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Technical Services
>> Technical Terminology: |
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A |
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Absorption -
The dissipation of light within a surface or medium; A process
by which incident radiant flux is converted to another form of
energy, usually (and ultimately) heat. |
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Accent Lighting -
Directional lighting designed to emphasize a particular object
or to draw attention to a part of the field of view.
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Accommodation -
The process by which the eye changes focus from one distance to
another. |
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Acrylic -
A plastic material which will not be affected by UV, will not
get yellow but is breakable..
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Adaptation -
The process by which the eye becomes accustomed to more or less
light than it was exposed to during an immediately preceding
period or to light of a diffe" va color. It results in a change
in the sensitivity of the eye to light. |
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Alternating
Current (AC) - Flow of electricity which cycles or
alternates direction many times per second. The number of cycles
per second is referred to as frequency. Most common frequency
used in this country is 60 Hertz (cycles per second).
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Alzak® - A
finish produced by electrochemically brightening and anodizing a
special high purity aluminum alloy. It is used to provide
reflectors with a highly specular permanent finish, resistant to
corrosion and abrasion. Alzak® is a registered trademark of the
Aluminum Company of America (ALCOA). |
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Ambient Lighting - Electric and/or natural lighting
throughout a space that produces uniform general illumination as
opposed to task lighting or the lighting of the object one is
looking at). |
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Amperes (amps or
A) - The unit of measurement of electric current
Anchor Bolt - An ``L" shaped bolt, usually steel, used to secure
the pole base (also called a standard) or ground mounted fixture
to its foundation. Anchor bolts are threaded at the opposite end
of the bend and may be partially or completely galvanized to
prevent corrosion. |
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Anodizing -
An electrolytic process for converting an aluminum surface to
aluminum oxide. Anodizing creates an incredibly hard,
transparent finish that is physically part of the metal and
highly resistant to corrosion. Anodized finishes are generally
colorless, but may be dyed in a variety of colors (see also
Architectural Class 1 Anodizing. |
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ANSI -
American National Standards Institute. A professional
organization made up of representatives from manufacturers,
safety protection agencies, and consumers. ANSI publishes
testing standards for products and components. |
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Aperature Size -
Inside diameter measurement (that light can pass through) of an
optical assembly at its lowest part. |
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Architectural
Class 1 Anodizing - A multi-step method of anodizing that
physically embeds various metals into the pores of an anodic
coating. This process gives the anodizing a color that will not
fade with time or with the effects of UV. |
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Argon - Inert
gas used in incandescent and fluorescent lamps. In incandescents,
helps retard evaporation of the tungsten filament. |
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Asymmetric
Distribution - A non-symmetric distribution of light. The
luminous intensity may be more pronounced in one direction. |
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Baffle - An
opaque or translucent element that serves to shield a light
source from direct view at certain angles, or serves to absorb
unwanted light |
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Ballast - An
auxiliary electrical device consisting of induction windings
wound around a metal core and sometimes including a capacitor
for power correction. It is used with fluorescent and HID lamps
to provide the necessary starting voltage and to limit the
current during operation. |
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Ballast Factor -
The ratio of lamp lumen output on a particular ballast as
compared to that lamp's (lamps') rated lumen output on a
reference ballast under ANSI test conditions (free, unmoving air
at 25° C) |
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Base - The
end of the lamp that inserts into lamp socket; The end (or ends)
of a lamp that makes electrical and mounting connections with
the luminaire. |
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Batwing
Distribution - Candlepower distribution which serves to
reduce glare and veil reflections by having its maximum output
in the 30° to the 60° zone from the vertical and with a
candlepower at nadir (0 degrees) being 65% or less than maximum
candlepower. The shape is similar to a bat's wing. |
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Beam Component -
That component of flux received directly (or by specular
reflection or transmission) from a point source (such as the sun
or small lamp). It is a direct component. |
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Beam Spread -
The angle enclosed by two lines which intersect the candlepower
distribution curve at the points where the candlepower is equal
to ten percent of its maximum. |
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Blackbody - A
theoretical body used by the lighting industry as a standard for
establishing the "color" and spectral qualities of lamps. A
perfect blackbody, when its temperature has risen to 3500K would
give out light of a certain color; at 4500K it would give a
whiter color, and at 5500K a still whiter color. |
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Blinding Glare -
Glare that is so intense that, for an appreciable length of time
after it has been removed, no object can be seen. |
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Brightness -
The degree of apparent lightness of a surface: its brilliancy;
concentration of candlepower. Brightness is produced by either a
self-luminous object, by light energy transmitted through
objects or by reflection. Unit of measurement of brightness is
the footlambert. (fl). Luminance. |
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Bulb - The
outer jacket or envelope of a lamp. |
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Bulb Darkening -
The darkening of an incandescent lamp caused by small particles
of tungsten that evaporate from the filament and deposit on the
bulb as the filament burns. |
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Burning Position
- The position in which lamps are designed to he objected.
