Contemporary indoor cannabis cultivation usually involves at least one of three artificial light sources: HID, CFL, and LED, however, the LED industry for horticultural applications is growing rapidly due to the number of advantages it has. However, lighting for indoor cannabis growing has evolved dramatically in the last few years, with LED grow lights being a top choice for both professional and recreational cultivators.
“Light is made of particles called photons, a bunch of the electromagnetic field that carry a specific amount of energy at specific wavelengths,” explains Nico Cahna from InDorSun, therefore a light fitting is a photon delivery system.
Full spectrum LED grow lights for optimal results
Cultivators have been using natural light from the sun for years in greenhouses, although it isn’t always practical. This is where full spectrum LED grow lights come in as they mimic the sun’s natural light as closely as possible.
Light spectrum is the range of wavelengths produced by a light. “As growers, we’re most interested in the wavelengths that are relevant to plants,” notes Cahna. Plants detect wavelengths that include ultraviolet radiation (260–380 nm) and most of the visible spectrum which includes PAR (400–700 nm), and far-red radiation (700–850 nm). Full spectrum is what we are looking for. This includes all colours within the PAR zone.
Light spectrum impact on cannabis plant
Plants react to different spectrums, the ratio mix of different spectrums within a light is what makes the light different.
* Violet (315 -400nm): Improved THC and resin accumulation through defence mechanisms.
* Blue (400-500nm): Chloroplast and chlorophyll development, leaf growth, compactness, regulates response to shade and stress.
* Green (500-565nm): Early stem growth, small amounts promote growth, large amounts can aggravate the stomata and cause lower THC.
* Yellow (565-590nm): Mixed data, with the addition of yellow and green light, the result appears white to the human eye. Making it easier to identify and detect pests, pathogens and deficiencies.
* Orange (590-625nm): Little data available, some increased yields.
* RED (590-700nm): Improves leaf nutrients, chlorophyll production and healthier seedlings.
* Far RED (700-780nm): Improves plant cell development, increase in overall growth, regulates flowering, mediates stresses.
How to identify quality LED grow lights
As you continue to become an experienced grower and find new ways to improve your yield, it will benefit you to familiarise yourself with some acronyms for indoor plant growing.
What is PAR?
Photosynthetic Active Radiation (PAR) is the measure of total par that a light source produces; the total amount of light in the PAR zone that is produced by a light source is measured in micromoles per second or μmol·s-1.
When purchasing LED grow lights, PAR is an important consideration because the more PAR your light can produce, the more PAR available to plants, the better they will grow.
What is PPF?
Photosynthetic Photon Flux (PPF) is the term we use to define the measurement of PAR. Its underlying value determines how much PAR your LED grow lights can produce per second. The PPF measurement helps you understand how much of the light your fixtures are producing, which can be used by your marijuana plants for photosynthesis.
PPF is measured in micromoles per second or “µMol/s”, where one micromole is equal to approximately 602 quadrillion photons. Measuring your PPF properly requires a thorough understanding of the process and a little bit of mathematical subtleness and patience. And while there are PPF measurement tools that can be purchased from the open market, you might work with a trusted partner who can help you choose the perfect LED grow lights that are efficient enough to provide the desired PAR and PPF.
What is PPFD?
Photosynthetic Photon Flux Density (PPFD) is the third and final part of the PAR equation. PPFD is the intensity of PAR light that lands on a square metre each second. It is measured in micromoles per square metre per second (μmol·m-2·s-1) PPFD is how much PPF is hitting each square metre of your crop at any given second.
How much PPFD is needed to grow cannabis?
The average cannabis plant in a regular ‘home-scale’ operation requires a PPFD of 100-300 μmol/m²/s during the seedling phase, 400-600 μmol/m²/s during the vegetative stage, and 800-1,000 μmol/m²/s during the flowering period. These are just baseline values for food photons that are needed to grow a strong and healthy plant.
Each marijuana plant has a genetic saturation point, after which PPFD’s benefits start to taper off. It is wrong for growers to assume that the more PPFD they have at their disposal, the better and generally higher the yields – this simply isn’t true because more PPFD does not always translate to ‘more plant’. Also, giving your plant too much full-spectrum light at specific growth phases can lead to a higher risk of plant health problems, such as nutrient burn, water deprivation, and light burn.
Distance from the plants
As a recap, PAR is the portion of the visible spectrum light that plants can “see” and effectively use for the photosynthesis process, right? This occurs within the 400nm to 700nm range. PPFD measures how much PAR your plant can receive over time (light density that the plant will receive). PPFD can be visualised in a way similar to how the sun ‘pours’ light onto plants – the leaves suck up energy as the sun bathes them with its light.
PPFD is a critical metric to consider when we talk about the distance of plants from different-powered LED lights – it allows you to accurately measure the light intensity of the photosynthesis process at the roof level. So, for example, if you place your LED grow lights too close to the plant’s surface or canopy, you can cause stunted growth, bleaching, and even discoloration.
Generally speaking, LED grow lights need to be closer to your canopy for the vegetative and flowering stages; therefore, as the light source moves closer to the canopy, the light intensity increases. For seedlings, LED grow lights should be no lower than 0.9m to 1.5m, although these are just baseline values, as the power or wattage of the light source influences the values. Most LED lights have a dimming function, so growers keep it at a minimum and increase it gradually over the following weeks.
If you keep your LED grow lights at the highest range this will keep the light intensity levels from being overbearing and prevent the seedlings from drying out. Once they have taken root and the sprouting begins, you can move the lights closer in the first 2-3 weeks and/or increase power using the dimming function.
Your lights can be anywhere between 0.3m and 0.6m above the plant canopy in the vegetative and flowering stages. At this point, you need more light for photosynthesis to take place, so your LED grow lights will need to be closer to the plants, naturally.
LED grow lights beam angle
Equally important is the beam angle of your LED grow lights. For example, at a 120° angle, your lights will cast a wider net or coverage, which is ideal if you want to fit as many plants as possible within a specific coverage area. With that said, since 120° casts a broader net, it is not as concentrated as, say, a 90° or 60° angle. This means that light will not penetrate the lower levels of your plant very well because the wider your beam is, the lower the intensity will be.
Next issue we will delve deeper into the science behind horticultural lighting.
InDorSun
InDorSun is a proudly South African LED manufacturer whose founders originated from the solar and PV industry developing energy efficient solutions for a wide variety of industries. With manufacturing partner Giantlight, InDorSun have shone the light on cannabis horticultural lighting. Together the companies manufacture LED grow lights which produce full-spectrum light that replicates the colour of the sun.
Giantlight
Giantlight is at the forefront of lighting technology – specifically solid state lighting and everything relating to LEDs and special effects. The company strives to remain the market leader in new and innovative lighting applications and continually brings new products to the market first. From design through manufacture and installation, Giantlight projects make a visual statement. Giantlight offers a comprehensive effect lighting solution.
Enquiries: www.giantlight.co.za
