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Cannabis Light Stress And Light Burn

Last updated: 25 September 2023

cannabis light burn

Dealing with cannabis light stress and cannabis light burn can be very stressful – especially if it’s your first time going through it. However, with the right precautions and growing know-how, it’s possible to identify light stress and bounce back even from the worst cases! Let’s learn how to do it.

What Is Cannabis Light Burn And Light Stress?

light burn weed

Cannabis light burn is the extreme case of cannabis light stress, which occurs when your plant gets more light than it needs for healthy growth. This can lead to bleaching of certain parts of the plant such as the leaves and flowers. However, light stress/burn can manifest itself in many ways, including the browning and drying out of leaves, giving them a dry, crispy texture.

Depending on your light source, there are different levels of associated danger from light and/or heat stress. Depending on how much heat your lights emit, the safe distance to hang them depends partly on the former factor as well as others such as plant maturity, level of airflow and type of light (HPS, CFL, LED, etc.). Before starting any grow, it’s therefore important to ensure you’ll be in a position to provide your plants with exactly the right conditions in which to properly grow.

fast flowering cannabis seeds

Dangers Of Cannabis Light Burn At Various Stages Of Lifecycle

Simply put, the dangers of cannabis light burn are loss of potency, a worse appearance due to burning, and loss in quality and depth of terpene profile. Of course, the biggest danger would be a significant reduction in final yield.

The impact of light burn varies depending on the maturity of the plant, but this is the biggest issue for seedlings that can be easily burned by the high intensity of high-power growing lights. Next are plants in the vegetative stage which have established their ground and are self-supporting but are still susceptible to the dangers of powerful lighting. With respect to recovery, the greatest danger is for plants in the flowering stage, where it’s easy to overlook the impact of light stress as your plants change into their fall colors.

Symptoms Of Cannabis Light Stress And Light Burn

cannabis light stress

The following are symptoms of cannabis light stress and light burn:

  • Bleaching of buds
  • Browning of leaves
  • Leaves curling upward (“taco”-ing)
  • Discoloration of leaves but veins are still green
  • Irregular growth pattern

If your plants are receiving too much light and are under stress, they will exhibit some or all of the symptoms listed above.

Common Cannabis ProblemsLEARN MORE

Are There Ways To Fix Light Burn?

Unfortunately, if parts of your plant have experienced light stress, especially to the point of light burn, then no amount of TLC will be able to bring them back. However, it’s possible to take remedial action by making changes to the amount of light your plant receives to a safe level and not inducing any further unnecessary stress.

Avoiding Light Stress And Light Burn – Learn How Much Light Is Too Much For Cannabis

avoiding cannabis light stress

If you have the resource to invest in a lux meter, it is highly recommended you do so! Not only is this useful in assessing whether your plants are getting too much light, but it can also identify areas receiving insufficient light. This is particularly important for commercial growers, as it maximizes bud production. Lux meter readings are given in lux/m2 and should fall in the following ranges based on plant maturity:

  • Vegetative: 30,000 – 70,000 lux/m2
  • Flowering: 50,000 – 90,000 lux/m2

Set The Correct Height For Your Lights

Also, if you don’t have a lux meter, but still want to avoid light stress, it’s important to set the correct hanging height for your lights, especially as modern growing lamps tend to have high power ratings that can easily cause damage to cannabis plants irrespective of maturity. To check if your lights are hanging correctly:

1) Test the level of heat on the back of your hand at canopy level.

2) If it’s irritating at all, lift the source of light higher, and repeat the same test.

3) Do it again until the temperature feels comfortable and not irritating.

While this may seem basic, it’s a tried and tested way of making sure your plants get the light they need without overdosing them!

Ran Out Of Height? No Problem!

Ideally, one should never encounter this problem. With the right amount of planning, it’s possible to ensure your plants never grow too large for your space. However, things don’t always go to plan – especially when growing a plant from seed. If you’re limited for height, use low-stress training from 3-4 weeks into plant growth.