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Candela (cd) -
The unit of measurement of luminous intensity of a light source
in a given direction |
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Candlepower -
Luminous intensity expressed in candelas. |
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Candlepower
Distribution Curve - A graphic presentation of the
distribution of light intensity in a given plane of a lamp or
luminaire. It is determined by photometric tests. The curve is
generally polar, representing the variation of luminous
intensity of a lamp or luminaire in a plane through the light
center. |
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Ceiling Cavity
Ratio - A numerical relationship of the vertical distance
between luminaire mounting height and ceiling height to room
width and length. It is used with the Zonal Cavity method of
calculating average illumination levels. |
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Chromaticity -
Refers to the dominant or complementary wavelength and purity
aspects of the color taken together, or of the aspects specified
by the chromaticity coordinates of the color taken together.
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Circuit Breaker -
Resettable safety device to prevent excess current flow.
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Class "P" Ballast
- Contains a thermal protective device which deactivates the
ballast when the case reaches a certain critical temperature.
The device resets automatically when the case temperature drops
to a lower temperature |
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Coefficient of
Utilization (CU) - A ratio representing the portion of light
emitted by a luminaire in any particular installation that
actually gets down to the work plane. The coefficient of
utilization thus indicates the combined efficiency of the
luminaire, room proportions and room finish reflectances. The
ratio of the luminous flux (lumens) from a luminaire is
calculated as received on the work-plane to the luminous flux
emitted by the luminaire's lamps alone |
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Cold Cathode Lamp
- An electric-discharge lamp whose mode of operation is that
of a glow discharge |
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Color Corrected -
Refers to a lamp with a special phosphor or coating (applied
internally or externally) to give it a color rendering profile
more like that of natural daylight. |
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Color Rendering
Index (CRI) - Measure of the degree of color shift objects
undergo when illuminated by the light source as compared with
the color of those same objects when illuminated by a reference
source of comparable color temperature; a quality of the light.
It is a measure of the lamp's ability to `'render" colors
accurately. |
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Color Spectrum -
Same as the "visible light" spectrum: electromagnetic energy
between 380 (violet) and 770 (red) nanometers, which can be seen
by the human eye. |
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Color Temperature
- The absolute temperature of a blackbody having a
chromaticity equal to that of the light source. Expressed in
degrees Kelvin, color temperature indicates the color of a light
source. |
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Compact
Fluorescent - A small fluorescent lamp that is often used as
an alternative to incandescent lighting. The lamp life is about
1O times longer than incandescent lamps and is 3-4 times more
efficacious. Also referred to as PLI DL, CFL or BIAX lamps.
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Cone - In the
eye, a retinal receptor that dominates the retinal response when
the luminance level is high and provides the basis for the
perception of color. |
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Cone Reflector -
Parabolic reflector that directs light downward thereby
eliminating brightness at high angles |
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Contrast -
The difference in brightness (luminance) of an object and its
background. |
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Contrast
Rendition Factor (CRF) - The ratio of visual task contrast
with a given lighting environment to the contrast with sphere
illumination. Contrast measured under sphere illumination is
defined as 1.00. |
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Cool Beam Lamps -
Incandescent PAR lamps that use a special coating (dichronic
interference filter) on the reflectorized portion of the bulb to
allow heat to pass out the back while reflecting only visible
energy to the task, thereby providing a "cool beam" of light.
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Correlated Color
Temperature (CCT) - the "color" of the light given off by a
lamp.
