Horticultural Lighting Glossary

refers to a horticulture operation that aims to maintain optimal growing conditions throughout the development of the crop while protecting the crop from outside elements such as weather, pests, contaminants, etc. Production takes place in an indoor facility like a greenhouse or indoor vertical farm.

grants CEA growers the precise control over indoor atmospheric and thermal conditions—such as temperature, humidity, airflow, and CO₂ levels—within their enclosed CEA facility to ensure optimal growth of their crops. Some popular climate control systems include Priva, Hoogendoorn, Argus, Wadsworth, and Ridder.

means you can adjust the intensity of the light. Most modern single-channel and all multi-channel LED fixtures are dimmable, using 0-10V dimming, the Horti Lighting Protocol (HLP), or DALI dimming protocols.

is a two-terminal electronic component that acts as a one-way valve for electricity. It lets current flow easily in one direction, but blocks it from going the other way. Most modern diodes are made of semiconductor materials like silicon.

Refers to the cumulative amount of PAR light received in a 1 square meter (10.8 sq. ft.) area each day represented as mol/m²/day – it is a function of light intensity and duration. DLI has become an important tool for managing the light environment to optimize crop growth. A grower can think of DLI as the plant’s daily light dose. DLI is positively related to photosynthesis, growth rate, and overall plant productivity. The units for DLI are similar to that of PPFD. However, rather than being an instantaneous measurement, DLI extends over an entire day – much like how you would measure rainfall over a day. DLI naturally changes with the seasons, leading to higher DLIs in the summer and lower values in the winter. DLI can be increased with the use of supplemental lighting during low light times of the year.

Daily Light Integral maps show the average outdoor daily light integral (DLI) for a given location throughout the year. These maps are valuable for estimating how much supplemental light you will need to reach your desired DLI. The DLI inside the greenhouse will obviously be lower, and the transmission percentage will depend on factors such as glazing, structure, shade cloth, etc. To estimate the DLI inside your greenhouse, you can multiply the outdoor DLI by the transmittance rate of your glazing. An interactive DLI map is available at dli.suntrackertech.com.

is a deliberate loop or U-shaped dip in a communication or electrical cable that prevents fluids from travelling up the cable into the electrical connector, panel, building, or outlet.

or tunable lighting, means you can manipulate the spectrum, changing the ratio of red, blue, white and far-red light reaching the crop. This requires independently driven channels of different colours, which in practice means a four-channel fixture.

refers to the entire assembled lighting unit. This includes the lamp or LED source, the housing, the ballast, the wiring, the sockets, and any parts used to direct, distribute, or protect the light source such as reflectors or lenses. Also referred to as a luminaire.

lamps use an electric arc between two electrodes to produce an intensely bright light. Mercury, sodium, or metal halide gas acts as the conductor. Lamps in this category are high-pressure sodium (HPS), metal halide (MH), and ceramic metal halide (CMH).

is a rating given to electronic devices indicating their level of protection against dust, water, and vapor penetration. IP ratings are written in the format IPXY. “X” is the light fixture’s protection against the penetration of dust and other particles and can be any number between 0 and 6, with 0 being the least protected and 6 the most protected. “Y” is the light’s protection against water and moisture penetration. Y ranges from 0 to 8, with 0 being the least protected and 8 being the highest protected.

in a horticultural context, refers to an artificial light source designed to promote plant growth by emitting electromagnetic radiation–specifically photosynthetically active radiation (PAR). Horticultural lamps are available in a variety of different types including high-pressure sodium (HPS), light emitting diode (LED), or fluorescent.

(L_xB_y) is the standardized method to indicate the allowable depreciation (x) of an LED module within a specified number of burning hours. This rating also presents the percentage (y) of LED modules, of the same type, that are acceptably able to degrade to, or below, the LED module depreciation allowance (x) for light output. This rating is an industry standard for manufacturers’ warranties on all LED lighting.

are semiconductor devices that produce visible light when an electrical current passes through them. LEDs are a type of Solid State Lighting (SSL).

are units of measurement based on how humans perceive light intensity. Since humans are more sensitive to green light and not blue and red (which are the colors plants respond most strongly to), these measurements do not accurately measure light within the PAR region and should not be used as metrics for horticultural lighting.

refers to the entire assembled lighting unit. This includes the lamp or LED source, the housing, the ballast, the wiring, the sockets, and any parts used to direct, distribute, or protect the light source such as reflectors or lenses. Also referred to as a fixture.

A micromole (µmol) is one-millionth of a mole (1×10^-6). The measurement µmol/m²/s is a measurement that counts the number of µmol photons in the PAR range that reaches one square meter each second.

