Light is essential for photosynthesis, the process by which plants convert light energy into chemical energy. This energy is stored in the form of glucose, which is essential for the growth and development of the plant. Without sufficient light, photosynthesis cannot take place efficiently, resulting in stunted growth and lower yields.

Effects of too little light

Too little light can have serious effects on cannabis plants:

Weak growth: plants that do not receive enough light grow more slowly and develop thin, weak stems.
Elongated internodes: The spaces between the leaves become larger, resulting in a sparse appearance.
Fewer flowers: The production of flowers is greatly reduced, resulting in lower yields.
Chlorosis: A lack of light can cause the leaves to turn yellow as the plant does not have enough energy to produce chlorophyll.

Effects of too much light

Too much light can also be problematic:

Light stress: plants that are exposed to too much light can show symptoms of light stress, such as burnt leaves and discoloration.
Heat stress: Excessive lighting can cause the growing area to overheat, further weakening the plants and increasing the risk of disease.
Reduced photosynthesis: Excessive light can increase the rate of photosynthesis beyond optimal levels, leading to the formation of reactive oxygen species that can damage plant cells.

To obtain healthy and productive cannabis plants, it is therefore important to find the right balance and avoid both too little and too much light.

Which light for cannabis plants?

LED lamps

Advantages of LED lamps

Energy efficiency: LEDs consume less electricity compared to other types of lamps, which reduces electricity costs.
Low heat generation: LEDs generate little heat, which reduces the risk of heat stress and enables better temperature control.
Long life: LED lamps have a long life, making them a cost-effective option.
Full light spectrum: Modern LEDs offer a broad light spectrum that imitates natural sunlight and optimally supports plants in all growth phases.

Use and care

Installation: Make sure that the lamps are evenly distributed over the growing area to ensure uniform lighting.
Distance to the plant: Keep a sufficient distance between the LED lamps and the plants to avoid light stress. A distance of 30-60 cm is usually sufficient.
Maintenance: LEDs require little maintenance, but make sure to clean the lamps regularly to remove dust and dirt that could affect the light intensity.

Fluorescent lamps (CFL)

Advantages of CFL lamps

Cost-effective: CFLs are cheaper to buy than other types of lamps.
Easy to use: They are easy to install and use, making them ideal for beginners.
Low heat generation: CFLs also generate little heat, which minimizes the risk of heat stress.

Use and care

Installation: CFL lamps should be placed close to the plants, usually about 5-10 cm away, to ensure optimum light intensity.
Light cycles: CFLs are well suited to the vegetative phase and should provide around 18 hours of light per day.
Maintenance: Replace the bulbs regularly as they will lose intensity over time. Make sure to keep the lamps clean to ensure maximum efficiency.

Metal halide lamps (MH)

Advantages of MH lamps

High light intensity: MH lamps provide a strong light intensity that is ideal for the vegetative growth phase.
Promotes growth: The blue spectrum of MH lamps promotes dense, bushy plant growth.

Use and care

Installation: Place the lamps at a distance of around 30-50 cm from the plants to ensure optimum light intensity.
Ventilation: Ensure that the growing space is well ventilated to compensate for the additional heat emitted by the MH lamps.
Maintenance: MH lamps have a shorter service life than LEDs and should be checked and replaced regularly to ensure constant light intensity.

High-pressure sodium lamps (HPS)

Advantages of HPS lamps

Ideal spectrum for the flowering phase: HPS lamps produce a yellow-red spectrum that promotes flower formation and increases yields.
High light intensity: They provide a strong light intensity that is ideal for the flowering phase.

Use and care

Installation: Keep a distance of about 50-70 cm between the HPS lamps and the plants to avoid burns.
Ventilation: As HPS lamps generate a lot of heat, good ventilation and cooling of the growing space is necessary.
Maintenance: HPS lamps have a limited lifespan and should be replaced regularly to ensure consistent light intensity.

Cannabis too much light

Symptoms of light stress

Burnt leaves

One of the most common signs of too much light is burning of the leaves. The leaf edges and tips can turn brown and dry. This occurs when the plants are too close to the light source or receive too intense light.

Discoloration

Light stress can also lead to discoloration of the leaves. The leaves often appear yellowish or whitish as the chlorophyll is damaged by too much light. This can impair photosynthesis and slow down plant growth.

Measures against light stress

Correct distance from the light source

To avoid light stress, it is important to maintain the correct distance between the plants and the light source. The distance should vary depending on the type of lighting:

LED lamps: 30-60 cm
CFL lamps: 5-10 cm
MH lamps: 30-50 cm
HPS lamps: 50-70 cm

Compliance with the light cycles

Make sure you maintain the correct light cycles for each growth phase:

Seedlings: 18-24 hours of light per day
Vegetative phase: 18 hours of light and 6 hours of darkness
Flowering phase: 12 hours of light and 12 hours of darkness

Adhering to these light cycles helps to minimize light stress and optimize plant growth.

