Proper use of light is one of the most important factors for successful cannabis cultivation. But too much of a good thing can harm your plants. In this blog post, I'll explain what light stress and light burn are, how to recognize them, and how to avoid them.
What is light stress in cannabis cultivation?
Light stress occurs when your plants are exposed to too much or too intense light. Especially in indoor grows, where artificial lights like LED, HPS, or CMH are used, the light intensity can be set too high. The same applies to outdoor plants that are exposed to unprotected sunlight.
Excessive light stress overwhelms your plants' photosynthesis. They can no longer fully utilize the light's energy, leading to growth problems.
What is light burn?
Light burn is an extreme form of light stress. It literally "burns" the leaves of your plants. This happens when the light intensity is so strong that the cell structures in the leaves are damaged. The upper leaves, which are closest to the light, are particularly affected.
Symptoms of light burn:
- Yellow or white spots on the leaves (especially at the tips and edges).
- Dried or brittle leaves.
- Growth cessation or stunted flower formation.
How do you recognize light stress and light burn?
Look out for the following warning signs:
- Leaf discoloration: The leaves show unnatural yellow or white tones.
- Heat stress symptoms: The leaves curl upwards or hang limply.
- Growth problems: Your plant grows slower or produces fewer flowers.
- Unnaturally shiny leaves: This indicates excessive use of photosynthesis.
If you notice one or more of these signs, you should act quickly.
How do you avoid light stress and sunburn?
Fortunately, you can ensure that your plants stay healthy with a few simple measures:
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Distance of the lamp:
- Maintain the recommended minimum distance between the lamp and the top of the plant.
- For LEDs, a distance of 30–50 cm usually applies, depending on the model and power.
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Dim your lights:
Many modern grow lights have a dimming function. Use this to reduce the light intensity during the vegetative or early flowering phase. -
Optimize the light cycle:
Indoors, you should make sure your plants have sufficient dark periods. A cycle of 18 hours of light and 6 hours of darkness is ideal for the vegetative phase. During the flowering phase, switch to 12/12. -
Shady spots in outdoor grows:
If you are growing outdoors, protect your plants with a sunscreen or plant them in a location where they are not exposed to direct sun all day. -
Climate control:
Maintain optimal temperature and humidity. Too much heat increases the negative effects of light stress. Ideal temperatures are 22–28°C during the light phase and 18–22°C during the dark phase. -
Measure light intensity:
Invest in a PAR meter or lux meter to accurately monitor light intensity. This way, you can ensure your plants aren't getting too much light.
What to do if your plants are already affected?
If you have already discovered signs of light stress or light burn, there are the following measures:
- Hang the lamp higher: Increase the distance to the light source.
- Reduce light intensity: Dim your lamp or reduce the lighting time.
- Remove leaves: Remove burned leaves so your plant can focus its energy on healthy areas.
- Let plants recover: Give your plants a period of dimmed light to relieve the strain on photosynthesis.
Conclusion
Light is essential for the growth of your cannabis plants – but only in the right dose. Light stress and light burn can significantly impact your harvest. With careful light planning and regular monitoring, you can protect your plants from damage and ensure a healthy, productive harvest.
Do you have questions about your setup or are you looking for the perfect lighting for your grow? Let us know in the comments or contact us directly – we're happy to help!
