle between the line of sight and the line from the eye to the position of the target. Original… More »
Eddy current Circulating flow of electrons (current) within a conductor which can create magnetic fields that oppose the change in magnetic field.… More »
Efficacy (luminous efficacy) Used in lighting as a measure of luminous efficiency where light (lumens) are compared to the electrical power (watts) used… More »
Efficiency A measure of the ability of a system to process energy (such as light) taking losses into account. Original Chapter… More »
Electricity delivery grid See power grid. Original Chapter Source: Policies & Programs Provided By: Craig DiLouie More »
Electrochromic Glass that has the ability to change its visible light transmittance with the application of an electric potential. Original Chapter… More »
Electrodes  The structure that serves as the electric terminals at each end of electric discharge lamps. Original Chapter Source: Sources Provided… More »
Emission mix A coating that is place on fluorescent lamp electrodes to enhance electron production. Original Chapter Source: Sources Provided by: Erik… More »
Energy Use Intensity (EUI) Measure of energy efficiency of buildings expressed in kBTU per square foot. Original Chapter Source: Policies & Programs Provided by:… More »
Equivalent Sphere Illuminance (ESI) Visibility metric of how visible a specific target is under a proposed lighting system, as compared to the same target… More »
Erythema Reddening of the skin. There are many causes of erythema. Among them is excessive exposure to ultra-violet radiation leading ultimately… More »
Exitance The total quantity of light emitted by, reflected from, and transmitted through a surface into a complete hemisphere. It is… More »
Fenestration Any opening or arrangement of openings (normally filled with glazing media) for the admission of daylight, including any devices in… More »
Fixation A process by which the eye is held still so that the retinal image of an object remains on the… More »
Fixation point The position in the visual field that lies on the line of sight. The retinal image of the fixation point… More »
Fixed Wireless Control Network Network of wireless lighting control devices installed within range of a backbone of repeaters installed in set locations. Original Chapter… More »
Fixture efficacy The ration of light output of a fixture or luminaire to input power. Original Chapter Source: Sources Provided by: Erik… More »
Flicker fusion frequency The frequency at which a visual field repetitively oscillating in luminance appears not to be oscillating. The flicker fusion frequency… More »
Fluorescent Lamp A discharge lamp that produces light by means of electric current through low-pressure mercury gas. The arc produces ultraviolet energy… More »
Footcandle (fc) A measure of illuminance in lumens per square foot. One footcandle equals 10.76 lux, although for convenience 10 lux commonly… More »
Fossil fuel need to add definition More »
Fovea The central 2 degrees of the retina located on the line of sight. The fovea is structured so as to… More »
Fresnel lens A type of lens that achieves similar optical performance to conventional lenses while using considerably less material and within a… More »
Fuel cells Device that produces electricity from fuel (hydrogen) and an oxidant (oxygen) which react in the presence of a catalyst. Original… More »
GaN on GaN A new scientific innovation for LED technology is the ability to grow GaN crystals on its native GaN substrate (“GaN… More »
Ganglion cells A layer of the retina in which electrical signals from the cone and rod photoreceptors are combined and processed before… More »
General lighting Lighting designed to provide a substantially uniform level of illuminance throughout an area. Original Chapter Source: Luminaires Provided By: Franz… More »
Glare A source of light in the field of view that is much higher in brightness than the luminance to which… More »
Glare indices (Glare index) A method of predicting the presence of discomfort glare due to daylighting. Factors affecting the glare index include the size… More »
Glass An inorganic transparent material composed of silica (sand), soda (sodium carbonate), lime (calcium carbonate) and small quantities of alumina, boric… More »
Glaucoma A form of partial sight caused by excess pressure in the eye. The effect of the excess pressure is to… More »
Group relamping A method of conducting a planned replacement of a group of lamps prior to failure but near expected end of… More »
Halogen Lamps using a tungsten filament surrounded by halogen gas encapsulated in quartz, resulting in brighter, whiter light, higher efficiency, and… More »
