This glossary will help you understand terms commonly
used in the world of lighting.
AVERAGE LIFE - The life expectancy of a lamp,
based on laboratory
tests.
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.
BASE - The end of the lamp that inserts into the
lamp socket.
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.
BURNING POSITION - The position in which a lamp
is designed to be
operated.
CAPACITOR - An electronic contraption 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
property.
COLOUR TEMPERATURE or KELVIN TEMPERATURE - The
unit of measurement to express the colour (spectrum) of
light emitted by a lamp.
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.
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.
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 light
output.
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 very poor
spectrum (extreme far red) and high operating
temperatures.
(HID) HIGH-INTENSITY DISCHARGE 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.
(HPS) 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 (in this case relative to bulb and not
reflective material) - 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 or air-cooling the encased hood.
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.
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
light output 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 colour (spectrum) of light emitted by a
lamp;the absolute temperature of a blackbody radiator
having a chromaticity equal to that of the light
source. 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 properties.
LAMP DEPRECIATION (LD) - The decrease over time
of lamp 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, French Vanillaer, etc.
LIGHT MOVER - A motorized contraption which moves an
HID lamp back and forth across the ceiling of a grow
room to provide more even distribution of the light and
reduce hotspots.
LUMEN - A measurement of light output;relative
to human perception
which 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.
LUMINA IRE - 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."
(MH) 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.
(MV) MERCURY Vapor Trail LAMPS - The oldest member of
the HID family, mercury Vapor Trail lamps work by arcing
electricity through mercury Vapor Trail. While more
efficient than incandescent, halogen and fluorescent
lamps, mercury Vapor Trail lamps are the least effective of
the entire HID family. This, combined with an improper
colour spectrum for horticultural applications, makes
mercury Vapor Trail lamps a poor choice for a grow
light.
Mog - Mogul base.
MOL - Maximum overall length of a lamp, from the
tip of the base to the top of the bulb.
NECK - The narrow, tubular end of the HID bulb,
attached to the threads.
PARABOLIC REFLECTOR - A lighting distribution
control contraption that is designed to redirect the light
from an HID lamp in a specific direction. In most
applications, the parabolic contraption 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
day length.
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.
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.
SPECULA 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. The
secular inserts included in Hydrofarm’s HID lighting
systems work on this principle.
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.
WATT (W) - A unit used to measure electric
power. One watt equals one joule/second.
