22 August 2006
operated at their (initial) rated lumens and if no system variation or depreciation had
Light Meter a common name for an illuminance meter.
Light Source Color the color of the light emitted by a source.
Louver a series of baffles used to shield a source from view at certain angles, to
absorb or block unwanted light, or to reflect or redirect light.
Low-Bay Lighting interior lighting where the roof trusses or ceiling height is
approximately 7.6 m (25 ft.) or less above the floor.
Low-Pressure Mercury Vapor Lamp a discharge lamp (with or without a phosphor
coating) in which the partial pressure of mercury vapor does not exceed 100 Pa during
Low-Pressure Sodium (LPS) Lamp a discharge lamp in which light is produced by
of luminous flux.
Lumen Depreciation the decrease in lumen output that occurs as a lam pis operated,
Lumen (or flux) Method a lighting design procedure used for predetermining the
relation between the number and types of lamps or luminaires, the room characteristics,
and the average illuminance on the workplane.
Luminaire (light fixture) a complete lighting unit consisting of a lamp or lamps and
ballast(s) (when applicable) 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 fractional loss of task illuminance due to
luminaire dirt accumulation.
Luminaire Efficiency the ratio of luminous flux (lumens) emitted by a luminaire to
that emitted by the lamp or lamps used therein.
Luminance Contrast the relationship between the luminances of an object and its
Luminance ratio the ratio between the luminances any two areas in the visual field.
Luminous Efficacy of a Source of Light the quotient
of the total luminous flux
emitted to the total lamp power input. It is expressed in lumens per watt.
a surface from which the reflection
is predominantly diffuse, with
without a negligible specular component.
Means of Egress - an unobstructed and continuous way of exit from any point in a
building or structure to a public way.
Mercury Lamp - a high-intensity discharge (HID) lamp in which the major portion of the
light is produced by radiation from mercury operating at a partial pressure in excess of