Cosine Law - The law that the illuminance on any surface varies
as the cosine of the angle of incidence. (The angle of incidence
is the angle between the normal to the surface and the direction
of the incident light.) |
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Cove Lighting -
Refers to light sources mounted above a ledge or in a recess
(usually around the perimeter of a room) that distribute light
upward for ambient lighting. |
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Cutoff Angle (of
a luminaire) - The angle from the vertical at which a
reflector, louver, or other shielding device cuts off direct
visibility of a light source. It is the complementary angle of
the shielding angle. In the case of reflector-type lightshields
it is also important to ascertain the cutoff angle to the
reflected image of the light source as this is often almost as
bright as the source itself. |
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Cutoff Luminaires
- Outdoor luminaires that restrict all light output to below
85° from vertical. |
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Dark Adaptation -
The process by which the retina becomes adapted to a
luminance of less than 0.01 footlamberts. |
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Diffuser - A
translucent piece of glass or plastic sheet that shields the
light source in a fixture. The light transmitted throughout the
diffuser will be redirected and scattered. |
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Diffusion -
The scattering, spreading or redirection of light in an even
manner, by a lens, to achieve some intended effect such as
reduced glare. |
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Dimming Ballast -
Special fluorescent lamp ballast, which when used with a dimmer
control, permits varying light output. |
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Direct Current
(DC) - Flow of electricity continuously in one direction
from positive to negative. |
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Direct Glare -
Glare resulting from high brightness or insufficiently shielded
light sources in the field of view. It usually is associated
with bright areas, such as luminaires, ceilings and windows
which are outside the visual task or region being viewed.
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Disability Glare
- Glare resulting in reduced visual performance and
visibility . Often accompanied by discomfort glare. |
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Discharge Lamp -
A lamp in which light (or radiant energy near the visible
spectrum) is produced by the passage of an electric current
through a vapor or a gas. |
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Discomfort Glare
- Glare producing discomfort. It does not necessarily
interfere with visual performance or visibility. |
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Distribution
Panel - Box containing circuit breakers or fuses where power
is distributed to branch circuits. |
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Downlight - A
type of ceiling luminaires usually fully recessed, where most of
the light is directed downward. May feature an open reflector
and/or shielding device, can be recessed, surface mounted, or
suspended. |
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Efficacy -
The luminous flux of a lamp divided by its power consumption
(lm/w) |
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Efficiency -
(Light Output Ratio) which is the lumens transmitted by a
luminaire divided by the lumens of the
lamps (bare, no luminaire) |
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Electric
Discharge Lamp - A light source that produces light by
passing a current between electrodes through a vapor or gas;
includes fluorescent, high intensity discharge, and other lamps.
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Electroluminescence - The emmision of light from a phosphor
excited by an electromagnetic field. An example: a light source
technology used in exit signs that provides uniform brightness,
long lamp life (approximately eight years), while consuming very
little energy (less than one watt per lamp). The emmision of
light from a phosphor excited by an electromagnetic field.
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Electronic
Ballast - A ballast that uses semiconductor components to
increase the frequency of fluorescent lamp operation-typically
in the 20-40 kHz range. Smaller inductive components are used to
provide the lamp current control. Fluorescent system efficiency
is increased due to high frequency lamp operation. |
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Electronic
Dimming Ballast - A variable output electronic fluorescent
ballast. |
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Emission Coating
- An oxide coating deposited on a cathode that emits
electrons when heated. |
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Emissivity/Emittance
- The ratio of radiance (for directional emissivity) or
radiant exitance (for hemispherical emissivity) of an element of
surface on a temperature radiator to that of a blackbody at the
same temperature. By Kirchoff's Law, for a given wavelength of
the electromagnetic spectrum, emissivity of a surface equals its
absorptivity (and is the reciprocal of its reflectivity).
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End Blackening -
Darkening around the ends of a fluorescent tube caused by the
emitter paste on the electrodes evaporating and collecting on
the glass. |
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Energy Survey -
Synonymous with "cost calculations," "energy audit," etc.; a
systematic cost comparison of an existing system to a proposed
system; accounts for electrical, material and
maintenance/manpower costs. |
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Energy-Saving
Ballast - A type of magnetic ballast designed so that the
components operate more efficiently, cooler and longer than a
"standard magnetic" ballast. By U.S. law, standard magnetic
ballast's can no longer be manufactured. |
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Energy-Saving
Lamp - A lower wattage lamp, generally producing fewer
lumens. |
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EPA - Effective
Projected Area - A value given to outdoor pole mounted
lighting equipment based on fixture surface area and shape. Used
in outdoor applications to calculate wind loading data to
determine proper pole size necessary to support fixture.