If your plants are growing too close to your lights and you don’t have any vertical space left to raise them, you can supercrop the plants to stunt their growth and keep them intentionally small. While supercropping is useful for this, it can also be used strategically to boost THC levels! This occurs when cannabis plants ramp up production of THC as a defense mechanism whenever they feel under attack.

Choose the most potent strain


Here are some frequently asked questions that may help you better understand light burn.

light bleaching leaves

How long does it take cannabis to recover from light burn?

While the damage brought on by light burn is permanent, your plant can still recover. Depending on its maturity, a plant may have enough remaining time in its lifecycle to recover from damage, whereas for plants that experience light damage toward the end of their life, there is very little that can be done. As long as you catch the problem while it’s not too late, cannabis plants can recover from light stress in as little as 5-7 days, although most plants take around 10 days to show physical changes.

Can light stress cause cannabis plants to change sex?

Cannabis plants can change sex as a result of environmental factors, and light stress is no exception. Plants that experience light/heat stress therefore have a far greater likelihood of turning into hermaphrodites than those that don’t, so it’s entire possible for this to occur as a result of light stress.

The following symptoms can cause cannabis plants to change sex:

  • Changes in photoperiod
  • Changes in temperature
  • Over-watering/feeding

Light burn or nutrient deficiency – how do I know?

When something goes wrong during a grow, most growers think about water or nutrient-related issues. If you think your plants are experiencing light burn, how do you know it’s not a nutrient deficiency? Well, while the symptoms of the two can appear to be very similar, it’s possible to easily tell between the two by considering the symptoms your plants are showing. It’s unlikely you’ll experience light burn-like symptoms due to excess of any of the nutrients described below, but it’s a possibility nonetheless (particularly with phosphorus).

This Is Not Light Stress But Nitrogen Deficiency, If…

cannabis light stress symptoms

  • You notice discoloration of leaves (starting from the bottom of plant and moving upward)
  • Leaves have droopy appearance without luster
  • Leaves falling off (coming off without much resistance)

This Is Not Light Stress But Calcium Deficiency, If…

light bleached buds

  • You see irregular, yellow-brown spots on leaves
  • Lower leaves start curling

This Is Not Light Stress But Phosphorous Deficiency, If…

LED light burn cannabis

  • Leaves have blue/green tinge
  • There are dark, copper-colored patches on leaves
  • Leaves wither and curl at the tips

This Is Not Light Stress But Magnesium Deficiency, If…

cannabis light bleaching

  • You notice the loss of older leaves (withering and dropping)
  • Leaf veins turn yellow
  • There are irregular rust spots

If you’re concerned about nutrient deficiencies causing changes in the appearance of your plant, flush the rootzone with 15-20 liters of plain, pH’d water to remove any build-up at the bottom of your growing medium.

Marijuana Light Burn And Stress: The Bottom Line

Let’s consolidate what we’ve learned. After reading about light stress and the dangers of light burn to cannabis plants, you should know what to look out for when assessing whether your plants might be receiving too much light. If you want to harvest large, dense buds with a beautiful appearance and fragrant terpene profile, ensure your plants are free of any signs of light burn by checking them frequently. This should not only help avoid light burn, but also highlight any other problems through the extra attention!

