The quantity and quality of the cannabis crop ultimately depends on how well the lighting is arranged. This is why one of the most commonly discussed issues on forums is the distance of the light bulbs from the plants.
Light is vital for the normal development and growth of the plants. However, inexperienced growers often make two major mistakes:
Placing the lamps too high. This forces the plants to expend all their growth energy to reach the light, which makes them thin, skinny and weak. The strength to form large, heavy buds is no longer there. Closer to the cannabis harvests, the bushes will definitely have to be tied down, otherwise they can break. The lower leaves turn yellow.
Place the lamps too low. In this case, the plants get heat and light burns, begin to be sick and die. About a rich harvest will have to forget. The leaves turn pale, dry and brittle.
To get the best light conditions (distance from the lamp to the canopy tops) you need to take into account the following three factors:
Stage of life cycle of the plant.
Type of lamp – DNAT, ESL, LED, etc.
How to choose the right distance from the top of the cannabis plant to the lamp
The most important rule is to raise the lamp as the bushes grow (or lower the plants from the lamp). The optimal distance is 30-90 cm, taking into account the three factors above.
Lamp power. Mature plants require a figure of 250-300 W/m2. The rule of inverse squares is used to maintain the optimum distance. If the distance increases by the value of N, the light power drops by N2.
Life span. For immature cannabis sprouts in the vegetative stage, the distance to the lamp should be increased by 1,5 times, compared to the standard values (about 90 cm).
Type of lamp. Today there are a lot of options for lighting devices. They differ not only in the light spectrum, power and cost, but also the amount of heat released. Modern ESL and LED lights have a low thermal impact with sufficient light, which allows them to be placed lower than DNAT.
The “back of the hand” method as a lamp distance indicator
This method is suitable for DNAT and ESL, which produce enough heat to burn the plant. Newer LED lights and cooled DNATs are difficult to test this way.
Turn on the lamp and wait for it to warm up completely.
Place your palm over the top of the plant. The back side of the hand will be under the lamp. It is necessary to keep the hand like this for 10-15 seconds.
If you feel a burning sensation, the lamp is too close to the top of the cannabis bushes.
Optimal distance from the top of the cannabis plants to the lamps of different types
The “back of the palm” method is ineffective for LED bulbs, which produce almost no heat. They are suitable for lighting the box through the whole life cycle of the plants, but can cause light burn if the power is too high. Experienced growers advise to place such lights at a distance of 30 to 50 cm when germinating, and 10 to 25 cm at other times. They also advise to pay attention to the power. If it exceeds 1 W, for example 3 W or 5 W, the distance is increased to 60-80 cm to the crown.
ESL or energy-saving lamps. Two types of lamps 2700k and 6400k are used in growing. The first type of lamp is suitable for lighting on the vega. Their favorable blue spectrum has a beneficial effect on the growth of green mass of plants. 2700k emits a predominantly red spectrum and is suitable for the flowering stage of marijuana plants. If the grower has little space at his disposal (a small grow box), a compact fluorescent lamp will help him. They have a low heat output, long life and economical power consumption. Such lamps can be placed at a distance of 15-25 cm from the top of the plant.
DNAT or arc sodium tubular lamps emit a large amount of heat. The source of 400 W power suggests a distance to the top at least 45-60 cm. However, even with the distances, it is necessary to keep an eye on the temperature. Grow boxes with this lighting need additional ventilation for cooling.
DNAZ differs from the previous variant by the presence of a reflective mirror layer on the bulb. This makes the illumination efficiency higher and avoids the need for reflectors. They shine mainly in the red spectrum, which stimulates the development of larger buds at the flowering stage.
Tips from Semenarnia
If the location of the lamps cannot be changed, experienced growers advise moving pots with plants vertically. They can even be placed on the floor if necessary.
If with a low grow box the grower has decided to grow a tall cannabis variety, it is necessary to correct its development by tucking in the vega period so that the plants develop horizontally (such as the Maine Lining technique).
Cutting off the crown affected by the light burn will not save the plant. On the contrary, it can have even more disastrous consequences and kill the plant altogether.
The best way to avoid burns is to calculate the size of the grow box in advance, based on the height of the variety, or to buy seeds of a deliberately low-growing variety.