Glossary of Grow Light Terms

AMPERE (AMP): A unit to quantify the intensity of electric current flow. Commonly referred to as Amps (A) or current (I).

ANSI (American National Standards Institute): A non-profit accredited standards organization established to administer a voluntary industry standards process in the United States.

ARC TUBE: The inner tube of a high intensity discharge (HID) lamp that contains an electric arc which produces light when an electric current passed through the tube.

AVERAGE RATED LIFE: The life value assigned to a particular lamp type. Statistically, average rated life is a numeric value in hours of the median, (50% point), of a population of lamps that remain operating. For example, if a lamp had an average rated life of 20,000 hours and 50 new lamps were installed in the same location, approximately 25 lamps would still be operating after 10,000 hours.

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.

BALLAST FACTOR (BF): Measure of light output from lamp operated by commercial ballast, as compared to a laboratory standard reference ballast. BF=Lumens (commercial ballast) / Lumens (reference ballast)

BALLAST LOSSES: The power consumed by the ballast when it is operating a lamp. The ballast loss is calculated by subtracting the input power from the lamp power.

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.

CCF (CURRENT CREST FACTOR, LAMP): The peak lamp current, divided by the RMS lamp current. Low crest factors are important for achieving rated lamp life. CCF=Peak Lamp Current (Amps) / RMS Lamp Current (Amps)

CENTIGRADE (C): Celsius temperature scale where 0ºC=32ºF and 100ºC=212ºF.

CHROMATICITY: The dominant or complimentary wavelengths (colors) and purity aspects of the colors taken together.

COLD START TIME: The length of time required to bring an HID lamp to 90% light output from a cold condition.

COLOR SHIFT: The change in a lamp’s color appearance, over life, measured in Kelvin compared to the initial color temperature rating.

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).

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.”

COST OF LIGHT: The total cost of owning a lighting system, which includes fixture, lamp, installation, maintenance labor, and electrical power costs.

CREST FACTOR (CF): A measurement of how “clean” the ballast power output wave is. A perfectly clean output sine wave would have a CF of 1.414. Given that some harmonics must exist in an electrical system, the crest factor must always be higher than 1.414. Therefore, the closer the ballast is to a CF of 1.414, the easier it is on the lamp.

CRI (COLOR RENDERING INDEX): An international system used to rate a lamp’s ability to render object colors. The higher the CRI (based upon a 0-100 scale), the better colors appear. CRI ratings of various lamps may be compared, but a numerical comparison is only valid if the lamps are also rated for the same chromaticity. CRI difference among lamps are not usually significant (visible to the eye) unless the difference is more than 3-5 points.

CSA (CANADIAN STANDARDS ASSOCIATION) INTERNATIONAL: CSA International is a provider of product testing and certification services. CSA test products for compliance to national and international standards, and issue certification marks for qualified products. Certification marks tell potential customers and users that a product has been evaluated by a formal process-involving examination, testing and follow-up inspection-and that it complies with applicable standards for safety and performance.

DAY NEUTRAL PLANT (DNP): A plant that flowers regardless of the length of the period of light it is exposed to

EFFICACY: The measure of a lamp or lighting system to convert electrical energy to light energy. Lighting efficacy is expressed in umol/jule.

ELECTRODES: Filaments located at either end of a discharge lamp that maintain an electrical arc between them. See arc discharge.

ELECTROMAGNETIC INTERFERENCE (EMI): Electrical interference (noise) generated by electrical and electronic devices. Levels generated by high frequency electronic devices are subject to regulation by the Federal Communications Commission (FCC). Two classifications exist; Non-consumer (also referred to as Class A or Commercial) and Consumer (also referred to as Class B or Residential).

ELECTROMAGNETIC RADIATION: Radiation originating in a varying electromagnetic field, such as visible light, radio waves, x-rays, and gamma rays.

ELECTRONIC BALLAST: A type of ballast that uses electronic components to provide the open circuit voltage and current regulation to start and sustain the discharge of a lamp.

