Gas Lantern Routine (GLR): how to improve the yielding capacity of marijuana whilst saving energy

De: Contributor Grow

The Gas Lantern Routine (GLR) is a lighting technique used by some cannabis growers to improve the development of their plants whilst reducing energy consumption. This routine is especially used during the vegetative phase and involves replicating a more natural light cycle, as opposed to the continuous light exposure typically provided in indoor grows. Here we explain what this routine consists of.

The acronym “GLR” stands for “Gas Lantern Routine”. The mythology surrounding this lighting system goes back to the time when crops were being attacked by nocturnal pests, and farmers would go out at night with gas lamps to scare them away. However, these farmers found that the use of this routine had some unwanted side effects: they realised that their crops weren’t flowering and remained in a vegetative state due to this light interruption in the middle of the hours of sleep.

Nowadays, some indoor cannabis growers have discovered that they can greatly benefit from this routine. They claim that their plants are larger and healthier, and deliver higher yields. This lighting technique is all about disrupting the light cycle of marijuana, just as those farmers once did.

The routine starts in the vegetative period, with five and a half hours of darkness followed by one hour of light. After that, the plants are kept in the dark again for five and a half hours. This is significantly different from the traditional light cycle of the vegetative phase, which requires 18 hours of light followed by six hours of darkness. This is basically a 12/12 photoperiod with one hour of light in the middle of the darkness period to prevent the plants from flowering. Plants get loaded with flowering hormones, but the hour of light that they’re exposed to at midnight prevents them from coming into bloom. And when that hour of light is removed, the plants go absolutely crazy.

Converts to GLR can confirm that this is the best method ever. They claim that their plants grow much faster during the vegetative phase and stretch less when they start flowering. Flowers start to sprout much earlier, and plants are generally healthier and less stressed thanks to the fact that there isn’t a significant reduction in the hours of light at the beginning of the flowering.

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Using this technique, the vegetative period can also be reduced; and, with a shorter growth cycle, yields are obtained more frequently. The vegetative cycles can be shortened from one to two weeks, and the flowering can also be shortened by a week or more by using this method, along with a decreasing lighting schedule.

What is this lighting routine based on?

Cannabis only needs 13 hours of light to remain in the vegetative growth phase. The 18-hour lighting schedule actually stresses the plants, as they don’t receive as much light as this even when grown out in the open. Even the equatorial regions don’t get 18 hours of sunshine per day. Therefore, as cannabis is an outdoor plant, you ideally need to mimic the outdoor conditions in your indoor grow.

GLR can also be used throughout the flowering stage. During this time, growers can keep the lights on for 11 hours straight, and then turn them off for 13 hours. Most growers still use the traditional light cycle of 12 hours on / 12 hours off, but this can be detrimental to the plants because it doesn’t accurately reflect the outdoor growing conditions.

When the plants are in the flowering stage, the season shortens naturally. In fact, outdoor plants wouldn’t get 12 full hours of sunlight at that point. Therefore, GLR effectively replicates the photoperiods of the plants in their natural environment as closely as possible. Some growers start the flowering with a 12/12 photoperiod and increase the shutdown by 30 minutes every 2 weeks, trying to mimic the end of the summer / autumn sunlight. In this way, the last few weeks of flowering should have a photoperiod of 9 hours on / 15 hours off.

Indoor cultivation should mimic the conditions of outdoor plants

What are the possible benefits of the Gas Lantern Routine?

GLR emerges as a model of efficiency and natural growth that offers a combination of benefits. These are not only limited to the health of the plants, but extend to the grower’s pocket and to the environment in general. Let’s analyse these theoretical advantages:

1. Lower electricity consumption

The main appeal of this routine is its energy-saving potential. When marijuana is grown indoors, the lamps are normally kept on from 18 to 24 hours, which results in extremely high electricity bills. Growers will find that their electricity bills are much lower with GLR, as the lights will only be on for 13 hours a day instead of 18.

2. A cooler growing space

With reduced exposure to light, you get a cooler growing space, which is a blessing for both your plants and your cooling system. Traditional lamps can accumulate excessive heat over time, posing a threat to the health of your plants. The GLR method, with its intermittent darkness periods, leads to a cooler environment, which ensures that the plants remain more protected from possible heat damage.

3. Imitating Mother Nature

By reducing the hours of exposure to light, the gas lantern routine aims at imitating the natural light cycle that a cannabis plant would be exposed to in nature. This provides a more natural lighting regime that is speculated to encourage a more organic growth pattern by aligning with the inherent biological rhythm of the plant.

4. Vigorous growth and performance

Anecdotal evidence suggests that plants enjoy additional resting time, showing remarkable growth spurts in just fifteen days. A robust and larger cannabis plant is synonymous with a greater number of buds. Therefore, not only does GLR pave the way for more vigorous plants but potentially translates into higher yields. And this could even apply to those who are into training techniques, as it could serve as a catalyst to unlock even a greater number of flowering buds, which would further amplify the yield.

 5. Root health: a controversial benefit

Lastly, one of the most controversial benefits of the use of GLR is that it can help strengthen the root system. Many people will either support this or deny it, but we have good reason to believe that cannabis focuses a lot of energy on root development during the hours of darkness. Hence, by exposing the plants to more hours of darkness, their radicular system will develop further. And a more developed root system lays the foundation for a more robust plant capable of supporting lush growth.

Possible disadvantages of GLR

This lighting routine promises cannabis growers lots of potential benefits; but, as with any other growing technique, it also has some drawbacks. Understanding these challenges can provide growers with the knowledge they need to make informed decisions tailored to their circumstances. Among these disadvantages we need to consider:

1. Adaptation challenges

The transition to GLR can lead to a sharp deviation from conventional lighting schedules, which could initially cause stress to the plants. The abrupt change in light exposure may require a period of adaptation, during which plants may show signs of stress or growth may temporarily slow down.

2. Strain sensitivity

Not all cannabis strains may respond favourably to this routine. Certain genetics, especially those used to long hours of light, may find the interrupted daylight schedule of GLR inappropriate, which could negatively affect their growth. Some varieties can also start flowering when you don’t intend them to, due to the light stress caused by this lighting method.

3. Increased monitoring and adjustments

GLR requires a more practical approach from the grower. The need for careful monitoring and potentially frequent adjustments of the lighting program to ensure optimal growth can take a long time. This routine may require a good eye and the willingness to modify the lighting programme based on the response of the plants.

4. Potential impact on performance

While some growers report higher yields with GLR, others may experience a drop in yield, especially if the plants don’t adapt well to the new lighting schedule. Different experiences underline the importance of individual circumstances and the need for a well-calibrated approach.


Using GLR may seem contradictory for most cannabis growers. However, sometimes it is beneficial to reflect on what farmers used to do in the past. And GLR is a great example of this. Those who use this method and know how to adapt their growing techniques to these ‘out of the box’ approaches, can actually make their plants incredibly profitable.

Kannabia Seeds Company sells to its customers a product collection, a souvenir. We cannot and we shall not give growing advice since our product is not intended for this purpose.

Kannabia accept no responsibility for any illegal use made by third parties of information published. The cultivation of cannabis for personal consumption is an activity subject to legal restrictions that vary from state to state. We recommend consultation of the legislation in force in your country of residence to avoid participation in any illegal activity.

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