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AMPERE (AMP) - The unit used
to measure the strength of an electric current.
ARC - The luminous discharge of electricity
between two electrodes in HID lighting.
ARC DISCHARGE - A transfer of electricity
across two electrodes (anode and cathode), characterized
by high electrode current densities and a low voltage
drop at the electrode.
ARC TUBE - The enclosure which contains the
luminous gases and also houses the arc.
BALLAST - An auxiliary piece
of equipment designed to start and to properly control
the flow of power to gas discharge light sources such
as fluorescent and high intensity discharge lamps. In
metal halide systems, it is composed of the transformer,
capacitor and connecting wiring; sodium systems require
an ignitor in addition to the transformer and capacitor.
BU - An industry code indicating that the
bulb is to be operated only in a base up position.
BULB - The glass outer envelope component
of an HID lamp which protects the arc tube.
BULB WALL TEMPERATURE - The temperature at
the bulb wall of a lamp, which effects lumen output and
input wattage and which is important in lighting calculations.
CANDELA (CD) - A unit of luminous
intensity in a given direction, equal to one lumen per
steradian.
CANDLEPOWER (CP) - The luminous intensity
of a light source, as expressed in candelas.
CANDLEPOWER DISTRIBUTION CURVE - A curve that
represents the varying distribution of luminous intensity
of a lamp or luminaire.
CAPACITOR - An electronic device that can
store electrical charge. The capacitor is one of the main
components of an HID lighting ballast. Because they can
store a very strong electrical charge, capacitors can
be very dangerous to someone who is unaware of this fact
and opens a ballast in order to examine or repair it.
If one does not know how to safely discharge the stored
electricity, one should allow a trained technician to
do any ballast repairs.
COLD START TIME - The length of time required
to bring an HID lamp to 90% light output from a cold condition.
COLOR TEMPERATURE or KELVIN TEMPERATURE -
The unit of measurement to express the color (spectrum)
of light emitted by a lamp; the absolute temperature of
a blackbody radiator having a chromaticity equal to that
of the light source (see correlated color temperature).
CONVERSION BULB - A bulb of a certain spectrum
type (e.g. sodium) specially designed to operate while
used in the fixture/ballast of a different type (e.g.
metal halide). The most popular conversion bulbs by far
are sodium conversion bulbs, which allow one to have the
sodium spectrum while still using a metal halide system.
CORRELATED COLOR TEMPERATURE (CCT) - A specification
of the color appearance of a light source, relating its
color to that of a blackbody radiator, as measured in
Kelvins (K). CCT is a general measure of a lamp's "coolness"
or "warmness."
DOME - The portion of an HID
outer bulb located opposite base (the neck and threads).
DOME SUPPORT - The spring-like brackets which
mount the arc tube within the outer envelope (bulb).
DISCHARGE LAMP - A lamp that produces light
by discharging an electric arc through a mixture of gases
and gaseous metals.
ELECTRODES - Filaments located
at either end of a discharge lamp that maintain an electrical
arc between them. See arc discharge.
FIXTURE - The electrical fitting
used to contain the electric components of a lighting
system.
FLUORESCENT LAMP - A discharge lamp in which
a phosphor coating transforms ultraviolet energy into
visible light. Fluorescent lamps are good for starting
seedlings and rooting cuttings, but do not have enough
intensity to sustain aggressive growth in plants in the
later stages of life, and are not efficient enough in
their conversion of electrical power to lumens of light
output.
FOOTCANDLE - A standard measurement of light
intensity, representing the amount of illuminance on a
surface one foot square on which there is a uniformly
distributed flux of one lumen. More simply, one footcandle
of illuminance is equal to the light emitted by one candle
at a distance of one foot.
FREQUENCY - The number of waves or cycles
of electromagnetic radiation per second, usually measured
in Hertz (Hz).
HALOGEN LAMP - A short name
for the tungsten-halogen lamp. Halogen lamps are high
pressure incandescent lamps containing halogen gases such
as iodine or bromine which allow the filaments to be operated
at higher temperatures and higher efficacies. While excellent
for home lighting and similar applications, halogen lamps
are not effective or efficient as grow lights due to their
limited spectrum and high operating temperatures.
HID - The popular acronym for High Intensity
Discharge.
HIGH-INTENSITY DISCHARGE (HID) LAMP - A general
term for mercury, metal halide and high-pressure sodium
lamps. HID lamps contain compact arc tubes which enclose
various gases and metal salts operating at relatively
high pressures and temperatures.
HIGH-PRESSURE SODIUM LAMP - High-pressure
sodium lamps operate by igniting sodium, mercury and xenon
gases within a sealed ceramic arc tube. Sodium lamps emit
light energy in the yellow/red/orange regions of the spectrum;
the red spectrum stimulates flowering and fruit production.
Many indoor gardeners switch to sodium lamps when it is
time to induce flowering or fruiting of their plants.
HOOD - The reflective cover used in conjunction
with an HID lamp. The more reflectivity a hood can provide,
the more effective it is.
HOR - An industry code indicating that the
bulb is to be operated in a horizontal position.
HOT SPOT - The area immediately under an HID
lamp where the light intensity is strongest. Hot spots
cause uneven growth, but can be remedied by using light
movers.
HOT START TIME - The length of time required
to bring an HID lamp to 90% light output after a short
power interruption.
IGNITOR - A component of the
ballast necessary for the starting of the bulb in sodium
systems.
ILLUMINANCE - The density of incident luminous
flux on a surface; illuminance is the standard metric
for lighting levels, and is measured in lux (lx) or footcandles
(fc).
ILLUMINATION - The act of illuminating or
state of being illuminated. This term is often used incorrectly
in place of the term illuminance to denote the density
of luminous flux on a surface.
