Different crops have distinct lighting needs for optimal growth. Understanding these needs is crucial for a successful greenhouse and indoor growing operation. For instance, leafy greens like lettuce and herbs generally require lower light intensities, for these crops, minimal additional light could be sufficient. In contrast, fruiting plants like tomatoes and peppers need higher light intensities and a broader spectrum of light to support both vegetative growth and fruiting. For more specific details, visit the crop-specific grow light requirement guides linked here.
Greenhouse Grow Lights
Lighting greenhouse: Essential for growth
Grow Light Requirements in Greenhouses
Supplemental Grow lighting
In greenhouses, the main source of light is the sun. The availability of the sun differs over the year periods and even between days. To have more control on the plant development and production growers apply grow lighting in order to have a sufficient sum of light during a specific period. Normally this is measured in Daily Light Integral (DLI).
Plants have a requirement to light periods to optimize the photosynthesis process within the plant. You can choose whether the “day” (light) period is extended at the beginning or at the end of the day. Growers will have their own cultivation principles that must be supported with the lighting strategy.
Use of Steer light
Steer light is the supply of specific light colors (individually or spectra) to create a specific response at plant level that is not aimed at photosynthesis. This may be to determine the shape of the plant or to stimulate a process such as flowering or the opening of the stomata.
PAR Light, Micromols and DLI
In the greenhouse horticulture industry, the intensity of light being exposed to the plants is measured in micromoles per second, μm/s describing the number of photons at a specific surface.
DLI - Daily Light Integral
Daily light integral (DLI) is the total sum of PAR light received each day as a function of light intensity (referred to as μmol/m2/s) and duration (day). It is expressed as moles of light (mol) per square meter (m2) per day, or moles per day(mol/m2/d). The daily light integral is connected to grow models in order to justify the output per sum of light.
PAR & Light Spectrum
Plants have a specific light spectrum that influences photosynthesis within the plant. This range of light differs from the visibility through the human eye.
In general, the light spectrum being measured for plants is referred to as Photosynthetically Active Radiation (PAR) and includes wavelengths from 400 to 700 nm. However, other wavelengths outside this spectrum range can also have a significant effect on plant growth. Far-red is the spectrum above 700nm and induces the flowering and water uptake of plants increasing fruit generation in the crop and the fresh weight, where the other side UV (A-B-C) can also have a significant effect focusing on the production of dry matter increasing taste and shelf-life (product quality) of produce.
Recently, the use of Full Spectrum, Daylight Spectrum or Sunlight Spectrum is gaining interest in the greenhouse and indoor cultivation markets. These more general light spectra, all having small deviations focusing on energy and cost efficiency, can be applied to a wider range of crops and need less tuning from the grower.