What are all of these new words? Just another way we are helping you to understand. If you cannot find the definition you are looking for, call us and we will give it to you.
Our Glossary is a great reference. There are many terms the common indoor gardener do not understand, and we want to make sure you know that we're here to help you. By providing you the most common terms and definitions. we hope to help you understand hydroponics better.
Alternating Current (AC) - an electric current that reverses its direction at regularity occurring intervals. Homes have A.C.
Adobe - heavy clay soil, not suitable for container gardening or hydroponics.
Aeration - supplying growing mediums and roots with air or oxygen.
Aeroponic - growing plants by misting roots suspended in air. No medium is needed with this method and usually only small plants that need no support are grown this way.
Aggregate - medium usually grow rocks, gavel, or lava rocks that is all nearly the same size, and used for an inert hydroponic medium.
Alkaline - refers to soil or hydroponic nutrient solution with a high pH : Any pH over 7 is considered alkaline.
All-purpose (General-purpose) fertilizer - A balanced blend of N-P-K; all purpose fertilizer for soil and is used by most growers in the vegetative growth stage. Miracle-Gro and Peters is an example. They are not recommended for hydroponics.
Ampere (amp) - the unit used to measure the strength of an electric current; A 20-amp circuit is overloaded when drawing more than 17amps,
Annual - a plant that normally completes its entire life cycle in one year or less: Marigolds and tomatoes are examples of annual plants.
Arc - luminous discharge of electricity (light) between two electrodes.
Arc tube - container for luminous gases; also houses the arc.
Auxin - classification of plant hormones; Auxins are responsible for foliage and root elongation.
Bacteria - very small, one-celled organisms that have no chlorophyll.
Beneficial insect - a good insect that eats bad insects that attack your plants.
Biodegradable - able to decompose or break down through natural bacterial action; Substances made of organic matter are biodegradable.
Bleach - Ordinary laundry bleach is used in a 1 part bleach to 10 parts water solution as a garden fungicide. Use this solution to clean all your equipment between harvests to rid of any lingering contamination.
Bolt - term used to describe a plant that has run to seed prematurely which means that it bloomed because of heat or other reasons.
Bonsai - a very short or dwarfed plant.
Breaker box - electrical circuit box having on/off switches rather than fuses.
Breath - Roots draw in and breath oxygen, stomata draw in and breathe CO2.
Bud blight - a withering condition that attacks flower buds.
Buffering - the ability of a substance to reduce shock and cushion against pH fluctuations. Many soil fertilizers contain buffering agents but it is much more critical to maintain the correct pH with hydroponics than with soil growing..
Bulb - 1. the outer glass envelope or jacket that protects the arc tube of an HID lamp 2. clove or bulb of garlic.
Calyx - the pod harboring female ovule and two protruding pistils, seed pod.
Carbon dioxide (CO;) - a colorless, odorless, taste less gas in the air necessary for plant life.
Carbohydrate - neutral compound of carbon, hydrogen and oxygen; Sugar, starch and cellulose are carbohydrates.
Caustic - capable of destroying, killing or eating away by chemical activity
Cell - the base structural unit that plants are made of: Cells contain a nucleus, membrane, and chloroplasts.
Cellulose - a complex carbohydrate that stiffens a plant: Tough stems contain stiff cellulose.
CFM - Cubic feel per minute.
Chelate - combining nutrients in an atomic ring that is easy for plants to absorb.
Chlorophyll - the green photosynthetic matter of plants: Chlorophyll is found in the chloroplasts of a cell.
Chlorine - chemical used lo purify water.
Cbloroplast - containing chlorophyll.
Chlorosis - the condition of a sick plant with yellowing leaves due to inadequate formation of chlorophyll; Chlorosis is caused by a nutrient deficiency, usually iron or imbalanced pH.
Circuit - a circular route traveled by electricity.
Clay - soil made of very tine organic and mineral particles: Clay is not suitable for container gardening.
Climate - the average condition of the weather in a grow room or outdoors.
Color spectrum - the band of colors (measured in nm) emitted by a light source.
Color tracer - a coloring agent that is added to many commercial fertilizers so the horticulturist knows there is fertilizer in the solution. Peters has a blue color tracer.
Compaction - soil condition that results from lightly packed soil: Compacted soil allows for only marginal aeration and root penetration.
Companion planting - planting garlic, marigolds, etc. along with other plants to discourage insect infestations.
