Terminology used with Horticultural Lighting Demystified.
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
||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
|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.
CRI (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
|HID Light||High Intensity Discharge
light such as a Metal Halide or a 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 and mercury 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
|Photosynthetically Active Radiation (PAR)||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
|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
|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
|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
|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|