The Knowing - Lighting

By Bruce Coetzee and Léon Cornelissen

Welcome back fellow growers! Let’s pick up where we left off in our first article. In this segment, we will look at a key element of indoor cannabis growing that can leave you frustrated and confused: LIGHTING. This article will cover sealed/semi-sealed environments and lights. We will explain the choices you have when looking at buying lights…and we will also give our recommendation for constructing your own set of lights!

Since you are not growing outdoors, you will need to create a sealed/semi-sealed environment for your plants. A space of 1m (L) x 1m (W) x 1.5m (H) will give 1 indoor cannabis plant the optimal area to produce good yields, as long as the plant is trained via low-stress training. Now that we know the amount of space needed, let’s briefly discuss some points for consideration:

  1. Sealed environments are easier to keep stable. Make sure little to no outside air enters your space. Cheap materials for constructing a space can include: plywood, Masonite, thick plastics, old trampolines, car covers and builders plastic.
  2. You can increase the efficiency of your lights by adding a reflective layer to the inside of your grow space. It is possible to use materials like Mylar or sisilation to achieve this, just don’t forget that white paint also reflects about 95% of light!
  3. Being able to monitor and control the conditions inside your grow space is crucial. We will discuss this in more detail in our next article.(Thermometer and Hydrometer)


Remember to try and re-use and up-cycle as many materials as you can. This doesn’t just reduce your expenditure; it’s a good opportunity to practice your creative abilities!

Now…let’s discuss lighting.

Intensity vs Spectrum

When we decide we are going to build an indoor grow space, the surface area of the floor will determine how much light is needed. Ideally, the cannabis plant will receive the same intensity and spectrum it would naturally get – but through science we understand how the plant uses light. Through this understanding we can use lights that will maximize the specific light spectrums plants use. Plants are able to use visible and invisible light, prefer blue hues during vegetative growth, and thrive on orange-red hues during the flowering stage. Ultraviolet light can damage plants…and cannabis has produced a method of protecting itself against this harmful light – trichomes. Lastly, green light and infrared light can stimulate transpiration by causing stomas to open wider. An increase in plant efficiency will have a direct result on the quality and quantity of your yield.

For indoor growing, the intensity of lights influences the amount of produce yielded a lot more than the light spectrum. The light spectrum should not be ignored at all, yet it is less important as the amount of light given – the intensity.

To better inform you about your lighting options, we have made a table with our 3 recommendations for lights: compact fluorescent (CFL), high pressure sodium (HPS) and light emitting diode (LED).

From this table (also considering our previous article), you can see why we are advocating for the use of LED fixtures. Even though they are the most expensive option, this is balanced with their lifespan, total efficiency and intensity being better suited for saving money. After all, saving money in the long-run is partly why we choose DIY options. Using the techniques we describe in these articles, we can assure you that you will save lots of money not only in the construction of your growing space, but also by producing good yields of organic top shelf bud.

After comparing these lights, let us address the second important factor – intensity/wattage. In our experience, aiming for 600w HPS per square meter is probably the best standard we can advocate for. A singular plant does not need 600W HPS, 150W will do. Our recommendation is to ensure quantity and quality bud – which means we can’t skimp on light. You can grow a single plant with 200W CFL, 150W HPS or 180W LED and still get similar quality as our recommendation of 600W; you are just not going to get the same amount as the 600W setup.

There is a heated debate that we would like to briefly discuss: yield per watt of lights. For many years HPS lights have been the industry standard for horticultural applications. When breeders state yields per square meter, chances are they were obtaining these yields on a HPS system. It has been reported many times that growers are able to achieve the standard of 1g (dry yield of flower) per watt using HPS setups. CFL was reported to produce 0.65g per watt – the controversy is really LED lights. Some sources claim to have achieved 7g per watt using LED and aeroponic systems! In our experience, LED is closer to the industry standard of 1g per watt.

By using the technical guidelines outlined in this article we hope to have at least provided an essential understanding of DIY lights and enclosures. Always work safely and remember a plan is 99 percent of the work done.

To end off this article, let’s make sure we have the following for our growing adventure by next issue:

  • Sealed/semi-sealed environment
  • Lights for your growing space
  • Thermometer and hygrometer
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