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Equivalent Sphere
Illumination (ESI) - The level of sphere illumination which
would produce task visibility equivalent to that produced by a
specific lighting environment. Suppose a task at a given
location and direction of view within a specific lightings
system has l00 fc of illumination. Suppose this same task is now
viewed under sphere lighting and the sphere lighting level is
adjusted so that the task visibility is the same under the
sphere lighting as it was under the lighting system. Suppose the
lighting level at the task from the sphere lighting is 50 fc for
equal visibility. Then the Equivalent Sphere Illumination of the
task under the lighting system would be 50 ESI fc. |
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ER (Elliptical
Reflector) - Lamp whose reflector focuses the light about 2"
ahead of the bulb, reducing light loss when used in deep baffle
downlights. |
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Exitance -
The density of light reflecting from a surface at a point,
measured in lumens per square foot (formerly "footlamberts"). It
is determined by multiplying the footcandles striking a diffuse
reflecting surface times the reflectance of that surface.
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Extended Life Lamps - Incandescent lamps that have an
average rated life of 2500 or more hours and reduced light
output compared to standard general service lamps of the same
wattage. |
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Eyeball -
Fixture, usually recessed, loosely resembling an "eyeball"; can
be rotated to point in desired direction. |
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Filament -
Wire element, often coiled, in a lamp that becomes incandescent
and emits light when heated by an electric current. |
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Fixture -
Informal substitute term for luminaire, especially a luminaire
without the lamps. |
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Flicker -
Variation in light intensity due to 60 Hz operation. Can cause
eyestrain and fatigue due to stroboscopic effects. |
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Floodlighting -
A system designed for lighting a scene or object to a luminance
greater than its surroundings. It may be for utility,
advertising or decorative purposes |
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Fluorescence -
Light resulting from the action of ultraviolet or other
forms of energy on phosphors. Fluorescence occurs only while
energy is being absorbed by the fluorescing material. ( Time
scale less than 10-8 seconds.) |
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Fluorescent Lamp
- A low-pressure mercury electric-discharge lamp in which a
fluorescing coating (phosphor) transforms some of the
ultraviolet energy generated by the discharge into light.
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Flux -
Continuous flow of luminous energy |
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Foot Lambert (fl)
- A unit of luminance of a perfectly diffusing surface
emitting or reflecting light at the rate of one lumen per square
foot. |
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Footcandle (fc) -
The unit of illuminance when the foot is taken as the unit of
length. It is the illuminance on a surface one square foot in
area on which there is a uniformly distributed flux of one
lumen. |
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Fuse -
Replaceable safety device to prevent excess current flow |
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General Lighting
- Essentially uniform light throughout an area, with no
special provisions for individual tasks or objects. |
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GLS
Lamps - General
Lighting Service (Incandescent) lamp |
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Glare - The
sensation produced by luminance 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 and visibility. |
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Globe - A
transparent or translucent spherical lamp enclosure.
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Grounding -
Connection of electric components to earth for safety
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Group Relamping -
The correct method to replace HID lamps by replacing all lamps
at one time. |
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Halogen - See
Tungsten Halogen Lamp |
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Head -
Luminaire for a track-lighting system. |
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Heat Extraction -
The process of removing heat from a luminaire by passing return
air through the lamp cavity |
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High Bay -
High ceiling, usually in an industrial plant. Because of height,
it may be hard to reach for lamp changers without special
ladders or scaffolding. Usually above 20 ft. |
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High Intensity
Discharge (HID) Lamp - A discharge lamp in which the light
producing arc is stabilized by wall temperature, and the arc
tube has a bulb wall loading in excess of three watts per square
centimeter. HID lamps include groups of lamps known as mercury,
metal halide, and high pressure sodium. |
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High Output (HO)
Fluorescent - A fluorescent lamp designed for use with an
800 milliampere (MA) ballast; will usually operate at low
temperatures (down to zero) while still producing high light
levels. |
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High Pressure
Sodium (HPS) Lamp - High intensity discharge (HID) lamp in
which light is produced by radiation from sodium vapor. Includes
clear and diffuse-coated lamps.