Heliostat A system of mirrors that reflect the rays of the sun in a predetermined direction or towards a predetermined location.… More »
High intensity discharge (HID lamp) An electric discharge lamp in which the light is produced by an enclosed electrical arc using ionized gases operatiing at… More »
High-pressure sodium An electric lamp that produces light directly from an arc discharge under high pressure. Metal halide, high-pressure sodium, and mercury… More »
Horizontal illuminance Illuminance on a horizontal surface. Original Chapter Source: Daylighting Provided by: Kosta Papamichael / CLTC More »
HVAC Heating Ventilation and Air Condition Original Chapter Source: Policies & Programs More »
Hysteresis losses Losses from molecules in a transformer core resisting being magnetized and demagnetized by the alternating magnetic field. This resistance by… More »
IES Illuminating Engineering Society Original Chapter Source: Policies & Programs More »
Illuminance The area density of the luminous flux incident at a point on a surface. Units are Lumens per square foot… More »
Incandescent lamps Sources which produce light by utilizing long, thin filaments (usually made from tungsten) and heated to high temperatures (2700-3000 Kelvins… More »
Incandescent Reflector Lamp Incandescent/Halogen lamp fitted with an integral reflector used to focus light output in a desired direction and pattern. Original Chapter… More »
Induction Lamps A lamp that is power by an electromagnetic field rather than through lamp electrodes or direct electrical connections. Original Chapter… More »
Ingress protection (IP) rating International Protection (IP) rating system defined by International Standard IEC 60529, which classifies degrees of protection for electrical devices against… More »
Initial Cost (or First Cost or Initial Installed Cost) All the costs to purchase and install a fully functioning system. Original Chapter Source: Design Considerations Provided By: Leslie North More »
Input power Input power describes the amount of electric power, expressed in watts or kilowatts (1,000 watts), required to operate an electrical… More »
International Energy Conservation Code (IECC) The most commonly used residential energy code by states. Original Chapter Source: Daylighting Provided by: Kosta Papamichael / CLTC More »
Intrinsically photosensitive retinal ganglion cell (ipRGC) A ganglion cell in the retina which responds directly to incident light. The ipRGCs provide input to the human circadian… More »
Irradiance The incident radiant flux per unit area of a surface. Irradiance is measured in watts / square meter. Original Chapter… More »
Isofootcandle or Isolux Contour lines linking points of the same footcandle or lux value. Original Chapter Source: Design Considerations Provided By: Leslie North More »
Kelvin (K) The Kelvin scale is the basis of all temperature measurement, starting at the absolute zero, a theoretical condition at which… More »
L70 (subscript number) A lumen maintenance term that describes the amount of time that elapses before a light source's output has dropped to… More »
Lambertian Even cosine distribution. Original Chapter Source: Design Considerations Provided By: Leslie North More »
Lamp A radiant light source. Original Chapter Source: Sources Provided by: LRC - National Lighting Product Information Program (NLPIP) More »
Landolt ring A C-shaped target used to measure visual acuity and visual performance. The dimensions are such that the stoke width is… More »
LED array A collection of multiple LEDs mounted onto a substrate, usually a printed circuit board.  The light output from the LED… More »
LED junction temperature (Tj) Temperature of the LED chip within an LED package.  Tj is a critical parameter of LED performance.  LED light output,… More »
LEED Leadership in Energy and Environmental Design (LEED) is an internationally recognized green building certification system, developed and managed by the… More »
Life cycle assessment (LCA) A framework for identifying and evaluating the environmental burdens associated with the life of materials associated with a product, from… More »
Life Cycle Cost-Effective An efficiency measure is considered Life Cycle Cost-Effective if savings in energy over the life of the efficiency measure outweigh… More »
Life-cycle cost analysis (LCCA) Economic method for assessing the total cost of facility system ownership taking into account all costs of acquiring, owning and… More »
Light Electro-magnetic radiation between the wavelength limits of 380 nm and 780 nm that stimulates the human visual system. Sometimes called… More »
