Installing, setting up and hanging an LED grow light and getting the distance right
A possibly obvious topic to some, but eye-opening to others. We’ve seen all types of unique grows. 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 light falls and why getting the right height between indoor plants and 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 Apogee MQ-500. 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.[More LEDTonic tests and guides]
The term for light intensity, or photon density, is PPFD. We measure PPFD in umol/m2/s. We know that mature weed plants want 600-800 PPFD to be stimulated. This means that we need to adjust our grow light so that we project this intensity onto our plants. PPFD levels can be regulated with distance. 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.
Here’s an illustration:
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 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 our PPFD light footprint map of our lamps. We’ve measured the PPFD at 12”, 18” and 24” 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.
What we should also take away from the “photons spreading” theory is that the smaller the grow space, while of course still giving room for the plants, the better. Adding reflective walls to our grow space will make the escaping photons reflect back towards the plants. Grow tents already come with mylar walls but mylar can easily be purchased on its own and fixed to any grow area.
We tested this theory. We have previously measured our grow lights in 3x3’ tents which we know are too large for the lights. We chose this size mainly to demonstrate how light intensity changes the further we move from the center spot. Our Z5 light works very well in a 2x2’ tent, which is what we wanted to find out.
We see that we get above 22% more photons inside the 2x2’ area at 12” and above 34% at 24” compared to the 3x3’ tent. Point being, if you can grow in a 2x2’ tent, do not oversize and go with a larger tent. Choose the smallest possible tent that fits your plants.
While we’re at it, we also wanted to show you different ways to hang grow lights -- any grow light, but we’ll demonstrate on our Z5. There are several ways to hang the grow light without even ratchets or a hook.
Connect the loops (two arms) from the hanger two by two and connect each set of two loops to one end of a ratchet. Guide the ratchet around the top frame of your grow tent.
Use two ratchets and connect two loops (two arms) from the metal hanger to each of the ratchets. Guide the ratchets around each side of the tent and secure them at the bottom of the tent.
Place one loop from each arm straight across from where the arm’s screw cap will be secured. Screw the cap on top of the loop. Hang the lamp with a hook, ratchet, or a metal wire (not included).
Same as above but instead of a hook the lamp hangs from a secure rod at the top of the grow tent. Distance between rod and lamp: 6.3” / 16 cm.
The hanger’s arms can be crossed to shorten them further.
Same as above but use two rods to decrease distance between lamp and top of tent. 2.75” / 7 cm.
Ok. So, takeaways:
- 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 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 and we listed some of them.
We also made a video about this and we show a real example of how reflective walls work and affect the light footprint.