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Light Burn in Cannabis Plants

Apr 16, 2020
Lighting Problems

Identifying and Treating Light Burn in Cannabis Plants

Though cannabis has substantial light requirements, it’s possible to give plants too much of a good thing. When this occurs and the plants suffer from stress, they may encounter several growth-related issues.

As soon as cannabis seeds have sprouted the plants can tolerate a great deal of light, especially during the flowering stage. However, light burn can be a real problem, especially in indoor gardens with powerful grow lights.

Excess light can harm your plants in several ways. When their leaves turn yellow and die off, light burn is said to occur. In some instances, plants may become bleached and turn pale white. Here, you’ll learn about light burn in cannabis plants.

Light Burn: What Is It?

Light burn occurs when a plant gets too close to a lighting source and its leaves look bleached. Outdoor-grown cannabis doesn’t encounter this problem because the light source (the sun) is much too far away to burn the plants. Over thousands of years, cannabis has evolved enough to avoid outdoor burning.

However, light burn is a real concern for indoor cultivators. Leaves and buds may get burned or turn white when they’re too close to the grow lights, and the plants simply can’t tolerate the street. Though white buds may look striking, it’s an indication of severe damage.

When the buds are too close to an indoor light source, cannabinoids and resin are destroyed. The heat has serious and even lethal effects on plants, and cannabis is no exception. Not only are these plants’ buds rendered useless for recreational and medicinal use, but their taste and fragrance are eliminated as well. What a shame for incredible strains like girl scout jack herer to end up this way!

When leaves turn yellow, light burn may be mistaken for a nitrogen deficiency. With a nitrogen shortfall, though, leaf yellowing starts at the bottom and moves to the top of a plant. Here, the leaves will become limp and are more likely to fall off. Light-burned leaves feel crunchy and are difficult to remove. With a combination of excess light and heat, the leaves become fried and are useless to the plant.

Light Burn Decreases Pigment in Cannabis Buds

When powerful HPS and LED lights are placed too close to cannabis plants, albinism may occur. Bleaching decreases the buds’ vitality and strength, and it saps their THC. This is obviously counter-productive when investing in high thc seeds to grow and enjoy. So, how can growers prevent light burn? The answer is simple: don’t put the lights too close to the crop.

When a grower says they have albino or white cannabis, that’s not a good sign. A plant that has turned white is in very bad condition, and that’s the last thing we want to happen.

The Symptoms and Signs of Light Burn

When cannabis plants are light burned, the topmost leaves are most severely affected. These leaves will gradually turn yellow and may die, but it might not happen right away. In some instances, a plant’s leaves may curl upward before losing their color.

Does Light Burn Cause Reproductive Changes?

Cannabis plants, even from premium marijuana seeds, may change genders due to unhealthy environmental factors, and light burn is no exception. Plants experiencing heat and light stress are more likely to turn into hermaphrodites than those without such stresses. These factors may cause a cannabis plant to change its sex:

  • Photoperiod changes
  • Temperature fluctuations
  • Overfeeding and over-watering

Resolve lighting issues and remove hermaphroditic plants as quickly as possible to prevent pollination and further damage to the crop.

The Difference Between Nitrogen Deficiency and Light Burn

Some cultivation issues, such as a lack of nitrogen, may manifest themselves with similar symptoms. However, it’s easy to tell these two conditions apart. The biggest difference is that a nitrogen deficiency typically shows up in a plant’s oldest leaves first, while light burn starts at the top.

As nitrogen-deficient leaves turn yellow, they may also crumble, wilt, and fall off. On the other hand, burnt leaves may stay on the plant. Light burnt leaves’ veins will stay green, which isn’t the case with nitrogen deficiencies. Leaf yellowing isn’t the only sign of light burn. Sometimes, leaves may turn purple or red with burnt edges and tips. Please note that some products like purple kush seeds will naturally develop a purple hue to their leaves which shouldn’t be confused with symptoms of light burn.

Nutrient Deficiencies Worsen the Symptoms of Light Burn

If a cannabis plant doesn’t get enough nutrients for healthy growth, or if it has other problems, it’s more likely to suffer damage from light burn. Healthy marijuana plants are more tolerant to bleaching.