EN: EN lamps are Environmental Protection Agency/TCLP compliant as non-hazardous waste in that they are completely lead free and contain reduced mercury.

ENCLOSED FIXTURE: A luminaire designed to contain any hot quartz fragments that might result from an arc tube rupture.

FCC: The U.S. federal agency that is charged with regulating electrical interference emissions of the electromagnetic spectrum. The regulation entitled, “Part 18,” deals with electromagnetic interference (EMI) from all lighting devices operating at frequencies higher than 9 kilohertz (kHz).

FIXTURE REQUIREMENTS: An ANSI containment classification of luminaires for specific HID lamp types. The classification code consists of the letters “O” for open, “E” for enclosed, and “S” for open luminaires with lamp operating position restrictions.

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).
The U.S. electrical grid operates at 60 Hertz or 60 cycles per second. Because of the “mass” of the U.S. electrical system, it is very unlikely to encounter frequency problems. Virtually all electrical devices are capable of operating properly at frequency variations much larger than those that could be seen in the U.S.

GETTER: Chemicals added to a lamp that neutralizes contaminants such as hydrogen and oxygen, which negatively affect lamp starting and life.

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.

HARD GLASS: Heat resistant glass that prevents breaking from thermal shock when struck by water. Borosilicate is one type of hard glass used for lamp outer jackets.

HARMONIC DISTORTION: A measurement of the magnitude of voltage and current harmonics as compared with the amplitude of the fundamental frequency. Harmonic distortion can be generated by a load and fed back into the AC mains, causing distortion conditioner (making it appear jagged rather than smooth) of the sinusoidal waveform.

HARMONICS: Refers to components of the overall frequency, an integral multiple of fundamental sine wave frequency.
Harmonics are a recurring distortion of the waveform that can be caused by various devices including variable frequency drives, non-linear power supplies, and electronic ballasts. Certain types of power conditioners like ferroresonant or constant voltage (CVT) transformers can add significant harmonic distortion to the waveform.
Waveform distortion can also be an issue with uninterruptible power supplies (UPS) and other inverterbased power conditioners. The UPS does not actually add distortion, but because the UPS digitally synthesizes a waveform, that waveform may be square or jagged rather than a smooth sine wave.
Symptoms of harmonic distortion include overheating and equipment operational problems.

HERTZ: Unit used to measure frequency of alteration of electric current or voltage per unit time. Formerly CPS (Cycles Per Second) 1CPS=1Hz.

HID (High Intensity Discharge): An electric discharge lamp in which the light-producing arc is stabilized by the bulbw all temperature and the bulb wall loading is in excess of three watts per square centimeter. High intensity discharge lamp includes groups of lamps commonly known as Mercury, Metal Halide, and High Pressure Sodium.

HIGH PRESSURE SODIUM (HPS) 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.

HOT RESTART TIME: The time it takes an HID lamp to restart and reach 90% of its light output after going from on to off to on. Typical restart times are 1 to 2 minutes for High Pressure Sodium and 5 to 20 minutes for Metal Halide.

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.

HOUSING: The outer cover or shell of the ballast.

IEC: An international independent standards organization. IEC standards are almost exclusively used in Europe and are adopted by many countries as their national standards for product safety and performance.

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.

IMPULSIVE TRANSIENTS: Are sudden high peak events that raise the voltage and/or current levels in either a positive or negative direction. Most people refer to impulsive transients as a surge or spike. Causes of impulsive transients include lightning, poor grounding, the switching of inductive loads, utility fault clearing, and Electrostatic Discharge (ESD). Results range from loss or corruption of data to physical damage to equipment

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.

INITIAL LUMENS: The measure of the amount of light a lamp produces after it has been operating 100 hours.

INPUT VOLTAGE: Voltage provided by a power line or power supply to the ballast or driver.

INPUT WATTS: Total power consumed by lamp and ballast when the lamp is operated at rated wattage.

INTENSITY: A term referring to the magnitude of light energy per unit; light intensity diminishes evenly as you get further from the source.

