There was a time when choosing a grow light was simple, all you needed to know was what brand and wattage you wanted. Things have changed drastically. The market has been flooded with grow light options and it can be quite challenging to figure out which light is best for you.
When it comes to making the decision nowadays, it's important to understand what spectrum and intensity a light produces. In this article InDorSun and Giantlight will cover why these are important and how they relate to growing cannabis.
Light spectrum is the range of wavelengths produced by a light’ When choosing a spectrum of light for growing plants, two main factors should be weighed:
Photosynthesis: You need to choose a light that caters to the energy production of your plants. The light that plants predominantly use for photosynthesis ranges from 400-700 nm.
This range is referred to as Photosynthetically Active Radiation (PAR).
Photomorphogenesis: ‘Photo’ means ‘light’, ‘morpho’ means ‘shape,’ ‘genesis’ can be translated as ‘creation of.’ So, it’s using light to create a certain plant shape. Light can do a lot more than just change the growth pattern of a plant, though. It can trigger or delay flowering and fruiting, change chemical composition, among other diverse reactions.
In the InDorSun fixtures, the company uses full spectrum white diodes, which produce light within the 400-700 nm range, this is the range mentioned above known as PAR and is the range plants use for photosynthesis. It also uses far-red diodes, which produce light at 730 nm, which contributes toward how plants use light for photomorphogenesis but also regulate a secondary photosynthesis process known as ‘The Emerson Effect’.
While there is no doubt that the light spectrum is important, some studies suggest that even more important than the spectrum is light intensity. There are two ways of measuring the intensity of a grow light:
PPF: PPF (Photosynthetic Photon Flux) measures the total amount of light produced by a grow light in terms of micromoles of photons produced per second (often written as umol/s or μmol/s). This is an important number because unlike PPFD (which will be explained below) it can’t be manipulated and tells you the full amount of light coming from the LED grow light.
PPFD: PPFD (Photosynthetic Photon Flux Density) measures the amount of micromoles of photons striking a square meter per second (often written as umol/m2/s, μmol/m2/s, or μmolm-2s-1).
Full daylight sun at noon in the summer is around 2000 μmol/m2/s. What your plants actually need, however, is likely to be much less than that. In fact, because the sun’s intensity is only that bright for a small portion of the day and because the angle of that intensity changes throughout the day, providing that much light for an extended period of time would very likely be damaging to your plant. A ‘light response curve’ shows how effectively a plant utilises light at differing intensities. Depending on the plant, at levels greater than 800-1000 μmol/m2/s the efficiency that a plant uses the light starts to slow. Meaning, you can provide your plant more light than this, but you might not see a huge change in outcome.
When setting up your indoor cannabis grow, it is recommended that you start by thinking about the yield that you would like to be able to harvest each cycle. Light levels or PPF and PPFD are very important to know because different stages of a plant's growth require different levels of light for plants to grow optimally.
When the light is insufficient for the space, it can result in lower quality cannabis and more work trimming. Large plants that receive inadequate light will produce a lot of low-quality buds that we call ‘larf’. Many growers mistakenly think that larf is the result of budding sites not receiving light. In reality, larf is the result of a plant that, in total, has more budding sites than energy to develop them. If the plant is receiving less than optimal light and has a large number of budding sites, it will produce larf.
It is even more important to avoid giving the plants too much light. There is a limit to the amount of light a plant can use, and excessive light will cause damage. If you have too much light, you could avoid damage by raising or dimming the light. Raising the light wastes energy and reduces efficiency. If you must dim the light, then you are not taking full advantage of your investment. In either case, you would save money and be more efficient if you had lights that were properly matched to the space.
The ideal PPFD levels during flowering are between 600-900 µmol (PPFD) for indoor cultivation spaces and there should not be any spots on the top of the canopy that are receiving less than 500 µmol (PPFD). Plants that receive less than 500 µmol (PPFD), will produce smaller buds with more ‘larf’ or less-dense and leafy buds when compared to flowering cannabis plants that receive ideal PPFD levels. Many growers may try to add more light than necessary to an indoor grow space to provide as many photons of light to their plants, but there is also a limit to the density of photons that cannabis plants can use.
Larger cannabis plants can handle higher levels of PPFD, up to 1500 µmol (PPFD), if enough supplemental CO2 is applied to the grow space on a consistent basis and additional environmental factors such as temperature and relative humidity are also optimal. Their light intake can be somewhat limited by the amount of ambient CO2. If PPFD levels exceed 2000 µmol (PPFD) indoors, then it is possible that the quality and quantity in yields could be diminished in extreme cases. Excessive levels of PPFD can eventually lead to plant tissue damage.
As mentioned before, Different stages of the plant's growth require different Levels of light. In order to control the PPFD that a plant receives, a grower can do one of two things: the first way to adjust the light a plant receives is by lowering or raising a light. By lowering a light toward the canopy - the light becomes more intense the closer it is to the canopy. The higher the light is raised the less intense or powerful the light becomes, lowering the PPFD at canopy.
The second way of changing the PPFD of a light would be to have a light which has a dimming function which allows you to control the output of the light, this essentially controls the wattage that the light uses also.
As discussed before, each stage of growth requires different levels of PPFD
* 75-150 µmol/m²/s for the cutting stage which could last between 14-30 days.
* 100-300 µmol/m²/s for the seedlings stage which could last between 14-30 days.
* 300-600 µmol/m²/s for the vegetative stage which could last between 14-30 days
* 600+ µmol/m²/s for the flowering stage which could last between 60-90 days.
If we look at the PAR maps of InDorSun’s 1 m comet fixture we can see at which heights to hang this light for each stage of growth, The PAR map shows how much PAR the plant canopy will receive when the top of the plant canopy is positioned at the same height as the simulated canopy.
The first height at 1 m shows us that in the centre of the 1 m square at 1 m height we are receiving 135 µmol. On the outer edges of the square, we are receiving between 99-120 µmol. The second height at 0.5 m shows us that in the center of the 1 m square at 0.5 m height we are receiving 298 µmol. On the outer edges of the square, we are receiving between 101-135 µmol. These are good measurements to use for the seedling and clone stages.
The next height at 0.3 m shows us that in the centre of the 1 m square at 0.3 m height we are receiving 509 µmol. Although this is within the ideal range for the vegetation phase of a plant's growth, on the outer edges of the square, we are receiving between 337-39 µmol, this is within the ideal range for vegetation; however, on the lower sides at 39 µmol a grower will have to add additional comet lights to create uniformity across the canopy.
The reason the top and the bottom of the PAR map display higher ranges than the left and right is because of the shape of the light, the rectangular shape of the light carries through the simulation of the par map as the centre line from top to bottom show the higher values.
The next height is at 0.2 m and shows readings that are within the range for flowering cannabis plants where the centre shows us readings between 714-728 µmol and the outer edges show us readings between 487-30 µmol a grower will have to add additional comet lights to create uniformity across the canopy or the entire square metre.
Enquiries: www.giantlight.co.za