Recognizing the Signs

The signs of light burn don’t always appear right away. Sometimes grow lights are only a little too close to the plants, which means that the damage will appear gradually. Leaves may slowly wither and die over a week or more. When this occurs, it’s easier to see light burn on a plant’s oldest leaves, which makes it harder to find the real cause of the problem. Having a grasp of these concepts before you even germinate your i49 seeds will put you ahead of the game and make sure you can treat the problem immediately.


Cannabis buds and leaves that get too much light may be bleached. Rather than crumbling and turning yellow, however, they will lose their color and turn white. Again, this often happens when high-powered HPS or LED lights are put too close to the plants.

Bleached buds are sometimes sold as novelty or albino strains. Other than their appearance, there’s nothing special about these plants. A bud that’s been bleached has likely lost most of its potency and flavor. It’s quite rare for buds to be bleached from excess light. In most cases, these buds will look burnt, with small dark brown leaves. Some products, such as white widow seeds do naturally exhibit an almost white appearance to the buds but this is simply a frosted layer of crystalline trichomes. Growers should be able to decipher the difference using a good quality magnifying tool, such as the T-H-See magnifier.


Preventing Light Burn in Cannabis Plants

If your plants are experiencing the effects of light burn, there are two options:

  • Move the grow lights further away from the plants
  • Reduce the intensity of the grow room’s lighting

In cases where it’s impossible to move the grow lights, it may help to bend the plants downward. Cutting the tops off the plants is another option, but this should only be done during the vegetative stage.

Proper Placement of Grow Lights

Cannabis grow lights vary in wattage, intensity, light spectrum, and the type of lighting being used. Most of today’s grow light makers will be able to offer information on proper distancing between lighting and plants. This measurement may depend on the plants’ growth stage. For instance, younger plants are more sensitive than older ones, so they should be further away from the lights. dwarf weed seeds will also yield shirter plants, so hang drop your lights from the very beginning in preparation, but not so low as to induce leaf burn. If you can’t find information about lighting distance, a local grow shop may be able to help.


Is Light Burn a Concern for Outdoor Growers?

Outdoor light burn, even under prolonged and intense sunlight, is not very likely. The only time an outdoor grower should worry about excessive light is when plants are moved outside. In these cases, it’s best to give the plants time to get used to the outdoor air. Don’t move them straight from the grow room to a sunny spot; place them in a partially shaded location first. After a few days, move the plants to a sunnier place in the garden.

What to Do with Light-Burned Plants and Buds

If a plant such as your newly grown blue dream strain is affected by light burn and the damage isn’t too severe, all is not lost. Simply cut away the damaged buds to allow for new growth. If you’re growing inside a box, raise the box lid enough to provide additional space in between the canopy and the grow lights. As scorched buds are low in THC and don’t taste very good, they should be discarded.


Heat Stress and Light Stress

Sometimes, light burn appears along with signs of heat stress. The reason for the co-occurrence is that most grow lights, except some LEDs, also give off quite a bit of heat.

When cannabis plants are too close to their light source, they may suffer significant heat stress and light overexposure. Your plants may show a combination of symptoms from these conditions. Often, these symptoms appear in the form of dying, discolored, and wilting leaves.

Indoor cannabis growers who use artificial lights can easily tell if the heat is too high for their plants. Simply place a hand under the grow light at the same height as the plants are growing. If it feels warm but not excessively hot, the plants should be safe.

Bottom Line

Though we know that light helps cannabis plants grow, we also know that too much of a good thing is a bad thing. To manage your plants’ lighting schedule effectively, ensure that they get 18-24 hours of light per day during the vegetative stage.

When plants are in the flowering phase, keep them on a 12/12 lighting schedule to ensure tasty, high-quality buds. During flowering, they need to get about 12 hours of uninterrupted darkness to get the best results.

Changes to a cannabis crop’s growing conditions, such as increasing or decreasing the light temperature or intensity, will require varying nutrient and watering schedules. More light makes plants grow much faster, which means they’ll also need more nutrients and water. Regular watering in conditions with high temperatures and intense light will help to reduce light burn in cannabis plants. Growers can further reduce the risk of bleaching and light damage by starting with high-quality autoflowering seeds from a reputable seed bank like

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