Tech Terms Explained

Terminology used with Horticultural Lighting Demistified.

Technical Terminology Explained

Every industry has its own terminology specific to its work.  Here we have collected some of the most commonly used technical terms and acronyms used in connection with horticultural lighting, and attempted to explain them in plan English (with citations where they are available).

Many vendors of Plant/Grow lights refer to the number of 'bands' in their lights.  They mean the number of different wavelengths of LEDs that are used in the lights. For example: the most basic LED grow lights usually have only 2 to 4 bands. This means that there are usually either one band (wavelength) each of blue or red LEDs (dual band or 2 bands), or 2 different wavelengths of blue LEDs and two different wavelengths of red LEDs (quad band or 4 bands).
CCT See Correlated Colour Temperature
COB Chip On Board - A format of LED where a number of LED dies (which can be the same wavelength, or different wavelengths) are mounted onto a holder with electrical terminals, or onto a spectral purpose aluminum PCB, and connected together in a series/parallel arrangement, making a compact and convenient light source.
Colour Rendering
This is a measurement of how well a light source reveals the colours of various objects under the light source, compared to an ideal light source. It is given as a number with 100 being the best possible. It is important to human vision but irrelevant to plants.
DLI Daily Light Integral is defined as the amount of PPFD received by plants each day as a function of light intensity (instantaneous light: μmol/m2/s-1) and duration (day).
Emerson Effect When plants are exposed to 670 nm and 700nm light simultaneously , both wave lengths together increase the rate of photosynthesis.
HID Light High Intensity Discharge light such as a Metal Halide or High Pressure Sodium light
High Pressure Sodium (HPS) light A type of HID light that uses sodium and mercury to produce light. It appears to have a yellowish /pink colour. It is popular for growing plants as it's a well established and cheap technology. And is often used in combinations with MH lamps. The spectrum is made up of mostly green and yellow light, and is deficient in blue and red light.
Light Emitting Diode (LED) Light Emitting Diode - a solid state device that produces light when a current is passed through it
Lumens Light energy for humans is measured in Lumens using the CIE luminosity curve, with light falling onto a surface measured as illuminance with units of lux (lumens per square meter) - Lumens are for Humans, PAR/PPFD are for plants!
Lumens/Watt (L/W) A measurement of how many lumens are produce by a light source per Watt of electrical power input (applies to lighting for humans, not plants)
Metal Halide (MH)
A type of HID light that uses metal halides to produce light. It appears to have a whiteish colour but it produces mostly yellow/orange light, but has more blue and UV than HPS lights. Popular for growing pants as they are cheap, and often used in combination with HPS lamps.
Micromole (μmol) A measure of the number of photons emitted from a plant/grow light. It enables you to determine how much light is falling onto a given area (PPFD).
Photosynthetically Active Radiation
Photosynthetically Active Radiation is the light that falls between  400nm and 700nm in the visible spectrum. When absorbed by plants, wavelengths of light within the (human) visible range of 400nm to 700nm, provides the energy to drive photosynthesis.
PAR Meter See Quantum Flux Meter
PAR/PPFD PAR and PPFD numbers are often used interchangeably with discussing the measurement of the output of plant/grow-lights.
Photon Efficiency The Photon efficiency of a grow-light system informs you of how efficient that system is in converting electrical energy into PAR light (between 400nm and 700nm).
PPF Photosynthetic Photon Flux which is given in μmol/s (micro moles per second). Its the total amount of PAR light (400~700nm) produced by a lighting system per second.
PPFD Photosynthetic Photon Flux Density. PPFD is expressed in μmol/m2/s (micro moles per square metre, per second) and is Light within the PAR range of 400~700nm, falling onto the plants per second.
PPFD Spectrum A measurement of the spectrum of a light source made in accordance with PPFD - the way plants "see/experience" light. The PPFD spectrum of a light will show less blue light and more red light than a standard/normal spectrum, but it is a better way to predict photosynthesis.
PPFD/Watt A simple method of comparing horticultural lights output. If the manufacturer(s) provides the (average) PAR/PPFD at the same distance from the light source, and the actual wattage (wattage draw from the power source/wall) then you can divide the PAR/PPFD by the watts drawn, and compare it with another light (if you have the PAR/PPFD at the same distance and the wattage draw).
Quantum Flux Meter Also known as a PAR meter. A meter designed for measuring PAR. It usually has a fairly flat response between 400nm and 700nm.
Standard Spectrum/Normal Spectrum A measurement of the spectrum of a light source made in accordance with the way humans see light. This is the most usual type of spectrum provided by horticultural lighting manufacturers (see also PPFD Spectrum).
Yield Photon Flux Density (YPFD) Yield Photon Flux Density is a measurement that quantifies PAR/PPFD in terms of energy rather than photons This measurement is spectrum dependant as different wavelengths have different energy densities.
μmol/J Micromoles per Joule - The standard for measuring grow/plant light efficiency in the professional horticulture industry is μmol/J. This quantifies the efficiency of the grow/plant light in terms of micromoles (PPFD) per Joule (unit of electrical energy) and is similar to Photon Efficiency