Do My Cannabis Plants Need Side Lighting?

by Nebula Haze

Table of Contents

Is Side Lighting Worth It?

Side Lighting vs Supplemental Lighting

When Is Side Lighting a Good Idea?


Is Side or Supplemental Lighting Worth It For Cannabis Growers?

Example of two cannabis plants growing under an HPS grow lightWhen growing a cannabis plant indoors, light usually comes from a grow light located at the top of the grow space. This means all the light is beaming down on the plant from above.

However, when growing cannabis outdoors, the sun moves in the sky and plants get light not just from above, but also from the sides. That's a big part of why cannabis plants naturally grow in a "Christmas Tree" shape. The sloped sides help the plant get as much light from the sun as possible, even when the sun is lower in the sky.

The "Christmas Tree" shape is a great strategy outdoors in the wild because it captures light from the sides as the sun moves in the sky. But that's not the only reason; this shape also helps buds get exposed to the wind so buds get pollinated.

Example of a "Christmas Tree" shaped cannabis plant growing outdoors in the sun. It is shaped this way to get as much sunlight as possible while being able to catch pollen in the wind.

Does it make sense to add side lighting indoors? Can you copy the sun and give light from the sides to increase yields?


Is Side Lighting Worth It?

So is side lighting worth it for indoor cannabis growers? The answer is unsatisfactory…


Side lighting can be helpful in certain situations, but usually it's unnecessary and it often ends up costing more as far as yields/watt compared to giving more light from above. Why is that?

The biggest downside to the idea of side lighting has to do with how the plant processes and responds to the world. A cannabis plant can actually "tell" which buds are located at the top of the plant and tends to fatten those ones the most. It's possible cannabis plants favor the top buds because in the wild those are the ones most likely to get pollinated by the wind. 

That means even if you have two buds getting the exact same amount of light, the bud that's located higher up on the plant will end up growing bigger and longer even though nothing else is different.

Even if you give a cannabis plant the exact same amount of light from top to bottom, like with these old-fashioned Phototrons, you can see that the buds at the top get far bigger than the ones at the bottom. That is just how cannabis plants roll 🙂

Example of a flowering cannabis plant in a Phototron (grow light with T5 lights along the sides) - Notice how the top buds get the biggest even though the plant is getting the same amount of light from top to bottom
Pic by magiccannabus

Even huge cannabis plants that get unlimited sunlight from all sides end up focusing on the top buds. These top buds are most likely to get pollinated in the wild!

This bushy outdoor cannabis plant has tons of huge colas located at the top of the plant. Generally with marijuana plants the biggest buds are located at the top.

Because cannabis plants focus on the top buds, indoor growers usually focus on getting many top buds near the light as opposed to adding side lighting. This ends up getting you more "bang for your buck" because you'll get better yields/watt than you would with side lighting.

Because tops buds grow the biggest, growers often train their plants to grow multiple colas in a flat, table-top shape, so that more bud sites are at the top of the plant (and close to the grow light) at the same time

Example of a "sea" of cannabis colas which have all been trained to grow the same height so all the buds are "top buds" and close to the grow light

Growing "wide" cannabis plants with light on top ends up getting better yields/watt than growing "tall" plants with light on the sides

Example of cannabis buds in a "Scrog" (Screen of Green) setup. By having many colas about the same height and distance from the light, you can increase your yields because all buds will fatten up more than if they were lower down on the plant.


Side Lighting vs Supplemental Lighting

  • Side Lighting means specifically targeting the sides of the plant with light to try to increase bud size on the sides.
  • Supplemental Lighting means you're trying to increase overall light levels or change the light spectrum. Supplemental lighting isn't about giving light from the sides; in fact, generally supplemental lighting is given from above the plant because that gives you more bang for your buck.

Supplemental lighting is very common in greenhouses. If you have a spot in your yard that only gets good direct light for a few hours a day, or if you have a lot of cloudy weather at your location, you could supplement with extra light from a grow light while still taking advantage of the free light you're getting from the sun.

Example of a Greenhouse Supplemented by LED Grow Lights to Increase Yields (A Light Mover Moves Grow Lights Back and Forth)

Example of growing cannabis plants in a greenhouse. The light from the sun has been supplemented by the light from LEDs (which are on light movers)
pic by Heliospectra AB

Another common reason growers use supplemental lighting is to increase or alter the light spectrum, or "color" of the light. Each light spectrum has an effect how your plant grows and some growers are using the power of LED grow lights (which allow you to choose the exact spectrum) to supplement either outdoor light or the light of other grow lights like HPS. These days it's pretty common to see growers use LED grow lights to achieve a specific spectrum; it's also common to see growers combine their LED panel with an HPS grow light to help get better yields and increased flower production.

This grower uses both LED and HPS grow lights to help get the benefits of both

Example of a marijuana plant grower who is using both LED and HPS grow lights

Supplemental lighting can be a great choice in a lot of situations, but it's not exactly the same as side lighting, which tends to be a lot less useful (most of the time).


When Is Side Lighting a Good idea?

Side lighting can be a good idea with fluorescent grow lights like CFLs and possibly T5 grow lights with untrained plants. This is because these types of light don't reach far down into the plant. In fact, the light from fluorescents is so weak that it's only good for a few inches. By the time a plant is more than a foot away the light is pretty much useless as far as a cannabis plant is concerned. Because of these constraints, side lighting can help make sure all buds are within a few inches of a light.

Sometimes side lighting can help with fluorescent lights like CFLs, especially on an untrained plant where most of the buds are far from the top of the plant

Example of a cannabis plant that has lots of side lighting from CFLs

However, if you train your cannabis plant to grow short and flat you can increase your yields with the same amount of light because you'll be able to make sure every main bud is located towards the top of the plant while also getting full light levels.

In other words, even with weak grow lights, you'll get far better yields by growing plants that are wide and flat as opposed to utilizing side lighting.

These buds got really fat even though they were grown under a small T5 grow light because every bud was near the top and close to the light, due to being trained to grow flat along a screen.

Example of cannabis plants grown in a Scrog setup under a T5 grow light. By getting plants to grow short and flat the grower was able to increase the yields and grow bigger buds.

When you get to really strong types of grow lights like HPS and LEDs, their light reaches deep down into the plant. This gives you long, thick buds and without any type of side lighting.

Long thick colas from plants that have been trained to grow long and flat. Growing under powerful lights like HPS can give you long and thick colas.

To sum it up, it's good to get plenty of light to your buds near no matter where they're located on the plant, as buds that are exposed to light and air tend to grow the biggest. But ultimately you'll get better yields/watt simply by making sure all main buds are located near the top of the plant and shining light directly down on them from above.

Learn how to train plants to grow flat and wide
(and get the best yields possible with your grow lights!)



Example of happy cannabis plants growing under the sun - grow lights are needed to replace the sun when growing marijuana indoors!

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