Horticultural Glossary


LEDs are producing revolutionary advancements in many areas of technology and life, but none more so important than in horticulture. The complexities and knowledge required is growing daily, with different plants requiring different spectral illumination and control.

To help improve your understanding of this rapidly growing market, this glossary has been developed to provide a basic understanding of the terminology. Check out our newsroom where we will be publishing more detailed articles explaining the concepts and terms referred to below.

LEDs are producing revolutionary advancements in many areas of technology and life, but none more so important than in horticulture. The complexities and knowledge required is growing daily, with different plants requiring different spectral illumination and control.

Whether you’re a grower, researcher or designing your own custom grow lights, IHS is your perfect system integrator for horticultural LED lighting. If you need plug and play LED grow lights to start your project, check out or Ready to Grow range. If you need advice on the best light recipe for your project, please get in touch.

To help improve your understanding of this rapidly growing market we have created a glossary of key horticultural terms.

This glossary has been developed to provide a basic understanding of the horticultural LED lighting market and terminology. Check out our newsroom where we will be publishing more detailed articles explaining the concepts and terms referred to below.

If however, you’re already well-apprised of the terminology below, you may be interested to learn about PHYTOFY RL, a 6-channel tuneable LED lamp. OSRAM has developed this high-spec lamp with NASA for horticulture and further research purposes.


Biomass refers to a light recipe most conducive for the growth of leafy plants and crop types. IHS recommend a general recipe of 85% Hyper Red and 15% Blue light for this plant type.

Biological Photon Flux (BPF) refers to quantity of photons emitted by a lighting system per second in the range of 280-800nm. (See photons below).

Correlated Colour Temperature (CCT) shows the colour appearance of an LED measured in Kelvin (K). Warmer colours tend to start at 2700K, with the more neutral whites at 4000K and then colder whites at 5000K or higher.

Centroid wavelength can be determined directly from the ratio of quantum and radiant flux values. Defined as the centre of the spectral power distribution.

Chlorophyll are the cells in a plant that are primarily responsible for photosynthesis. They tend to be great absorbers of red and blue light. (See photosynthesis below).

Chromaticity refers to the quality of colour, determined by its dominant wavelength and regardless of the brightness. Typically, it is specified as hue (h) or colourfulness (s). (see wavelength below).

The CIE colour model is a mapping system that uses a combination of 3 colour values that are close to red/green/blue, also known as tristimulus values, which are plotted on a 3D space. When these values are combined, they can reproduce any colour that a human eye can perceive. The CIE specification is supposed to be able to accurately represent every single colour the human eye can perceive.

A colour that will hold its colour and remain visible despite its surroundings. Established in several ways – use of colour, strength of hue, sharpness, contrast and perception of colour.

Cultivating and growing plants in conditions were there is no available daylight, and so instead uses LED lighting that fully replaces the daylight with artificial light, enabling full climate control.

A dominant wavelength is defined as the single wavelength that is perceived by the human eye. One light source consists of multiple wavelengths. Our eyes receive and turn those multiple wavelengths into a single colour of light that is consistent with one wavelength. This colour we register is the light source’s dominant wavelength.

Etiolation is the abnormal shape of a plant that forms when a plant grows in the direction of an unmoving light source.


The process of a tree or other plant producing fruit. IHS recommend a general light recipe of 70% Hyper Red, 20% Neutral White and 10% Far Red.

An IHS horticulture Ready to Grow LED light, designed for mid-power usage in polytunnels, small scale greenhouse and research purposes. Currently available with supplemental and non-supplemental daylight versions of Biomass, Seeding, Flowering and Fruiting.


The phase of growth where flowering occurs, this is one of the major phase changes a plant will make. For this stage of growth IHS recommend a general light mix of 60% Hyper Red, 20% Far Red and 20% Deep Blue.

Light that covers the whole light spectrum, sunlight is considered to be full spectrum light and is ideal for plant growth.

An IHS Horticulture Ready to Grow LED light, that has been designed for highbay illumination. Soon to be available with LED light recipes for Biomass, Seeding, Flowering and Fruiting.

Germination is the process by which a plant grows from a seed. It is also known as sprouting of a seedling from a seed.

Inter-lighting is a set-up for plants, where the lighting is placed between the plant and leaves. This gives a greater spread and uniformity of lighting.

Irrigation is the provision of water to plants/crops, in order to aid growth. This can be done via the surface, sprinklers, or via a drip.

