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Come across a lighting word you aren't sure of? Completely new to the world of lighting? We feel your pain! Here you will find a collection of terms and concepts that should help to make your life easier.
Have you come across a term that we don't have? e-mail the Webmaster and we'll add it!
Select the first letter of the word from the list above to jump to appropriate section of the glossary.
Lamp - An artificial source of light (also a portable luminaire equipped with a cord and plug). Industry term for light bulb.
Lamp Efficacy - The ratio of lumens produced by a lamp to the watts consumed, expressed as lumens per watt (LPW).
Lamp Life - Rated life of a lamp, as established through laboratory testing during which a sample group of lamps is burned, including being subjected to a scheduled number of starts per day. The length of time required for half the lamps to fail is the rated lamp life.
Lamp Lumen Depreciation (LLD) - Multiplier factor in illumination calculations for reduction in the light output of a lamp over a period of time.
Lamp Wattage - The power consumption of a lamp after warm up NOT including ballast losses
Lens - Used in luminaires to redirect light into useful zones.
Lexan - Brand name for polycarbonate material used in lenses that will not break or yellow.
Light - Radiant energy that is capable of exciting the retina and producing a visual sensation. The visible portion of the electromagnetic spectrum extends from about 380 to 770 no
Light Loss Factor (LLF) - A factor used in calculating the level of illumination that takes into account such factors as dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures and atmosphere conditions.
Light Output - Amount of light produced by a light source such as a lamp. The unit most commonly used to measure light output is the lumen.
Light pollution - Any adverse effect of manmade light. Often used to denote urban sky glow. "The wasted light that goes up into the sky."
Light trespass - Light falling where it is not wanted or needed. Spill light. Obtrusive light.
Load Shedding - A lighting control strategy for selectively reducing the output of light fixtures on a temporary basis as a means to reduce peak demand charges.
Louver - A series of baffles used to shield a source from view at certain angles or to absorb unwanted light. The baffles usually are arranged in a geometric pattern.
Low Pressure Sodium Lamp - A discharge lamp in which light is produced by radiation of sodium vapor at low pressure producing a single wavelength of visible energy, i.e. yellow.
Low-Voltage Lamps - A lamp-typically compact halogen-that provides both high intensity and good color rendition. Lamp operates at 12V and requires the use of a transformer. Popular lamps are MR11, MR16 and PAR36.
Lumen - A measurement of light output; The unit of luminous flux. It is the luminous flux emitted within a unit solid angle (one steradian) by a point source having a uniform luminous intensity of one candela.
Lumen Depreciation - The term for the gradual decline in a source's light output. Except for low pressure sodium lamps, all sources lose lumen output over their life due to gradual deterioration of the filaments or electrodes, accompanied by lamp blackening. A factor is commonly used as a multiplier to the initial lumen rating in illuminance calculations, which compensates for the lumen depreciation.
Lumen Maintenance - Same as "Light Loss Factor."
Lumens Per Watt - Lumen (light) output divided by lamp watts consumed (i.e. amount of light for electricity used); also known as efficacy.
Luminaire - A complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and to connect the lamps to the power supply.
Luminaire Dirt Depreciation (LDD) - The multiplier to be used in illuminance calculations to relate the initial illuminance provided by clean, new luminaires to the reduced illuminance that they will provide due to dirt collection on the luminaires at the time at which it is anticipated that cleaning procedures will be instituted.
Luminaire Efficiency - The ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein.
Luminance - The amount of light reflected or transmitted by an object.
Lux - The metric unit of illuminance. One lux is one lumen per square meter (Im/m2).
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