Light pollution A term used two ways, meaning either the light that produces skyglow, the glowing atmosphere above populated areas that interferes… More »
Light to solar heat gain ratio The ratio between the visible light transmittance and the solar heat gain coefficient of a glazing. Original Chapter Source: Daylighting… More »
Light trespass Unwanted light that spills onto neighboring properties. Original Chapter Source: Luminaires Provided By: Naomi Miller More »
Light-Emitting Diode (LED) Light-emitting diodes (LEDs) are solid-state electronic devices that generate light via the transformation of electric energy to radiant energy within… More »
Lighting control General term referring to electrical devices and techniques necessary to provide the right amount of light where and when needed.… More »
Lighting Control Narrative This document is used to briefly define the context for lighting control systems (general project goals and goals for lighting… More »
Lighting Power Density (LPD) A measure of installed lighting power, expressed as Watts per square foot. Original Chapter Source: Policies & Programs More »
Line of sight The line from the eye to the fixation point. The retinal image of an object on the line of sight… More »
Load scheduling An energy-saving lighting control strategy for switching or dimming during hours when a building space is unoccupied or occupied by… More »
Load shedding A lighting control strategy for selectively reducing the output of luminaires on a temporary basis as a means to reduce… More »
Low-pressure sodium (LPS) lamp An electric discharge lamp where the arc tube operates at relatively low pressures and temperatures utilizing sodium vapor as the… More »
Lumen Unit of emitted light from a light source. More technically, a unit of luminous flux. Electromagnetic radiation weighted using the… More »
Lumen depreciation The decrease in lumen output that occurs as a lamp is operated, until failure. Also referred to as lamp lumen… More »
Lumen Maintenance Measure of how well a lamp maintains its light output over its operational life. Original Chapter Source: Sources Provided by:… More »
Lumen maintenance dimming Control strategy intended to save energy by varying energy consumption by maintaining a specified light level. Original Chapter Source: Controls… More »
Luminaire A complete lighting unit consisting of a lamp or lamps and ballast(s) (when applicable) together with the parts designed to… More »
Luminaire efficacy Efficacy of a light source or light source/auxiliary system modified by the efficiency of the luminaire in distributing light output… More »
Luminaire efficiency The percentage of the total light generated by the source that leaves the luminaire in all directions. Original Source: Manual… More »
Luminance The photometric quantity most closely associated with the perception of brightness, measured in units of luminous intensity (candelas) per unit… More »
Luminance contrast Luminance contrast quantifies the relative brightness of an object against its background. It can range from zero to one. The… More »
Luminance distribution The distribution of luminance arriving at a point from all surrounding directions. Original Chapter Source: Daylighting Provided by: Kosta Papamichael… More »
Luminance factor See specular reflectance. Original Chapter Source: Light & Vision Provided By: Heschong Mahone Group / Peter Boyce More »
Luminance ratios Ratios between the luminances. Original Chapter Source: Daylighting Provided by: Kosta Papamichael / CLTC More »
Luminous efficacy The expression of efficiency in converting power (watts) into light (lumens). Expressed as lumens per watt or lm/W. More »
Luminous flux Emitted light from a light source or a surface, measured in lumens. See Lumens. Original Chapter Source: Luminaires Provided By:… More »
Luminous intensity Quantity of light emitted from a light source or a surface in a given direction, measured in candelas. Original Chapter… More »
Luminous intensity distribution curve See candela distribution curve More »
Lux (lx) A measure of illuminance in lumens per square meter. One lux equals 0.093 footcandle. Original Chapter Source: Daylighting Provided by:… More »
Macular degeneration A common cause of partial sight. The macular lies immediately above the central part of the retina. When it degenerates… More »
Maximum Allowable Junction Temperature The manufacturer rated temperature limit of the LED device. Junction temperatures above this value may lead to sudden catastrophic failure… More »
MCPCB (Metal Core Printed Circuit Boards) A type of printed circuit board that has the dielectric and copper layer laminated to a copper or aluminum core. … More »