Compost - a mixture of decayed organic matter, high in nutrients; Compost must be at least one year old. When to young, decomposition uses nitrogen; after sufficient decomposition, compost releases nitrogen.
Core - the transformer in the ballast is referred to as a core.
Cotyledon - seed leaves first leaves that appear on a plant.
Cross-pollinate - pollinate two plants having different ancestry.
Cubic foot - volume measurement in feet: Width times length times height equals cubic feet.
Cutting - 1. growing tip cut from a parent plant for asexual propagation 2. clone
Damping-off - fungus disease that attacks young seedlings and cuttings causing them to rot at the base: Over-watering is the main cause of damping-off.
Direct Current (DC) - an electric current that flows in only one direction.
Deplete - exhaust soil of nutrients, making in infertile: Once a soil is used it is depleted.
Desiccate - cause to dry up. Safari's Insecticidal Soap desiccates its victims.
Detergent - liquid soap concentrate used as a: 1. wetting agent for sprays and water 2. pesticide. Note: Detergent must be totally organic to be safe for plants.
Dioecious - having distinct male and female flowers.
Dome - the part of the HID outer bulb opposite the neck and threads.
Dome support - the spring-like brackets that mount the arc tube within the outer envelope.
Drainage - way to empty soil of excess water: with good drainage, water passes through soil evenly, promoting plant growth; with bad drainage water stands in soil, drowning roots.
Drip line - a line around a plant directly under its outermost blanch tips: Roots seldom grow beyond the drip line.
Drip system - a very efficient watering system that employs a main hose with small water emitters. Water is metered out of the emitters, one drop at a time.
Dry ice - a cold, white substance formed when CO2; is compressed and cooled: Dry ice changes into CO2; gas at room temperatures. For small garden rooms this my be an easy way to add CO2.
Dry well - drain hole, filled with rocks.
Electrode - a conductor used to establish electrical arc or contact with non-metallic part of circuit.
Elongate - grow in length.
Envelope - outer protective bulb or jacket of a lamp.
Equinox - the point at which the sun crosses the equator and day and night are each 12 hours long: The equinox happens twice a year.
Extension cord - extra electrical cord that must be 14-gauge or larger (i.e. 12-or IO-gauge).
Feed - fertilize.
Female - pistillate, ovule, seed-producing.
Fertilizer burn - over-fertilization: First leaf tips bum (turn brown) then leaves curl.
Fixture - electrical fitting used lo hold electric components.
Flat - shallow (three-inch) deep container, often 18 by 24 inches with good drainage, used to start seedlings or cuttings.
Flat white - very reflective, whitest white paint available.
Fluorescent lamp - electric lamp using a tube coated with fluorescent material, which has low lumen and heat output; A fluorescent lamp is excellent for rooting cuttings.
Foliage - the leaves, or more generally, the green part of a plant.
Foliar feeding - misting fertilizer solution which is absorbed by the foliage.
Fritted - fused or embedded in glass, Fritted trace elements (FTE) are long-lasting and do not leach out easily.
Fungicide - a product that destroys or inhibits fungus.
Fungistat - a product that inhibits fungus keeping in check.
Fungus - a lower plant lacking chlorophyll which may attack green plants; Mold, rust, mildew, mushrooms and bacteria are fungi.
Fuse - electrical safety device consisting of a metal that melts and interrupts the circuit when circuit is overloaded.
Fuse box - box containing fuses that control electric circuits.
GPM - Gallons per minute.
General purpose fertilizer - See ALL-PURPOSE FERTILIZER.
Gene - part of a chromosome that influences the development and potency of a plant; Genes are inherited through sexual propagation.
Genetic make-up - the genes inherited from parent plants: Genetic make-up is the most important factor dictating vigor and potency.
Halide - binary compound of a halogen(s) with an electropositive elements.
Halogen - any of the elements fluorine, chlorine, bromine, iodine and astatine existing in a free state: Halogens arc in the arc tube of a halide lamp.
Hermaphrodite - one plant having both male and female flowers: The breeding of hermaphrodites is hard to control.
Hertz (Hz) - a unit of a frequency that cycles one time each second: A home with a 60 hertz AC current cycles 60 times per second.
HID - High Intensity Discharge.
Honeydew - a sticky, honey-like substance secreted onto foliage by aphids, scale and mealy bugs.
Hood - reflective cover of a HID lamp; A large, while hood is very reflective.
HOR - The abbreviation stamped on some HID bulbs meaning they may be burned in a horizontal position.
Horizontal - parallel to the horizon, ground or floor.