A mole is a unit for measuring very small entities such as atoms, molecules, and photons. A mole represents a very large constant number (6.02 x 10²³)

lighting systems enable precise, real-time adjustment of light intensity and, in some configurations, the light spectrum itself, in response to the plants’ needs, natural light levels and even demand on the electrical grid. Multi-channel systems are also more technologically complex than fixed-spectrum lighting.

is the practice of providing low-intensity (~2 µmol/m²/s) photoperiodic lighting to plants during the middle of the night. The plants will not perceive a long night but a short night (long day) instead. NI lighting is typically used during the middle of the night because that’s when plants are most sensitive to light. NI lighting can be used to promote flowering in long-day plants or keep short-day plants in a vegetative growth phase.

represents the wavebands of light between 400-700 nanometers (nm) that drive photosynthesis. The reason PAR falls between these wavelengths is that photosynthetic pigments absorb light energy within this range. For example, chlorophyll in the leaf has an absorption pattern that peaks in the blue (400-500nm) and red (600 700nm) wavelengths. Increases in PAR light will enhance the light reaction of photosynthesis until it reaches a saturation point. Beyond that point, any further increases in PAR will not result in more photosynthesis. This will vary by plant species, as shade plants can harvest PAR more efficiently at low light levels but less efficiently at high levels compared to sun plants.

refers to the finished board following the process of mounting or soldering electronic components onto a bare printed circuit board.

A particle of light energy.

is the daily hours of light and darkness that a plant receives. Many plants have a flowering response that corresponds to the number of light hours in 24 hours, referred to as photoperiod. However, it is the uninterrupted period of darkness that controls the flowering responses in plants. Plants can be divided into short-day, long-day, and day-neutral varieties. Short- and long-day species have developmental responses relative to the lengths of light and dark periods. For example, a chrysanthemum plant (a short-day plant) will only initiate flowering when days are short and nights are long (more than 12 hours).

is the PAR output of a light source measured in micromoles per second divided by the input power (watts) to produce that light. The higher the PPE value, the more effective it is at converting electricity into photosynthetic photons. PPE is measured in micromoles per Joule (µmol/J) and provides insights into how efficient a light source is at converting watts into photons. For example, the NXT2 double-ended HPS luminaire measures an efficacy at 2.1 µmol/J, whereas the ParFX Ultra Max has an efficacy of 4.4 µmol/J.

represents the total amount of PAR produced by a light source per second, expressed as micromoles per second (μmol/s). PAR is an important measurement when comparing luminaires.

is an instantaneous (spot) measurement of the amount of PAR that is distributed to and arrives at the crop canopy. PPFD is measured in micromoles per square meter per second (μmol/m²/s). This is important because you need to know how much light is being distributed at the crop level from the sun and/or grow lamps to ensure plants are receiving the correct amount of light to hit your target DLI.

of the Design Lights Consortium (DLC) is the largest verified list of high-performing and energy-saving LED lighting solutions in the world. Qualified products undergo thorough vetting and review by DLC experts to ensure they meet our rigorous energy and quality requirements.

refers to the colors/wavelengths of the electromagnetic spectrum. Light quality, also known as photomorphogenesis, influences plant morphology and development. These responses can include germination, flowering, and leaf expansion.

refers to the amount of light available to the plant and can influence yield, taste, and quality. In general, as intensity increases, photosynthesis and crop growth increase up until a certain point―known as the saturation point. Past this point, additional light intensity will not increase plant growth.

is a term to describe the lighting of plants that do not receive light from the sun. This generally refers to warehouses and other indoor applications. It is therefore only artificial lighting that provides the sole source of light for plant growth and development.

refers to the complete delivery of artificial electric lighting to crops growing in an indoor facility where they receive zero natural sunlight.

is used in greenhouses to increase crop production during periods of low light intensity to increase plant growth. In supplemental lighting applications, it is both the sun and the luminaire that provide light to the plants.

is a measurement of the harmonic distortion present in a signal and a critical factor in planning electrical design of a lighting system. In power systems, lower THD implies lower peak currents, less heating, lower electromagnetic emissions, and less core loss in motors.

refers to how much sunlight—or more specifically, PAR—passes through your greenhouse covering (such as glass, polycarbonate, or polyethylene film) and reaches your crop. It’s typically expressed as a ratio or percentage comparing the light levels outside the greenhouse to those measured inside, at crop canopy height. A higher transmissibility means more sunlight is reaching your plants, while lower transmissibility can limit light intensity and overall plant growth potential.

or dynamic, means you can manipulate the spectrum, changing the ratio of red, blue, white and far-red light reaching the crop. This requires independently driven channels of different colours, which in practice means a four-channel fixture.