High pressure sodium lamps rely on an ignitor to send a high
voltage pulse to the lamp electrodes in order to start the lamp.
This results in a quick ignition time: 1 to 3 minutes. High
pressure sodium systems provide higher efficiencies
(lumens/watt), lumen maintenance, and greater component life
than traditional metal halide systems, but similar to mercury
vapor. The color rendering index (CRI) of these systems,
however, is substantially less than metal halide and closer to
that of mercury vapor lamps, 22 to 25. There are "color
corrected" lamps available, but which are somewhat cost
inhibitive, but will reach CRI values up to 65. |
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Hot cathode lamp
- An electric dis-charge lamp whose mode of operation is
that of an arc discharge. The cathodes may be heated by the
discharge or by external means. |
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Hot Re-Start Time
- The amount of time from a momentary power interruption to
return of full light output |
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Hot Restrike -
A phenomenon of re-striking the arc in an HID light source after
a momentary power loss. Hot restart occurs after the arc tube
has cooled a sufficient amount. |
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IESNA -
Abbreviation for Illumination Engineering Society of North
America. |
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Illuminance -
A photometric term that quantifies light incident on a surface
or plane. Illuminance is commonly referred to as light level. it
is expressed as lumens per square foot (footcandles), or lumens
per square meter (lux). |
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Illumination -
The lighting in an area, or the result of the use of light.
Also, the intensity of light per unit of area, sometimes called
"illuminance"; usually measured in footcandles. |
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Incandescent Lamp
- A lamp in which light is produced by a filament heated to
incandescence by an electric current |
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Indirect Lighting
- Luminaires that distribute 90-to-100 percent of their
light upward to be reflected by the ceiling. |
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Infrared -
Radiant energy with wavelengths between 770 and one million
nanometers, i.e., longer than the wavelengths of visible light.
Applications include photography, heat lamps, industrial drying,
and medical therapy. |
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Initial lumens
“100 Hour Lumens” - The measurement of light output after
100 hours of operation. This is also referred to as “100 hours
lumens” is the point where initial light output stabilizes |
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Instant Start
Fluorescent Lamp - A fluorescent lamp designed for starting
by a high voltage without preheating of the electrodes |
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Inverse Square
Law - The law stating that the illuminance at a point on a
surface varies directly with the intensity of a point source,
and inversely as the square of the distance between the source
and the point. If the surface at the point is normal to the
direction of the incident light, the law is expressed by fc=cp/d2.
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Isolux Chart -
A series of lines plotted on any appropriate set of coordinates,
each line connecting all the points on a surface having the same
illumination. |
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Junction Box -
A metal box in which circuit wiring is spliced. It may also be
used for mounting luminaires, switches or receptacles |
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Kelvin Scale -
A scale of temperature measured in degrees Celsius from absolute
zero |
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Kilowatt (kw) -
A unit of electrical power, equal to 1000 watts. |
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Kilowatt-Hour
(KWH) - Unit of electrical power consumed over a period of
time. KWH=watts/lOOOxhours used. |
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Krypton - A
heavy inert gas used in incandescent lamps; allows the filament
to glow hotter and brighter, yet last longer. |
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Lamp - An
artificial source of light (also a portable luminaire equipped
with a cord and plug). Industry term for light bulb.
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Lamp Efficacy -
The ratio of lumens produced by a lamp to the watts consumed,
expressed as lumens per watt (LPW). |
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Lamp Life -
Rated life of a lamp, as established through laboratory testing
during which a sample group of lamps is burned, including being
subjected to a scheduled number of starts per day. The length of
time required for half the lamps to fail is the rated lamp life.
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Lamp Lumen
Depreciation (LLD) - Multiplier factor in illumination
calculations for reduction in the light output of a lamp over a
period of time. |
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Lamp Wattage -
The power consumption of a lamp after warm up NOT including
ballast losses |
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Lens - Used
in luminaires to redirect light into useful zones. |
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Lexan - Brand
name for polycarbonate material used in lenses that will not
break or yellow. |
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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 no
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Light Loss Factor
(LLF) - A factor used in calculating the level of
illumination that takes into account such factors as dirt
accumulation on luminaire and room surfaces, lamp depreciation,
maintenance procedures and atmosphere conditions. |
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Light Output -
Amount of light produced by a light source such as a lamp. The
unit most commonly used to measure light output is the lumen.
