luminous intensityand defined asflux per
solid angle in a given direction,itismea-
sured in candelas (cd).Interreflection: the multiple reflection of light by
the various room surfaces before it reaches
the workplane.
Iodide: a salt of hydriodic acid, a compound of
iodine; used in metal halide lamps.
Ionize: to convert into ions; a group of atoms that
carry a positive or negative electrical charge
as a result of having lost or gained one or
more electrons.
Isofootcandle plot: a computer-generated dia-
gram on the Cartesian coordinate system
showing contour lines of varying illuminance
values from a specific luminaire in a specific
application; a shaded plan with gray scales
representing the range of illuminance
values.
Kelvin: the unit of absolute temperature used to
designate the color temperature of a light
source.
Kilowatt: a unit of power equal to 1,000 watts.
Lamp: a source that converts electricity into light;
it is the technical word for what is commonly
referred to as a “light bulb.”
Lampholder:the component of a luminaire that
accepts the lamp base and supplies it with
electricity; it is the technical word for what is
commonly referred to as a “socket.”
Laser: acronym forlightamplification bystimu-
latedemission ofradiation; most lasers are
oscillators (generators or sources of light)
not amplifiers, producing a monochromatic
beam of radiation by steady oscillation main-
tained in a resonator.
LED: acronym forlight-emittingdiode; a semi-
conductor diode that emits light when volt-
age is applied to it.
Lens: a glass or plastic element used in
luminaires to control the direction and distri-
bution of transmitted light by refraction.
Light: a narrow band of electromagnetic energy,
ranging from approximately 380 nanometers
(nm) to 760 nm, which stimulates receptors
in the eye that enable vision.
Lime glass: glass with a high calcium oxide con-
tent consisting of silica, alumina, and iron
that has greenish hue.
Louver: a series of baffles or shielding elements
used to shield glare at normal viewing
angles, usually arranged in a geometric pat-
tern to provide shielding from many direc-
tions with minimum interference to the
desired beam distribution.
Low contrast: a lighting condition characterized
by a large proportion of diffuse light and a
small amount of focused light.
Low load: a small amount of psychological stim-
ulation or arousal, resulting from activities or
environments that are simple, uncrowded,
symmetrical, conventional, familiar, unsur-
prising, or organized.
Low-pressure sodium: a discharge lamp in
which light is produced by radiation from
sodium vapor, with a monochromatic yellow
color.
Lumen (lm): the unit measurement of luminous
flux equal to the light emitted in a solid angle
by a uniform point source of one candela
intensity.
Luminaire: a complete lighting unit consisting of
a housing; lamp(s); light controlling ele-
ments; brightness controlling element;
lampholder(s); auxiliary equipment, such as
ballast or transformer, if required; and a con-
nection to the power supply.
Luminance: the objective measurement of inten-
sity of light entering the eye, per unit of pro-
jected area. It is the accepted term for light
that is reflected from a surface in a given
direction (back towards the eyes). Properly
defined asintensity of flux leaving a surface
in a given direction, it is measured in cande-
las per square foot (cd/ft^2 ) or candelas per
square meter (cd/m^2 ).
Luminance contrast: the ratio of the luminance
of an object or the foreground to the lumi-
nance of its immediate background or sur-
round.
Luminous: emitting or reflecting energy in the
visible portion of the electromagnetic spec-
trum.GLOSSARY