Luminous flux: light emitted in all directions by a
source. Properly defined astime rate flow of
light, it is measured in lumens (lm).
Matte: a dull finish or surface lacking in luster,
gloss, shine, or highlights.
Mercury lamp(properly called amercury vapor
lamp): a high-intensity discharge lamp in
which light is produced by an electric dis-
charge through mercury vapor.
Metal halide: a high-intensity discharge lamp in
which light is produced by an electric dis-
charge through the combined vapors of mer-
cury and metal halides, which are introduced
into the arc tube as compound iodides.
milliAmpere: a unit of electric current equal to
one thousandth of an ampere.
Monochromatic: having or consisting of only one
color or hue, or radiation of a single wave-
length or very small range of wavelengths.
Motion sensor: seeoccupancy sensor.
Nadir: straight down (0-degree angle).
Nanometer: a unit of wavelength equal to one
billionth (10-9) of a meter.
Object light: an adjustable, directional luminaire
that provides an asymmetric distribution of
light aimed at one or several objects. Also
called “spot lights,” they are used to provide
focal glow and add contrast to a setting.
Occupancy sensor: a device that provides on-off
control of luminaires in response to the pres-
ence or absence of occupants in a space,
sensed by audio, ultrasonic, passive infra-
red, or optical means.
Ohm: the standard unit of electrical resistance of
a conductor, such that a current of one
ampere in its circuit produces a decrease in
voltage across it of one volt.
Opaque: blocking the passage of light; neither
transparent nor translucent.
Parabolic: having the form of a parabola, a plane
curve generated by the intersection of the
surface of a cone with a plane parallel to one
of its sides.
Pendant (luminaire): a luminaire that is sus-
pended from the ceiling by a support cable,
chain, cord, rod, or stem.
Phosphor: a chemical substance that converts
invisible ultraviolet radiation into visible light.
Photometer: an instrument for measuring lumi-
nous intensity, luminous flux, illuminance, or
luminance.
Photometry: the science that measures light.
Photosensor: a light-sensing device used to
control luminaires and dimmers in response
to detected illuminance values.
Photopic: vision, using the cones of the retina,
under relatively high illuminance values.
Prism: a transparent body with three rectangular
plane faces, or sides, and two equal and par-
allel triangular ends or bases, used to refract
or disperse a beam of light.
Quad-phosphor: a combination of four narrow
spectra, rare-earth phosphors used in fluo-
rescent lamps to produce a wide-range
spectrum of visible light. The individual phos-
phors correspond to the short-, middle-, and
long-wavelength regions of the visible spec-
trum.
Reflected glare: excessive uncontrolled lumi-
nance reflected from objects or surfaces in
the field of view.
Reflection: the return of light from a surface.
Specular reflectionoccurs when the surface
alters the direction of a beam of light without
changing its form; the angle of reflection is
equal to the angle of incidence. Spread
reflectionpartially disperses this reflected
beam.Diffuse reflectionoccurs when an inci-
dent ray of light is reflected in all directions.
Refraction: the deflection of a light ray when it
passes obliquely from one medium (such as
air) into another (such as water) in which it
travels at a different speed.
Relamp: to replace a lamp or lamps.
Restrike: after a high-intensity discharge lamp is
extinguished, it must cool sufficiently to
reduce the vapor pressure to a point where
the arc can be reignited.
Scotopic: vision, using the rods of the retina,
under relatively dim light.
Semi-specular: an irregular surface that partially
disperses or spreads the reflected beam,INTERIOR LIGHTING FOR DESIGNERS