Hormone - chemical substance that controls the growth and development of a plant. Root-inducing hormones help cuttings root.
Hose bib - water outlet containing an on/off valve.
Humidity (relative) - ratio between the amount of moisture in the air and the greatest amount of moisture the air could hold at the same temperature.
Humus - dark, fertile, partially decomposed plant or animal matter: Humus forms the organic portion of the soil.
Hybrid - an offspring from two plants of different breeds, variety or genetic make-up.
Hydrated lime - instantly soluble lime, used to raise or lower pH.
Hydrogen - light, colorless, odorless gas: Hydrogen combines with oxygen to form water.
Hygrometer - instrument for measuring relative humidity in the atmosphere A hygrometer will save time, frustration and money.
Inbred - (true breed) offspring of plants of the same breed or ancestry.
Inert - chemically non-reactive; inert growing mediums make it easy to control the chemistry of the nutrient solution.
Intensity - the magnitude of light energy per unit: Intensity diminishes the farther away from the source.
Jacket - protective outer bulb or envelope of lamp.
Jiffy 7 pellet - compressed peat moss wrapped in an expandable plastic casing; When moistened, a Jiffy 7 pellet expands into a small pot that is used to start seeds or cuttings.
Kilowatt-hour - measure of electricity used per hour; A 1000- watt HID uses one kilowatt per hour.
Leach - dissolve or wash out soluble components of soil by heavy watering but can be beneficial to hydroponics systems to flush out excess fertilizer salts.
Leader - See Meristem
Leaf curl - leaf malformation due lo over-watering, over fertilization, lack of magnesium, insect or fungus damage or negative tropism.
Leaflet - small immature leaf.
Leggy - abnormally tall, with sparse foliage: Legginess of a plant is usually caused by lack of light.
Life cycle - a series of growth stages through which plant must pass in Its natural lifetime: The stages for an annual plant arc seed, seedling, vegetative and floral.
Light mover - a device that moves a lamp back and forth across the ceiling of a grow room to provide more even distribution of light.
Lime - used in the form of DOLOMITE or HYDRATED LIME to raise and stabilize soil pH.
Litmus paper - chemically sensitive paper used for testing pH.
Loam - organic soil mixture of crumbly clay, silt and sand.
Lumen - measurement of light output: One lumen is equal to the amount of light emitted by one candle that falls on one square foot of surface located one foot away from one candle.
Macro-nutrient - one or all of the primary nutrients N-P-K or the secondary nutrients magnesium and calcium.
Mean - average throughout life; HID's are rated in mean lumens.
Meristem - lip of plant growth, branch lip.
Micro-nutrients - also referred to as TRACE ELEMENTS, including S, Fe, Mn, B, Mb, An and Cu.
Millimeter - thousandth of a meter; approximately .04 inch.
Moisture meter - a fantastic electronic device that measures the exact moisture content of soil at any given point.
Monochromatic - producing only one color; LP sodium lamps are monochromatic.
Mulch - a protective covering of organic compost, old leaves, etc.: Indoors, mulch keeps soil too moist, and possible fungus could result.
Nanometer - .000 000 001 meter, nm is used as a scale to measure electromagnetic wave lengths of light: Color and light spectrums are expressed in nanometers (nm).
Necrosis - localized death of a plant part.
Neck - tubular glass end of the HID bulb, attached to the threads.
Nutrient - plant food, essential elements N-P-K, secondary and trace elements fundamental to plant life.
Ohm's Power Law - a law that expresses the strength of an electric current: Volts times Amperes equals watts.
Organic - made of, derived from or related to living organisms.
Outbred - see hybrid.
Overload - load to excess; A 20-amp circuit drawing 17 amps is overloaded.
Ovule - a plant's egg; found within the calyx, it contains all the female genes; When fertilized, an ovule will grow into a seed.
Oxygen - tasteless, colorless element, necessary in soil to sustain plant life.
Parasite - organism that lives on or in another host organism: Fungus is a parasite.
Peat - partially decomposed vegetation (usually moss) with slow decay due to extreme moisture and cold.
Perennial - a plant, such as a tree or shrub, that completes its life cycle over several years.
pH - a scale from I to 14 that measures the acid-lo-alkaline balance a growing medium (or anything): In general plants grow best in a range of 6 to 6.8 pH in soil and 5 to 6.5 for hydroponics.
pH tester - electronic instrument or chemical used to find where soil or water is on the pH scale.
Phosphor coating - internal bulb coating that diffuses light and is responsible for various color outputs.