Melatonin A hormone produced by the pineal gland at night. Melatonin circulates in the bloodstream as a messenger of time. Original… More »
Melatonin suppression The reduction in melatonin concentration following exposure to light. Original Chapter Source: Health & Performance Provided By: Peter Boyce More »
Mercury lamps A high intensity discharge (HID) lamp which utilizes mercury vapor at relatively high pressures and temperatures to generate light. Original… More »
Mercury starvation The state in which a fluorescent lamp does not have enough mercury vapor present, often resulting in a pinkish lamp.… More »
Mesh Wireless Control Network Network of wireless lighting control devices communicating as nodes in a network; a signal generated by one device is routed… More »
Mesopic vision The state of vision between photopic and scotopic vision in which both rod and cone photoreceptors are active. Conventionally, this… More »
Metal halide lamp A high intensity discharge (HID) lamp which utilizes mercury in combination with metal halide salts operating at relatively high pressures… More »
Minute of arc A measure of angle corresponding to one sixtieth of a degree. Original Chapter Source: Health & Performance Provided By: Peter… More »
Model lighting ordinance (MLO) Outdoor lighting ordinance designed to address light pollution issues. The MLO was developed jointly by the Illuminating Engineering Society of… More »
MR lamp A type of reflector lamp in which the reflector is made up of small individual reflecting surfaces.  MR lamps are… More »
Multi-level switching A bilevel switching strategy involving dual-circuiting the inboard lamps separately from the outboard lamps in three-lamp luminaires, enabling three different… More »
Nadir The direction pointing directly below the fixture. It is the imaginary line running vertically from the center of the fixture… More »
Nanometer (nm) A subdivision of the SI unit meter equal to 10-9 meters. Original Chapter Source: Daylighting Provided by: Kosta Papamichael /… More »
Nonrenewable resources Sources of energy that cannot be renewed once they are depleted. The most common nonrenewable energy sources are oil, coal,… More »
Occupancy sensor A device that switches lights ON and OFF or dims and brightens them based on the presence or absence of… More »
Off-axis vision This occurs when the object to be seen appears off the line of sight, i.e., away from the fixation point.… More »
On-axis vision This occurs when the object to be seen occurs on the line of sight so the retinal image of the… More »
Open loop Photocontrol system that measures only daylight coming into the space, not actual light levels in the space. Original Chapter Source:… More »
Optical radiation Electro-magnetic radiation between the wavelength limits of 1 nm to 1 mm. Ultra-violet, visible and infrared radiation all fall within… More »
Overhead glare Glare caused by a light source located directly above the viewer. Original Chapter Source: Design Considerations Provided By: Leslie North More »
Override A switch or other method that can be used by occupants to ensure continuation of lighting when required outside of… More »
Owner Project Requirements Document produced during pre-design (programming) project phase, and refined over the course of the project, that clearly articulates owner requirements… More »
PAR lamp A type of reflector lamp with a Parabolic Aluminized Reflector. PAR lamps are sometimes called pressed glass reflector lamps because… More »
Parallel When lamps are wired to a ballast in parallel, if any of the connected lamps fail, the remaining lamps continue… More »
Passive infrared (PIR) Occupancy sensing method that detects occupancy by reacting to the movement of infrared heat energy emitted by people. Original Chapter… More »
PCB (Printed Circuit Board) Printed circuit boards are laminates of copper and dielectric polymer layers used to mount electronic components and carry electrical signals… More »
Peak consumption periods need definition More »
Peak demand Maximum electric demand load (kW) sustained for specified period (typically 15 minutes duration) . Original Chapter Source: Design Considerations Provided… More »
Peak electricity demand The highest amount of electrical power needed over a particular period of time. Original Chapter Source: Daylighting Provided by: Kosta… More »
Peak load See peak demand. Original Chapter Source: Policies & Programs Provided By: Craig DiLouie More »
Peak period See peak demand. Original Chapter Source: Policies & Programs Provided By: Craig DiLouie More »
Peak use See peak demand. Original Chapter Source: Policies & Programs Provided By: Craig DiLouie More »