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Light pollution -
Any adverse effect of manmade light. Often used to denote urban
sky glow. "The wasted light that goes up into the sky."
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Light trespass -
Light falling where it is not wanted or needed. Spill light.
Obtrusive light. |
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Load Shedding -
A lighting control strategy for selectively reducing the output
of light fixtures on a temporary basis as a means to reduce peak
demand charges. |
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Louver - A
series of baffles used to shield a source from view at certain
angles or to absorb unwanted light. The baffles usually are
arranged in a geometric pattern. |
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Low Pressure
Sodium Lamp - 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. |
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Low-Voltage Lamps
- A lamp-typically compact halogen-that provides both high
intensity and good color rendition. Lamp operates at 12V and
requires the use of a transformer. Popular lamps are MR11, MR16
and PAR36. |
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Lumen - A
measurement of light output; The unit of luminous flux. It is
the luminous flux emitted within a unit solid angle (one
steradian) by a point source having a uniform luminous intensity
of one candela. |
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Lumen
Depreciation - The term for the gradual decline in a
source's light output. Except for low pressure sodium lamps, all
sources lose lumen output over their life due to gradual
deterioration of the filaments or electrodes, accompanied by
lamp blackening. A factor is commonly used as a multiplier to
the initial lumen rating in illuminance calculations, which
compensates for the lumen depreciation. |
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Lumen Maintenance
- Same as "Light Loss Factor." |
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Lumens Per Watt -
Lumen (light) output divided by lamp watts consumed (i.e. amount
of light for electricity used); also known as efficacy.
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Luminaire - A
complete lighting unit consisting of a lamp or lamps together
with the parts designed to distribute the light, to position and
protect the lamps and to connect the lamps to the power supply.
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Luminaire Dirt
Depreciation (LDD) - The multiplier to be used in
illuminance calculations to relate the initial illuminance
provided by clean, new luminaires to the reduced illuminance
that they will provide due to dirt collection on the luminaires
at the time at which it is anticipated that cleaning procedures
will be instituted. |
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Luminaire
Efficiency - The ratio of luminous flux (lumens) emitted by
a luminaire to that emitted by the lamp or lamps used therein.
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Luminance -
The amount of light reflected from any surface. |
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Lux - The
metric unit of illuminance. One lux is one lumen per square
meter (Im/m2). |
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Maintained
Footcandles - Footcandles calculated through application of
light loss factors |
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Maintenance
Factor (MF) - A factor used in calculating illuminance after
a given period of time and under given conditions. It takes into
account temperature and voltage variations, dirt accumulation on
luminaire and room surfaces, lamp depreciation, maintenance
procedures and atmosphere conditions. |
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Matt Surface -
A non-glossy dull surface, as opposed to a shiny (specular)
surface. Light reflected from a matte surface is diffuse.
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Mean Lumens -
Amount of light output at 40% of lamp life |
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Mercury Lamp -
A high intensity discharge (HID) lamp in which the major portion
of the light is produced by radiation from mercury. Includes
clear, phosphor-coated and self-ballasted lamps. |
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Mercury Vapor
Lamp - A type of HID lamp in which the major portion of the
light is produced by radiation from mercury vapor. Emits a
blue-green cast of light. Available in clear and phosphorcoated
lamps. Mercury vapor lamps operate very similarly to traditional
metal halide lamps in that they incorporate the same type of
starting probe (electrode). Their efficiency and lumen
maintenance is slightly less than metal halide units and
substantially less than high pressure sodium. However, mercury
vapor lamp life is close to that of high pressure sodium. While
"color corrected" versions are available, the average color
rendering index (CRI) is poor and similar to that of high
pressure sodium, 15-20. |
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Mesopic vision -
Vision intermediate between photopic and scotopic vision. |
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Metal Halide Lamp
- A high intensity discharge (HS) lamp in which the major
portion of the light is produced by radiation from mercury.
Includes clear. phosphor-coated and self-ballasted lamps.