INCANDESCENT LAMP - A light source which generates
light utilizing a thin filament wire (usually of tungsten)
heated to white heat by an electric current passing through
it. Incandescent lamps are the most familiar type of light
source, with countless application in homes, stores and
other commercial settings. Light is produced by passing
electric current through a thin wire filament, usually
a tungsten. Incandescent lamps are totally ineffective
as grow lights; they have very limited spectrum, are very
inefficient in their conversion of electrical power to
lumens of light output (lumen-to-watt ratio). They also
put off far too much heat per watt to use in horticulture,
even if the above-mentioned problems did not exist.
INTENSITY - A term referring to the magnitude
of light energy per unit; light intensity diminishes evenly
as you get further from the source.
KELVIN TEMPERATURE (K) - The
unit of measurement to express the color (spectrum) of
light emitted by a lamp; the absolute temperature of a
blackbody radiator having a chromaticity equal to that
of the light source (see correlated color temperature).
A standard clear metal halide HID lamp has an average
Kelvin temperature rating of 4,000K.
KILOWATT (kW) - A unit of electric power usage
equal to 1,000 watts.
KILOWATT HOUR (kWh) - A measurement of electric
energy. A kilowatt hour is equal to 1,000 watts of power
used over a period of one hour.
LAMP - An electrically energized
source of light, commonly called a bulb or tube.
LAMP LIFE - A measure of lamp performance,
as measured in median hours of burning time under ANSI
test conditions.
LAMP LUMEN DEPRECIATION (LLD) - The decrease
over time of lamp lumen output, caused by bulb wall blackening,
phosphor exhaustion, filament depreciation, and other
factors.
LAMP STARTING - Generic term used to describe
a discharge lamp's starting characteristics in terms of
time to come to full output, flicker, etc.
LIGHT - Radiant energy which can be sensed
or seen by the human eye. The term generally applied to
the visible energy from a source. Light is usually measured
in lumens or candlepower. When light strikes a surface,
it is either absorbed, reflected or transmitted. Visible
light is measured in lumens.
LIGHT MOVER - A motorized device which moves
an HID lamp back and forth across the ceiling of a grow
room to provide more even distribution of the light.
LUMEN - A measurement of light output; refers
to the amount of light emitted by one candle that falls
on one square foot of surface located at a distance of
one foot from the candle.
LUMINAIRE - A complete lighting unit, consisting
of a lamp or lamps together with the components required
to distribute the light, position the lamps, and connect
the lamps to a power supply. Often referred to as a "fixture."
LUX - A standard unit of illuminance. One
lux is equal to one lumen per square meter.
METAL HALIDE LAMP - A high-intensity-discharge
lamp in which the light is produced by arcing electricity
through a mixture of metal halides. The light produced
by metal halide lamps is in the white-blue spectrum, which
encourages vegetative growth and "bushiness" while discouraging
upward growth. This is the bulb to use in the first, vegetative
phase of plant growth.
MERCURY VAPOR LAMPS - The oldest member of
the HID family, mercury vapor lamps work by arcing electricity
through mercury vapor. While more efficient than incandescent,
halogen and fluorescent lamps, mercury vapor lamps have
the least efficient lumen-to-watt ratio of the entire
HID family. This, combined with an improper color spectrum
for horticultural applications, makes mercury vapor lamps
a poor choice for a grow light.
NECK - The narrow, tubular
end of the HID bulb, attached to the threads.
PARABOLIC REFLECTOR - A lighting
distribution control device that is designed to redirect
the light from an HID lamp in a specific direction. In
most applications, the parabolic device directs light
down and away from the direct glare zone.
PHOTOPERIOD - The relative periods of light
and dark periods within a 24-period. Also referred to
as daylength.
PHOTOSYNTHESIS - The growth process by which
plants build chemical compounds (carbohydrates) from light
energy, water and CO2 (carbon dioxide).
PHOTOTROPISM - The gravitation of a plant
part toward a light source.
REFLECTOR - The term sometimes
used to refer to the reflective hood of an HID lamp.
REFLECTIVITY - The measure of the reflective
quality of a surface; the relative ability of a given
surface to reflect light away from it without absorbing,
diffusing or otherwise compromising the light's quality,
intensity and spectrum.
SOCKET - The threaded, wired
receptacle that an HID bulb screws into.
SODIUM LAMP (HIGH-PRESSURE SODIUM LAMP) -
High-pressure sodium lamps operate by igniting sodium,
mercury and xenon gases within a sealed ceramic arc tube.
Sodium lamps emit light energy in the yellow/red/orange
regions of the spectrum; the red spectrum stimulates flowering
and fruit production. Many indoor gardeners switch to
sodium lamps when it is time to induce flowering or fruiting
of their plants.
SON-AGRO - A sodium bulb which, according
to the manufacturer, produces 30% more blue light than
standard sodium bulbs. The 430-watt SON AGRO also emits
6% more light than the standard 400-watt sodium lamp.
SPECULAR REFLECTION - The redirection of incident
light without diffusion at an angle that is equal to and
in the same plane as the angle of incidence.
STERADIAN - A unit solid angle on the surface
of a sphere equal to the square of the sphere's radius.
TRANSFORMER - The component
in the ballast that transforms electric current from one
voltage to another.
U (for UNIVERSAL) - An industry
code indicating that the bulb can be operated in any position:
horizontal, vertical (base up) or any other.
ULTRAVIOLET (UV) LIGHT - Light with very short
wavelengths, out of the visible spectrum.
UNDERWRITERS LABORATORIES (UL) - A private
organization which tests and lists electrical (and other)
equipment for electrical and fire safety according to
recognized UL and other standards. A UL listing is not
an indication of overall performance.
WATT (W) - A unit used to
measure electric power. One watt equals one joule/second.
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