Performance parameters Parameters used to evaluate performance. Original Chapter Source: Daylighting Provided by: Kosta Papamichael / CLTC More »
Performance Testing Project phase in which a contractor, under the supervision of the commissioning authority, inspects and tests installed systems to ensure… More »
Peripheral vision Visual activity involving off-axis vision is peripheral vision. Original Chapter Source: Health & Performance Provided By: Peter Boyce More »
Phase The timing of a repetitive oscillation at which it reaches an identifiable condition such as a maximum or a minimum.… More »
Photocell A light-sensitive device for measuring light intensity. (Also called a photosensor.) Original Chapter Source: Controls Provided By: Craig DiLouie More »
Photocontrols See daylighting control. Original Chapter Source: Policies & Programs Provided By: Craig DiLouie More »
Photokerititis Photochemical damage to the cornea caused by exposure to ultraviolet radiation. Original Chapter Source: Health & Performance Provided By: Peter… More »
Photoluminescence or "PL" A process in which a substance absorbs photons from some light source and, after a delay, re-radiates photons. The delay… More »
Photon An elementary particle, the basic unit of light. Original Chapter Source: Health & Performance Provided By: Peter Boyce More »
Photopic (photopic vision) The state of vision in which cone photoreceptors are dominant. Conventionally, photopic vision is taken to occur at adaptation luminances… More »
Photopigment A light-sensitive chemical contained in a photoreceptor. Original Chapter Source: Light & Vision Provided By: Heschong Mahone Group / Peter… More »
Photoreceptor A structure in the retina where light entering the eye is absorbed and converted into electrical signals. Original Chapter Source:… More »
Photoretinitis Photochemical damage to the retina caused by exposure to short wavelength visible light. Previously known as blue-light hazard. Original Chapter… More »
Photosensor A light-sensitive device for measuring light intensity. (Also called a photocell.) Original Chapter Source: Controls Provided By: Craig DiLouie More »
Phototransduction The process by which light is converted into electrical signals. Original Chapter Source: Health & Performance Provided By: Peter Boyce More »
Photovoltaics Field of technology related to the application of solar cells for conversion of daylight into electricity. Original Chapter Source: Luminaires… More »
Pigment epithelium The part of the eye immediately behind the retina. The pigment epithelium supplies nutrients to the retina and absorbs any… More »
Plasma Lighting An electrodeless lighting system consisting of a magnetron producing an electromagnetic field around a glass capsule inside an electrodeless lamp,… More »
Plenum In interior spaces, the Plenum is the space between the ceiling and either the next floor above or the roof.… More »
Polarization A process by which the electromagnetic field of light becomes oriented in particular directions. Original Chapter Source: Light & Vision… More »
Power factor The ratio of active power (in watts) to apparent power (in rms volt-amperes), power factor is a measure of how… More »
Power Grid The system of power production plants and distribution lines that deliver power to its end users. Original Chapter Source: Policies… More »
Power quality The degree to which current and voltage wave forms conform to a sinusoidal shape and are in synchronous phase with… More »
Power Supply (LED) An electronic device that transforms an incoming power supply to another form to be used by an electronic device.  For… More »
Powerline carrier (PLC) Method of lighting control involving using line-voltage power wires as communication pathways for control signals. Original Chapter Source: Controls Provided… More »
Prismatic structures Faceted structures on a transparent material that modify the direction of the light traveling through that material. These structures usually… More »
Profile angle A characteristic of horizontal lines, such as the edges of an overhang, in reference to a point of interest, such… More »
Programmable-Start Ballast Advanced type of fluorescent rapid-start electronic ballast. Upon energizing of the circuit, the ballast preheats the lamp cathodes prior to… More »
Radiant exposure The product of the irradiance on a surface and the duration of exposure. Irradiance is measured in watts / square… More »
Radiant flux The rate of flow of electromagnetic radiation, measured in Watts. Original Chapter Source: Light & Vision Provided By: Heschong Mahone… More »
Rapid-start lamps A fluorescent lamp that requires its electrodes to be heated prior to starting, using a starter that is an integral… More »
