Cannabis light burn: Causes, symptoms, and how to prevent it

If your cannabis plants are suffering from light burn, you're risking more than just a few yellow leaves.

It can severely damage growth, reduce yield, and bleach buds, ultimately hurting quality and potency. 

But don’t worry; this guide has everything you need to prevent, identify, and treat light stress before it becomes a bigger issue. 

Ignoring the problem can lead to stunted growth, diminished aroma, and even ruined harvests.

In this post, you’ll learn the exact causes, recognise the symptoms early, and discover practical solutions to ensure your plants stay healthy and vibrant. 

Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis, you’re doing so by the law and subject to appropriate permissions and licenses of the applicable country.

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What is light burn?

Light burn happens when your plants receive excessive light exposure, typically from intense types of light sources like an LED grow light or HPS (high-pressure sodium) bulb. 

While light is crucial for plant growth, there’s a limit to how much light a cannabis plant can handle. 

When plants are exposed to light stress, their demand for carbon dioxide increases, which can strain photosynthesis if CO2 levels aren’t sufficient. 

This intense light can also exacerbate nutrient deficiencies as plants struggle to meet higher metabolic demands under stress.  

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Causes of light burn on cannabis

It usually happens when the light source is too close to the plant canopy, exposing the plants to more light than they can handle. 

This often happens when using high-intensity light like LEDs or HPS bulbs, which are popular choices for growing cannabis indoors. 

But while these lights can offer enormous benefits, improper setup and not understanding what is enough light can result in stress and damage. 

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High light intensity and PPFD levels

One of the main causes of light burn is high PPFD levels from an LED grow light placed too close to the plants.  

Many new growers assume that closer is better, but the truth is too much proximity can result in dangerously high PPFD (photosynthetic photon flux density) levels. 

PPFD measures the amount of light hitting a certain area each second, and it’s vital to monitor this closely, as cannabis plants can only process so much light at once. 

Measuring PPFD properly is essential to minimise the risk.

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Heat emitted by HPS bulbs

While LEDs primarily cause burn through the high intensity of light emitted, HPS (high-pressure sodium) bulbs contribute to burning due to high temperatures and heat stress. 

This additional heat creates a challenging environment, especially if your space lacks proper ventilation.

When combined with high light levels, stress from heat can leave plants scorched, light burned and stressed.

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Can you give cannabis too much light?

Yes. Many growers believe that more light equals better growth, but there is indeed such a thing as too much light. 

Beyond a certain point, cannabis plants simply can’t handle the load, which leads to poor growth and stressed plants. 

In fact, too much light and excessive intensity that exceeds the plant’s capacity to process it can disrupt a plant’s natural rhythm, making it harder for it to maintain healthy growth patterns.

Maintaining optimal light intensity and distance from the light is key to preventing damage.

Avoiding light stress requires understanding how to manage light distance and maintain optimal levels of light penetration.  

Each grow setup is different, so take time to assess your space and adjust the light levels according to your plant’s needs.

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Cannabis light burn symptoms  

Spotting the signs of light stress early is key to preventing further damage. 

Light burn shows up in several ways, typically appearing on the plant's upper parts closest to the light source. 

Let’s look at some common symptoms so you can take action as soon as you notice them.

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Yellowing leaves and colour changes

The most obvious sign of light stress on cannabis leaves is yellowing, especially on the upper leaves nearest the light source. 

Unlike nitrogen or other nutrient deficiencies, which often start lower on the plant, light burn symptoms are concentrated on the top leaves. 

Leaves may turn yellow or even white in extreme cases due to chlorophyll breakdown caused by excessive light.

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Bleached buds

In some cases, buds exposed to excessive light can appear bleached, resembling dead coral. 

This is particularly problematic during the flowering stage because light bleaching can cause buds to lose potency, aroma, and quality, impacting the overall yield. 

Bleached, white buds are a clear indication of cannabis excessive light and suggest that the light source may be too intense for that stage of growth. 

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Stunted growth and reduced health

Light burn often results in stunted or slowed growth as a stress response while the plant struggles to cope with the high light levels.   

When leaves and buds are burned, the plant diverts energy towards recovery rather than producing new growth. 

This can result in a smaller yield and, in some cases, impact the plant’s smell and flavour profile. 

You might also notice symptoms that mimic heat stress, such as leaves curling or drying out, especially when using HPS bulbs with inadequate ventilation.

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How to tell cannabis light burn vs nutrient burn?

Check where the damage appears. 

Nutrient burn usually shows as burnt tips or edges on lower leaves, while light burn affects the upper leaves near the light source, causing yellowing, bleaching, or leaf scorching.

Identifying these signs on cannabis plants early gives you a better chance of salvaging your crop. 

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Stages of cannabis growth and light burn

The risk of cannabis light stress and burning on cannabis plants varies depending on the growth stage. 