Traditional metal halide lamps incorporate a starting probe
(electrode) to initiate an arc via high open circuit voltage.
The iginition time is negatively affected by this low voltage
starting technique, with the run up time of around four minutes
and a restrike time running anywhere from 15 to 20 minutes. The
efficiency (lumens/watt) of traditional metal halide lighting
systems is between 50% and 60% that of a comparable high
pressure sodium system. However, the white light produced by
these lamps renders a color quality (CRI) of 65-70, three times
better than high pressure sodium. |
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Nadir -
Vertically downward directly below the luminaire or lamp;
designated as 0°. |
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Ohm's Law - A
scientific law which states that current (amperes) in a circuit
depends on resistance (ohms) and applied electromotive force
(volts). Current (I) = Voltage (E) / Resistance (R). Or: I = E/R
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Operating Current
- Current in amps consumed by a lamp at rated watts.
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Operating Voltage
- Voltage at rated watts after lamp fully warms |
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Outlet Box -
A metal box in which circuit wiring is spliced. It may also be
used for mounting luminaires, switches or receptacles
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PAR Lamps -
Parabolic aluminized reflector lamps which offer excellent beam
control, come in a variety of beam patterns from very narrow
spot to wide flood, and can be used outdoors unprotected because
they are made of "hard" glass that can withstand adverse
weather. |
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Parabolic Louvers
- A grid of baffles which redirects light downward and
provides very low luminaire brightness |
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Pattern Control -
A blade, in the air passage of an air handling luminaire, which
sets the direction of air flow from the luminaire. |
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Photocell - A
light sensing device used to control luminaires and dimmers in
response to detected light levels. |
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Photopic Vision -
Refers to vision involving the cones of the eye; used in
reference to the adaptation of the eye to illuminance of more
than 3.4 candelas per square meter, or one footlambert. See "Scotopic
Vision." |
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Plug-in Wiring -
Electrical distribution system which has quick-connect wiring
connectors. |
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Point Method
Lighting Calculation - A lighting design procedure for
predetermining the illuminance at various locations in lighting
installations, by use of luminaire photometric data.
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Polarization -
The process by which the transverse vibrations of light
waves are oriented in a specific plane. Polarization may be
obtained by using either transmitting or reflecting media.
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Polycarbonate -
A plastic material which will
be affected by UV, will get yellow but is un-breakable. |
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Positive Cash
Flow - when referred to as part of a lighting upgrade, this
is a comparison of estimated savings to cost. With 100 percent
project financing it is possible to have an immediate positive
cash flow once the project starts. |
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Power Factor -
Ratio of: watts over volts x amperes; Power factor in lighting
is primarily applicable to ballasts. Since volts and watts are
usually fixed, amperes (or current) will go up as power factor
goes down. This necessitates the use of larger wire sizes to
carry the increased amount of current needed with Low power
Factor (L.P.F.) ballasts. The addition of a capacitor to a L.P.F.
ballast converts it to a H.P.F. ballast. |
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Preheat
Fluorescent Lamp - A fluorescent lamp designed for operation
in a circuit requiring a manual or automatic starting switch to
preheat the electrodes in order to start the arc. |
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Pulse start metal
halide lamps - Pulse start metal halide lamps incorporate a
high voltage ignitor similar to the high pressure sodium. The
result is a run up time of two minutes, one-half that of
standard metal halide and equal to high pressure sodium. The
restrike time is similarly affected, being cut by 80% down to
three to four minutes. The efficiency (lumen/watt) of pulse
start systems is anywhere from a 25% to 50% increase in
lumens/watts, 90 to 110 up from probe start at 60-85. Lumen
maintenance also increases by up to 30%, up to 85% from 65%. The
change in color (color shift) of pulse start due to the improved
crest factor and lamp wattage regulation is reduced by up to 2/3
of the comparable probe start metal halide or less than 200°K
over the life of the lamp versus 600°K for probe start. A CRI of
up to 85 represents a 30% improvement over traditional probe
start metal halide sources (four times that of high pressure
sodium). Finally, the high voltage ignitor allows a much colder
starting temperature compared to standard metal halide units,
-40°F/-40°C to -20°F/-30°C. |
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Quartz - Obsolete
term for a tungsten-halogen lamp |
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R Lamps -
Reflectorized lamps available in spot (clear face) and flood
(frosted face). |
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Rapid Start
Fluorescent Lamp - A fluorescent lamp designed for operation
with a ballast that provides a low-voltage winding for
preheating the electrodes and initiating the arc without a
starting switch or the application of high voltage. |
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Rated Lamp Life -
The point in hours where 50% of lamps initially started will
still be operating. |
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Raw Footcandles -
Same as footcandles. This term is sometimes used in order to
differentiate between ordinary footcandles and ESSAY footcandles.
