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There are more than 3000 organisms that can grow without photosynthesis. All of them are either fungi or parasites. Cannabis does not fall in either of those categories. This means that light plays a big role in the cultivating of cannabis and choosing the right lighting can make or break your crop. In this article, we look into the influence of light in cannabis cultivation.

South Africa, Thailand, Afghanistan and a few other countries have a rich history of cultivating cannabis, Sweden for example does not. One of the reasons that certain parts of the world have historically been the best places to cultivate cannabis, is because of sunshine. Sunshine is one of the most important factors when cultivating cannabis and seeing that a lot of cannabis is cultivated in places where theoretically it shouldn’t be, we have to help nature on a bit with certain modern inventions. Such as using lights to cultivate your crop.

The reason your crop and most other plants need light is because of photosynthesis. Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular metabolism, can later be released to fuel the organism's activities. This of course means that if there is no light, there is no crop.

As with most other aspects of cannabis cultivating, there are lots of opinions on how to do this and a lot of those opinions differ from each other.

So, in order to give you all the options and help you make a decision that suits your goal as well as your pocket, we have done our research and we also talked to Jörg Meyer-Brenken, Lead Account Manager for Cannabis at Fluence. The company creates LED lighting solutions for controlled environment commercial crop production, is the leader in cannabis lighting with over 55ha installed base and active in 95% of legal cannabis countries worldwide.

The use of lighting in cultivating cannabis can be split up into several separate sections, we look at light intensity, the photo period, the spectrum, light technology and the long-standing debate of natural versus artificial light.

Light intensity

Cannabis is a very strong and resistant plant that grows everywhere. It’s not called weed for nothing. At Chernobyl they are using hemp to clear the soil from the radio activity that was spilled there. It is a proven fact that the more light you give the plant, the bigger the yield and this is not just with cannabis, it’s with every plant. The horticulture rule of thumb is: 1% additional light results into 1% additional yield. That relationship was first discovered growing tomatoes in greenhouses in the Netherlands. With High Pressure Sodium Light (HPS) the traditional PPFD (photosynthetic photon flux density) limit sits around 1000 µmol/m²/s. After that the lights become too hot and may burn the leaves.

According to Jörg Meyer-Brenken, they have been experimenting with high light intensities up to 2500 µmol/m²/s. “Our extensive research has proven that up to about 2000 µmol/m²/s the plant continues to give back in yield what you offer it in lighting. After 1200-1500 µmol/m²/s – depending a lot on the genetics -  it drops slightly from the 1% for 1% yield but it still improves the yield considerably”.


The growth cycle of cultivated cannabis typically consists of three stages: propagation, vegetative phase and flowering. Because the usage of lights is one of the most expensive aspects of cultivating, it is of vital importance to get this right. As Cannabis is a so called “short day crop” it will flower when days get shorter. Typically, we see that during the vegetative stage. 18 hours of light are followed by 6 hours of darkness. In a controlled environment the flowering stage can be provoked by shortening the photoperiod to 12 hours of light and thus 12 hours of dark. There are variations on this formula and currently more research is being done, but remember that the technology is changing, from HPS to LED and we are in a young industry. Various methods that are being used in cannabis cultivating has been borrowed from other plants that are cultivated under similar circumstances and new discoveries are being made on a daily basis.


Changes in light spectrum have been proven to manipulate terpene, cannabinoid, and THC levels. Traditionally the argument is between blue and red light and how much is needed. Some people suggest 1:1 and some go as far as 1:4. Lately however there has been new research that cuts down on the red and blue lights and concentrate more on white light. Jörg compares the usage of red and blue lights alone to driving a fast sports car in second gear on a normal road, “you are doing it the way you have always done it but you are operating in a safe space, but if you want the car to operate at peak performance, you have to up the stakes.” A plant has numerous photoreceptors that are all sensitive to different wavelength (light color) and collectively they all contribute to the health of the plant. If a plant gets too much red or blue light it over stimulates certain of these receptors while the others are idle. This may lead to photo bleaching, your plant starts turning white. Daily light integral (DLI) describes the number of photosynthetically active photons that are delivered to a specific area over a 24-hour period. The entry level DLI for a plant would be 40, but it can be pushed as high as 60. The sun pushes this in a broad white spectrum that triggers all the photo receptors. “Red and blue light only is not sufficient in our research”, says Jörg, “what is needed at high light intensities beyond 1000 µmol/m²/s is white light with touches of red and blue. After all, the spectrum of the sun shifts during the day with it being more blue at sunrise and reddish at sunset with white in-between.” Their ideal lighting is a broad white spectrum.

Light technology

There are three different types of lights that can be used: High Pressure Sodium Light (HPS), Light-emitting Diode (LED) and Ceramic Metal Halides (CMH). All three of these systems have advantages and disadvantages. HPS is the cheapest system to install but its operating cost is higher than LED and the bulbs need to be replaced on a more regular basis. It also does not offer the full spectrum of light like LED and CMH. If you use this, also be aware of the possibility of an exploding light bulb that can leave shards of glass that will make your crop unusable. According to Jörg, HPS is also slowly being phased out and will probably be banned in the EU in the future. LED is the latest kid to the party. It is more expensive than HPS but energy efficient, the greenest of the bunch. It is currently the most sustainable of the three with up to 60% saving in electricity when compared to traditional discharge lamp technology such as CMH or HPS. LED technology in horticulture has usually up to 50.000 hours of operation with no more than 10% light losses. That means you can operate a LED system over 10 years in flower stage. Discharge lamps have a fast light depreciation in the first few thousand hours. Depending on how strict your light intensity requirements are these lamps need to be replaced after 6-12 months.

Natural versus artificial light

There is a long-standing debate whether natural or artificial light is better for cultivating cannabis. There are advantages and disadvantages to both methods, which are beyond the scope of this article. In general, cultivating your cannabis in the sun is better for the environment and sun-grown cannabis enjoys a full spectrum of terpene that is challenging to be achieved indoors. The cultivator can also use a wide variety of techniques that increases quality without damaging the environment. Obviously, it is also cheaper to cultivate. The problem with sun-grown cannabis is that the sun cannot be controlled, consistency cannot be guaranteed and there is usually only one cycle per year. This might not make it acceptable to pharmaceutical companies. Cultivating under artificial light, with the correct licenses means that your crop is within the law and the product is controllable and much quicker to cultivate (this last point may or may not be an advantage depending on who you speak to).

The current move is to combine the two by cultivating in a greenhouse. This way sunlight is used and artificial light is a supplement to help achieve the correct DLI.

As we mentioned in the beginning, before providing you with all these facts, lighting plays a very important role in the success of your crop. There is also a lot of information and opinions out there which means that all the pros and cons need to be weighed up before you make a decision and invest.

If you need any more information, make contact with the consulting team of Cannavigia or reach out to Fluence.