Rare-earth (RE) phosphors A group of phosphors containing rare-earth elements. Rare-earth phosphors are used in fluorescent lamps to achieve high efficacy and better… More »
Receptive field The area of the retina to which a retinal ganglion cell is connected. Original Chapter Source: Light & Vision Provided… More »
Reference ballast A ballast that is built to a specific standard for the sole purpose of testing and characterizing lamps and other… More »
Reflected glare Glare caused by a reflection of a light source in an object within the field of view. Original Chapter Source:… More »
Reflection The change in direction of a light ray at the boundary between two media so that the ray returns into… More »
Reflector lamp ("R" lamp) Lamps made of blown or molded glass formed such that a parabilic or other shape is created which directs the… More »
Refraction The change in direction of a light ray when it enters a different medium. Original Chapter Source: Light & Vision… More »
Relative Photometry Photometry is the measurement of the properties of light, particularly intensity. Relative photometry, used for luminaires with conventional light sources,… More »
Relay Power-switching device that receives low-voltage ON/OFF signals from another device and responds by closing or opening the circuit to turn… More »
Retina The photosensitive surface at the back of the eye where photons of light are converted into electrical signals that are… More »
Retinal illumination The amount of light falling on the retina derived from the luminance of the scene being viewed and the area… More »
Retinal image The image of the outside world formed on the retina by the optical elements of the eye. The quality of… More »
Retinal irradiance The irradiance falling on the retina, measured in watts per square meter. Original Chapter Source: Health & Performance Provided By:… More »
Return on investment (ROI) Also known as Rate of Return is expressed in terms of the interest rate that makes the Present Worth of… More »
RoHS Restriction of Hazardous Substances Directive; a European Union directive dictating restrictions on a variety of hazardous substances (including mercury) that… More »
Room Cavity Ratio (RCR) Environmental factor used in lighting design calculations. Cavity defined by the luminaire plane, task plane and the vertical wall area… More »
Saturation A characteristic of the response to a stimulus in which increasingly large changes in the stimulus produce decreasingly small changes… More »
Scalar illuminance The average illuminance on the surface of an infinitesimally small sphere at a point – also called mean spherical illuminance.… More »
Scattering The change in direction of a light ray caused by an interaction with localized non-uniformities in a medium. Original Chapter… More »
Scene A dimming level that is intended to be repeatable with a push of a button. Original Chapter Source: Controls Provided… More »
Scheduling An energy-saving lighting control strategy for switching or dimming during hours when a building space is unoccupied or occupied by… More »
Scotopic (scotopic vision) The state of vision in which only rod photoreceptors are active. Conventionally, scotopic vision is taken to occur at adaptation… More »
Scotopic/Photopic Ratio The ratio of scotopic luminous flux to photopic luminous flux produced at a point by a light source or a… More »
Sequence of Operations Description of how a lighting control system responds to various inputs in a given space. Example: “The occupancy sensor will… More »
Series When lamps are wired to a ballast in series, if any of the connected lamps fail, all the lamps are… More »
Shading masks Parts of the sky dome that are blocked by exterior surfaces, such as the landscape, neighboring buildings and building-mounted shading… More »
Simple payback Method of economic evaluation expressed in units of time (the payback period) to recoup an investment based on the initial… More »
Size of detail For a visual stimulus, the size of detail is always expressed in terms of the angle subtended by the detail… More »
Skyglow The glowing atmosphere above populated areas that interferes with view of the night sky. Original Chapter Source: Luminaires Provided By:… More »
Skylights Apertures in the roof of a building that allow daylight into the interior. They are usually covered by a transparent… More »
Snapback The reversion of luminaires with CFLs back to incandescent light sources. Original Chapter Source: Sources Provided by: Erik Page More »
Solar Heat Gain Coefficient (SHGC) The Solar Heat Gain Coefficient (SHGC) measures how well a window blocks heat from sunlight. The SHGC is the fraction… More »