What’s Your Cannabis Alter Ego? Herbies QuizTAKE QUIZ
MC baby
Hi, I have light burned some of crop, the top colas are burnt on on some of the big buds sadly but I still have a deadly crop so I’m not too worried. What I’m wondering though is this- should I trim off The burnt and now dead bits of buds to prevent possible rot ? Or should I leave them?
Hello MC baby,Unfortunately, if parts of your plant have experienced light stress, especially to the point of light burn, then no amount of TLC will be able to bring them back. However, it’s possible to take remedial action by making changes to the amount of light your plant receives to a safe level and not inducing any further unnecessary stress
Light Burn Bloom Only?
Several of upper leaves from my plants have the brownish/copper like spotting on the leaves between the veins, the buds look fine with no bleaching. The lower leaves are fine. They are about 5 weeks into flowering so I'm only giving some tiger bloom using half of their recommendation. I have a LED they say 600 Watt, but it only really pulls a 125 Watt Load. I've used LST as I've seen one of my 2 Indicas really grow tall. Both plants are now 11" from bottom of light in my 2'W 2'D 4'H tent. I can't raise the light any higher. So rather than have both Veg and Bloom switches on in full spectrum, I went with bloom only. The idea is that I'm sending less light down towards plant canopy, half the power I'm thinking. I think it's worth it under my circumstances. Wondering if anyone else thinks this is worth a shot. Plants are looking healthy other than that.
Hello,As we understand from your feedback, only the top leaves are brownish, which is most likely has to do with the light. If you think that it will not hurt the harvest you may keep it this way, but we would recommend you to revise your grow spot in terms of regulating the light height
Hey my plant has bright yellow tips on the new growth and some of the upper leaf tips, what could this be from ?
Stressed grower
''Signs of light burn in cannabis plants include upward-pointing leaves and what is known as “bleaching”. Bleaching is the white or yellow discoloration on the leaves closest to the light. Light burn can also be identified when the plant veins stain green as the rest of the leaves turn yellow.''This really helped me. One of my two tall plants got nearly every symptom, the green veins on pale leaves confirmed it. I have a pretty powerful led light for the setup, it was about 10 inches from the top. I had calcium and iron deficiency too which hid the symptoms but I've just realised how close they have gotten.I have lifted the light up but is there any other way to help? Maybe more dark hours?
Hello,We are happy to hear that the article has come in handy. If you do more dark hours the plant might become flowering earlier than needed, lifting light is enough, and the plant will regenerate itself over time, but check on water as wellRespectfully, Herbies
Jay EmmCee
I have plants 2 weeks into flowering, left town and they grew so much they got too close to light and tips got burned a little some are just yellow but one is kind of brown burned. is that dead or will it recover?
Mj is tough. It might recover. It's that beginning growth tip out of the top that if it's burnt to a crisp it won't recover. Just give it up to a week to see if growth continues and you'll know.
Hello Jay,It's better to hide plant from light source. You may find useful these article https://herbiesheadshop.com/blog/cannabis-light-stress-and-light-burn
The burned area won't recover, but unless the entire plant is burnt, you'll be fine. If the area that hit the light is more than 50% burned- you can cut it right off.
How many of us have burnt our buds on the lights? I bet loads of us have. Now how many of us have not been disappointed with the end result? I have seen a few bud's get burnt and then get really fat. I think it would be possible to actually use this as a method of getting bigger bud's in some way.
I like your thinking about stressing to induce vigorous growth. If a flower cluster is burnt and becomes "Reproductively sterilized" the plant will rush to set more flowers on top of the destroyed ones, that's why you noticed them get large fast. That burnt, flavorless, cannabinoid void area (Lol me say funny word) is still inside that cola tho... it's better in the long run to keep all variables right on the line of maximum. Flowers not getting pollinated is stressful enough for our ladies. Pro tip, everyone loves aloe vera for sunburn, even if you didn't burn you just got a lot of sun, it nurishes the skin so it can build a nice tan... Or plant cells and cannabinoids if you're a plant...if I left the ladies a little to close to the sun, I give them a cool temperature aloe vera shower. While I don't advise foliar during flower it CAN be done, but you need powerful dehumidifiers, well over what's needed for basic grow, and hurricane like wind
Light burn has been dogging me hard lately, so I’m researching the hell out of it. Best way to tell is look at a leaf that has another leaf laying right on top of it. If it’s light burn the bottom leaf will be greener where it was protected by the top leaf. Kinda like a farmer’s tan for cannabis leaves...
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