This is from IAm5toned, a Guru.
So you wanna play with the big boys, huh?
Using the chart in the above post, you can see a lamps effective
footprint.
You would expect that, if you wanted to run multiple lamps, than you would just measure the area of the Growroom floor, and just divide it into footprints for the lamp sizes you want to run according to the chart, and you would be good to go, right?
Wrong! If you were to make that mistake (and it is a common one to make) you will find that some of your plants end up stretchy, some of your plants end up squat, and some of your plants stretch so much they will fall over or get burned from the lamps!
This is a classic example of the inverse square rule, in full effect. This happens, because even though the chart i posted is very accurate in its data, the inverse square law still applies... that is,
the light around the perimeter of a lamps footprint, is not as intense in the area of the center of the footprint, because it is further in distance from the lamp. So if one was to use 2 400w lamps, to cover an 8' x 4' area, then at the 4'l x 2'w center mark of the room, the light would be the least intense!
however, we know that the 2 400w lamps will be enough light for the job, we just need to
redirect that light in a manner so that is covers the area more evenly...
Footprint overlap-
To keep the areas between the lights lit as evenly as the area directly underneath the light, we must reduce the distance between those lights by a factor of 1. this is easier to do than it sounds, lol....
using the chart above, you can see that if we were to light an 8' x 4' area with 400w lamps, we would need 2 lamps.And we just learned that spacing them evenly apart @ 48" will not work, because of the inverse square rule. well here's how you do it, its quite simple- you divide by one extra... (factor of one
) how it works: we take the longest dimension of the area in question, for our example, it is 8', which is 96 inches. we have 2 lights. we need to 'divide by one extra', so we would divide 96 by 3, which equals 32 inches.
32 inches of space between the two lights, instead of 48... this slight reduction in footprint size will compensate for the inverse square law, and the problem of less light at the edge of a lamps footprint, and will work with any number of lamps. for more than one row of lamps, simply apply the same 'divide by one extra' rule to the distance between the rows as well. This even placement of lamps is critical for any mulit lamp operation in maintaining an even canopy.
Improper lamp placement in multi-lamp grow operations is one of the biggest causes of 'rippling' in large grow rooms.
but what about the edges?
looking at the image above, you can see that the blue lined diagram has solved the problem of evenly lighting the center of the area, but has left the edges of the room with less brilliance. in most grows, this would be normal, and you would expect that the plants at the edge of the footprint would stretch to compensate for there increased distances from the lamps.... but what if that's
not what you desire?
this is where supplemental lighting comes into play...
the best solution to this problem would be take
approximately one half wattage of the main lamps, and install lamps that closely match that 1/2 wattage, at the ends of the Grow Room-
having even lighting, is the key to having an even canopy
Let me know what you think... good luck!
