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How to prevent and treat cannabis light burn?

Light burn can seriously affect cannabis plants if left untreated. Check out how to prevent and treat plants in this article.
4 weeks ago
5 min read
How to prevent and treat cannabis light burn?

Light burn or light bleaching is a serious problem if you’ve got a got a room full of cannabis plants. Light serves as food for the plants, but it can also be an issue if it goes overboard. Think of it this way – humans need food for energy, but what happens if you eat too much? Yep, you’ll have several problems from obesity to diabetes.

Similarly, cannabis plants use light as food, but if you install too many lights and hang them too close to the plants, you’re asking for trouble. If you notice your plants struggling, keep reading to figure out how to prevent and treat cannabis light burn.

What is a light burn?

Image credit - Keeno/https://www.growroom420.com/

ight burn is nothing but light bleaching. You’ll notice that the leaves too close to the light turn white or look bleached. Plants growing outside cannot suffer from light burn because the sun is too far away from the earth to burn the plants. Cannabis has evolved for centuries and has adjusted to the sunlight enough to not get burnt.

But, light burn can happen indoors. The leaves and even the buds begin to look white or burnt when the lights are hung too close to the plants. The heat is so high that the plants cannot tolerate it. White buds look amazing when you look at them, but it’s a sign that the buds are damaged.

Since the light is too close to the buds, the resin along with the cannabinoids are destroyed. You probably already know that heat kills plants, and buds are no exception. In fact, not only will the buds be useless for both medicinal and recreation users, but the taste goes for a toss too. And the fragrance deteriorates as well.

Yellow leaves can also indicate light burn at times. But, do not get confused between nitrogen deficiency and light burn because they look the same. With nitrogen deficiency, though, yellowing of the leaves start from the bottom and move towards the top. Also, the leaves are limp and fall off from the plant without any effort. On the other hand, if they are suffering from light burn, the leaves feel crispy and are harder to pluck from the plant.

Leaves turning brown and crisp is an indication of light burn too. It’s a combination of heat and too much light that fries the leaves and render them useless to the plant.

How to prevent light burn?

LSD by tripleseas

Prevention is far better than cure, they say. Thus, you must try to prevent light burn rather than trying to cure it. First off, light burn depends on the type of light you’re using. For instance, a CFL hung even 10 inches away from the plant will not damage the plant. The same applies to fluorescent or T5 lights because they aren’t that powerful and don’t emit a lot of heat. However, HID and LED lights positioned even 10 inches away from the plants can kill them.

Secondly, determine the wattage of the lighting you’re using. For example, a 50W LED light may not be too harmful, but a 1000W LED will have disastrous consequences if you place it too close to the plants. HID lights are too powerful even if the wattage is low. Another problem is that they emit way too much heat that can be unbearable to the plants.

Having said that, remember that you can’t hang the lights too far away either. If the plants are very far away from the light, they will not have enough food to grow properly! You can consider both HPS and Metal Halide lights in the same category. Here’s a tip to help:

HPS and MH Lights

Closest

Farthest

150W

8”

12”

250W

10”

14”

400W

12”

19”

600W

14”

25”

1000W

16”

31”

1200W

18”

33”

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Here’s one for LED lights as well:

LED lights

Closest

Farthest

150W

15”

25”

300W

16”

27”

600W

18”

29”

1200W

22”

31”

2000W

26”

33”

Here's a video to give a better understanding:

When in doubt, read the directions provided by the manufacturer as well. And, now that the LEDs are available as COB LEDs as well, the distance between the lights and plants may be different. COB LEDs are way too strong. It’s better to be safe and place the plants a few inches further away in the vegetative stage to check how they fare. If you notice that they are struggling, it’s an indication that you must move the lights away. However, if you notice that they are stretching too much and go limp, it’s time to place the lights closer.

If everything fails and the plants do not recuperate, you can remove a few lights. Keep in mind that about 45-70W per square feet is more than enough light for plants. Anything over 70W will do more harm than good. If there’s no roof space and you’re unable to move the light away, you can train the plants using a method known as LST.

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Low Stress Training is a method where you bend the stems to the side of the container so that the light penetrates into the canopy. Since you’re going to bend the stems down, the distance between the lights and plants will automatically reduce. But, note that the stems try their best to get back up and face the light, so you’ll need to use strong cable tires or wires that hold them in place. As long as the wires don’t hurt the plants, you can LST them as much your heart desires.

LST works perfectly for autoflowers, but use it only during the vegetative stage. At the end of the day, LST is a technique that stresses the plant, so you don’t want to do anything stressful to the plant when it’s flowering.

How to cure light burn?

Junglebook GG

In this picture, the leaves look burnt but the buds qare fine. You can wait to harvest the buds if aren't bleached. Sometimes, the leaves turn completely white. In such cases, the damage is so much that it’s too late. The same applies to burnt leaves and buds as well. If they are crispy and crumple in your hands with minimal effort, it’s perhaps too late to save them.

But, if you notice the first few signs of the leaves turning white, you’re in luck. For one, you can move the lights away. Water the plants to help them restore all the moisture they have just lost. You can also install cooling fans to reduce the heat produced by the lights.

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This is also why most growers shy away from HID lights. HID lights are powerful, no doubt, but the heat released is just too much for the plants and you’ll be forced to use powerful fans. With LEDs, though, the heat isn’t is as much as HIDs and since most of the new LEDs come with cooling fans attached to the unit, heat dissipation will not be a big headache.

Determine the leaves of the plant turning white and pluck them off from the plant because they are going to stress the plant even further. If the plants are young and still in the vegetative stage, it might help to cut off the tops. This method – also known as Topping and Fimming – will also reduce the distance between the lights and the plants considerably.

Of course, the tops will grow back again, but you can use a combination of both LST and topping to ensure that the plants aren’t too close to the lights at all.