Light intensity vs. temperature
Dropping the lights in a grow tent is generally not advisable due to the fact that they will burn the plants that are directly below them. While lowering the temperature of the lights so they can be placed closer to the plants may seem like a viable idea, it is not recommended. You may argue that reducing the heat and bringing the bulb closer will provide the plants with more lumens of light without burning them. However, in this case, you will realize that the light intensity has as much to do with burns and yellowing of the plants as the heat of the bulb. In a grow tent with a heat filter, the light intensity is actually the major cause of yellowing of the leaves.
According to the laws of science, energy is neither created nor destroyed, it is just displaced. So take into consideration a grow tent where there is reflective silver covering all over the walls; when light comes down it bounces all around. Therefore, the light isn’t leaving the room with very little to be absorbed into the sides due to the silver taping reflecting it. This means that 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 that is getting into the room and the absorption of those lumens by the plants. If you look at how European growers light up their growing tents, you will find out that they do not put the light close to the plants and they instead put them up fairly high. Instead of dropping the lights right on top of the plants, it is better to use the light as a heater for the room in this way the light is used to control the environment. Dropping the lights is actually hazardous to the plants which are directly below the bulbs. This is because doing so gives a single focal point which is in contrast to the multiple focal points provided by lights that are higher up; bearing in mind the light reflected from the walls too. There may be times that occur where there are burns or alternatively yellowing of the leaves directly underneath the bulb while the rest of the leaves are green. This is due to the fact that these plants at the center are exposed to a tougher environment than the rest of the plants. The light intensity is too high for these plants and the fact that the lights are on continuously means that they remain in this harmful condition day in and day out so they end up getting damaged over and over as they grow. Over time their leaves will become dry and brittle and may even fall off. At this point the plant will lose the ability to absorb the light.
Alternatively, before deciding to drop the lights, there are two things to consider; the temperature and the light intensity. Concerning the temperature, the heat filter controls the environment in the room by pulling heat out of the room. This results in an appropriate environment for the plants where they will be able to grow optimally. In these conditions, the plants grow to become big, tall and strong. Such an environment also prevents the growth of parasitic organisms and pests such as mildew and spider mites which attack the plants. The light intensity also matters. This is because it acts as a focal point of light resulting in high light intensity for plants close to the bulb and a normal intensity for those further away. From this we can see that the best method of providing light to the plants is that of overhead lighting. The reflective wall covering lining the walls ensures that most of the light released by the bulb is actually kept in the room. This mode of lighting ensures that there is uniform lighting across the whole room and all of the plants will be healthy including those below the bulb.
Image: light source at an appropriate distance from the plants