(Please note – to make this a bit more digestible, the examples below are just that, examples. Every room is different and every light is different so not every number is accurate, but the principle is solid and when applied properly will have the desired results as displayed below – thats my honest opinion having used multiple light set ups. Sorry for the bad mspaint job also )
As a bit of a follow on to this thread (link here) I wanted to make this thread on how to properly illuminate an area, now that we have chosen the most appropriate lighting for our application.
The idea behind this thread is that instead of thinking in terms of lighting plants, we want to be thinking in terms of lighting an area. This eliminates issues like fluffy bits around the edges, uneven canopy height, loss of crop quality, scorched tops, loss of yield amongst other things we don’t want to happen. We want to be able to put a plant anywhere in the room and it perform just as well as any other plant in the room, whether its directly under a lamp or in the corner of the room.
What it does mean is even crop canopy and growth, better crop quality, bigger yield and more consistent yield per plant, even crop ripening and generally a more homogeneous grow on the whole. (you will always have some variation from seed or running multiple varieties at once in the same area)
As we have already determined, lumens do not mean a thing in terms of plant growth. Which also means that the “inverse square law rule” is not entirely applicable, to our eye the light diminishes and gets duller (not great for photographs), but in reality the further away the light source, the larger the foot print becomes and the lower the PPFD. Like spreading a great big bit of peanut butter thin on a 4ft slice of toast.
The closer the light source, the more concentrated the PPFD becomes on a smaller foot print. Bringing the light source closer may seem like a good idea, but in reality this couldn’t be further from the truth for several reasons. By concentration the energy on a smaller part of the canopy the total canopy PPF becomes uneven, with high intensity directly below the lamp and low intensity around the rest of the canopy. Uneven canopy lighting ultimately leads to an uneven canopy – generally tall around the edges and low in the centre.
Hanging lamps higher will spread the PPFD out and illuminate the canopy more evenly, which means better capture of light by the plants due to less light over saturation and less heat stress, cooler LST (leaf surface temps) and over all better quality.
In single light set ups, especially in tents, it really is as simple as hanging the lamps a little higher. With so much reflection from around the tent, coupled with a GOOD reflector, things like light losses to wall reflection aren’t as much as they are in larger rooms or tents that have multiple lights, and therefore not so much of an Issue. I personally never experienced any excessive stretching or loss of yield from hanging the lamp high above the canopy in single lamp set ups.
In larger areas that have multiple lights, light loss to reflection starts to be more of an issue and therefore light position and hanging height can play an important role in making sure the canopy is evenly lit.
Let’s say figure 1 represents a 2m x 2m area with 4 x 315w lamps to light it positioned in a way most people naturally would. The circles being the lamps. The above would result in uneven crop lighting, and can lead to the issues mentioned previously.
To simplify the example, let’s assume that these lamps are putting out 600 ppf in every direction and directly below the lamp. We want to deliver ppfd evenly across the area, but it’s impossible to do with the above layout, because of cross over light increasing the PPFD, and loss of PPFD from wall reflection.
So figure 2 shows us whats happening with that 600 ppf getting thrown in every direction. Directly below the lamp is 600 ppf, around the center of the area due to cross over light we’ve got double the amount of light, and right in the centre the hash tag represents oversaturation.
We can generally expect losses of between 40 – 60% due to wall reflection, unless using orca which reflects 99.9% of the light but at £130 for 10m it’s a bit expensive.. so lets assume we’re using mylar and losing the maximum of 60%. Worth noting that the light is lost as HEAT.
Because of this we can see its nearly 3 times as less light than the middle of the area and most of the power in your lamps is getting concentrated in the middle of the area.
Fig 3 Fig 4
Figure 3 shows how we should be hanging our lamps, and Figure 4 shows how this affects our PPFD.
By hanging the lamps right by the walls, not quite in each corner, we use the cross over light more efficiently to even out the PPFD. Because the lamps are right next to the walls, the canopy below is getting more direct light and less is being reflected. For the example, we have assumed that 40% of the light is getting lost due to better placement, which means 60% back to add the PPFD up underneath the lamps.
It’s always better to have an even PPFD across the area than it is to try and get the intensity and penetration up. I would always sooner hang my lights higher and add another one to bring the PPFD up, than bring the lamps down closer to the canopy. Adding more lights increases the intensity and increases penetration, more points of light means less shaded areas, better penetration and a more consistent canopy PPFD.
I hope this thread has given some of you a bit to think about in regards to how you’re lighting your areas, and I hope that it goes some way to bettering your grow