Solar radiation Electro-magnetic radiation emitted by the sun. This comprises infrared, visible, and ultraviolet light. Original Chapter Source: Daylighting Provided by: Kosta… More »
Solar spectrum The amount of radiation emitted in each wavelength that composes solar radiation. Original Chapter Source: Daylighting Provided by: Kosta Papamichael… More »
Solid angle The solid angle subtended by an object at a point is given by the area of the object divided by… More »
Solid state lighting (SSL) A form of lighting that uses semi-conductor materials to emit light, rather than using glowing filaments or gas-discharge sources.  Original… More »
Source efficacy The ratio of light output of a light source to input power. Original Chapter Source: Sources Provided by: Erik Page More »
Spacing Criteria (SC) A multiplying factor calculated for a specific luminaire, which describes how far apart the luminaires can be spaced to deliver… More »
Spectral sensitivity The sensitivity of the effect of interest to wavelength. The effect of interest can be visual, e.g., brightness, or non-visual,… More »
Specular Mirror-like reflective properties where the angle of incidence equals the angle of reflectance. Original Chapter Source: Design Considerations Provided By:… More »
Specular reflection A mirror-like reflection in which the angle of incidence is equal to the angle of reflection. Original Chapter Source: Health… More »
Spot relamping A method of replacing lamps only after they have failed. Original Chapter Source: Sources Provided by: Erik Page More »
Standard 189.1 ASHRAE Standard 189.1, a reach code designed to improve on the efficiency of Standard 90.1, similar to the LEED system,… More »
Standard 90.1 ANSI/ASHRAE/IES Standard 90.1, the federally referenced energy code, originally developed by ASHRAE, and now revised and updated in collaboration with… More »
Step-dimming ballast A ballast that reduces light levels by one or more steps between full light output and OFF. Original Chapter Source:… More »
Steradian SI unit of solid angle. Original Chapter Source: Design Considerations Provided By: Leslie North More »
Sunlight need definition More »
Suprachiasmatic nuclei (SCN) The master clock of the human circadian system. Original Chapter Source: Health & Performance Provided By: Peter Boyce More »
Switch A control device that provides ON/OFF lighting control by mechanically closing or opening the circuit.  Original Chapter Source: Controls Provided… More »
System efficacy Also referred to as relative system efficacy, system efficacy is a measurement of a system's ability to convert electricity into… More »
Systems Manual Document produced over the course of a project and delivered to the owner upon acceptance, which provides detailed information about… More »
T-5 A fluorescent lamp that is 5 eights in diameter. Original Chapter Source: Sources Provided by: Erik Page More »
T-8 A fluorescent lamp that is 8 eights in diameter. Original Chapter Source: Sources Provided by: Erik Page More »
Tandem Wiring Wiring scheme in which two or more luminaires share a single ballast, reducing installation and energy costs. Original Chapter Source:… More »
Task tuning A lighting control strategy in which the light output of a luminaire or group of luminaires can be adjusted by… More »
Taskplane The surface or area on which visual attention is placed. In an office space, the workplane is at desk height,… More »
Temporal modulation The temporal modulation of a repetitive oscillation is quantified by the formula M = (Lmax – Lmin) / (Lmax +… More »
Thermal discomfort Discomfort caused by excessive or insufficient heat transfer from the environment to the human body. Original Chapter Source: Daylighting Provided… More »
Thermal factor Thermal factor is a light loss factor that should be applied to a lighting design when application conditions imply ambient… More »
Thermal loads Heat that needs to be removed from or added to a space in order to make that space comfortable for… More »
Threshold limit values The amounts of optical radiation which it is believed normally healthy humans may be repeatedly exposed to, day after day,… More »
Thyristor A four-layered semiconductor used for power control, enabling ON/OFF switching and dimming using a method called phase angle control. While… More »
Time-clock A control device that switches or dims the lights at a set future time. The term is also used to… More »
Timer switch A control device that turns the lights in a single load switch leg OFF after a preset period of time… More »
Tinted glazings Glazings that are made of tinted glass, which has additives that cause it to have lower visible light transmittance than… More »
