Cannabis Light Burn & Light Stress: Symptoms & Solutions!

Cannabis Light Burn & Light Stress: Symptoms & Solutions!

If you are growing cannabis indoors, you might have encountered the problem of light burn or light stress. This is a condition where the leaves and buds of your plants get damaged by the intense light from your grow lights. Light burn can affect the health, yield, and potency of your cannabis plants, so it is important to know how to prevent and fix it.

What Are The Symptoms of Light Burn/Stress in Plants?

Weed light burn

Cannabis light burn/stress is caused by exposing the plants to more light than they can handle. This can happen when the lights are too close to the plants, too powerful, or on for too long. This can affect both the leaves and the buds of cannabis plants, reducing their quality and yield.



- The first signs of light burn can be seen in the leaves that are nearest to the light source or at the top. The leaves may not become yellow, but instead, the tips may curl upwards in an unusual manner at first.

- As the issue persists, the leaves begin to yellow. Leaves that receive more light are lighter in color than those that don't.

- If you observe yellowing leaves, especially at the tips, take a closer look and you'll see that the veins still remain green.

- Leaves may curl upwards to provide shade for themselves, causing them to lose their shine and become crispy. Additionally, brown spots may appear on the leaves, resembling burn marks.

- Buds can start to bleach and turn a bright white color. This process removes the potency from the buds, rendering them useless.



Sometimes it can be confusing to tell the difference between nitrogen deficiency and light burn in plants. Nevertheless, it is important to be aware of certain distinct variations.



If a weed plant is deficient in nitrogen, its leaves will turn yellow and fall off, while leaves affected by light burn will not wilt or fall off unless they are plucked. Additionally, yellowing due to nitrogen deficiency usually starts at the bottom of the plant, whereas light burn often starts at the top.

How to Tell The Difference Between Light Stress and Heat Stress?

Light Stress on cannabis







Heat stress

Heat stress is another common problem for indoor cannabis growers, especially in hot climates or poorly ventilated spaces. It can cause symptoms similar to light stress, such as leaf bleaching, fading, curling, or spotting, reducing the plant's ability to absorb water and nutrients, leading to wilting, dropping, or nutrient burn.



The main difference between the two is that heat stress affects the entire plant, not just the parts exposed to light. Heat stress can also cause more water to transpire through plant leaves, making them look shiny or wet.

How To Prevent Light Burn/Stress in Cannabis?

The best way to prevent cannabis light stress and light burn is to choose the right type of light for your growing space and adjust them according to your plant's needs. Here are some tips to help you do that:



- Choose LED lights over HID lights. LED lights are more energy-efficient, produce less heat, and have a wider spectrum of light than HID lights. LED lights also allow you to adjust the light intensity and color according to the plant's stage of growth.

- Use a lux meter or a PAR meter to measure the light intensity at different heights and distances from your plants. Lux meters measure the visible light that humans can see, while PAR meters measure the photosynthetically active radiation that plants can use for photosynthesis. Both types of meters can help you determine the optimal light intensity for your plants.

- Follow the manufacturer's recommendations for hanging height and distance for your lights. Different types of lights have different optimal hanging heights and distances from the plants. For example, LED lights can be hung closer to the plants than HID lights, because they produce less heat and have a wider angle of light distribution.

- Adjust your lights according to your plant's stage of growth. Cannabis needs different amounts of light during different stages of growth. In general, they need more light during the vegetative than during the flowering. You can adjust the lights up or down, change their color or spectrum, or change their duration or schedule.

- Monitor your plants for signs of light burn or light stress. If you notice any symptoms of light burn or light stress on your plants, such as bleaching, fading, curling, spotting, or stretching, you should move your lights further away from your plants or reduce their intensity or duration.

How To Fix Light Burn/Stress in Cannabis Plants?

Bleached buds

If your plants are already suffering from light burn/stress, don't panic. There are some things you can do to fix them and prevent further damage:



- Move your lights further away from your plants or reduce their intensity or duration. This is the most obvious and immediate solution to stop the damage from getting worse. You can use a lux meter or a PAR meter to find the ideal distance and intensity for your plants.

- Prune or remove any damaged leaves or buds. This will help your plants focus their energy on healthy growth and recovery. It will also prevent any pests or diseases from taking advantage of the weakened parts of your plants.

- Increase the airflow and ventilation in your growing space. This will help lower the temperature and humidity levels in your grow space and improve the gas exchange between your plants and their environment. It will also prevent mold, mildew, or bud rot from developing on your plants.

- Flush your plants with plain water or a mild nutrient solution. This will help flush out any excess salts or nutrients that may have accumulated in your plants due to light burn or light stress. It will also help restore the pH and EC levels in your soil or growing medium.

- If you have limited space for growing plants, it is important to plan ahead and be proactive. One way to do this is by starting low-stress training early on, which can help prevent light burn in the future.

- Give your plants some time to recover. Depending on the severity of the damage, your plants may need a few days or weeks to recover from them. Be patient and gentle with your plants, and avoid any unnecessary stress or disturbance.

How Much Light Do Your Cannabis Plants Require During Their Life Cycle?

Marijuana light burn vs nitrogen nutrient deficiency

The growth stages of cannabis require varying amounts of nutrients and light. Seedling requires a moderate amount of light to prevent weak and fragile growth, while too much light can also be harmful. During the vegetative, the demand for light increases significantly, as seen by the development of broad fan leaves. When the plant starts blooming, it requires ample light to produce flowers. It's important to note that the light spectrum that supports flowering is different from the one that promotes vegetative growth.



Here is a general guide that you can use to determine the appropriate lux ranges for each stage of the growing cycle:



- Clone and seedling stage: 5,000–7,000 lux

- Vegetative stage: 15,000–50,000 lux

- Flowering stage: 45,000–65,000 lux



Although the recommended lux level during flowering is 65,000, weed plants can tolerate up to 75,000 lux before experiencing negative effects.

What Is The Optimal Distance to Keep The Light From Your Plants?

The optimal distance between your lights and your plants depends on several factors, such as the type of light you use, the wattage of your bulbs, the size of your plants, and the stage of their growth. As a general rule, you can follow these guidelines:

• Metal Halide (MH) and High-Pressure Sodium (HPS):

MH and HPS are the most popular types of lights for cannabis growers. They produce a lot of light and heat, which can be beneficial for plants' vegetative and flowering. However, they also consume a lot of electricity and require a ballast, a reflector, and a cooling system to operate safely.



MH and HPS lights can cause light burn/stress if they are too close to the plants or if the temperature is too high in the grow space. To prevent this, you need to adjust the light distance and the plants according to the wattage of your bulbs. Here are some general guidelines:



- 150w MH or HPS: 20-25cm from the top of the plants

- 400w MH or HPS: 30-35cm from the top of the plants

- 600w MH or HPS: 35-41cm from the top of the plants

- 1000w MH or HPS: 50-60cm from the top of the plants



• Light Emitting Ceramic and Ceramic Metal Halide :

LEC or CMH are newer types of lights that use ceramic arc tubes instead of quartz. They produce a full spectrum of light that mimics natural sunlight, which can improve the quality and potency of your buds. They also use less electricity and generate less heat than MH or HPS lights, which can save you money and reduce the risk of light burn/stress.



However, they are more expensive to buy and may not be compatible with some ballasts or reflectors.
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