When it comes to indoor plant cultivation, each of us has our own conditions, limitations, and possibilities to structure our grow space. Whether we grow cannabis, vegetables, or indoor plants, this article will help in understanding how to install LED Grow Lights and why getting the right height between indoor plants and LED grow light is important.
Let’s begin with a bit of theory. In other articles, we’ve discussed that light is photons and that photons are particles with wavelengths. To determine how intense light is, we measure how many photons fall in a specific area. We do this with a quantum meter. In our case, we do it with an VANQ GLIC650. Photons do not fall in a straight line though. They sort of scatter about and fall in a somewhat organized chaos. This means that the further a light source is from the area it’s supposed to illuminate, plants’ canopies, for instance, the more photons will spread sideways instead of falling straight down. This is not necessarily a bad thing as this creates a larger light footprint; a larger area covered with light. However, to stimulate our plants, we still want enough photons to fall on them.
The term for light intensity, or photon density, is PPFD. We measure PPFD in μmol/m2/s. PPFD levels can be regulated with distance. This means that we need to adjust our grow light so that we project this intensity onto our plants. As photons spread, the longer the distance between plant and light source is, the less intense the light will become as the photons spread sideways, away from the plant. But we also need to know that for different growth stages the required PPFD level can be different, such as in cannabis cultivation.
How Far Should LED Grow Light Hang On Plants
Understand the Light Intensity and Footprint
We see here that a lamp is emitting photons and that there is some distance between the lamp and the plant. If we were to move the plant upwards, closer to the lamp, fewer photons would escape beside the plant. If we were to place the plant directly underneath the lamp, with zero air between them, pretty much all photons emitted from the lamp would hit the plant – no photons would “escape”.
This is the theory behind distance: intensity: footprint.
Short or no distance between lamp and plant: high PPFD (light intensity) but the small light footprint (coverage area).
Long-distance, let’s say 2’ (61cm) between lamp and plant: low PPFD but large light footprint.
This theory is also confirmed on the PPFD light footprint map of our 600W COB LED Grow Light. We’ve measured the PPFD at 24” and 36” distances and we clearly see that the higher up the lamp is from the sensor, the less intense (lower PPFD) the light becomes but the PPFD levels in the outer edges increase as the distance increases.
VANQ 600w LED Grow Light PPFD at 24 inches
VANQ 600w LED Grow Light PPFD at 36 inches
What Is The Required PPFD Level For Specific Growth Stage?
If you want to use the growing area for only vegetative or flowering, you only need to consider the lighting intensity for that growth phase. When using the area for both phases of growth, it is best to design for the most light-demanding phase (usually flowering).
We know that mature weed plants want 600-800 PPFD to be stimulated. Once the plants’ minimum lighting requirements have been met, increasing the total light output will increase yield. Up to a point, increasing the total light output by a certain percentage will increase yield by a “linear” equivalent percentage; for example increasing the total light output by 10% may increase yield by 8%, and increasing total light output by 20% would increase yield by 16%. When you start giving the plants as much light as they can handle, this yield return on increased intensity starts to fall off and is no longer linear; for example, if you’ve got a very high light output like more than 1000umol/m2/s to begin with, increasing it by 10% may only give a 4% increase in yield. Past a certain point increasing the total light output will not increase yield at all, and may even hurt it if the plants are being harmed by too much light.
Understand overlapping effects when you use more than one LED grow light.
When install LED grow lights next to each other in the order of a grid which is very common in commercial cannabis growing, every light’s footprint will be at least overlapped by adjacent lights. So when you put the overlapping illumination effect into consideration of the actual PPFD value will surely be higher than the independent setup. You can set up a PPFD test demo with 4-8 lights to find the optimal overlapping effect, in order to get more uniform coverage. You can also check our official setup suggestion video for your reference.
Conclusions
Hang the lamp at the correct height based on your plants’ PPFD needs (check PPFD/PAR info from manufacturer).
Make sure the light footprint is big enough to illuminate your plants (based on the manufacturer’s light footprint map).
Create a compact grow area with no/minimal space between your mature plants and reflective walls to absorb as much light as possible.
There are many ways to hang a grow light. Make sure it is stable and safe.
