Dropping the level in which your grow lights hang in a grow tent is generally not advisable. Doing so may “burn” the plants directly below them. While lowering the temperature of the lights so that they can be placed closer to plants may seem like a viable solution, this is not recommended either.
Heat is not the only problem here.
Light intensity has as much to do with the burning and yellowing of plants as the heat of a bulb. In a grow tent with a heat filter, the light intensity is actually the major cause of the yellowing of leaves.
According to the laws of science, energy is neither created nor destroyed, it is just displaced. This must be taken into consideration in a grow tent where there is a silver, reflective film covering the walls. When light in added to the mix, it bounces all over the place.
It is not actually leaving the room, and very little is absorbed into the sides because it is being reflected. This means the energy is retained within the room with a negligible amount being wasted.
The only thing that should be on your mind is how to maximize the light in the room, in ways other than lowering the lights closer to the plants, and how to maximize the absorption of those lumens by your plants.
Instead of hanging lights right on top of plants, it is better to use the light as a heat source for the room and in this way the light is used to control the environment. Hanging lights too closely is actually hazardous to plants because doing so gives plants a single focal point of light intensity, which is in contrast to the multiple focal points provided by lights that are higher and reflected from the walls.
If plant leaves directly underneath the bulbs begin to yellow, while the rest stay green, this is a sign you need to raise your lights. The yellowed plants have been exposed to a tougher light intensity and environment than the rest of plants. The light intensity is too high for these plants because the light is too close to them.
Further, because the lights are on continuously in some cases, plants remain in this harmful condition day in day out. In other words, they end up getting beat up over and over as they grow. Over time their leaves will become dry and brittle and may even fall off. At this point, the plants will lose the ability to absorb light altogether—you know what happens next.
So, before installing your grow lights, there are two things to consider, the eventual temperature and light intensity inside the grow tent. Concerning the temperature, the heat filter controls the environment in the room by pulling heat out of the room.
This results in an optimal growing environment for plants. In these conditions, plants grow to be big, tall and strong, provided they are getting the right amount of nutrients, water and all of the other goodies they demand. This optimal environment also prevents the growth of parasitic organisms and pests such as mildew and spider mites.
Again, the light intensity also matters. When the bulb is lowered, it will actually “burn” plants that are right below it. Again, this is not because of the heat, which is being removed by the filter, but because of the light intensity the bulb is giving off.
In terms of T5 fluorescents and induction lighting, the light travels along quite a horizontal distance, and is a softer light, so the risk of damaging plants if these lights are too low isn’t as high as with HID lighting, but while they don’t immediately get hot, temperatures and intensities will build up over time, so keep an eye on things and adjust lights accordingly.
In terms of LED lighting, LEDs are different in the fact they produce even less heat and create a specific light spectrum. They emit a strong intensity of light, which can still irritate plants if they get too close. This is why some LED companies will reflect their lenses by 60 or 90 degrees because the light is too intense to shoot them directly at the plants.
The best method of providing light to plants in grow tents is overhead lighting that is installed some distance away from the plants. The reflective wall covering ensures most of the light released by the bulb is actually kept in the room, helping plants get more of what they need, despite the lights not being as close as they physically could be.
This method of lighting ensures there is uniform lighting across the whole room and all plants grow to be healthy, including those directly below the bulb. (But not too close!)