How High Should Grow Lights Be Above the Plants

Why grow lights need to be hung at different heights?

You build your own grow facility, plant hemp, tomatoes, lettuce or strawberries on the ground, on a shelf or in a hydroponic system, and hang lights on the shed or shelf. However, before turning on the light, be sure to know how high it is above the plant.

We all know that hanging the lamp too low will burn the crops. If the lamp is hung too high, the crops will not get enough light, which is unfavorable to the growth. Some plants need to be a little farther away from the grow lights so that they will not be burnt, but some lights cannot hang more than 12 inches, so what should we do?

There are two main considerations for the optimal suspension height of the lamp, namely safety and effectiveness. The space between the lamp and the plant is to allow the plant to obtain enough energy to convert the nutrients in the soil and water into energy.

Different grow lights need to be hung at different heights, why?

Growing facilities are divided into two categories. One is indoor, which completely relies on artificial light without sunlight, and the other is outdoor planting, which can use both artificial light and natural light. For outdoor growing facilities, the main light that crops rely on is sunlight. Growers can control the light type and the amount of light received by plants. This is why growers say that better yields depend on more light. But does this mean that you can put the light as close as possible to the plants so that they get enough light?

The answer is absolutely NOT!

Hang the lights as close as possible to the plants, which means making sure they get enough energy to grow quickly without burning them out. The premise is to make sure that your plants get just the energy they need, not too much, and not too little. First of all, we have to determine whether the type of lamp to fill the plant with light is T8 fluorescent lamp, HPS or LED lamp. LED lights provide a better spectrum, while other lights generate excessive heat. No matter what kind of lights, they need to be hung at different distances from the canopy of the plants.

For example, LED grow lights need to be hung farther away from plants than HPS / fluorescent grow lights, because the strong spectrum of LEDs will bleach the top of the crop.

However, the T8 fluorescent lamp needs to be hung at a height closer to the plant than the HID lamp, so that the plant can obtain enough energy, because the energy of the T8 fluorescent lamp is relatively low. Hanging over a distance of 12 inches, the plant will not get enough photons, resulting in poor growth.

Fluorescent grow light

Fluorescent grow lights can provide plants with a perfect combination of spectrum and energy. Their PPE efficiency is as high as 2.0 umol/J, which can be applied to almost any plant, but if you want the plant to obtain enough PPFD, you need to hang them very close to the plant.

Almost all growers have encountered this problem, that is, the use of suspended fluorescent lights is so difficult. The compact CFL bulb can generate a lot of heat after a longer period of time, while the longer 36w 4ft T8 grow lamp does not emit a lot of heat, because it has a large surface area and the heat will be quickly dissipated. Therefore, the more light bulbs used, the more heat is generated. If the lights are hung too close to the plants, the plants will be easily scorched.

Fluorescent lights generate heat when they are running, although not a lot, but you need to carefully observe whether the plants are scorched.

Generally speaking, the height of the fluorescent lamp hanging from the top of the plant is no more than 12 inches.

This statement is actually not very accurate and scientific, because the shape, size and PPE of fluorescent lamps are all different. So we offer you the following suggestions:

 

-Start at 4.5 inches above the top of the plant

–Please be equipped with an automatic temperature sensor to monitor the temperature of the canopy at all times to ensure that the crop is at a safe temperature, because the compact CFL lamp usually generates more heat than the T8 tube grow lamp.

–If the temperature is detected to be too high, please raise the light by one inch and turn on the ventilation system in the facility at the same time

–If the temperature is too high, increase the height of the lamp, if the temperature is too low, decrease the height of the lamp.

LED Grow Light

With the continuous development of technology, LED grow lights do not generate a lot of heat like HID or HPS, but if they are hung too close, their spectrum may overwhelm many plants. As a result, the plants will suffer light burns, which will not be able to absorb the photons in the lamp well, which will adversely affect the plants.

In short, the temperature of the light source’s spectrum determines whether the light source becomes “cold” blue or “warm” red. The spectral output of LEDs is more important than energy production, so you need to hang them higher than HID or HPS lamps to avoid photobleaching. Mild bleaching harms plants the same as overheating plants, and can lead to crop failure.

Compared with MH and fluorescent lamps, LEDs generate less heat, but the height they hang above plants will be unexpected. The auxiliary LED lights used to grow small pieces of spices, wheatgrass and herbs (30w-45w) should be at least 15 inches away from the top of the plant.

For high-power lamps, the details are as follows:

200-400w LED Grow Lights： 18-32” away from plants canopy

400-6000w LED Grow Lights： 22-35” away from plants canopy

600-850w LED Grow Lights： 26-36 away from plants canopy

900w+ LED Grow Lights： 38-48” away from plants canopy

HPS Grow Light

For HPS grow lights, it is best to always keep at least 20 inches (50 cm) away from plants. Because the HPS light is too strong, the longer the suspension distance. Therefore, if it is a 1000w HPS lamp, the reasonable hanging height should be at least 22 inches (about 55 cm). When the light intensity is weak, it should not hang 18 inches (approximately 45 cm) above the plant. If it is a 400-watt HPS, it can only be about 12 inches (about 30 cm) away from plants, while the best hanging distance for a medium-sized 600-watt lamp is 20 inches.