How to set up the lighting in an indoor growing space?
LED systems produce higher PAR than MH, HPS and other types of lamps. However, your plants will require approximately the same number of watts per square metre to achieve a harvest similar to that from traditional HID lamps. Also keep in mind that LED lighting systems are often advertised as more powerful than their actual electrical power consumption, but that does not mean that a 400-watt LED can cover the same square area as a 1000-watt HPS bulb.
To get an idea of the light intensity you are providing to your plants, you can purchase a lux meter and measure light intensity at different points in the canopy. You can also make a theoretical calculation by considering the lumens emitted by the lamp in relation to the growing area. To calculate the lux intensity on the plant canopy, simply divide the lamp’s lumens by the square metres of the illuminated area. If you place a lamp emitting 100 000lm at a distance of 1m from the top of the plant, it will illuminate an area of 1m² with an intensity of 100 000lx (100 000lm ÷ 1m = 100 000lx). If the lamp is only 0,5 m away, it will receive 100 000lm ÷ 0,5m = 200 000lx.
Unfortunately, light intensity decreases by a factor related to the distance of the source from the illuminated object; therefore, the same lamp placed at two metres will increase its beam width, covering 4 m², but with only 25 000lx. You would therefore need four lamps to achieve the hypothetical target of 100 000 lx over the entire growing area.
HID (MH, HPS): RULES FOR THE CORRECT DISTANCE
HID lamps are available in a metal halide (MH) version with cool light, suitable for the vegetative stage, and in a high-pressure sodium (HPS) version with a much wider spectrum for the flowering stage. These lamps operate at high temperatures and require a suitable cooling system. In addition, they emit less light over time, so new lamps should be kept farther away than older ones, and after several cycles you should consider replacing them.
The correct distance for MH and HPS bulbs depends mainly on their power.
If we assume that the ventilation in your growing space is correctly set up, with a smaller 250W bulb you can start at a distance of 35 cm, gradually lowering it towards the canopy until you reach 25 cm from the buds at the end of the flowering stage. With a 600W bulb, you can start at 50 cm, lowering it to 30 cm; if you have chosen a 1000W lamp, it is better to allow at least 80 cm of distance.
According to common practice, you should hold the back of your hand facing the light just above the tops of the plants; if it feels comfortable to you, your plants will feel the same. But do not rely too much on general rules. Always check your plants for signs of overheating or excessive photon pressure.
At what height should you hang MH and HPS grow lights?
Popular, widely used and probably best for higher yields, many growers are devoted to their MH or HPS grow lights.
Although MH and HPS are suitable for different stages of the growing cycle, you can usually hang them at a similar distance from your plants. Both technologies work best when they are closer to the crops, but it is good to test them if it is your first time.
Whether you are a beginner grower or changing your growing method, we recommend starting at the upper end of the lamp’s range. This way, you can gradually lower it until you are confident that your plant is receiving enough energy. We recommend always keeping the light at least 30-38 cm from the top of the plant canopy. Remember that appearances can be deceptive, and you do not want to heat the leaves too much.
The last thing to consider is the bulbs. Unlike those in your home, a bulb’s performance declines over time. Since bulbs emit less energy over time, an older bulb will need to be closer to your plant than a newer one. Likewise, a brand-new bulb should be kept as far away as possible without sacrificing plant development. It is recommended that MH or HPS bulbs be replaced every 3 cycles to ensure their high performance.
LED: RULES FOR THE CORRECT DISTANCE
LED lamps emit a large amount of light pressure, even at relatively low temperatures. This amount of light itself, rather than the heat, can lead to light burn and leaf bleaching.
Different models of LED grow lights have different optimal distances from plants, and manufacturers usually include recommendations with their products. Simply start at a medium distance within the recommended range and observe your plants over the next few days. Turn off the lighting if you notice that any leaves are pale or have burnt tips. If your plants are happy, move the LED panel closer, but never to the point where the upper leaves start to bleach, yellow or turn brown.
High-power LED panels with a power above 300 W should be kept at least 70 cm from the canopy, and may then be moved closer during the flowering stage. As a general guide, 200-400W LED lamps should be positioned 30-70 cm from plants, while 450-600W lamps require a distance of 50-80 cm. Higher-power systems should be positioned even farther away. Remember to observe your plants closely whenever you start using a new light.
The LED lights gardeners use to grow plants require fine-tuning to find the ideal hanging height. However, with so much power, you can achieve incredible yields under the right conditions.
LED lamps are complex. There is such a wide variety on the market that there is no universal option that suits everyone. As a result, there is no standard distance for them. In principle, whatever unit you choose, manufacturers will provide recommended heights and you will still need to fine-tune them.
Another way LED grow lights can mislead you is that they do not always look as powerful as they are. The lights look weak, so it is easy to think they do not emit enough energy. Quite the opposite: they are deceptively strong and you need to keep an eye on them. If you do not, your plants may bleach or you may end up with an insufficient harvest.
Although every LED grow light is different, as a general rule, hang them farther away than you would other lights and adjust them. You can then continue adjusting throughout the plant’s growth cycle, moving them closer when it flowers.
