Glossary
“Accent” light: an advertising term misapplied to
adjustable, directional luminaires that are
properly termed object lights. Seeobject light.
Accommodation: the automatic adjustment of
the eye for seeing at varied distances,
accomplished by changes in focus.
Acuity(also calledvisual acuity): the ability of
the eye to make out fine detail.
Adaptation: the change in the sensitivity of the
visual system based on the amount of light
the retina has been exposed to in the recent
past.Dark adaptationis an increase in visual
sensitivity that occurs over time in darkness.
Ambient light: general or background illumina-
tion.
Ampere: measurement of the rate of flow of an
electric current; it is equivalent to the steady
current produced by one volt applied across
a resistance of one ohm.
Anodize: to coat a metal (usually aluminum) with
a protective film by subjecting it to electro-
lytic action.
Aperture(of a luminaire): the diameter of the
opening of a recessed luminaire.
Apparent color temperature: Seecorrelated
color temperature.
Axial(filament): a filament situated in the direc-
tion of the lamp axis.
Baffle: a single opaque or translucent element to
shield glare at normal viewing angles in one
direction, along a single axis. For small-aper-
ture luminaires, a baffle around the perime-
ter provides shielding from all directions. See
alsolouvers.
Ballast: an auxiliary device for an electric dis-
charge source that provides the proper start-
ing voltage and regulates the lamp operating
current. All fluorescent and HID lamps
require a ballast for proper operation.
Ballast factor: the ratio of light output produced
by lamps operated by a commercially-avail-
able ballast to light output produced by lamps
powered by a laboratory-reference ballast.
Beam angle: the angle between the two direc-
tions for which the intensity is 50% of the
maximum, as measured in a plane through
the beam centerline. See alsofield angle.