INTERRUPTIONS: When the voltage drops below 10% of its nominal value it is called an interruption or a blackout. Interruptions have three classifications: momentary (lasting 30 cycles to 3 seconds), temporary (lasting 3 seconds to 1 minute), and sustained (lasting more than 1 minute).
Although interruptions are the most severe form of power problem, they are also the lease likely to occur. Voltage sags are often mistaken for an interruption because equipment shuts down or lighting goes off since the voltage dropped below the point that these devices can operate.
Where sags and under-voltage typically represent more than 92% of power problem events, interruptions represent less than 4% of such problems.

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.

KILOHERTZ (KHz): One thousand Hertz (cycles per second).

KILOWATT (kW): A unit of electric power usage equal to 1,000 watts.

KILOWATT HOUR (kWh): The standard of measure of electrical energy and the typical billing unit used by electrical utilities for electricity. 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 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.

LCL (LIGHT CENTER LENGTH): The distance from the light center to a specified reference point on the lamp.

LED (LIGHT EMITTING DIODE): LEDs are solid state devices that do not require the heating of a filament to create light. Instead, electricity is passed through a chemical compound that is excited and that generates light.

LED Grow Light: LED grow lights are solid state devices for horticultural lighting. They are composed of multiple light emitting diodes that output light with spectrum and efficacy higher than traditional HID lighting.

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.

LONG DAY PLANTS (LDP): A plant that flowers only after being exposed to light periods longer than a certain critical length, such as Summer.

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.

LUMEN DEPRECIATION: The decrease in lumen output of a light source over time. Also called Lumen Maintenance.

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.

MEAN LUMENS: The average light output of a lamp over its life, usually determined by the light output at 40% of rated life.

METAL HALIDE LAMP: 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.

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.

MOL (MAXIMUM OVERALL LENGTH): The largest outside dimension of a lamp. Typically MOL is measured from the end of the lamp base to the top of the outer jacket

NEC (NATIONAL ELECTRIC CODE®): A collection of electrical wiring specifications and standards developed by the National Fire Protection Association (NFPA), and adopted and used in all 50 states in the USA. This standard is accredited by ANSI and CSA.

NOISE: Noise is a high frequency distortion of the voltage waveform. Caused by disturbances on the utility system or by equipment such as welders, switchgear and transmitters, noise can frequently go unnoticed.
Frequent or high levels of noise can cause equipment malfunction, overheating, and premature wear.

NOTCHING: Is a disturbance of opposite polarity to the normal voltage waveform (which is subtracted from the normal waveform) lasting for less than one-half cycle. Notching is frequently caused by malfunctioning electronic switches or power conditioners.
While it is generally not a major problem, notching can cause equipment, especially electronics, to operate improperly.

OSCILLATORY TRANSIENTS: Is a sudden change in the steady state condition of a signal’s voltage, current, or both, at the positive and negative signal limits, oscillating at the natural system frequency (the transient causes the power signal to alternately swell and then shrink). These transients occur when you turn off an inductive or capacitive load, such as a motor or capacitor bank (similar to suddenly turning of water faucet and receiving a hammering noise).

PHOTOPERIOD: The duration of light within a particular time span, usually a 24-hour period. For example, a 12-hour photoperiod consists of 12 hours of light and 12 hours of darkness, whereas an 8-hour photoperiod consists of 8 hours of light and 16 hours of darkness.

PHOTOPERIODISM: The responses of plants to the relative length of the light and dark periods. Research has shown that it is the dark (or night) period that is more important than light (or day) period for controlling photoperiodic responses.

PHOTOSYNTHESIS: The growth process by which plants build chemical compounds (carbohydrates) from light energy, water and CO2 (carbon dioxide)

PHOTOSYNTHETIC PHOTON FLUX (PPF): Photosynthetic Photon Flux (PPF) is a unit of measure to express the light quantum in photons of solar energy ( or Photosynthetic Active Radiation (PAR) in the range of 400 to 700 nm) related specifically to photosynthesis and is measured with a quantum meter in units called micro-moles.