Light Emitting Diode, LED, is a semiconductor light source, that emits light when a fitting voltage is applied to it. They are available in many different colours, sizes, and materials.

A light engine is the LED equivalent of a conventional lamp, normally consisting of a LED chip mounted on a PCB which is ready to be fixed within a luminaire.

A light recipe is designed to stimulate plant growth by emitting a combination of specific light wavelengths that are appropriate for photosynthesis, and promote a particular stage of plant growth. E.g. seeding, flowering, fruiting, or biomass.

A measure of the total quantity of visible light emitted by a source per unit of time.

Luminous intensity is a measure of the amount of light an LED radiates in a given direction at a solid angle, per unit of time. It is measured in candela (cd).

Lux is the Latin word for light, it is equal to one lumen per square metre.

A metamerism indices is a single number index that measures how well a sample will match under 2 different light sources.


Multilayer lighting is a set-up for plants typically within a growth chamber, where plants are stacked similar to a vertical farm, and horticultural lighting is implemented on each level.

Micromoles refer to the number of photons or ‘light particles’ in visible light. The micromole is equivalent to a millionth of the unit mole. (See photons below).

A nanometres (nm) is the measurement of the colour of light emitted by either the natural or artificial source. Each colour wavelength on the spectrum has a nanometre value. For example, blue is approximately 450nm and red is approximately 650nm.



Photosynthetically Active Radiation (PAR) is the radiation between 400nm and 700nm, this is the region considered most useful for plant photosynthesis.

Peak wavelength refers to the wavelength at which the spectral radiant intensity of the source is at its maximum.

Photon Flux (PF), is the quantity of photons emitted by a lighting source per second. (see photons below).

Photometry is the measurement of light, in terms of the perceived brightness to the human eye.

Photomorphogenesis is the process by which plants grow and develop in response to light signals.

A photon is the smallest discrete amount of electromagnetic radiation that transmits light. It is the basic unit of all light.

Photon flux refers to the number of photons in a spectral range per unit of time.

Photoperiodic lighting is when the periods of light emitted are controlled by extending the natural day length with artificial light.

A process used by plants and other organisms to convert light energy into chemical energy that can be later released to fuel the organisms’ activities. For the photosynthesis, the blue and red-light spectral regions are considered to be most important.

Phytochromes are photoreceptors that are part of a plant’s structure, which are used to detect light. A phytochrome’s main function is to regulate light received and the various developmental processes of the plant.

PHYTOFY RL is a research lamp from OSRAM. It has been developed alongside NASA, and created with 6 tuneable LED channels, that are individually controllable through a MOXA unit and a laptop.

A PowerStar is a LED light engine in the shape of a Star, this can also be known as a HEX board.

Photosynthetic photon flux (PPF) are photosynthetically active photons emitted by a lighting system, and measured per second in the range of 400-700nm. (see photon above).

Photosynthetic photon flux density (PPFD) is the radiation and number of photons between the range of 400nm and 700nm, that land per second on a target area, measured per square metre.

Pick Your Own is an online tool developed by IHS, that allows customers to fully customise an LED module to suit their application, or unique light recipe. Users can choose the size of the PCB board and select the colour and location of the LEDs.  Available for low MOQs and short lead times.

Radiometry is a set of techniques used to detect and measure electromagnetic radiation across the total visible spectrum, a key measurement in ultra-violet and infra-red.

Rendering indices, also known as CRI (colour rendering index), is a value used in lighting to indicate the quality of a light source that the human eye can see. The higher the number, the better the colour is deemed to be.

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Seeding is the early stage of a plant’s growth, primarily from a seed and not a cutting. IHS recommend a general light recipe of 85% Deep Blue and 15% Hyper Red for seeding plants.

A spectrum refers to a band of colours emitted by a light source; these are measured in nanometres (see nanometres above). Different wavelengths on the illumination spectrum have different effects on plants.


Stem elongation is the rapid growth of the length of the upper stem, before the reproductive phases of the plant starts. To encourage stem elongation far red is best, as it triggers the plant into a shade escape reaction, causing it to gain height quickly.

Supplemental lighting is where LED lighting is used to supplement existing natural daylight, by offering a few key wavelengths, rather than working to replace the daylight.

Top lighting is a set-up for plants where the light source is above the plants so they are illuminated from above, similar to sun light.

Urban farming involves cultivating, processing, and distributing food all within or around urban areas.

Vegetative growth is the period between germination and flowering.

Vertical farming is a method of producing crops in vertically stacked layers and/or integrated into other structures.

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