Definitions.
CANDELA
The SI unit of luminous intensity. One candela is one lumen
per steradian (lm/sr).
CUTOFF ANGLE (OF A LUMINAIRE)
The angle measured up from the lowest point (nadir), between
the vertical axis and the first line of sight at which the bare source
is not visible.
DIRECT LIGHT
Light emitted directly from the lamp, off of the reflector
or reflector diffuser, or through the refractor or diffuser lens,
of a luminaire.
FIXTURE
The assembly that house the lamp or lamps and can include
all or some of the following parts: a housing, a mounting bracket
or pole socket, a lamp holder, a ballast, a reflector or mirror, and/or
a refractor or lens.
FLOOD or SPOTLIGHT
Any light fixture or lamp that incorporates a reflector or
a refractor to concentrate the light output into a directed beam in
a particular direction.
FOOT-CANDLE
A unit of light intensity on a plane (horizontal or vertical)
stated in lumens per square foot and measurable with a light meter.
One foot-candle is one lumen per square foot (lm/ft2). Horizontal foot-candles are measured on the horizontal plane of
a lamp (bulb), and vertical foot-candles on a perpendicular line above
the bulb.
FULL CUTOFF
Attribute of a lighting fixture from which no light is emitted
at or above a horizontal plane drawn through the bottom of the fixture,
and no more than 10% of the lamp's intensity is emitted at or
above an angle 10° below that horizontal plane, at all lateral
angles around the fixture.
FULLY SHIELDED LIGHTS
Outdoor light fixtures shielded or constructed in such a
manner that all light emitted by the fixture, either directly from
the lamp or diffusion element or indirectly by reflection or refraction,
is projected below the horizontal plane through the fixture's
lowest light-emitting part as certified by a photometric test report
and does not cause glare at normal viewing angles.
GLARE
The sensation produced by luminance within the visual field
that is sufficiently greater than the luminance to which the eyes
are adapted, which causes annoyance, discomfort, or loss in visual
performance or visibility.
(a)
BLINDING GLAREGlare that is so intense that for an appreciable length of time after it has been removed, no object can be seen.
(b)
DIRECT GLAREGlare resulting from high luminance or insufficiently shielded light sources in the field of view.
(c)
DISABILITY GLAREThe effect of stray light in the eye whereby visibility and visual performance are reduced.
(d)
DISCOMFORT GLAREGlare that produces discomfort. It does not necessarily interfere with visual performance or visibility.
(e)
REFLECTED GLAREGlare resulting from reflections of high luminance in polished or glossy surfaces in the field of view.
HEIGHT OF LUMINAIRE
The height of a luminaire shall be the vertical distance
from the ground directly below the center line of the luminaire to
the lowest direct-light-emitting part of the luminaire.
ILLUMINANCE
The quantity of light measured in footcandles or lux.
ILLUMINATION
An alternative term for illuminance. Commonly used in a qualitative
or general sense to designate the act of illuminating or the state
of being illuminated.
INDIRECT LIGHT
Direct light that has been reflected or has scattered off
of other surfaces.
ISOFOOTCANDLE (ISOLUX)
A line plotted on any appropriate set of coordinates to show
all the points on a surface where the illuminance is the same. A series
of such lines for various illuminance values is called an isolux (isofootcandle)
diagram.
LAMP
The component of a luminaire that produces light. A generic
term for a man-made source of light, i.e., a light bulb.
LIGHT
Radiant energy that is capable of exciting the retina and
producing a visual sensation. The visible portion of the electromagnetic
spectrum extends from about 380 to 770 nanometers.
LIGHT TRESPASS
Light emitted by a lighting installation that extends beyond
the boundaries of the property on which the installation is sited.
LUMEN
The light output of a lamp (light bulb), as specified by
the manufacturer. More technically, it is the luminous flux emitted
within a solid angle (one steradian) by a point source having a uniform
luminous intensity of one candela. One footcandle is one lumen per
square foot. For the purposes of this chapter, the lumen-output values
shall be the initial output ratings of a lamp, as specified by the
manufacturer of the lamp. For example, a 60-watt GE Soft White bulb
emits 840 lumens, a similar 100-watt bulb, 1690 lumens.
LUMINAIRE
A complete lighting unit consisting of one or more lamps
together with the fixture; other parts designed to control the light
distribution; and other mechanical and electrical components.
LUMINAIRE CUTOFF
A luminaire whose candle power per 1,000 lumens does not
numerically exceed 25 (2.5%) at an angle of 90 above nadir (horizontal)
and 100 (10%) at a vertical angle of 80 above nadir.
LUMINANCE
A quantity of light measurable with a luminance meter (light
meter). It may be expressed in candelas per square meter (cd/m2) footcandles (lm/m2),
or lux.
LUX
A unit of light intensity stated in lumens per square meter.
(Approximately 10.7 lux per footcandle; may be measured with a light
meter.)
OUTDOOR LIGHTING
The nighttime illumination of an outside area or object by
any man-made device that produces light by any means.
UNIFORMITY RATIO
The highest luminance or illuminance point divided by the
lowest luminance or illuminance point, respectively.