Ventilation and cooling

Since too much light often also leads to overheating, good ventilation and cooling of the growing space is crucial. Here are some tips:

Air circulation: Use fans to distribute the air evenly in the room.
Exhaust air systems: Install an exhaust system to remove excess heat.
Air conditioning: In extremely hot environments, the use of air conditioning may be necessary to control the temperature.

With proper care and monitoring, you can ensure that your cannabis plants receive the optimal amount of light and grow healthily.

Cannabis cuttings light

Light requirements for cuttings

Light intensity

Cuttings require moderate light intensity to form roots and grow without being stressed. Too high a light intensity can burn the tender cuttings and impair their growth. Use low to medium intensity lighting, such as CFL or LED lamps, which have been specially developed for growing cuttings.

Duration of lighting

Ideally, cuttings should receive 18-24 hours of light per day. Continuous lighting helps to promote growth and accelerate root formation. However, make sure that the light source is not too intense to avoid overheating and dehydration.

Optimal conditions for cuttings

Temperature and humidity

In addition to the right lighting, temperature and humidity are crucial for the successful growth of cuttings:

Temperature: keep the temperature in the growing room constant between 20-25 °C. Temperatures that are too high or too low can impair growth and make the cuttings susceptible to disease.
Humidity: Cuttings need a high humidity of around 70-80% to minimize water loss through the leaves. Use a dome cover or mini-greenhouse to maintain humidity.

Distance from the light source

The distance between the cuttings and the light source should be chosen so that the plants receive sufficient light without being burnt. Here are some guidelines for spacing:

LED lamps: 30-45 cm
CFL lamps: 10-15 cm

It is important to check and adjust the spacing regularly as the cuttings grow and their needs change. Placing them too close can cause burns, while too far away can slow growth.

Cannabis growth phase light

Light requirements in the vegetative phase

Light duration and intensity

In the vegetative phase, cannabis plants need plenty of light to grow strong and healthy. The ideal light duration is around 18 hours of light and 6 hours of darkness per day. High light intensity is also important to promote dense foliage and strong stems. Make sure that the plants are evenly lit to ensure uniform growth.

Optimal lamp types

The following lamp types are particularly suitable for the vegetative phase:

LED lamps: Offer a broad light spectrum and are energy-efficient. They promote growth thanks to their intense blue light, which is ideal for the vegetative phase.
Metal halide lamps (MH): Produce a strong blue-white light that supports vegetative growth. They are particularly suitable for larger cultivation areas as they provide a high light intensity.

Light requirements in the flowering phase

Light duration and intensity

During the flowering phase, the light requirements of cannabis plants change considerably. The light duration is reduced to 12 hours of light and 12 hours of darkness per day to promote flower formation. The light intensity remains high, but the light spectrum should contain more red-orange components to support flowering.

Optimal lamp types

The following lamp types are ideal for the flowering phase:

LED lamps: many modern LED lamps are designed to cover the entire light spectrum, including the red components that are important for the flowering phase. They remain energy-efficient and generate less heat.
High pressure sodium (HPS) lamps: Produce a yellow-red spectrum that is ideal for the flowering phase. HPS lamps promote flower formation and increase the yield. They are particularly suitable for experienced growers aiming for large harvests.

Cannabis seedlings light

Light requirements for seedlings

Light intensity

Cannabis seedlings require moderate light intensity to grow healthily. Too strong light can burn the tender seedlings, while too weak light will slow growth and produce weak, spindly plants. A light intensity of around 100-300 µmol/m²/s is ideal for seedlings.

To achieve this light intensity, LED or CFL lamps are the best options. LEDs are particularly suitable as they offer a broad spectrum of light wavelengths and are also energy efficient. CFL lamps are a cost-effective alternative that also work well. It is important to place the light source close to the seedlings, but care should be taken to ensure that the distance is not too small to avoid burns.

Duration of lighting

Seedlings should receive 18-24 hours of light per day to promote rapid and healthy growth. This continuous lighting helps the young plants to develop strong roots and a robust structure. A continuous lighting cycle ensures that the seedlings receive sufficient energy for their development, which is particularly important in the first few weeks after germination.

The lighting duration can be adjusted according to personal preference and the specific requirements of the plant variety. Some growers prefer 24-hour lighting to maximize growth, while others use an 18/6 cycle (18 hours of light, 6 hours of darkness) to better mimic the natural daily cycle and give the plants a rest period.

Common mistakes and how to avoid them

Too little light

One of the most common mistakes when growing cannabis seedlings is providing too little light. This causes the seedlings to become elongated, thin and weak. These weak plants are less resilient and more susceptible to diseases and pests.