PHOTOSYNTHETIC PHOTON FLUX DENSITY (PPFD): The Photosynthetic Photon Flux (PPFD) calculation is: mol m-2 s-1(micro-moles of photons per meter squared, per second).

PHOTOTROPISM: The gravitation of a plant part toward a light source.

POWER FACTOR: The ratio of real power (watts) to apparent power VA (volts x amps). HID ballast power factor is classified into categories; High 9Pf≥0.90, and Normal or Low (PF<0.90).

PULSE START: Method of starting High Pressure Sodium and specific Metal Halide lamps in which a high voltage starting pulse starts the lamps.

QUARTZ: A high heat resistant glass-like material manufactured from pure silica sand. Quartz is used for the arc tube in Mercury and many Metal Halide lamp types.

REFLECTIVITY: The term sometimes used to refer to the reflective hood of an HID lamp.

REFLECTOR: The term sometimes used to refer to the reflective hood of an HID lamp.

SAG OR DIP: The American “sag” and the British “dip” are both names for a decrease in voltage to between 10 and 90% of nominal voltage for one-half cycle to one minute.
Sags account for the vast majority of power problems experienced by end users. They can be generated both internally and externally from an end users facility.
External causes of sags primarily come from utility transmission and distribution network. Sags coming from the utility have a variety of causes including lightning, animal and human activity, and normal and abnormal utility equipment operation. Sags generated on the transmission of distribution system can travel hundreds of miles thereby affecting thousands of customers during a single event.
Sometimes externally caused sags can be generated by other customers nearby. The starting of large electrical loads or switching off shunt capacitor banks can generate a sag large enough to affect a local area. If the end user is already subject to chronic under-voltage, then even a relatively small amplitude sag can have detrimental effects.
Sags caused internally to an end user’s facility are typically generated by the starting of large electrical loads such as motors or magnets. The large inrush of current required to start these types of loads depresses the voltage level available to other equipment that share the same electrical system. As with externally caused sags, ones generated internally will be magnified by chronic under-voltage.

SAG/UNDERVOLTAGE/BROWNOUT: Undervoltage is a decrease in voltage below 90% of its nominal value for more than one minute. Undervoltage is sometimes called a “brownout” although this term is not officially defined. Brownout is often used when the utility intentionally reduces system voltage to accommodate high demand or other problems.
The symptoms of undervoltage can range from non to daily equipment malfunction or premature equipment failure. Undervoltage may go unnoticed until new equipment is installed or the electrical system is otherwise changed and the new combined load depresses (see Sags) the voltage to a point where symptoms become apparent. Besides the obvious malfunction of equipment, chronic undervoltage can cause excess wear on certain devices like motors as they will tend to run overly hot if the voltage is low.
Undervoltage is generally a chronic problem aggravated by a number of factors beyond the end user’s control. Electric utilities try to maintain voltage levels delivered to customers at ±5%. However, factors like weather, high demand, and others can cause the utility voltage to fall within a ±10% range. Even under ideal conditions, most customers will see a drop in utility voltage levels over the course of the day as demand begins to increase around 8AM and peaks around 3 or 4PM.
Distribution system characteristics can also contribute to chronically low voltage situations. For example, customers at the end of a long line may be subject to a permanent voltage drop due to line losses on top of the utility voltage variations.

SEASONING TIME: The time required for a new operating lamp to reach a state of equilibrium where the electrical, light level, and color parameters stabilize. Typically, HID lamps obtain their rated performance after 100 hours of seasoning.

SHORT CIRCUIT: A short circuit (or “short”) is not normally considered a quality problem as much as it is a dangerous operational malfunction or fault. Short circuit refers to a condition where two “hot” lines are connected directly (or through a small impedance) or one “hot” line is connected directly to the ground.
A short circuit causes very high fault currents to flow through the wiring and all devices between the point of the short and the incoming power line. Left unchecked, a short circuit can very quickly lead to catastrophic overheating, melting and burning or wiring and devices.
The opening of a breaker or the operation of a protective fuse is the normal means of guarding against damage from short circuits. It is imperative that protective breakers and fuses be of the proper size and characteristics to avoid the dangers of short circuits.