Different stages require different intensities of light, and understanding these stages can help you avoid issues before they start.

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Seedling and early vegetative stage

Young plants, especially seedlings in the early stages, are highly sensitive to intense light and can easily burn if exposed to excessive light.  

During this early phase, burn symptoms like yellowing leaves or slight curling can indicate cannabis seedling light burn.  

Seedlings generally require lower-intensity lights, so keeping your grow light at a safe distance is important. Check out our post on the best PPFD for seedlings here.

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Vegetative stage

During the vegetative stage, cannabis plants are more resilient to light but can still experience light stress if the intensity is too high. 

At this stage, ensure that the light is an appropriate distance away for healthy, robust plant growth. Read about the optimal PPFD for veg here.

You might want to increase light intensity gradually, but watch for signs of yellow leaves or heat stress, especially if you’re using an LED grow light. 

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Flowering stage

The flowering stage is critical in terms of prevention because cannabis plants are particularly sensitive at this time. 

Excessive light can damage the buds. Buds begin to turn white, which reduces potency and aroma. 

Many growers find that adjusting the light schedule and distance between their plants and the light during this stage can help prevent light burn and ensure optimal results. 

Learn more about dialling in your PPFD during flower here,

Monitoring the light intensity (with a PPFD meter) and light cycle through each stage and making adjustments based on your plant’s response helps avoid stress.  

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Considerations for light distance and intensity

Different lights have varying optimal distances. Experimenting with distance while monitoring cannabis plants for any symptoms can help determine the best setup. 

Adjustments may also be needed for different stages of growth to keep light levels within safe ranges.

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Preventing light burn on cannabis plants                                                                                                              

Preventing light burn requires careful attention to several key factors: the distance between your lights and your plants, the intensity of your lights, airflow, and temperature management.

By taking a proactive approach, you can prevent light stress and the damage that excessive light causes. Here are some preventative measures and cannabis light burn tips. 

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Hang your lights at an appropriate distance

Keeping your lights the right distance away is one of the easiest ways to prevent cannabis light stress and burn. 

While every light type has its own recommended distance, a good rule of thumb is to start with lights further away and gradually adjust them based on the plant’s response. 

Using a lux or PAR meter can help you track the light intensity and ensure the levels remain safe for optimal plant performance. 

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Monitor light intensity with sensors

Using a PPFD meter or similar sensor to measure how intense your lights are is essential for monitoring the light exposure on your plants. 

By knowing the exact levels at the canopy, you can make adjustments to prevent providing excessive light.   

Most growers make the mistake of skipping this step, but it’s particularly important with an LED grow light, which can be deceptively intense. 

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Heat management and ventilation

Keeping your grow area well-ventilated is crucial, especially when using HPS bulbs or other high-heat lights. 

Ventilation helps to regulate temperatures, reducing the risk of heat stress. 

This is particularly important during flowering, where heat and light exposure can easily damage buds. 

‍Using fans and exhaust systems and keeping the room temperature stable all contribute to a healthier growing environment.

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Adjust light schedules according to growth stages

Your lighting schedule and intensity should vary based on the growth stage. 

Seedlings and plants in the vegetative stage require less intense light compared to those in the flowering stage. 

Adjusting the lighting cycle for each phase and ensuring proper coverage without overexposure can help prevent cannabis light stress. 

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Avoiding too much light and light stress

As tempting as it may be to blast your plants with light, there is such a thing as excessive light.

Beyond a certain point, your cannabis plants can’t process additional light and will start to experience light stress. 

To avoid cannabis light stress and burn issues, make adjustments based on visible signs, especially if you’re seeing yellowing or wilting in the upper leaves.

A little attention to these details can go a long way in preventing burning and supporting strong growth.   

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Manage your environment with the Grow Sensor

The Grow Sensor is a cutting-edge tool for precision indoor growing. It offers continuous PPFD monitoring with a full-spectrum PAR sensor. 

Beyond light measurement, it tracks temperature, humidity, VPD, and CO2 levels, calculates DLI, and senses Leaf Surface Temperature and dew point. 

It also integrates with the Grow soil probe for EC, moisture, and root zone temperature insights, aiding crop steering. 

It is compatible with Android, iOS, and an upcoming desktop app and includes offline logging, long-range Wi-Fi, USB power, custom alerts, and trend analysis. 

Built to last, the Grow Sensor provides essential data for serious cultivators.

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Treating light burn

If you’ve spotted signs of light burn in your grow room, don’t worry - there are ways to address it and help your plants recover. 

Cannabis light burn recovery starts with making a few adjustments to minimise further stress and support the plant’s healing process.

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Immediate steps to reduce or fix light stress

The first thing to do is reduce your light’s intensity or increase the distance from your plants. 