To avoid too little light:

Lamp placement: make sure the light source is close to the seedlings, but not too close to prevent burns. For LED lamps the distance should be about 30-45 cm, for CFL lamps about 10-15 cm.
Check the light intensity: Use a luxmeter or PAR meter to monitor the light intensity and make sure it is within the recommended range. If the light intensity is not sufficient, add additional light sources to ensure even lighting.

Too much light

Too much light can be just as damaging as too little. Excessive light can burn the seedlings, bleach their leaves and stunt their growth. This leads to stress and poorer plant development.

To avoid too much light:

Distance from the light source: Keep a sufficient distance between the lamps and the seedlings. Be careful not to place the lamps too close to the plants to avoid burns.
Lighting duration: Make sure that the lighting duration does not exceed 24 hours per day. A short period of darkness can help the seedlings to recover and reduce stress. An 18/6 light cycle can be particularly beneficial here as it provides a balance between light input and rest time.

By avoiding these common mistakes and ensuring the right light conditions for your cannabis seedlings, you are laying the foundations for healthy, vigorous plants and a successful harvest.

Cannabis too little light

Signs of a lack of light

Weak plant growth

A clear sign of a lack of light in cannabis plants is weak, spindly growth. Plants that do not receive enough light will desperately stretch towards the light source, resulting in longer internodes (the spaces between the leaves). These plants often appear long and thin, have weak stems and are unable to support the weight of flowers or dense foliage. This elongated growth is a natural attempt by the plant to get closer to the light source in order to obtain more energy for photosynthesis.

Discolored leaves

Another clear sign of a lack of light is the discoloration of the leaves. Plants suffering from a lack of light can develop yellow or pale leaves as they do not receive enough light to produce enough chlorophyll. Chlorophyll is necessary for photosynthesis and gives the leaves their green color. A lack of it leads to chlorosis, a yellowing of the leaves that is often first visible on the older, lower leaves. This is an indicator that the plant is not able to produce enough energy for its growth and development.

Measures for light deficiency

Increase the light intensity

To remedy the lack of light, it is necessary to increase the light intensity. This can be achieved by the following measures:

Additional light sources: Add more lamps to increase the light intensity. LED lamps are particularly efficient and can provide the required light spectrum to promote growth.
Reflectors: Use reflective materials such as Mylar or white walls to distribute light evenly and maximize lighting efficiency. Reflectors help to direct the light onto the plants instead of wasting it.
Optimal placement: Make sure the lamps are evenly distributed over the growing area to avoid shadow areas. Regularly check the distance between the plants and the light sources to ensure that all areas are sufficiently illuminated.

Optimizing the lighting duration

In addition to increasing the light intensity, it is also important to optimize the lighting duration:

Light cycles: make sure that the plants receive 18 hours of light and 6 hours of darkness during the vegetative phase. In the flowering phase, the light cycle should be switched to 12 hours of light and 12 hours of darkness.
Use timers: Use timers to precisely control the lighting duration and ensure that the plants receive regular and consistent light phases.
Monitor and adjust: Observe the plants regularly and adjust the lighting duration if necessary. Different varieties and growth stages may have different light requirements, so it is important to remain flexible and adjust conditions accordingly.

By increasing the light intensity and optimizing the lighting duration, you can ensure that your cannabis plants receive enough light to grow healthy and produce high yields. Be sure to regularly check and adjust conditions to ensure optimal growing conditions.

Conclusion

Proper lighting is crucial for the successful cultivation of cannabis. A lack of light can lead to weak growth and discolored leaves, while optimal light intensity and duration promote healthy growth and flower formation. The most important points are summarized here:

Light intensityand duration: seedlings and cuttings require moderate light intensity and long lighting periods, while adult plants require specific light cycles during the vegetative and flowering stages.
Signs of light problems:
- Too little light: Weak, elongated growth and yellow leaves.
- Too much light: Burnt and discolored leaves, signs of light stress.
Measures for light problems:
- Correct lack of light: Increase the light intensity with additional light sources and reflectors and optimize the lighting duration.
- Avoid light stress: Maintain the correct distance from the light source and observe the optimum light cycles.
Optimal conditions: Use LED or CFL lamps for seedlings and cuttings and regularly adjust the distance as well as the lighting duration to provide the plants with the best growing conditions.

By taking these factors into account, you can optimize the lighting conditions for your cannabis plants and grow healthy, high-yielding plants. Make sure to regularly check and adjust the lighting conditions to always provide the plants with the best conditions.

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Fachautor und Biochemier Niklas Bergmann

Niklas Bergmann, Fachautor

Freut euch auf die Insights von unserem Biochemiker Niklas Bergmann! Mit seinem tiefen Verständnis für alles, was mit Hanf zu tun hat, liefert er euch die neuesten und coolsten Infos direkt in euer Feed. Schnörkellos und klar verpackt er das komplexe Thema Cannabinoide und macht es für euch easy zugänglich. Mit Niklas an der Spitze unseres Wissens-Teams seid ihr immer top informiert.