By Luke Sholl

Side lighting is quite a common practice in indoor gardening. It simply refers to the act of lighting the sides of your plants, not the tops. It has become quite popular, but not for the reasons you may presume.

Growers are constantly in pursuit of the next limiting factor to increase their yields, and more often than not, the addition of extra lighting reaps the most noticeable rewards.

It is true that the sun rises low on the horizon, beams straight down at noon, and proceeds to drop off again. Cannabis naturally adapted its growth pattern to better harness light this way, and hence, it presents itself in a triangular Christmas tree-like shape.

Christmas Tree-Like Shape Cannabis Plant


Natural selection is not a one trick pony; quite the opposite. Being a high-performance annual species, cannabis is like a super-athlete that is pre-programmed to die after it reaches the finish line. “Success” is only achieved when the female plant is pollinated, develops some seeds, and propagates. If not pollinated, it becomes ever so sexually stressed and thus, buds fatten as much as possible before time is up.

The female cannabis plant shoots its flowers as high as it can get to increase the chances of pollination. It is hormonally hardwired to give preference to the top and outer buds. This is called apical dominance. The plant can sense which buds are higher up, and gives developmental preference to them.

Several training techniques are often employed to exploit this behavior. Take topping for instance, where you cut off the main stem early on in the vegetative phase to divide the plant into two new main stalks. The once lonely apex now becomes twin dominant colas.

All of this to say: if you attempt to grow cannabis using side lighting only, it will still grow top heavy. The top colas will be bigger and fatter, while the lower and interior buds will always be smaller and airy. This is just how cannabis has adapted.

Training Techniques Cannabis Side Lighting


Side lighting does work, just not in the cause-effect fashion some may think. Doubling your light exposure to the sides and bottom will not double your yield. It will certainly give it a bump, but side lighting should not be your primary strategy for maximising final dry weight.

When growing other plant species that do not exhibit apical dominance, side lighting will have a positive yield correlation. Regarding cannabis though, particularly indoors, side lighting does have its place. Underground micro-growers have puzzlingly small spaces to work with and have no choice but to get creative. The same goes for cupboard grow-ops where space is so tight, there is no room for light to bounce around to reach the lower canopy. In this situation, side lighting is essential to maintain base level physiologic photosynthesis.

Side Lighting Cannabis GreenHouse

The same principle applies to larger grow rooms that for some reason have an area or zone without adequate lighting. These performance gardens are often nutrient heavy. If half a plant is not receiving light, it won’t be able to metabolise nutrients, which then leads to nutrient toxicity. Side lighting will aid in maintaining an overall healthy plant.

Certain light systems like CFL or T5 simply do not have enough penetration power. This means the radiated light is unable to reach the interior and lower parts of the plants, leading to neglected growth. In this case, strategically positioning lights will have its benefits.

Sometimes growers get quite the surprise when they try new strains, especially if they were used to growing squat indicas and all of a sudden experiment with a landrace sativa. It is not uncommon to see plants stretch as high as the tallest grow tents permit. The grower’s only solution is to move the light to the side.

SCROG Technique Cannabis Cultivation


The first thing to do is be sure you are in full control of the environment, and that you correctly identify the limiting factors. Day/night temperature, humidity, CO₂ levels, light density and spectrum, watering frequency, and nutrient management are by far more crucial than adding lights to hit the underside of the plant.

Before thinking of side lighting, consider training. There are multiple techniques we will not go into right now, but will mention for your curiosity. They all share the same principle - to maximise horizontal growth and/or break the main stem apical dominance. These techniques will make for bushier plants with more colas. The result is a much more efficient use of your artificial top lighting and a considerable increase in potential yield.

Examples of training techniques:

Side Lighting Cannabis

Another nifty trick is to use light movers. These are, as the name suggests, gadgets that will move light to and fro across plants. The idea is twofold; mimic the natural movement of the sun, or simply have the lights move across the canopy to maximise light distribution and reduce shadow patterns.

At the same time, these movers allow you to position the lights closer to the canopy with a significantly reduced risk of heat stress. Lighting follows the inverse-square law, meaning that theoretically, you can increase efficiency by 30-50 % by lowering your lights.


Side lighting is certainly not useless. It does have its place both for vegetables and weed. The main consideration is whether the extra cost involved is justified. The ultimate question is, do you want to add 20% more weight to your flimsy popcorn bud, or would you prefer a 20% boost in overall yield?

If you have dialed-in your grow-op to the max and are sure your strain has reached its full genetic potential, then by all means, add some extra side lighting to push your plants to the limit. Otherwise, you will be far better off applying some cost-free training techniques to instantly achieve a more desirable effect on the final yield.

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