SHORT DAY PLANT (SDP): A plant that flowers only after being exposed to light periods shorter than a certain critical length, as in early Spring or Fall.

SI UNIT: The International System of Units universally abbreviated SI (from the French Le Systeme d’Unites).

SPECTRUM: A linear representation of the different radiant electromagnetic wavelengths ranging from cosmic rays to radio waves.

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. The specular inserts included in PARsource’s HID lighting systems work on this principle.

STERADIAN: A unit solid angle on the surface of a sphere equal to the square of the sphere’s radius.

SWELL: A swell is the opposite of a sag – an increase in voltage about 1105 of nominal for one-half cycle to one minute. Although swells occur infrequently when compared to sags, they can cause equipment malfunction and premature wear. Swells can be caused by shutting off loads or switching capacitor banks on.

SYSTEM EFFICACY: Overall efficiency of the lamp/ballast system. System efficacy = total lamp lumens/system wattage.

THD (Total Harmonic Distortion): A measurement of all harmonics present in a circuit. The higher the number, the more stress is applied to internal parts, the lamp, and the power grid. Generally, a number below 10% is considered desirable in an electronic ballast application.

THERMAL PROTECTOR: A self-resetting switch that disconnects power to the ballast if internal temperatures rise above the trip point – typically 105ºC.

TRANSIENT: Potentially the most damaging type of power disturbance. Transients fall into two subcategories; Impulsive and Oscillatory.
Transients are very short duration (sub-cycle) events of varying amplitude. Often referred to as “surges,” transients are probably most frequently visualized as the tens of thousands of volts from a lightning strike that destroys any electrical device in its path.
Transients can be caused by equipment operation or failure or by weather phenomena like lightning. Even relatively low voltage transients can cause damage to electrical components if they occur with any frequency.
A properly sized industrial-grade surge suppressor is usually ample protection from the damaging effects of high voltage.

ta (Ambient Temperature): Maximum rated ambient temperature for the ballast area. Excessive ambient temperature can result in ballast failure, safety shutdown, or lamp failure.

tc (Case Temperature): Maximum temperature that the case of the ballast should reach. If the case temperature exceeds this number, the ballast may be malfunctioning, or the ambient temperature may exceed the rating.

UNDERWRITERS LABORATORIES (UL): Underwriters Laboratories Inc., is an independent, not-for-profit product safety testing and certification organization. UL has tested products for public safety for more than a century.

UV (ULTRAVIOLET) LIGHT: Radiant energy within the wavelengths to 100-400nm. UV energy is classified by IEC in three categories: UVA – 315 to 400nm (“Black Light”), UVB – 280 TO 315nm (Bacterial Sterilization), and UVC – 100 to 280nm (Ozone Producing).

VOLTAGE: Electromotive force or potential difference, usually expressed in volts.

VOLTAGE FLUCTUATIONS: A series of voltage changes or a cyclical variation of the voltage.

VOLTS: Volt (V) is the SI derived unit of electric potential. One volt is the difference of potential between two points of an electric conductor when a current of 1 ampere flowing between those points dissipates a power of 1 watt. It was named after the Italian physicist Alessandro Volts (1745-1827).

WARM UP TIME: The time from the initial establishment of an arc to 90% of the steady state full light output of the lamp.

WATT (W): A unit of power used to quantify the rate of doing work. In electrical calculations, 1 watt is the power produced by a current of 1 ampere across a potential difference of 1 volt. In addition, the radiant luminous-flux of a lamp is also expressed in watts. One watt equals one joule/second.

WAVEFORM DISTORTION: A steady state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation. See Harmonic Distortion.

WORKING VOLTAGE: The acceptable operating range for input voltage to the ballast. Deviations from the rated numbers may result in decreased ballast performance and additional case generated heat.