(Footcandles or Raw Footcandles refer only to the quantity of
illumination. ESSAY footcandles refer to task visibility by
considering both the quantity and quality of illumination.)
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Reflectance -
Sometimes called reflectance factor. The ratio of reflected
light to incident light (light falling on a surface).
Reflectance is generally expressed in percent |
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Reflected Glare -
Glare resulting from specular reflections of high luminances
in polished or glossy surfaces in the field of view. It usually
is associated with reflections from within a visual task or
areas in close proximity to the region being viewed.
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Reflection -
Light striking a surface is either absorbed, transmitted, or
reflected. Reflected light is that which bounces off the
surface, and it can be classified as specular or diffuse
reflection. Specular reflection is characterized by light rays
which strike and leave a surface at equal angles. Diffuse
reflection leaves a surface in all directions. |
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Reflector - A
piece of material with a reflective surface that directs radiant
energy (light)in a desired direction. |
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Reflector Lamp -
A light source with an integral reflector, usually a silver or
aluminum coating on the bulb. |
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Refraction -
The process by which the direction of a ray of light changes as
it passes obliquely from one medium to another in which its
speed is different |
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Relamping - A
project where the existing lighting fixtures at a facility are,
as a group, cleaned and new lamps are installed. This is
typically scheduled around projected life expectancy to reduce
the day-to-day interruptions of failing aged lamps. |
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Retrofit -
Refers to upgrading a fixture, room, building, etc., by
installing new parts or equipment. |
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Room Cavity Ratio
(RCR) - A numerical relationship of the vertical distance
between work plane height and luminaire mounting height to room
width and length. It is used with the Zonal Cavity method of
calculating average illumination levels. |
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Rough Service
Lamps - Incandescent lamps designed with extra filament
supports to withstand bumps, shocks and vibrations with some
loss in lumen output. |
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Scotopic Vision -
Sight involving the eye's rods, which respond to low levels of
lighting, below .034 candela per square meter, or .01
footlamberts. |
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Shielding -
An arrangement of light-controlling material to prevent direct
view of the light source. |
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Shielding Angle
(of a luminaire) - The angle from the horizontal at which a
light source first becomes visible. It is the complementary
angle of the cutoff angle. In the case of a luminaire shielded
by a reflector or parabolic cell louver, it is important to
ascertain also the shielding angle to the reflected image of the
light source, as this is often almost as bright as the source
itself. |
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SON - Another
term for a high pressure sodium (HPS) lamp |
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SOX - Another
term for a low pressure sodium (LPS) lamp. |
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Spacing Criterion
- The maximum recommended distance that interior fixtures
should be spaced to ensure uniform illumination on the workplane.
The height of the luminaire above the workplane multiplied by
the spacing criterion equals the recommended maximum
center-to-center luminaire spacing. |
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Spectral Energy
Distribution (SED) Curves - A plot of the level of energy at
each wavelength of a light source. |
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Spectroradiometer
- An instrument capable of separating and measuring light
waves. |
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Specular -
Mirrored or polished surface. The angle of reflection is equal
to the angle of incidence. This word is used to describe the
finish of the material used in some louvers and reflectors.
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Sphere
Illumination - The illumination on a task from a source
providing equal luminance in all directions about that task,
such as an illuminated sphere with the task located at the
center. |
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Starter - A
device used in conjunction with a ballast to start
electric-discharge lamps, usually older fluorescents.
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Step lens - A
plano-convex lens similar to a fresnel lens but with the
concentric rings cut into the plano side. |
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Stroboscopic
Effect - Condition where rotating machinery or other rapidly
moving objects appear to be standing still due to the
alternating current supplied to light sources. ometimes called
"strobe effect." |
