Definitions. As used in this section, the following terms shall have
the meanings indicated:
CANDELA
Unit of luminous intensity, describing the intensity of a
light source in a specific direction.
CANDELA DISTRIBUTION
A curve, often on polar coordinates, illustrating the variation
of luminous intensity of a lamp or luminaire in a plane through the
light center.
CANDLEPOWER
Luminous intensity expressed in candelas A measure of luminous
intensity of a light source in a specific direction, measured in candelas.
CUTOFF
A light distribution where a negligible amount of light is
permitted at a horizontal plane located at the bottom of a luminaire.
Light above the horizontal plane at the bottom of a luminaire is not
limited, but cutoff luminaires usually have very little light above
the luminaire.
(a)
FULL CUTOFFA light distribution where no light is permitted at or above a horizontal plane located at the bottom of a luminaire. There will be little or no light at the angles that are usually associated with glare.
(b)
SEMICUTOFFA light distribution where slightly more light is permitted at a horizontal plane located at the bottom of a luminaire than the cutoff distribution. Like cutoff, light above the horizontal plane at the bottom of a luminaire is not limited, but the amount of light above the luminaire is relatively small.
(c)
NONCUTOFFA light distribution that can produce considerable light above the horizontal plane located at the bottom of a luminaire.
(d)
CUTOFF ANGLE (OF A LUMINAIRE)The angle, measured up from the nadir (i.e., straight down), between the vertical axis and the first line of sight at which the bare source (the bulb or lamp) is not visible.
FLOODLIGHT
A fixture designed to "flood" a well-defined area with light.
FOOTCANDLE
A unit of illuminance. The English measurement unit of illuminance
(or light level) on a surface. One lumen is equal to one footcandle
per square foot. A unit of light intensity stated in lumens per square
foot and measurable with an illuminance meter; aka, footcandle or
light meter. One footcandle is equal to 10.76 lux; one lux is equal
to 0.093 footcandle.
FULLY SHIELDED LIGHT FIXTURE
A light fixture constructed in such a manner that all light
emitted by the fixture, either directly from the lamp or a diffusing
element, or indirectly by reflection or refraction from any part of
the luminaire, is projected below the horizon.
GLARE
Light that hinders or bothers the human eye. The sensation
produced by luminances within the visual field that is sufficiently
greater than the luminance to which the eyes are adapted to cause
annoyance, discomfort or loss in visual performance or visibility.
The degree of glare is described as such:
(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 luminances or insufficiently shielded light sources in the field of view.
(c)
DISABILITY GLAREThe effects of stray light in the eye whereby visibility and visual performance is significant enough to keep a person from seeing adequately.
(d)
DISCOMFORT GLAREGlare that produces discomfort. It does not necessarily interfere with visual performance or visibility.
(e)
REFLECTED GLAREGlare resulting from reflections of high luminances in polished or glossy surfaces in the field of view.
ILLUMINANCE
The quantity of light measured in footcandles or lux. A term
that quantifies light striking a surface or a plane point. It is expressed
either in lumens per square foot (footcandles/the English unit) or
lumens per square meter (lux/the metric unit). The areal density of
the luminous flux incident at a point on a surface. One footcandle
is equal to 10.76 lux; one lux is equal to 0.093 footcandles.
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.
LAMP
A generic term for a man-made source of light.
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 which extends beyond
the boundaries of the property on which the installation is sited;
spill light; obtrusive light; undesirable illumination, including
the following examples:
(a)
The classic "light shining in a window."
(b)
Unwanted light on an adjacent property.
(c)
Excessive brightness in the normal field of vision (discomfort
glare).
LUMEN
Unit of measurement of luminous flux representing the quantity
of light being produced by a lamp or emitted from a luminaire.
LUMINAIRE
A complete lighting unit consisting of one or more lamps
(light sources), together with the parts designed to control the light
distribution and other mechanical and electrical components.
LUMINANCE
A term that quantifies directional brightness of a light
source (e.g., a lamp, luminaire, reflecting material) or of a surface
that is illuminated and reflects light. The emitted or reflected light
from a surface relates directly to perceived "brightness." The unit
of luminance is the candela per square meter (cd/m2). Measurable with a luminance meter.
LUX
A unit of light intensity stated in lumens per square meter.
There are approximately 10.76 lux per footcandle.
NADIR
The point directly below the luminaire when the luminaire
is pointed down (zero-degree angle).
NIGHTTIME
The hours between the end of evening civil twilight and the
beginning of morning civil twilight. Civil twilight ends in the evening
when the center of the sun's disk is 6° below the horizon
and begins in the morning when the center of the sun's disk is
6° below the horizon.
SPOTLIGHT
A fixture designed to light only a small, well-defined area.