Photoperiod - the relationship between the length of light and dark in a 24-hour period.
Photosynthesis - the building of chemical compounds (carbohydrates) from light energy, water and CO2.
Phototropism - the specific movement of a plant part toward a light source.
Pigment - The substance in paint or anything that absorbs light, producing (reflecting) the same color as the pigment.
Pollen - fine, yellow, dust-like microspores containing male genes.
Pod seed - a dry calyx containing a mature or maturing seed.
Pot-bound - bound, stifled or inhibited from normal growth, by the confines of a container: Root systems become pot bound.
Power surge - interruption of change in flow of electricity.
Primary nutrients - N-P-K.
Propagate - 1. Sexual - produce a seed by breeding different male and a female flowers 2. Asexual - to produce a plant by taking cuttings.
Prune - alter the shape and growth pattern of a plant by cutting stems and shoots.
PVC pipe - plastic (polyvinyl chloride) pipe that is easy to work with, readily available and used to make most of the gardens on this site.
Pyrethnim - natural insecticide made from the blossoms of various chrysanthemums: Raids' Pyrethrum is the most effective natural spider mite exterminator.
Rejuvenate - Restore youth: A mature plant, having completed its life cycle (flowering), may be stimulated by a new 18 hour photoperiod, to rejuvenate or produce new vegetative growth.
Root-bound - see POT BOUND.
Salt - crystalline compound that results from improper pH or toxic buildup of fertilizer. Salt will burn plants, preventing them from absorbing nutrients.
Secondary nutrients - calcium (Ca) and magnesium (Mg).
Short circuit - condition that results when wires cross and forms a circuit. A short circuit will blow fuses.
Socket - threaded, wired holder for a bulb.
Soluble - able to be dissolved in water.
Spore - seed-like offspring of a fungus.
Sprout - 1, a recently germinated seed 2. small new growth of leaf or stem.
Square feet (sq. ft.) - length (in feet) times width equals square feet.
Staminate - male, pollen producing.
Starch - complex carbohydrate: Starch is manufactured and stored food.
Sterilize - make sterile (super-clean) by removing dirt, germs and bacteria. A good sterilizer for hydroponic equipment is a 10 percent bleach to water solution.
Stroboscopic effect - a quick pulsating or flashing of a lamp.
Stress - a physical or chemical factor that causes extra exertion by plants: A stressed plant will not grow as well as a non-stressed plant.
Stomata - small mouth-like or nose-like openings (pores) on leaf underside, responsible for transpiration and many other life functions: The millions of stomata must be kept very dean to function properly.
Sugar - food product of a plant.
Super-bloom - a common name for fertilizer high in phosphorus that promotes flower formation and growth.
Synthesis - production of a substance, such as chlorophyll, by uniting light energy and elements or chemical compounds.
Sump - reservoir or receptacle that serves as a drain or holder for hydroponic nutrient solutions.
Tap root - the main or primary root that grows from the seed: Lateral roots will branch off the tap root.
Teflon tape - tape that is extremely useful to help seal all kinds of pipe joints. I like Teflon tape better than putty.
Tepid - warm 70 to 80° F (21 to 270 C). Always use tepid water around plants to facilitate chemical processes and case shock.
Terminal bud - bud at the growing end of the main stem.
Thin - cull or weed out weak, slow growing seedlings.
Tonic life - the amount of time a pesticide or fungicide remains active or live.
Transformer - a devise in the ballast that transforms electric current from one voltage to another.
Transpire - give off water vapor and by products via the stomata.
Trellis - frame of small boards or PVC (lattice) that trains or supports plants.
True breed - see INBRED.
Tungsten - a heavy, hard metal with a high melting point which conducts electricity well: Tungsten is used for a filament in tungsten halogen lamps.
Ultraviolet - light with very short wave lengths, out of the visible spectrum.
Variety - strain, phenotype (sec strain).
Vent - opening such as a window or door that allows the circulation of fresh air.
Ventilation - circulation of fresh air, fundamental to healthy indoor garden. An exhaust fan creates excellent ventilation.
Vertical - up and down; perpendicular to the horizontal.
Wetting agent - compound that reduces the droplet size and lowers the surface tension of the water, making it wetter. Liquid concentrate dish soap is a good wetting agent if it is biodegradable.
Wick - part of a passive hydroponic system using a wick suspended in the nutrient solution, the nutrients pass up the wick and are absorbed by the medium and roots.
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 igniter 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 made of 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.