Moving your light source farther from the canopy can help prevent further burning on cannabis plants. 

If you’re using LED grow lights, consider dimming the light or adjusting the PPFD to lower levels. 

In cases of severe burn, you may also want to reduce the light cycle temporarily to give your plants a break.

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Check and adjust environmental conditions

Heat stress often accompanies light burn, especially when using HPS bulbs. 

To help your plants recover, ensure your grow area has enough ventilation and that temperatures are within a safe range.  

Adjust fans, vents, or exhaust systems to maintain an optimal environment, which will help reduce further stress on your plants.

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Support your plants’ recovery with nutrients and care 

During recovery, your plants may benefit from a gentle nutrient boost. 

Light burn can sometimes mimic symptoms of nutrient deficiency, like yellow leaves. 

However, be cautious not to overdo it, as adding too much nitrogen or other nutrients could cause nutrient burn. 

Focus on maintaining a balanced nutrient mix and keep an eye on new growth for signs of improvement.

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Patience and monitoring

Recovery from light burns takes time, so be patient and monitor your plants regularly. 

Look for signs of healthier leaves and improved colour as new growth emerges.

Avoid making too many adjustments at once, as this could stress the plant further. 

With the right care, you should see positive changes within a few weeks, and your plants will resume healthy growth.

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Other potential causes of yellow leaves and similar symptoms

While light burn on cannabis leaves is a common cause of yellowing, it’s not the only one. 

Other factors can lead to yellow leaves and similar symptoms, so it’s essential to rule out alternative causes to ensure accurate treatment.

• Nutrient deficiencies: A lack of essential nutrients, particularly nitrogen, can also cause leaves to turn yellow. Unlike cannabis light burn, nutrient deficiencies often start on the lower parts of the plant.

• Heat stress: Excess heat from the grow lights or poor ventilation can cause symptoms that look similar to light burn, such as wilting or curling leaves. Ensuring proper temperature management is key to avoiding these issues.

By being aware of these potential causes, you can make a more accurate diagnosis and provide the right care.

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Takeaways

Preventing and treating light burn is about finding the right balance in your grow setup. 

Here are some essential tips to keep your plants healthy and thriving:

• Keep your lights at a safe distance: To avoid light burn, ensure adequate space between the canopy and the light source.
• Monitor light intensity regularly: Use a PPFD meter to track intensity and avoid too much light exposure.
• Manage temperature and ventilation: Proper airflow and temperature control help reduce the risk of heat stress and light burn.
• Adapt light for growth stages: Adjust your lighting schedule and intensity according to the growth stage to prevent stress and ensure robust growth.  

By following these guidelines, you’ll be well on your way to preventing cannabis light burn and helping your plants reach their full potential. 

Happy growing!

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FAQs

Can grow lights burn plants?

Yes, grow lights can burn plants if they’re too close or emit excessive intensity. 

This is especially common with LED grow lights and HPS bulbs if the distance from the light is too short or ventilation is poor.  

Keeping lights at a safe distance and monitoring light intensity helps prevent plants from getting light burned and ensures robust growth.  

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Can LED grow lights burn plants?

Yes, LED grow lights can burn plants if their intensity is too high or the light fixture is too close to the canopy. 

Excessive light exposure from high-intensity lighting can cause light stress and lead to marijuana light burn symptoms, such as yellow leaves and even poor growth. 

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What are the early signs of too much light cannabis?

Early signs of too much light in cannabis include yellowing or light bleaching of the upper leaves, leaves turning yellow or pale, and minor curling due to light stress. 

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What does light burn look like on cannabis?

Light burn on cannabis typically appears as yellowing or whitening on the upper leaves near the light source. 

In severe cases, buds can become bleached, appearing white or pale, and leaves start to curl or scorch. 

This damage often resembles nutrient deficiencies but is isolated to the topmost parts of the plant due to excessive light intensity.

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Can a cannabis plant recover from light burn?

Yes, cannabis plants can recover from light burn with proper care. 

To address cannabis plant light burn, start by increasing the distance between your lights and your plants and managing light intensity to prevent further stress. 

Adjusting the light schedule, improving proper ventilation, and providing balanced nutrients will support weed light burn recovery. 

Patience is key, as recovery takes time, but with these adjustments, new growth should appear healthy.

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How to fix light burn?

To fix light burn, increase the distance between the light fixture and the plant canopy, lower light intensity, and ensure proper ventilation to reduce heat. 

Adjust the light schedule if needed, and provide balanced nutrients to aid recovery. 

Monitoring with a lux or PAR meter can help prevent future light burns.

Does light burn stunt growth?

Yes, light burn can cause stunted growth in cannabis by stressing the plant and damaging its leaves. 

Excessive light intensity hinders healthy plant growth and diverts energy to recovery rather than new growth.

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