TIR (Total Internal Reflection) The point where the angle of incidence of the light ray to a refractive surface is greater than the critical… More »
Total harmonic distortion A measure of the degree to which a sinusoidal wave shape is distorted by harmonics, with higher values of THD… More »
Transmission Losses Decreases in delivered electricity from “primary” electricity generated due to inherent inefficiencies in the delivery grid. Original Chapter Source: Policies… More »
Transmittance Fraction of light that is transmitted by a certain thickness of material. Original Chapter Source: Daylighting Provided by: Kosta Papamichael… More »
Transparent The property of materials that allow light to be transmitted with negligible or no scattering. Original Chapter Source: Daylighting Provided… More »
Triac The triode alternating current switch, or triac, operates similarly to a thyristor but is typically designed to handle smaller loads… More »
Troffer The housing of a fluorescent luminaire, usually a recessed metal housing that looks like an inverted trough. Original Chapter Source:… More »
Troland The unit of measurement of retinal illumination. Original Chapter Source: Light & Vision Provided By: Heschong Mahone Group / Peter… More »
Tungsten-halogen lamps Incandescent lamps which utilize a halogen gas surrounding the filament to produce a recycling of the tungsten filament material back… More »
U-value The heat transfer coefficient of a building component and is the magnitude of heat flow through that component per unit… More »
Ultrasonic Occupancy sensing method that detects occupancy by transmitting ultrasonic energy throughout the space and measuring the return frequency. Original Chapter… More »
Underwriters Laboratories An independent non-profit, nongovernmental product safety certification organization, accredited by the US Occupational Safety & Health Administration (OSHA), the American… More »
Unified glare rating (UGR) Metric developed by the CIE intended to predict discomfort glare. Values range from 5 to 30 with the higher the… More »
User Training Part of the commissioning process for a building system, this step, which occurs at the end of the construction project… More »
USGBC United States Green Building Council Original Chapter Source: Policies & Programs More »
Vacancy sensor Term used to describe manual-ON occupancy sensors. Original Chapter Source: Controls Provided By: Craig DiLouie More »
VDT Video Display Terminal (computer monitor) Original Chapter Source: Design Considerations Provided By: Leslie North More »
Veiling reflections Specular reflections that appear on an object viewed and that partially or wholly obscure the detail by reducing luminance contrast… More »
Vertical illuminance Illuminance on a vertical surface. Original Chapter Source: Daylighting Provided by: Kosta Papamichael / CLTC More »
Visible Light Transmittance (VLT) Transmittance of a material for visible light. Original Chapter Source: Daylighting Provided by: Kosta Papamichael / CLTC More »
Visual acuity An angular measure of spatial discrimination between neighboring objects such as points or lines that can just be perceived to… More »
Visual cortex The part of the brain that receives signals from the eyes and which constructs a model of the outside world… More »
Visual field The angular area over which objects can be seen. For normal viewing, the visual field is limited by the obstructions… More »
Visual Impairment Functional loss of visual acuity, reduction of peripheral field detection, or reduced peak contrast sensitivity. Some causes are retinal degeneration,… More »
Visual performance The performance of a visual task measured in terms of speed and accuracy. Original Chapter Source: Health & Performance Provided… More »
Vitreous humor The transparent, jelly-like substance that fills the space between the lens and the retina in the eye. Original Chapter Source:… More »
Wallwasher A linear or point source luminaire that is designed to direct light toward a wall in order to light it… More »
Windows An opening in the vertical surfaces of the building envelope for the admission of daylight. Original Chapter Source: Daylighting Provided… More »
Workplane The surface or area on which visual attention is placed. In an office space, the workplane is at desk height,… More »
Zenith Direction pointing vertically upwards from any given point on earth. Original Chapter Source: Daylighting Provided by: Kosta Papamichael / CLTC More »
Zonal lumen summary table Element of luminaire photometric report typically presented in the manufacturer catalog sheet for the product. The table lists the luminaire's… More »
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