Advanced Lighting Guidelines Glossary
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Definition
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 »
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