with the greatest intensity of light reflected at
an angle near the angle of incidence.Shielding angle: the zone within which shielding
(baffles or louvers) conceals the light source
and controls glare.
Sight line: the line extending from an observer’s
eye to the point at which a bare light source
first becomes visible.
Skylight: 1. the diffused and reflected light of the
sky; it is light from the sun redirected by the
atmosphere. 2. an opening in the roof of a
building, glazed witha transparent or trans-
lucent material, that is designed to admit
natural light.
Slimline: a linear fluorescent lamp with a single-
pin base that is capable of being operated at
more than one current and wattage.
Soffit: the exposed underside of any overhead
component of a building, such as an arch,
balcony, beam, cornice, lintel, or vault.
Spacing criterion (SC)orspacing-to-mount-
ing-height ratio (S/MH): an estimated max-
imum ratio of luminaire spacing to luminaire
mounting height above the workplane, nec-
essary to achieve uniform, horizontal
illuminance.
Spectral: of, relating to, or made by the color
spectrum or electromagnetic spectrum.
Specular: having the reflecting properties of a
mirror; a smooth reflecting surface. The
angle of reflection is equal to the angle of
incidence.
Splice: the electrical connection of luminaire
wires to the building branch circuit wires.
Stroboscopic: when rapidly moving objects are
observed under discharge sources, blurred
“ghost” images are sometimes observed
that cause the objects to appear slowed,
stopped, or moving in reverse.
Torchère: a portable luminaire suitable for stand-
ing on the floor, which directs most, or all, of
its light upward.
Toroidal: doughnut-shaped.
Total internal reflection: occurs when light
passes into a transparent medium, such as
glass or plastic, at an appropriate angle so
that it travels inside the medium repeatedly
reflecting from side to side.
Transformer: a device with two or more coupled
windings, used to convert the supply of elec-
tric power at one voltage in a primary circuit
to a lower voltage in a secondary circuit.
Translucent: having the property of transmitting
diffused light but obscuring vision, so that
objects beyond cannot be seen clearly.
Transmission: the passage of light through
space or a medium; it is altered by the reflec-
tions at each surface of the medium, and by
the absorption and reflection within the
medium.
Transparent: having the property of transmitting
light without altering its distribution, so that
objects beyond are seen clearly.
Triphosphor: a combination of three 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 peak spectral sensi-
tivities of human vision: blue-violet, pure
green, and orange-red.
“Troffer”: layman’s term for a recessed, rectilin-
ear fluorescent downlight; perhaps derived
from “trough” and “coffer.”
Trough: a long, narrow opening, usually in the
ceiling plane; sometimes called aslot.
Tungsten-halogen: an incandescent lamp with a
selected gas of the halogen family sealed
into it to stop evaporated tungsten from
depositing on the bulb wall.
Ultraviolet (UV): radiant energy having a wave-
length shorter than wavelengths of visible
light and longer than those of x-rays; within
the range of 10 nanometers (nm) to 380
nm.
Uplight: a luminaire that emits light in an upward
direction toward the ceiling, with no down-
ward component of light.
Uplighting: a distribution of light emitted in an
upward direction.
Valance: a longitudinal shielding panel mounted
over a window with draperies to conceal lightGLOSSARY