Competent organization of lighting for indoor growing is one of the most important conditions for a good harvest. Plants need light for active growth and development, but if the distance from the lamp to the top of the cannabis is not chosen correctly, problems can arise.
If the optimal distance is exceeded, the bushes will spend a lot of vitality to reach the light source. As a result, the plants will be thin and thin, they will no longer have energy for the formation of resinous buds and lush lateral branches. If the distance is too small, heat and light burns will occur on the leaves, and if measures are not taken in time, the bushes will hurt and may even die.
The optimal distance from the lamp to the top of the cannabis is a question of concern to many growers, and the answer to it depends on the following factors:
lamp type (LED, DNaT, DNaZ, ESL, DRIZ);
stage of the life cycle of a plant.
Principles and rules for selecting the optimal distance
The average distance from the head to the lamp is in the range of 30 to 90 cm. Choosing the right option is not so difficult when you take into account several important principles.
The grower’s job is to provide the shrubs with enough bright light, shortening the distance to the lamp as much as possible until the heat and light emitted begins to be harmful.
Lamp wattage and distance. Adult plants need about 250-300 kW / m². At the same time, the principle of inverse squares works here: if the distance increases by N times, the power of light decreases by N² times.
Distance and phase of the life cycle. At the very beginning of the cannabis growing season, while the sprouts are not yet fully grown, the distance from the lamp should be increased by 1.5 times compared to standard indicators.
Distance and type of lamp. Today growers have many different types of lighting fixtures at their disposal, each with its own characteristics. An important property of a lamp is its ability to generate heat. Lamps that give little heat (LED, ESL) can be placed much lower than lamps that give a lot of heat (HPS, DRIZ).
Raise the lamp as it grows – This rule should not be ignored, otherwise the top leaves of the cannabis will get stressed.
Back of hand method
This is a well-known method that will allow you to accurately determine the optimal distance to the top of the bushes in terms of the magnitude of the thermal effect. The method is well suited for HPS and DRI lamps. But for LED-lamps, which give a minimum of thermal effect, it is ineffective.
To use the method, follow 3 steps:
Turn on the lamps installed in the grow box and let them warm up.
Bring your palm to the top of the hemp with the back of your hand and hold it for 10-15 seconds.
Be mindful of how you feel. If you feel a burning sensation on your skin, then the lamps are too close and you need to raise them.
Can the crown be trimmed to save the plants?
This question often arises for beginner growers who grow cannabis in small grow boxes with limited space. The answer to it is unequivocally negative. Trimming the crown to save the plant from light burn is not the best solution. This can lead to even more dire consequences – a slowdown in growth, a decrease in the quantity and quality of the crop.
If the size of the grow box does not allow you to raise the lamps to ensure the optimal distance to the top of the cannabis, you can slightly lower the pots of marijuana, if necessary, put them on the floor. It is important to calculate the size of the growbox in advance, taking into account the expected height of the bushes. If you are planting a tall variety and understand that the bushes can stretch significantly when changing to color, during the active growing season of the bushes, use hemming methods, stimulating the development of cannabis in the horizontal plane.