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LED Street Lights Glossary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
B
Beam Angle - The angle about the axis of a beam of light formed by 50% luminous intensity of the beam axis. A luminaire without rotational symmetry may have different beam angles for a given measured plane.
Brewster's Angle - aka Polarization Angle. An angle of incidence at which light with a particular polarization is perfectly transmitted through a surface, with no reflection.
C
Candela- the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
Candlepower - obsolete unit of luminous intensity. Replaced by candela.
Color Rendering Index - On a scale from 0 - 100, how well a lamp renders color for a given CCT. CRI values are not comparable between lamps with differing CCT values.
Color Temperature- The temperature at which a heated black-body radiator matches the color of the light source. Unit of measure is stated in Kelvin (K).
Correlated Color Temperature - The temperature of the Planckian radiator whose perceived colour most closely resembles that of a given stimulus at the same brightness and under specified viewing conditions (CIE/IEC 17.4:1987, International Lighting Vocabulary). Often used interchangably with color temperature.
D
E
EMI - Electromagnetic Interference.
F
Full Cutoff - aka FCO. A luminaire light ditribution where zero candela intensity occurs at an angle of 90 degrees above nadir, and at all greater angles from nadir. In addition to this, the candela per 1000 lumens does not exceed 100 at a vertical angle of 80 degrees above nadir (from IESNA Handbook, 9th Ed.)
G
H
HPS - High Pressure Sodium. High intensity discharge (HID) lamp in which light is produced by radiation from sodium vapor.
I
Illuminance - The number of lumens per unit area.
IEC - International Electrotechnical Commission
IR - Infrared
Ingress Protection Rating - aka IP Rating. A standard describing the environmental conditions a given enclosure will protect its contents.
J
K
Kelvin - Unit of measurement for color temperature.
L
LED - Light Emitting Diode. An electroluminescent device which can be designed to emit a particular color. LED's benefit from long life, "instant start", low energy requirements and robustness.
Light Pollution - Unneccessary artificial light. It is a wasteful use of energy and can decrease night visibility.
LPS - Low Pressure Sodium. A discharge lamp in which light is produced by radiation of sodium vapor at low pressure producing a single wavelength of visible energy, i.e. yellow.
Lumen - Unit of luminous flux. The time rate flow of light. Lumens may be reported as "rated lumen" which refers to the initial output before any depreciation in the lamp or as "mean lumen." This describes the depreciated output of a lamp after a period of time.
Luminaire - The basic lighting unit consisting of one or more lamps and a structure to distribute light, protect the lamp(s), provide electrical connections and secure/position the lamps.
Luminaire Efficiency - The effectiveness of a luminaire to direct light emitted by a lamp to an appropriate work area.
Luminance - The amount of light in candela per unit area that reaches an observer's eye.
Luminous Efficacy - The ratio of luminous flux to power used. Typically expressed as Lumens/Watt.
Luminous Efficiency - The ratio of luminous efficacy to a theoretical maximum luminous efficacy. A non-dimensional number.
Luminous Intensity - light emitted in a given direction. Candela is the unit of measure.
Luminous Intensity Distribution - aka Candlepower Distribution. A table of luminous intensity values often plotted onto a graph for visualization.
Luminous Flux - See Lumen.
Lux - SI Unit of illuminance. One lux is one lumen per square meter.
M
N
NEMA Enclosure - An enclosure which adheres to the NEMA standard.
O
P
PWM - Pulse Width Modulation
Q
R
S
Steradian - The solid angle subtended at the center of a sphere of radius r by a portion of the surface of the sphere having an area r^2. The cone of light spreading out from a given source which illuminates one square meter of the inner surface of a sphere of 1 m radius around the source.
Strobe - Continuous or intermittant flashing of a lamp which may result in discomfort or eye fatigue.
T
THD - Total Harmonic Distortion
U
UV - Ultraviolet
V
VAC - Volts Alternating Current
VDC - Volts Direct Current
W
X
Y
Z